INTERNET-DRAFT Charles H. Lindsey Usenet Format Working Group University of Manchester August 2002 News Article Format Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This Draft is intended as a standards track document, obsoleting RFC 1036, which itself dates from 1987. This Standard defines the format of Netnews articles and specifies the requirements to be met by software which originates, distributes, stores and displays them. Since the 1980s, Usenet has grown explosively, and many Internet and non-Internet sites now participate. In addition, the Netnews technology is now in widespread use for other purposes. Backward compatibility has been a major goal of this endeavour, but where this standard and earlier documents or practices conflict, this standard should be followed. In most such cases, current practice is already compatible with these changes. [The use of the words "this standard" within this document when referring to itself does not imply that this draft yet has pretensions to be a standard, but rather indicates what will become the case if and when it is accepted as an RFC with the status of a proposed or draft standard.] C. H. Lindsey [Page 1] News Article Format August 2002 [Remarks enclosed in square brackets and aligned with the left margin, such as this one, are not part of this draft, but are editorial notes to explain matters amongst ourselves, or to point out alternatives, or to assist the RFC Editor.] [In this draft, references to [NNTP] are to be replaced by [RFC 977], or else by references to the RFC arising from the series of drafts draft- ietf-nntpext-base-*.txt, in the event that such RFC has been accepted at the time this document is published. Likewise, if may be possible to replace references to [RFC 2279] by references to [RFC 2279bis].] Table of Contents 1. Introduction .................................................. 6 1.1. Basic Concepts ............................................ 6 1.2. Objectives ................................................ 7 1.3. Historical Outline ........................................ 7 1.4. Transport ................................................. 7 2. Definitions, Notations and Conventions ........................ 8 2.1. Definitions ............................................... 8 2.2. Textual Notations ......................................... 9 2.3. Relation To Email and MIME ................................ 11 2.4. Syntax .................................................... 11 2.4.1. Syntax Notation ....................................... 11 2.4.2. Syntax adapted from Email and MIME .................... 11 2.4.3. Syntax copied from other standards .................... 13 2.5. Language .................................................. 14 3. Changes to the existing protocols ............................. 15 3.1. Principal Changes ......................................... 15 3.2. Transitional Arrangements ................................. 15 4. Basic Format .................................................. 17 4.1. Syntax of News Articles ................................... 17 4.2. Headers ................................................... 18 4.2.1. Naming of Headers ..................................... 18 4.2.2. MIME-style Parameters ................................. 19 4.2.3. White Space and Continuations ......................... 20 4.2.4. Comments .............................................. 21 4.2.5. Header Properties ..................................... 22 4.2.5.1. Experimental Headers .............................. 22 4.2.5.2. Inheritable Headers ............................... 22 4.2.5.3. Variant Headers ................................... 23 4.2.6. Undesirable Headers ................................... 23 4.3. Body ...................................................... 23 4.3.1. Body Format Issues .................................... 23 4.3.2. Body Conventions ...................................... 24 4.4. Characters and Character Sets ............................. 26 4.4.1. Character Sets within Article Headers ................. 26 4.4.2. Character Sets within Article Bodies .................. 28 4.5. Size Limits ............................................... 28 4.6. Example ................................................... 29 5. Mandatory Headers ............................................. 30 5.1. Date ...................................................... 30 5.1.1. Examples .............................................. 31 C. H. Lindsey [Page 2] News Article Format August 2002 5.2. From ...................................................... 31 5.2.1. Examples: ............................................ 32 5.3. Message-ID ................................................ 32 5.4. Subject ................................................... 33 5.4.1. Examples .............................................. 34 5.5. Newsgroups ................................................ 35 5.5.1. Forbidden newsgroup-names ............................. 39 5.5.2. Encoded newsgroup-names ............................... 40 5.6. Path ...................................................... 41 5.6.1. Format ................................................ 41 5.6.2. Adding a path-identity to the Path-header ............. 42 5.6.3. The tail-entry ........................................ 43 5.6.4. Path-Delimiter Summary ................................ 43 5.6.5. Suggested Verification Methods ........................ 44 5.6.6. Example ............................................... 45 6. Optional Headers .............................................. 45 6.1. Reply-To .................................................. 46 6.1.1. Examples .............................................. 46 6.2. Sender .................................................... 46 6.3. Organization .............................................. 46 6.4. Keywords .................................................. 47 6.5. Summary ................................................... 47 6.6. Distribution .............................................. 47 6.7. Followup-To ............................................... 48 6.8. Mail-Copies-To ............................................ 49 6.9. Posted-And-Mailed ......................................... 50 6.10. References ............................................... 51 6.10.1. Examples ............................................. 51 6.11. Expires .................................................. 51 6.12. Archive .................................................. 52 6.13. Control .................................................. 52 6.14. Approved ................................................. 53 6.15. Supersedes ............................................... 54 6.16. Xref ..................................................... 55 6.17. Lines .................................................... 55 6.18. User-Agent ............................................... 56 6.18.1. Examples ............................................. 56 6.19. Injector-Info ............................................ 57 6.19.1. Usage of Injector-Info-parameters .................... 58 6.19.1.1. The posting-host-parameter ....................... 59 6.19.1.2. The posting-account-parameter .................... 59 6.19.1.3. The posting-sender-parameter ..................... 60 6.19.1.4. The posting-logging-parameter .................... 60 6.19.1.5. The posting-date-parameter ....................... 60 6.19.2. Example .............................................. 60 6.20. Complaints-To ............................................ 60 6.21. MIME headers ............................................. 61 6.21.1. Syntax ............................................... 61 6.21.2. Content-Type ......................................... 61 6.21.2.1. Message/partial .................................. 62 6.21.2.2. Message/rfc822 ................................... 63 6.21.2.3. Message/external-body ............................ 63 6.21.2.4. Multipart types .................................. 63 6.21.3. Content-Transfer-Encoding ............................ 63 C. H. Lindsey [Page 3] News Article Format August 2002 6.21.4. Character Sets ....................................... 65 6.21.5. Content Disposition .................................. 65 6.21.6. Definition of some new Content-Types ................. 65 6.21.6.1. Application/news-transmission .................... 66 6.21.6.2. Message/news obsoleted ........................... 67 6.22. Obsolete Headers ......................................... 67 7. Control Messages .............................................. 67 7.1. Digital Signature of Headers .............................. 68 7.2. Group Control Messages .................................... 68 7.2.1. The 'newgroup' Control Message ........................ 68 7.2.1.1. The Body of the 'newgroup' Control Message ........ 69 7.2.1.2. Application/news-groupinfo ........................ 70 7.2.1.3. Initial Articles .................................. 71 7.2.1.4. Example ........................................... 72 7.2.2. The 'rmgroup' Control Message ......................... 73 7.2.2.1. Example ........................................... 73 7.2.3. The 'mvgroup' Control Message ......................... 73 7.2.3.1. Example ........................................... 75 7.2.4. The 'checkgroups' Control Message ..................... 75 7.2.4.1. Application/news-checkgroups ...................... 76 7.3. Cancel .................................................... 77 7.4. Ihave, sendme ............................................. 78 7.5. Obsolete control messages. ............................... 79 8. Duties of Various Agents ...................................... 79 8.1. General principles to be followed ......................... 80 8.2. Duties of an Injecting Agent .............................. 80 8.2.1. Proto-articles ........................................ 80 8.2.2. Procedure to be followed by Injecting Agents .......... 81 8.3. Duties of a Relaying Agent ................................ 83 8.4. Duties of a Serving Agent ................................. 84 8.5. Duties of a Posting Agent ................................. 85 8.6. Duties of a Followup Agent ................................ 85 8.7. Duties of a Moderator ..................................... 86 8.8. Duties of a Gateway ....................................... 87 8.8.1. Duties of an Outgoing Gateway ......................... 88 8.8.2. Duties of an Incoming Gateway ......................... 90 8.8.3. Example ............................................... 92 9. Security and Related Considerations ........................... 93 9.1. Leakage ................................................... 93 9.2. Attacks ................................................... 93 9.2.1. Denial of Service ..................................... 93 9.2.2. Compromise of System Integrity ........................ 94 9.3. Liability ................................................. 96 10. IANA Considerations .......................................... 96 11. References ................................................... 96 12. Acknowledgements ............................................. 99 13. Contact Address .............................................. 100 Appendix A.1 - A-News Article Format .............................. 100 Appendix A.2 - Early B-News Article Format ........................ 101 Appendix A.3 - Obsolete Headers ................................... 101 Appendix A.4 - Obsolete Control Messages .......................... 102 Appendix B - Collected Syntax ..................................... 103 Appendix B.1 - Characters, Atoms and Folding ...................... 103 Appendix B.2 - Basic Forms ........................................ 105 C. H. Lindsey [Page 4] News Article Format August 2002 Appendix B.3 - Headers ............................................ 106 Appendix B.3.1 - Header outlines .................................. 106 Appendix B.3.2 - Control-message outlines ......................... 108 Appendix B.3.3 - Other header rules ............................... 109 Appendix C - Notices .............................................. 110 C. H. Lindsey [Page 5] News Article Format August 2002 1. Introduction 1.1. Basic Concepts "Netnews" is a set of protocols for generating, storing and retrieving news "articles" (which resemble email messages) and for exchanging them amongst a readership which is potentially widely distributed. It is organized around "newsgroups", with the expectation that each reader will be able to see all articles posted to each newsgroup in which he participates. These protocols most commonly use a flooding algorithm which propagates copies throughout a network of participating servers. Typically, only one copy is stored per server, and each server makes it available on demand to readers able to access that server. An important characteristic of Netnews is the lack of any requirement for a central administration or for the establishment of any controlling host to manage the network. A network which limits participation to some restricted set of hosts (within some company, for example) is a "closed" network; otherwise it is an "open" network. A set of hosts within a network which, by mutual arrangement, operates some variant (whether more or less restrictive) of the Netnews protocols is a "cooperating subnet". "Usenet" is a particular worldwide open network based upon the Netnews protocols, with the newsgroups being organized into recognized "hierarchies". Anybody can join (it is simply necessary to negotiate an exchange of articles with one or more other participating hosts). Usenet "belongs" to those who administer the hosts of which it is comprised. There is no Cabal with overall authority to direct what is to be be allowed. Nevertheless, there do exist agencies within Usenet that have authority to establish policies and to perform administrative functions, but such authority derives solely from the consent of those sites which choose to recognize it (and who can decline to exchange articles with sites which choose not to recognize it). Usually, the authority of such an agency is restricted to a particular hierarchy, or group of hierarchies. A "policy" is a rule intended to facilitate the smooth operation of a network by establishing parameters which restrict behaviour that, whilst technically unexceptionable, would nevertheless contravene some accepted standard of "Good Netkeeping". Since the ultimate beneficiaries of a network are its human readers, who will be less tolerant of poorly designed interfaces than mere computers, articles in breach of established policy can cause considerable annoyance to their recipients. Policies may well vary from network to network, from hierarchy to hierarchy within one network, and even between individual newsgroups within one hierarchy. It is assumed, for the purposes of this standard, that agencies with varying degrees of authority to establish such policies will exist, and that where they do not, policy will be established by mutual agreement. For the benefit of C. H. Lindsey [Page 6] News Article Format August 2002 networks and hierarchies without such established agencies, and to provide a basis upon which all agencies can build, this present standard often provides default policy parameters, usually introducing them by a phrase such as "As a matter of policy ...". 1.2. Objectives The purpose of this present standard is to define the format of articles and the protocols to be used for Netnews in general, and for Usenet in particular, and to set standards to be followed by software that implements those protocols. It is NOT the purpose of this standard to define how the authority of various agencies to exercise control or oversight of the various parts of Usenet is established (that is itself a matter of policy). Nevertheless, it is assumed that such authorities will exist, and tools are provided within the protocols for their use. 1.3. Historical Outline Network news originated as the medium of communication for Usenet, circa 1980. Since then, Usenet has grown explosively, and many Internet and non-Internet sites participate in it. In addition, the news technology is now in widespread use for other purposes, on the Internet and elsewhere. The earliest news interchange used the so-called "A News" article format. Shortly thereafter, an article format vaguely resembling Internet Mail was devised and used briefly. Both of those formats are completely obsolete; they are documented in Appendix A.1 and Appendix A.2 for historical reasons only. With publication of [RFC 850] in 1983, news articles came to closely resemble Internet Mail messages, with some restrictions and some additional headers. [RFC 1036] in 1987 updated [RFC 850] without making major changes. A Draft popularly referred to as "Son of 1036" [Son-of-1036] was written in 1994 by Henry Spencer. That document formed the original basis for this standard, and its author has endorsed this standard as its successor. Much is taken directly from Son of 1036, and it is hoped that we have followed its spirit and intentions. It is anticipated that [Son-of-1036] will be published as an Historic RFC, in a suitably relabelled form, following the publication of this standard. 1.4. Transport As in this standard's predecessors, the exact means used to transmit articles from one host to another is not specified. NNTP [NNTP] is the most common transmission method on the Internet, but much transmission takes place entirely independent of the Internet. Other methods in use include the UUCP protocol [RFC 976] extensively used in the early days of Usenet, FTP, downloading via satellite, tape archives, and physically delivered magnetic and optical media. C. H. Lindsey [Page 7] News Article Format August 2002 2. Definitions, Notations and Conventions 2.1. Definitions An "article" is the unit of news, analogous to an [RFC 2822] "message". A "proto-article" is one that has not yet been injected into the news system. A "message identifier" (5.3) is a unique identifier for an article, usually supplied by the "posting agent" which posted it or, failing that, by the "injecting agent". It distinguishes the article from every other article ever posted anywhere. Articles with the same message identifier are treated as if they are the same article regardless of any differences in the body or headers. A "newsgroup" is a single news forum, a logical bulletin board, having a name and nominally intended for articles on a specific topic. An article is "posted to" a single newsgroup or several newsgroups. When an article is posted to more than one newsgroup, it is said to be "crossposted"; note that this differs from posting the same text as part of each of several articles, one per newsgroup. A newsgroup may be "moderated", in which case submissions are not posted directly, but mailed to a "moderator" for consideration and possible posting. Moderators are typically human but may be implemented partially or entirely in software. A "hierarchy" is the set of all newsgroups whose names share a first component (as defined in 5.5). The term "sub-hierarchy" is also used where several initial components are shared. A "poster" is the person or software that composes and submits a possibly compliant article to a "posting agent". The poster is analogous to [RFC 2822]'s author(s). A "posting agent" is the software that assists posters to prepare proto-articles, in compliance with this standard. The proto-article is then passed on to an "injecting agent" for final checking and injection into the news stream. If the article is not compliant, or is rejected by the injecting agent, then the posting agent informs the poster with an explanation of the error. A "reader" is the person or software reading news articles. A "reading agent" is software which presents articles to a reader. A "followup" is an article containing a response to the contents of an earlier article (the followup's "precursor"). A "followup agent" is a combination of reading agent and posting agent that aids in the preparation and posting of a followup. C. H. Lindsey [Page 8] News Article Format August 2002 An (email) "address" is the mailbox [RFC 2822] (or more particularly the addr-spec within that mailbox) which directs the delivery of an email to its intended recipient, who is said to "own" that address. An article's "reply address" is the address to which mailed replies should be sent. This is the address specified in the article's From- header (5.2), unless it also has a Reply-To-header (6.1). A "sender" is the person or software (usually, but not always, the same as the poster) responsible for the operation of the posting agent or, which amounts to the same thing, for passing the article to the injecting agent. The sender is analogous to [RFC 2822]'s sender. An "injecting agent" takes the finished article from the posting agent (often via the NNTP "post" command) performs some final checks and passes it on to a relaying agent for general distribution. A "relaying agent" is software which receives allegedly compliant articles from injecting agents and/or other relaying agents, and possibly passes copies on to other relaying agents and serving agents. A "news database" is the set of articles and related structural information stored by a serving agent and made available for access by reading agents. A "serving agent" receives an article from a relaying agent and files it in a news database. It also provides an interface for reading agents to access the news database. A "control message" is an article which is marked as containing control information; a relaying or serving agent receiving such an article may (subject to the policies observed at that site) take actions beyond just filing and passing on the article. A "gateway" is software which receives news articles and converts them to messages of some other kind (e.g. mail to a mailing list), or vice versa; in essence it is a translating relaying agent that straddles boundaries between different methods of message exchange. The most common type of gateway connects newsgroup(s) to mailing list(s), either unidirectionally or bidirectionally, but there are also gateways between news networks using this standard's news format and those using other formats. 2.2. Textual Notations This standard contains explanatory NOTEs using the following format. These may be skipped by persons interested solely in the content of the specification. The purpose of the notes is to explain why choices were made, to place them in context, or to suggest possible implementation techniques. C. H. Lindsey [Page 9] News Article Format August 2002 NOTE: While such explanatory notes may seem superfluous in principle, they often help the less-than-omniscient reader grasp the purpose of the specification and the constraints involved. Given the limitations of natural language for descriptive purposes, this improves the probability that implementors and users will understand the true intent of the specification in cases where the wording is not entirely clear. "US-ASCII" is short for "the ANSI X3.4 character set" [ANSI X3.4]. While "ASCII" is often misused to refer to various character sets somewhat similar to X3.4, in this standard "US-ASCII" is used to mean X3.4 and only X3.4. US-ASCII is a 7 bit character set. Please note that this standard requires that all agents be 8 bit clean; that is, they must accept and transmit data without changing or omitting the 8th bit. Certain words, when capitalized, are used to define the significance of individual requirements. The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", "MAY" and "OPTIONAL", and any of those words associated with the word "NOT", are to be interpreted as described in [RFC 2119]. In addition, the word "Ought", when applied to a poster, or to actions of posting and similar agents which a poster may easily override, indicates a recommendation whose violation would do no more than breach established policy, or accepted best practice. NOTE: The use of "MUST" or "SHOULD" implies a requirement that would or could lead to interoperability problems if not followed. Although not following an "Ought" recommendation might do no worse than cause extreme irritation to other readers, particularly in the case of the publicly distributed Usenet, that is no reason not to take it seriously. The essential distinction is that enforcement of a "MUST" or "SHOULD" is a matter of ensuring correct implementation, whereas enforcement of an "Ought" is more a matter of sensible design or of social pressure (whose effectiveness should not be underestimated, even though it cannot be prescribed by this standard). NOTE: A requirement imposed on a relaying or serving agent regarding some particular article should be understood as applying only if that article is actually accepted for processing (since any agent may always reject any article entirely, for reasons of site policy). Throughout this standard we will give examples of various definitions, headers and other specifications. It needs to be remembered that these samples are for the aid of the reader only and do NOT define any specification themselves. In order to prevent possible conflict with "Real World" entities and people the top level domain ".example" is used in all sample domains and addresses. The hierarchy "example.*" is also used as a sample hierarchy. Information on the ".example" top level domain is in [RFC 2606]. C. H. Lindsey [Page 10] News Article Format August 2002 2.3. Relation To Email and MIME The primary intent of this standard is to describe the news article format. Insofar as news articles are a subset of the email message format augmented by some new headers, this standard incorporates many (though not all) of the provisions of [RFC 2822], with the aim of enabling news articles to pass through email systems and vice versa, provided only that they contain the minimum headers required for the mode of transport being used. Unfortunately, the match is not perfect, but it is the intention of this standard that gateways between Email and Netnews should be able to operate with the minimum of tinkering. Likewise, this standard incorporates many (though not all) of the provisions of the MIME standards [RFC 2045] et seq which, though designed with Email in mind, are mostly applicable to Netnews. 2.4. Syntax The complete syntax defined in this standard is repeated, for convenience, in Appendix B. 2.4.1. Syntax Notation This standard uses the Augmented Backus Naur Form described in [RFC 2234]. In particular, it makes significant use of the "incremental alternative" feature of that notation. For example, the two rules header = other-header header =/ Date-header are equivalent to the single rule header = other-header / Date-header 2.4.2. Syntax adapted from Email and MIME Much of the syntax of Netnews Articles is based on the corresponding syntax defined in [RFC 2822] or in the MIME specifications [RFC 2045] et seq, which are deemed to have been incorporated into this standard as required. However, there are some important differences arising from the fact that [RFC 2822] does not recognize anything other than US-ASCII characters, that it does not recognize the MIME headers [RFC 2045], and that it includes much syntax described as "obsolete" (which is excluded from this standard, as detailed below). NOTE: Netnews parsers historically have been much less permissive than Email parsers, and this is reflected in the modifications referred to, and in some further specific rules. The following syntactic rules therefore supersede the corresponding rules given in [RFC 2822] and [RFC 2045], thus allowing UTF-8 characters [RFC 2279] to appear in certain contexts (the five rules beginning with "strict-" reflect the corresponding original rules from [RFC 2822]). C. H. Lindsey [Page 11] News Article Format August 2002 UTF8-xtra-2-head= %xC2-DF UTF8-xtra-3-head= %xE0 %xA0-BF / %xE1-EC %x80-BF / %xED %x80-9F / %xEE-EF %x80-BF UTF8-xtra-4-head= %xF0 %x90-BF / %xF1-F7 %x80-BF UTF8-xtra-5-head= %xF8 %x88-BF / %xF9-FB %x80-BF UTF8-xtra-6-head= %xFC %x84-BF / %xFD %x80-BF UTF8-xtra-tail = %x80-BF UTF8-xtra-char = UTF8-xtra-2-head 1( UTF8-xtra-tail ) / UTF8-xtra-3-head 1( UTF8-xtra-tail ) / UTF8-xtra-4-head 2( UTF8-xtra-tail ) / UTF8-xtra-5-head 3( UTF8-xtra-tail ) / UTF8-xtra-6-head 4( UTF8-xtra-tail ) text = %d1-9 / ; all UTF-8 characters except %d11-12 / ; US-ASCII NUL, CR and LF %d14-127 / UTF8-xtra-char ctext = NO-WS-CTL / ; all of except %d33-39 / ; SP, HTAB, "(", ")" %d42-91 / ; "\" and DEL %d93-126 / UTF8-xtra-char qtext = NO-WS-CTL / ; all of except %d33 / ; SP, HTAB, "\" DQUOTE %d35-91 / ; and DEL %d93-126 / UTF8-xtra-char utext = NO-WS-CTL / ; Non white space controls %d33-126 / ; The rest of UTF-8 UTF8-xtra-char strict-text = %d1-9 / ; text restricted to %d11-12 / ; US-ASCII %d14-127 strict-qtext = NO-WS-CTL / ; qtext restricted to %d33 / ; US-ASCII %d35-91 / %d93-126 strict-quoted-pair = "\" strict-text strict-qcontent = strict-qtext / strict-quoted-pair strict-quoted-string = [CFWS] DQUOTE *( [FWS] strict-qcontent ) [FWS] DQUOTE [CFWS] unstructured = 1*( [FWS] utext ) [FWS] The syntax for UTF8-xtra-char excludes those redundant sequences of octets which cannot occur in UTF-8, as defined by [RFC 2279], either because they would not be the shortest possible encodings of some UCS character [ISO/IEC 10646], or they would represent one of the characters D800 through DFFF, disallowed in UCS because of their surrogate use in the UTF-16 encoding. These sequences MUST NOT be generated by posting agents. Where they occur inadvertently, they SHOULD be passed on untouched by other agents, but attempts to interpret them as malformed UTF-8 MUST NOT be made. However, if there C. H. Lindsey [Page 12] News Article Format August 2002 is reason to suppose they are representations of some other character set they MAY, as suggested in section 4.4.1, be interpreted as such. Observe, in contradistinction to [RFC 2822], that an unstructured header MUST contain at least one non-whitespace character (see also remarks about empty headers in 4.2.6). Wherever in this standard the syntax is stated to be taken from [RFC 2822], it is to be understood as the syntax defined by [RFC 2822] after making the above changes, but NOT including any syntax defined in section 4 ("Obsolete syntax") of [RFC 2822]. Software compliant with this standard MUST NOT generate any of the syntactic forms defined in that Obsolete Syntax, although it MAY accept such syntactic forms. Certain syntax from the MIME specifications [RFC 2045] et seq is also considered a part of this standard (see 6.21). 2.4.3. Syntax copied from other standards The following syntactic forms, taken from [RFC 2234] or from [RFC 2822], are repeated here for convenience only: ALPHA = %x41-5A / ; A-Z %x61-7A ; a-z CR = %x0D ; carriage return CRLF = CR LF DIGIT = %x30-39 ; 0-9 HTAB = %x09 ; horizontal tab LF = %x0A ; line feed SP = %x20 ; space NO-WS-CTL = %d1-8 / ; US-ASCII control characters %d11 / ; which do not include the %d12 / ; carriage return, line feed, %d14-31 / ; and whitespace characters %d127 specials = "(" / ")" / ; Special characters used in "<" / ">" / ; other parts of the syntax "[" / "]" / ":" / ";" / "@" / "\" / "," / "." / DQUOTE WSP = SP / HTAB ; whitespace characters FWS = ([*WSP CRLF] 1*WSP); folding whitespace ccontent = ctext / quoted-pair / comment comment = "(" *([FWS] ccontent) [FWS] ")" CFWS = *([FWS] comment) ( ([FWS] comment) / FWS ) DQUOTE = %d34 ; quote mark quoted-pair = "\" text C. H. Lindsey [Page 13] News Article Format August 2002 atext = ALPHA / DIGIT / "!" / "#" / ; Any US-ASCII character except "$" / "%" / ; controls, SP, and specials. "&" / "'" / ; Used for atoms "*" / "+" / "-" / "/" / "=" / "?" / "^" / "_" / "`" / "{" / "|" / "}" / "~" atom = [CFWS] 1*atext [CFWS] dot-atom = [CFWS] dot-atom-text [CFWS] dot-atom-text = 1*atext *( "." 1*atext ) qcontent = qtext / quoted-pair quoted-string = [CFWS] DQUOTE *( [FWS] qcontent ) [FWS] DQUOTE [CFWS] word = atom / quoted-string phrase = 1*word NOTE: Following [RFC 2234], literal text included in the syntax is to be regarded as case-insensitive. However, in contradistinction to [RFC 2822], the Netnews protocols are sensitive to case in some instances (as in newsgroup-names, some header parameters, etc.). Care has been taken to indicate this explicitly where required. As in [RFC 2822], where any quoted-pair appears it is to be interpreted as its text character alone. That is to say, the "\" character that appears as part of a quoted-pair is semantically "invisible". Again, as in [RFC 2822], strings of characters that include characters not syntactically allowed in some particular context may be incorporated into a quoted-string by "encapsulating" them between quote (DQUOTE, US-ASCII 34) characters, prefixing every quote and backslash character (and possibly other characters too) with a "\" so as to form a quoted-pair, and possibly introducing folding by prefixing some WSP with CRLF. The semantic value of a quoted-string (i.e. the result of reversing the encapsulation) is a string of characters which includes neither the optional CFWS outside of the quote characters, nor the quote characters themselves, nor any CRLF contained within any FWS between the two quote characters, nor the "\" which introduces any quoted- pair. 2.5. Language Various constant strings in this standard, such as header names and month names, are derived from English words. Despite their derivation, these words do NOT change when the poster or reader employing them is interacting in a language other than English. C. H. Lindsey [Page 14] News Article Format August 2002 Posting and reading agents MAY translate as appropriate in their interaction with the poster or reader, but the forms that actually appear in articles as transmitted MUST be the English-derived ones defined in this standard. 3. Changes to the existing protocols This standard prescribes many changes, clarifications and new features since the protocols described in [RFC 1036] and [Son-of- 1036]. It is the intention that they can be assimilated into Usenet as it presently operates without major interruption to the service, though some of the new features may not begin to show benefit until they become widely implemented. This section summarizes the main changes, and comments on some features of the transition. 3.1. Principal Changes o The [RFC 2822] conventions for parenthesis-enclosed comments in headers are supported. o Whitespace is permitted in Newsgroups-headers, permitting folding of such headers. Indeed, all headers can now be folded. o An enhanced syntax for the Path-header enables the injection point of and the route taken by an article to be determined with certainty. o Netnews is firmly established as an 8bit medium and all headers are deemed to be in the UTF-8 character set (thus permitting, in particular, the use of non-ASCII newsgroup-names). o Large parts of MIME are recognized as an integral part of Netnews. o There is a new Control message 'mvgroup' to facilitate moving a group to a different place (name) in a hierarchy. o There are several new headers defined, notably Archive, Complaints-To, Injector-Info, Mail-Copies-To, Posted-And-Mailed and User-Agent, leading to increased functionality. o Provision has been made for almost all headers to have MIME-style parameters (to be ignored if not recognized), thus facilitating extension of those headers in future standards. o Certain headers and Control messages (Appendix A.3 and Appendix A.4) have been made obsolete. o Distributions are expected to be checked at the receiving end, as well as the sending end, of a relaying link. o There are numerous other small changes, clarifications and enhancements. 3.2. Transitional Arrangements An important distinction must be made between serving and relaying agents, which are responsible for the distribution and storage of news articles, and user agents, which are responsible for interactions with users. It is important that the former should be upgraded to conform to this standard as soon as possible to provide the benefit of the enhanced facilities. Fortunately, the number of distinct implementations of such agents is rather small, at least so far as the main "backbone" of Usenet is concerned, and many of the C. H. Lindsey [Page 15] News Article Format August 2002 new features are already supported. Contrariwise, there are a great number of implementations of user agents, installed on a vastly greater number of small sites. Therefore, the new functionality has been designed so that existing agents may continue to be used, although the full benefits may not be realised until a substantial proportion of them have been upgraded. In the list which follows, care has been taken to distinguish the implications for both kinds of agent. o [RFC 2822] style comments in headers do not affect serving and relaying agents (note that the Message-ID-, Newsgroups-, Distribution- and Path-headers do not contain them). They are unlikely to hinder their proper display in existing reading agents except in the case of the References-header in agents which thread articles. Therefore, it is provided that they SHOULD NOT be generated except where permitted by the previous standards. o Because of its importance to all serving agents, the extension permitting whitespace and folding in Newsgroups-headers SHOULD NOT be used until it has been widely deployed amongst relaying agents. User agents are unaffected. o The new style of Path-header is already consistent with the previous standards. However, the intention is that relaying agents should eventually reject articles in the old style, and so this possibility should be offered as a configurable option in relaying agents. User agents are unaffected. o The vast majority of serving, relaying and transport agents are believed to be already 8bit clean (in the slightly restricted sense in which that term is used in the MIME standards). User agents that do not implement MIME may be disadvantaged, but no more so than at present when faced with 8bit characters (which currently abound in spite of the previous standards). o The introduction of MIME reflects a practice that is already widespread. Articles in strict compliance with the previous standards (using strict US-ASCII) will be unaffected. Many user agents already support it, at least to the extent of widely used charsets such as ISO-8859-1. Users expecting to read articles using other charsets will need to acquire suitable reading agents. It is not intended, in general, that any single user agent will be able to display every charset known to IANA, but all such agents MUST support US-ASCII. Serving and relaying agents are not affected. o The use of the UTF-8 charset for headers will not affect any existing usage that complies with the previous standards, since US-ASCII is a strict subset of UTF-8. Insofar as newsgroup-names containing non-ASCII characters can now be expected to arise, some support from serving and relaying agents will be desirable, although it has been established that most current serving agents can already cope with such names without modification (although perhaps not in an ideal manner). Note that it is not necessary for serving and relaying agents to understand all the characters available in UTF-8, though it is desirable for them to be displayable for diagnostic purposes via some escape mechanism C. H. Lindsey [Page 16] News Article Format August 2002 using, for example, the visible subset of US-ASCII. For users expecting to use the more exotic possibilities available under UTF-8, the remarks already made in connection with MIME will apply. o The new Control: mvgroup command will need to be implemented in serving agents. For the benefit of older serving agents it is therefore RECOMMENDED that it be followed shortly by a corresponding newgroup command and it MUST always be followed by a rmgroup command for the old group after a reasonable overlap period. An implementation of the mvgroup command as an alias for the newgroup command would thus be minimally conforming. User agents are unaffected. o All the headers newly introduced by this standard can safely be ignored by existing software, albeit with loss of the new functionality. 4. Basic Format 4.1. Syntax of News Articles The overall syntax of a news article is: article = 1*( header CRLF ) separator body header = other-header other-header = header-name ":" 1*SP other-content header-name = 1*name-character *( "-" 1*name-character ) name-character = ALPHA / DIGIT other-content = separator = CRLF body = *( *998text CRLF ) However, the rule given above for header is incomplete. Further alternatives will be added incrementally as the various Netnews headers are introduced in this standard (or in future extensions), using the "=/" notation defined in [RFC 2234]. For example, a typical USENET-header would be defined as follows: header =/ USENET-header USENET-header = "USENET" ":" SP USENET-content *( ";" ( USENET-parameter / other-parameter ) ) USENET-content = USENET-parameter = where the USENET-parameter, which MUST always be of the same syntactic form as an other-parameter (see below), is not provided in all headers, and even the other-parameter is omitted in some cases cases (see 4.2.2). Observe that "USENET" is (and MUST be) of the syntactic form of a header-name. other-parameter = parameter = attribute "=" value attribute = [CFWS] token [CFWS] C. H. Lindsey [Page 17] News Article Format August 2002 x-token = "x-" token token = 1* tspecials = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" / DQUOTE / "/" / "[" / "]" / "?" / "=" value = [CFWS] token [CFWS] / quoted-string An article consists of some headers followed by a body. An empty line separates the two. The headers contain structured information about the article and its transmission. A header begins with a header-name identifying it, and can be continued onto subsequent lines as described in section 4.2.3. The body is largely unstructured text significant only to the poster and the readers. NOTE: Terminology here follows the current custom in the news community, rather than the [RFC 2822] convention of referring to what is here called a "header" as a "header-field" or "field". Note that the separator line MUST be truly empty, not just a line containing white space. Further empty lines following it are part of the body, as are empty lines at the end of the article. NOTE: The syntax above defines the canonical form of a news article as a sequence of lines each terminated by CRLF. This does not prevent serving agents or transport agents from storing or handling the article in other formats (e.g. using a single LF in place of CRLF) so long as the overall effects achieved are as defined by this standard when operating on the canonical form. 4.2. Headers The order of headers in an article is not significant. However, posting agents are encouraged to put mandatory headers (section 5) first, followed by optional headers (section 6), followed by experimental headers and headers not defined in this standard or its extensions. Relaying agents MUST NOT change the order of the headers in an article. 4.2.1. Naming of Headers Despite the restrictions on header-name syntax imposed by the grammar, relaying and reading agents SHOULD tolerate header-names containing any US-ASCII printable character other than colon (":", US-ASCII 58). Whilst relaying agents MUST accept, and pass on unaltered, any non- variant header whose header-name is syntactically correct, and reading agents MUST enable them to be displayed, at least optionally, posting and injecting agents SHOULD NOT generate headers other than o headers established by this standard or any extension to it; o those recognized by other IETF-established standards, notably the Email standard [RFC 2822] and its extensions, excluding any explicitly deprecated for Netnews (e.g. see section 9.2.1 for the C. H. Lindsey [Page 18] News Article Format August 2002 deprecated Disposition-Notification-To-header); or, alternatively, those listed in some future IANA registry of recognized headers; o experimental headers beginning with "X-" (as defined in 4.2.5.1); o on a provisional basis only, headers related to new protocols under development which are the subject of (or intended to be the subject of) some IETF-approved RFC (whether Informational, Experimental or Standards-Track). However, software SHOULD NOT attempt to interpret headers not specifically intended to be meaningful in the Netnews environment. Header-names are case-insensitive. There is a preferred case convention, which posters and posting agents Ought to use: each hyphen-separated "word" has its initial letter (if any) in uppercase and the rest in lowercase, except that some abbreviations have all letters uppercase (e.g. "Message-ID" and "MIME-Version"). The forms given in the various rules defining headers in this standard are the preferred forms for them. Relaying and reading agents MUST, however, tolerate articles not obeying this convention. 4.2.2. MIME-style Parameters The possibility of allowing MIME-style parameters (whether header- specific ones or generic other-parameters) to appear in virtually all headers is provided mainly for the purpose of allowing future extensions to existing headers, since only a very few specific parameters are defined in this standard. Observe that such parameters do not, in general, occur in headers defined in other standards, except for the MIME standards [RFC 2045] et seq. and their extensions. Other-parameters (whether those defined elsewhere or experimental parameters whose attribute is an x-token) MAY be used, where the syntax so allows, in any of the headers defined in this standard or its extensions except that, at present, they SHOULD NOT be used in headers in widespread use prior to the introduction of this standard (this restriction is likely to be removed in a future version of this standard). Nevertheless, compliant software MUST accept such parameters where required by this standard (ignoring them if their meaning is unknown) and SHOULD accept (and ignore) them in all structured headers wherever defined. NOTE: The syntax does not permit other-parameters in unstructured headers (where they are unnecessary) or in certain headers (notably the From-, Reply-To-, Mail-Copies-To- and Complaints-To-headers) containing address-lists or mailbox-lists (so that agents can simply replace the header-name by "To" or "Cc" to obtain a header immediately suitable for sending Email, and also so as to avoid some minor parsing problems with
es). Each header-specific MIME-style parameter introduced in this standard is described by specifying (a) the token to be used in its attribute, and C. H. Lindsey [Page 19] News Article Format August 2002 (b) the syntax rule(s) defining the object(s) permitted in its value. If a value object is not of the syntactic form of a token, it MUST (and otherwise MAY) be encapsulated in a quoted-string (see 2.4.3). Observe that the syntax of a parameter also allows additional WSP, folding and comments. The semantics of a parameter is always to associate the token in its attribute with the object represented by the token, or the semantic value (2.4.3) of the quoted-string, contained in its value. For example, the posting-sender-parameter (6.19) is defined to be where sender-value = mailbox / "verified" A valid posting-sender-parameter would be sender = "\"Joe D. Bloggs\" " (authinfo) The comment (syntactically part of the quoted-string) is irrelevant. The actual mailbox (to be used, for example, if email is to be sent to the sender) is "Joe D. Bloggs" 4.2.3. White Space and Continuations Each header is logically a single line of characters comprising the header-name, the colon with its following SP, the content, and any parameters. For convenience, however, the content and parameters can be "folded" into a multiple line representation by inserting a CRLF before any WSP contained within any FWS or CFWS (but not any other SP or HTAB) allowed by this standard. For example, the header: Approved: modname@modsite.example (Moderator of example.foo.bar) can be represented as: Approved: modname@modsite.example (Moderator of example.foo.bar) FWS occurs at many places in the syntax (usually within a CFWS) in order to allow the inclusion of comments, whitespace and folding. The syntax is in fact ambiguous insofar as it sometimes allows two consecutive instantiations of FWS (as least one of which is always optional), or of an optional FWS followed by an explicit CRLF. However, all such cases MUST be treated as if the optional instantiation (or one of them) had not been allowed. It is thus precluded that any line of a header should be made up of whitespace characters and nothing else (for such a line might otherwise have been interpreted by a non-compliant agent as the separator between the headers and the body of the article). NOTE: This does not lead to semantic ambiguity because, unless specifically stated otherwise, the presence or absence of folding, a comment or additional WSP has no semantic meaning and, in particular, it is a matter of indifference whether it forms a part of the syntactic construct preceding it or the one following it. C. H. Lindsey [Page 20] News Article Format August 2002 NOTE: It may be observed that the content part of every header begins and ends with an optional CFWS (or FWS in the case of a few headers). Moreover, every parameter also begins and ends with an optional CFWS. NOTE: Although contents are defined in such a way that folding can take place between many of the lexical tokens (and even within some of them), folding should be limited to placing the CRLF at higher-level syntactic breaks, and should also avoid leaving trailing WSP on the preceding line. For instance, if a header-content is defined as comma-separated values, it is recommended that folding occur after the comma separating the values, even if it is allowed elsewhere. In accordance with the syntax, the header-name on the first line MUST be followed by a SP (even if the rest of the header is empty, but see 4.2.6). Even though the syntax allows otherwise, at least some of the content MUST appear on that first line (to avoid the possibility of harm by any non-compliant agent that might eliminate a trailing WSP). Although posting agents are REQUIRED to enforce these restrictions, relaying and serving agents SHOULD accept articles that violate them. NOTE: This standard differs from [RFC 2822] in requiring that SP following the colon (it was also an [RFC 1036] requirement). Posters and posting agents SHOULD use SP, not HTAB, where white space is desired in headers (some existing software expects this). Relaying and serving agents SHOULD accept HTAB in all such cases, however. 4.2.4. Comments Strings of characters which are treated as comments may be included in headers wherever the syntactic element CFWS occurs. They consist of characters enclosed in parentheses. Comments may be nested. NOTE: Although CFWS occurs wherever whitespace is allowed in almost all headers, there are exceptions where only FWS is permitted (hence folding but no comments). Notably, this happens in the case of the Message-ID-, Newsgroups-, Distribution-, Path- and Followup-To-headers, and within the Date-header except right at the end. A comment is normally used to provide some human readable informational text, except at the end of a mailbox which contains no phrase, as in fred@foo.bar.example (Fred Bloggs) as opposed to "Fred Bloggs" . The former is a deprecated, but commonly encountered, usage and reading agents SHOULD take special note of such comments as indicating the name of the person whose mailbox it is. In all other situations a comment is semantically interpreted as a single SP. C. H. Lindsey [Page 21] News Article Format August 2002 Since a comment is allowed to contain FWS, folding is permitted within it as well as immediately preceding and immediately following it. Also note that, since quoted-pair is allowed in a comment, the parenthesis and backslash characters may appear in a comment so long as they appear as a quoted-pair. Semantically, the enclosing parentheses are not part of the content of the comment; the content is what is contained between the two parentheses. Since comments have not hitherto been permitted in news articles, except in a few specified places, posters and posting-agents SHOULD NOT insert them except in those places, namely following addresses in From and similar headers, and to indicate the name of the timezone in Date-headers. However, compliant software MUST accept them in all places where they are syntactically allowed. 4.2.5. Header Properties There are three special properties that may apply to particular headers, namely: "experimental", "inheritable", and "variant". When a header is defined, in this (or any future) standard, as having one (or possibly more) of these properties, it is subject to special treatment, as indicated below. 4.2.5.1. Experimental Headers Experimental headers are those whose header-names begin with "X-". They are to be used for experimental Netnews features, or for enabling additional material to be propagated with an article. They are not (and will not be) defined by this, or any, standard. NOTE: Experimental headers are suitable for situations where they need only to be human readable. They are not intended to be recognized by widely deployed Netnews software and, should such a requirement be envisaged, it is preferable to use a normal header on the provisional basis set out in section 4.2.1. 4.2.5.2. Inheritable Headers Subject only to the overriding ability of the poster to determine the contents of the headers in a proto-article, headers with the inheritable property MUST be copied by followup agents (perhaps with some modification) into the followup article, and headers without that property MUST NOT be so copied. Examples include: o Newsgroups (5.5) - copied from the precursor, subject to any Followup-To-header. o Subject (5.4) - modified by prefixing with "Re: ", but otherwise copied from the precursor. o References (6.10) - copied from the precursor, with the addition of the precursor's Message-ID. o Distribution (6.6) - copied from the precursor. NOTE: The Keywords-header is not inheritable, though some older newsreaders treated it as such. C. H. Lindsey [Page 22] News Article Format August 2002 4.2.5.3. Variant Headers Headers with the variant property may differ between (or even be completely absent from) copies of the same article as stored or relayed throughout a Netnews system. The manner of the difference (or absence) MUST be as specified in this (or any future) standard. Typically, these headers are modified as articles are propagated, or they reflect the status of the article on a particular serving agent, or cooperating group of such agents. The variant header MAY be placed anywhere within the headers (though placing it first is recommended). The principal examples are: o Path (5.6) - augmented at each relaying agent that an article passes through. o Xref (6.16) - used to keep track of the article locators of crossposted articles so that newsreaders serviced by a particular serving agent can mark such articles as read. 4.2.6. Undesirable Headers A header whose content is empty is said to be an empty header (in fact, no such headers are defined by this standard). Relaying and reading agents SHOULD NOT consider presence or absence of an empty header to alter the semantics of an article (although syntactic rules, such as requirements that certain header-names appear at most once, MUST still be satisfied). Posting and injecting agents SHOULD delete empty headers from articles before posting them; relaying agents MUST pass them untouched. Headers that merely state defaults explicitly (e.g., a Followup-To- header with the same content as the Newsgroups-header, or a MIME Content-Type-header with contents "text/plain; charset=us-ascii") or state information that reading agents can typically determine easily themselves (e.g. the length of the body in octets) are redundant and posters and posting agents Ought Not to include them. 4.3. Body 4.3.1. Body Format Issues The body of an article SHOULD NOT be empty. A posting or injecting agent which does not reject such an article entirely SHOULD at least issue a warning message to the poster and supply a non-empty body. Note that the separator line MUST be present even if the body is empty. NOTE: Some existing news software is known to react badly to body-less articles, hence the request for posting and injecting agents to insert a body in such cases. The sentence "This article was probably generated by a buggy news reader" has traditionally been used in this situation. Note that an article body is a sequence of lines terminated by CRLFs, not arbitrary binary data, and in particular it MUST end with a CRLF. However, relaying and serving agents SHOULD treat the body of an C. H. Lindsey [Page 23] News Article Format August 2002 article as an uninterpreted sequence of octets (except as mandated by changes of CRLF representation and by control message processing, as in 7.2.4) and SHOULD avoid imposing constraints on it. See also section 4.5. Posters SHOULD avoid using control characters and escape sequences except for tab (US-ASCII 9), formfeed (US-ASCII 12) and, possibly, backspace (US-ASCII 8). Tab signifies sufficient horizontal white space to reach the next of a set of fixed positions; posters are warned that there is no standard set of positions, so tabs should be avoided if precise spacing is essential. Formfeed (which is sometimes referred to as the "spoiler character") signifies a point at which a reading agent Ought to pause and await reader interaction before displaying further text. NOTE: Passing other control characters or escape sequences unaltered to a display or printing device is likely to have unpredictable results, except in the case of a device adapted to the special needs of some particular character set. NOTE: Backspace was historically used for underlining, done by an underscore (US-ASCII 95), a backspace, and a character, repeated for each character that should be underlined. Posters are warned that underlining is not available on all output devices or supported by all reading agents and is best not relied on for essential meaning. 4.3.2. Body Conventions A body is by default an uninterpreted sequence of octets for most of the purposes of this standard. However, a MIME Content-Type-header may impose some structure or intended interpretation upon it, and may also specify the character set in accordance with which the octets are to be interpreted. The following conventions for quotations, attributions and signatures, although not mandated by this standard, describe widely used practices. They are documented here in order to establish their correct usage, and the use of the words "MUST", "SHOULD", etc. is to be understood in that context. It is conventional for followup agents to enable the incorporation of the followed-up article (the "precursor") as a quotation. This SHOULD be done by prefacing each line of the quoted text (even if it is empty) with the character ">" (or perhaps with "> " in the case of a previously unquoted line). This will result in multiple levels of ">" when quoted content itself contains quoted content, and it will also facilitate the automatic analysis of articles. NOTE: Posters should edit quoted context to trim it down to the minimum necessary. However, followup agents Ought Not to attempt to enforce this beyond issuing a warning (past attempts to do so have been found to be notably counter-productive). C. H. Lindsey [Page 24] News Article Format August 2002 The followup agent SHOULD also precede the quoted content by an "attribution line" (however, readers are warned not to assume that they are accurate, especially within multiply nested quotations). The following convention for such lines is intended to facilitate their automatic recognition and processing by sophisticated reading agents. The attribution SHOULD contain the name and/or the email address of the precursor's poster, as in Joe D. Bloggs wrote: or Helmut Schmidt schrieb: The attribution MAY contain also a single newsgroup-name (the one from which the followup is being made), the precursor's Message-ID and/or the precursor's Date and Time. Any of these that are present, SHOULD precede the name and/or email address. However, the inclusion or not of such fields Ought always to be under the control of the poster. To enable this line, and the Message-ID and the email address within it, to be recognized (for example to enable suitable reading agents to retrieve the precursor or email its poster by clicking on them), the following conventions SHOULD be observed: o The precursor's Message-ID SHOULD be enclosed within <...> or o The precursor's poster's email address SHOULD be enclosed within <...> o The various fields may be separated by arbitrary text and they may be folded in the same way as headers, but attributions SHOULD always be terminated by a ":" followed by CRLF. Further examples: On comp.foo in <1234@bar.example> on 24 Dec 2001 16:40:20 +0000, Joe D. Bloggs wrote: Am 24. Dez 2001 schrieb Helmut Schmidt : A "personal signature" is a short closing text automatically added to the end of articles by posting agents, identifying the poster and giving his network addresses, etc. Whenever a poster or posting agent appends such a signature to an article, it MUST be preceded with a delimiter line containing (only) two hyphens (US-ASCII 45) followed by one SP (US-ASCII 32). The signature is considered to extend from the last occurrence of that delimiter up to the end of the article (or up to the end of the part in the case of a multipart MIME body). Followup agents, when incorporating quoted text from a precursor, Ought Not to include the signature in the quotation. Posting agents Ought to discourage (at least with a warning) signatures of excessive length (4 lines is a commonly accepted limit). C. H. Lindsey [Page 25] News Article Format August 2002 4.4. Characters and Character Sets Transmission paths for news articles MUST treat news articles as uninterpreted sequences of octets, excluding the values 0 (US-ASCII NUL) and 13 and 10 (US-ASCII CR and LF, which MUST ONLY appear in the combination CRLF which denotes a line separator). NOTE: this corresponds to the range of octets permitted for MIME "8bit data" [RFC 2045]. Thus raw binary data cannot be transmitted in an article body except by the use of a Content- Transfer-Encoding such as base64. Character data is represented by octets in accordance with some encoding scheme (UTF-8 for headers, and determined by the Content- Type- and Content-Transfer-Encoding-headers for bodies). If it comes to a relaying agent's attention that it is being asked to pass an article using the Content-Transfer-Encoding "8bit" to a relaying agent that does not support it, it SHOULD report this error to its administrator. It MUST refuse to pass the article and MUST NOT re-encode it with different MIME encodings. NOTE: This strategy will do little harm. The target relaying agent is unlikely to be able to make use of the article on its own servers, and the usual flooding algorithm will likely find some alternative route to get the article to destinations where it is needed. 4.4.1. Character Sets within Article Headers Within article headers, characters are represented as octets according to the UTF-8 encoding scheme [RFC 2279] or [ISO/IEC 10646], and hence all the characters in Unicode [UNICODE 3.2] or in the Universal Multiple-Octet Coded Character Set (UCS) [ISO/IEC 10646] (which is essentially a superset of Unicode and expected to remain so) are potentially available. However, processing all octets in the same manner as US-ASCII characters should ensure correct behaviour in most situations. NOTE: UTF-8 is an encoding for the [ISO/IEC 10646] character set (in both its 16 and 32 bit forms) with the property that any octet less than 128 immediately represents the corresponding US-ASCII character, thus ensuring upwards compatibility with previous practice. Non-ASCII characters from Unicode are represented by sequences of octets satisfying the syntax of a UTF8-xtra-char (2.4.2), which excludes certain octet sequences not explicitly permitted by [RFC 2279]. Unicode includes all characters from the ISO-8859 series of characters sets [ISO 8859] (which includes all Cyrillic, Greek and Arabic characters) together with the more elaborate characters used in Asian countries. See the NOTEs in the following section for the appropriate treatment of Unicode characters by reading agents. C. H. Lindsey [Page 26] News Article Format August 2002 [The sentence mentioning [RFC 2279] could be simplified if [RFC 2279bis] has been accepted by the time this standard is published.] Notwithstanding the great flexibility permitted by UTF-8, there is need for restraint in its use in order that the essential components of headers may be discerned using reading agents that cannot present the full Unicode range. In particular, header-names and tokens MUST be in US-ASCII, and certain other components of headers, as defined elsewhere in this standard - notably msg-ids, date-times, dot-atoms, domains and path-identities - MUST be in US-ASCII. Comments, phrases (as in mailboxes) and unstructured headers (such as the Subject-, Organization- and Summary-headers) MAY use the full range of UTF-8 characters, but SHOULD nevertheless be invariant under Unicode normalization NFC [UNICODE 3.2]. NOTE: Unicode allows for composite characters made up of a starter character - which can be a letter, number, punctuation mark, or symbol - plus zero or more combining marks (such as accents, diacritics, and similar). The requirement that a composite be invariant under normalization NFC means that, where it could be written in more than one way, only one particular one of those ways is allowed (for example, the single character E-acute is preferred over E followed by a non-spacing acute accent, and A-ring is preferred over the Angstrom symbol). At least for the main European languages, for which all the needed composites are already available as single characters, it is unlikely that posting agents will need to take any special steps to ensure normalization. In the particular case of newsgroup-names (see 5.5) there are more stringent requirements regarding the normalization and other usages of Unicode. Where the use of non-ASCII characters is permitted as above, they MAY be encoded in UTF-8 and they MAY be encoded using the MIME mechanisms defined in [RFC 2047] and [RFC 2231], but only in those contexts explicitly mentioned in those documents (unstructured headers, phrases and comments in the one, quoted-strings within parameters in the other). Encoding by other means is not compliant with this standard. Nevertheless, encoding using other character sets (with no indication of which one beyond the user's ability to guess based upon other clues in the article, or custom within the newsgroup) has been in use in some hierarchies, and such usage may be expected to continue for some period after the introduction of this standard. Reading agents MUST support the use of UTF-8, [RFC 2047] and [RFC 2231] in headers and they MAY, when it is detected that none of these has been used, attempt to interpet the header according to whatever other character set can be deduced, or has been configued as a default by the reader. NOTE: It is possible to determine, with a high degree of accuracy, when a given text containing octets with the 8th bit set was not encoded using UTF-8, and using this test to recover C. H. Lindsey [Page 27] News Article Format August 2002 such non-compliant texts is therefore commended where no other harm could arise. Exceptionally, Newsgroups-headers (5.5) MUST use UTF-8 in order to ensure that they appear in their canonical form (in any case, a Newsgroups-header is not one of the acceptable contexts of [RFC 2047]). Certain exceptions to this rule are provided (8.7 and 8.8.1) for use when mailing to moderators and other gatewaying applications. NOTE: The choice between UTF-8 and [RFC 2047] when posting depends on various factors. Some reading agents do not recogize [RFC 2047], and some are incapable of decoding UTF-8 (though there in an increasing tendency for modern reading agents to understand, or to be configurable to understand, both). Since headers encoded in UTF-8 are currently prohibited in Email, special consideration needs to be given to articles that are both posted and mailed (6.9) or which are mailed to moderators (see 8.2.2). Posters and implementors of posting agents need to take account of all these factors when deciding which method to use. 4.4.2. Character Sets within Article Bodies Within article bodies, characters are represented as octets according to the encoding scheme implied by any Content-Transfer-Encoding- and Content-Type-headers [RFC 2045]. In the absence of such headers, reading agents cannot be relied upon to display correctly more than the US-ASCII characters, though they MUST display at least those. NOTE: Observe that reading agents are not forbidden to "guess" when confronted with unannounced non-ASCII characters, and in particular it would be reasonable at least to test whether they were in the form of valid UTF-8 (see also the suggestion for such a test in 4.4.1). NOTE: It is not expected that reading agents will necessarily be able to present characters in all possible character sets. For example, a reading agent might be able to present only the ISO- 8859-1 (Latin 1) characters [ISO 8859], in which case it Ought to present undisplayable characters using some distinctive glyph, or by exhibiting a suitable warning. Followup agents MUST be careful to apply appropriate encodings to the outbound followup. A followup to an article containing non-ASCII material is very likely to contain non-ASCII material itself. 4.5. Size Limits Posting agents SHOULD endeavour to keep all header lines, so far as is possible, within 79 characters by folding them at suitable places (see 4.2.3). However, posting agents MUST permit the poster to include longer headers if he so insists, and compliant software MUST support headers of at least 998 octets. Likewise, injecting agents SHOULD fold any headers generated automatically by themselves. C. H. Lindsey [Page 28] News Article Format August 2002 Relaying agents MUST NOT fold headers (i.e. they must pass on the folding as received). NOTE: There is NO restriction on the number of lines into which a header may be split, and hence there is NO restriction on the total length of a header (in particular it may, by suitable folding, be made to exceed the 998 octets restriction pertaining to a single header line). The syntax provides for the lines of a body to be up to 998 octets in length, not including the CRLF. All software compliant with this standard MUST support lines of at least that length, both in headers and in bodies, and all such software SHOULD support lines of arbitrary length. In particular, relaying agents MUST transmit lines of arbitrary length without truncation or any other modification. NOTE: The limit of 998 octets is consistent with the corresponding limit in [RFC 2822]. In plain-text messages (those with no MIME headers, or those with a MIME Content-Type of text/plain) posting agents Ought to endeavour to keep the length of body lines within some reasonable limit. The size of this limit is a matter of policy, the default being to keep within 79 characters at most, and preferably within 72 characters (to allow room for quoting in followups). Exceptionally, posting agents Ought Not to adjust the length of quoted lines in followups unless they are able to reformat them in a consistent manner. Moreover, posting agents MUST permit the poster to include longer lines if he so insists. NOTE: Plain-text messages are intended to be displayed "as-is" without any special action (such as automatic line splitting) on the part of the recipient. The policy limit (e.g. 72 or 79) should be expressed as a number of characters (as they will be displayed by a reading agent) rather than as the number of octets used to encode them. NOTE: This standard provides no upper bound on the overall size of a single article, but neither does it forbid relaying agents from dropping articles of excessive length. It is, however, suggested that any limits thought appropriate by particular agents would be more appropriately expressed in megabytes than in kilobytes. 4.6. Example Here is a sample article: Path: server.example/unknown.site2.example@site2.example/ relay.site.example/site.example/injector.site.example%jsmith Newsgroups: example.announce,example.chat Message-ID: <9urrt98y53@site1.example> From: Ann Example Subject: Announcing a new sample article. C. H. Lindsey [Page 29] News Article Format August 2002 Date: Wed, 27 Mar 2002 12:12:50 +0300 Approved: example.announce moderator Followup-To: example.chat Reply-To: Ann Example Expires: Mon, 22 Apr 2002 12:12:50 +0300 Organization: Site1, The Number one site for examples. User-Agent: ExampleNews/3.14 (Unix) Keywords: example, announcement, standards, RFC 1036, Usefor Summary: The URL for the next standard. Injector-Info: injector.site.example; posting-host=du003.site.example Complaints-To: abuse@site.example Just a quick announcement that a new standard example article has been released; it is in the new USEFOR standard obtainable from ftp.ietf.org. Ann. -- Ann Example Sample Poster to the Stars "The opinions in this article are bloody good ones" - J. Clarke. [The RFC Editor is invited to change the above Date and Expires headers to match the actual publication dates and to insert its correct URL.] 5. Mandatory Headers An article MUST have one, and only one, of each of the following headers: Date, From, Message-ID, Subject, Newsgroups, Path. Note also that there are situations, discussed in the relevant parts of section 6, where References-, Sender-, or Approved-headers are mandatory. In control messages, specific values are required for certain headers. A proto-article (see 8.2.1) may lack some of these mandatory headers, but they MUST then be supplied by the injecting agent. 5.1. Date The Date-header contains the date and time that the article was prepared by the poster ready for transmission and SHOULD express the poster's local time. The content syntax makes use of syntax defined in [RFC 2822], subject to the following revised definition of zone. header =/ Date-header Date-header = "Date" ":" SP Date-content *( ";" other-parameter ) Date-content = date-time zone = (( "+" / "-" ) 4DIGIT) / "UT" / "GMT" The forms "UT" and "GMT" (indicating universal time) are to be regarded as obsolete synonyms for "+0000". They MUST be be accepted, and passed on unchanged, by all agents, but they MUST NOT be generated as part of new articles by posting and injecting agents. C. H. Lindsey [Page 30] News Article Format August 2002 The date-time MUST be semantically valid as required by [RFC 2822]. Although folding white space is permitted throughout the date-time syntax, it is RECOMMENDED that a single space be used in each place that FWS appears (whether it is required or optional). NOTE: A convention that is sometimes followed is to add a comment, after the date-time, containing the time zone in human-readable form, but many of the abbreviations commonly used for this purpose are ambiguous. The value given by the is the only definitive form. In order to prevent the reinjection of expired articles into the news stream, relaying and serving agents MUST refuse "stale" articles whose Date-header predates the earliest articles of which they normally keep record, or which is more than 24 hours into the future (though they MAY use a margin less than that 24 hours). Relaying agents MUST NOT modify the Date-header in transit. 5.1.1. Examples Date: Sat, 26 May 2001 11:13:00 -0500 (EST) Date: 26 May 2001 16:13 +0000 Date: 26 May 2001 16:13 GMT (Obsolete) 5.2. From The From-header contains the email address(es), possibly including the full name(s), of the article's poster(s). The content syntax makes use of syntax defined in [RFC 2822], subject to the following revised definition of local-part. header =/ From-header From-header = "From" ":" SP From-content From-content = mailbox-list addr-spec = local-part "@" domain local-part = dot-atom / strict-quoted-string NOTE: This syntax ensures that the local-part of an addr-spec is restricted to pure US-ASCII (and is thus in strict compliance with [RFC 2822]), whilst allowing any UTF-8 character to be used in a preceding quoted-string containing the poster's full name. If some future extension to the Email protocols should relax this restriction, one would expect the Netnews protocols to follow. Observe that there is no provision for parameters in this header, or in other headers containing addresses likely to be used for sending email (see 4.2.2). Each mailbox in the From-content SHOULD be a valid address, belonging to the poster(s) of the article, or person or agent on whose behalf the post is being sent (see the Sender-header, 6.2). When, for whatever reason, the poster does not wish to include such an address, the From-content SHOULD then be an address which ends in the top C. H. Lindsey [Page 31] News Article Format August 2002 level domain of ".invalid" [RFC 2606]. NOTE: Since such addresses ending in ".invalid" are undeliverable, user agents Ought to warn any user attempting to reply to them and Ought Not, in any case, to attempt to deliver to them (since that would be pointless anyway). Whether or not a valid address can subsequently be extracted from such an address falls outside the scope of this standard (obviously, posters wishing to disguise their address need to do more than just add ".invalid" to it). Be warned, however, that some injecting agents which are unable to detect that the address belongs to the poster may choose to insert a Sender-header (but see 8.2.2) or some entry in an Injector-Info-header (6.19) which discloses some valid address for the poster. 5.2.1. Examples: From: John Smith From: "John Smith" , dave@isp.example From: "John D. Smith" , andrew@isp.example, fred@site2.example From: Jan Jones From: Jan Jones From: dave@isp.example (Dave Smith) NOTE: the last example shows a now deprecated convention of putting a poster's full name in a comment following the mailbox, rather than in a phrase at the start of it. Observe also the use of the quoted-string "John D. Smith" which is required on account of presence of the '.' character, and which would also have been required had any UTF8-xtra-char been present. 5.3. Message-ID The Message-ID-header contains the article's message identifier, a unique identifier distinguishing the article from every other article. The content syntax makes use of syntax defined in [RFC 2822], subject to the following revised definitions of msg-id, no- fold-quote and no-fold-literal. header =/ Message-ID-header Message-ID-header = "Message-ID" ":" SP Message-ID-content *( ";" other-parameter ) Message-ID-content = [FWS] msg-id [FWS] msg-id = "<" id-left "@" id-right ">" id-left = dot-atom-text / no-fold-quote id-right = dot-atom-text / no-fold-literal no-fold-quote = DQUOTE *( strict-qtext / "\\" / "\" DQUOTE ) qspecial *( strict-qtext / "\\" / "\" DQUOTE ) DQUOTE C. H. Lindsey [Page 32] News Article Format August 2002 qspecial = "(" / ")" / ; same as specials except "<" / ">" / ; "\" and DQUOTE quoted "[" / "]" / ":" / ";" / "@" / "\\" / "," / "." / "\" DQUOTE no-fold-literal = "[" *( dtext / "\[" / "\]" / "\\" ) "]" The msg-id MUST NOT be more than 250 octets in length. NOTE: Observe that, in contrast to the corresponding header in [RFC 2822], the syntax does not allow comments within the Message-ID-header; this is to simplify processing by relaying and serving agents and to ensure interoperability with existing implementations. The restriction to strict-qtext ensures that no UTF8-xtra-char can appear. Msg-ids as defined here are a "normalized" subset of those defined by [RFC 2822], ensuring that no string of characters is quoted unless strictly necessary (it must contain at least one qspecial) and no single character is prefixed by a "\" in the form of a quoted-pair unless strictly necessary, and moreover there is no possibility for WSP to occur, whether quoted or not. The length restriction ensures that systems which accept message identifiers as a parameter when retrieving an article (e.g. [NNTP]) can rely on a bounded length. Observe that msg-id includes the '<' and '>'. An agent generating an article's message identifier MUST ensure that it is unique (as also required in [RFC 2822]) and that it is chosen in such a way that it will NEVER recur in either Netnews or Email. Moreover, even though commonly derived from the domain name of the originating site (and domain names are case-insensitive), a message identifier MUST NOT be altered in any way during transport, or when copied (as into a References-header), and thus a simple (case- sensitive) comparison of octets will always suffice to recognize that same message identifier wherever it subsequently reappears. NOTE: These requirements are to be contrasted with those of the un-normalized msg-ids defined by [RFC 2822], which may perfectly legitimately become normalized (or vice versa) during transport or copying in email systems. NOTE: Some old software may treat message identifiers that differ only in case within their id-right part as equivalent, and implementors of agents that generate message identifiers should be aware of this. 5.4. Subject The Subject-header contains a short string identifying the topic of the message. This is an inheritable header (4.2.5.2) to be copied into the Subject-header of any followup, in which case the new C. H. Lindsey [Page 33] News Article Format August 2002 Subject-content SHOULD then default to the string "Re: " (a "back reference") followed by the contents of the pure-subject of the precursor. Any leading "Re: " in that pure-subject MUST be stripped. header =/ Subject-header Subject-header = "Subject" ":" SP Subject-content Subject-content = [ [FWS] back-reference ] pure-subject pure-subject = unstructured back-reference = %x52.65.3A.20 ; which is a case-sensitive "Re: " The pure-subject MUST NOT begin with "Re: ". NOTE: The syntax of unstructured differs from that prescribed in [RFC 2822], so ensuring that the Subject-content is not permitted to be completely empty, or to consist of WSP only (see remarks in 4.2.6 concerning undesirable headers). Followup agents MAY remove strings that are known to be used erroneously as back-reference (such as "Re(2): ", "Re:", "RE: ", or "Sv: ") from the Subject-content when composing the subject of a followup, and add a correct back-reference in front of the result. NOTE: that would be "SHOULD remove instances" except that we cannot find a sufficiently robust and simple algorithm to do the necessary natural language processing. Followup agents MUST NOT use any other string except "Re: " as a back reference. Specifically, a translation of "Re: " into a local language or usage MUST NOT be used. NOTE: "Re" is an abbreviation for the Latin "In re", meaning "in the matter of", and not an abbreviation of "Reference" as is sometimes erroneously supposed. Agents SHOULD NOT depend on nor enforce the use of back references by followup agents. For compatibility with legacy news software, the Subject-content of a control message (i.e. an article that also contains a Control-header) MAY start with the string "cmsg ", and non-control messages MUST NOT start with the string "cmsg ". See also section 6.13. 5.4.1. Examples In the following examples, please note that only "Re: " is mandated by this standard. "was: " is a convention used by many English- speaking posters to signal a change in subject matter. Software can always recognize such changes from the References-header. Subject: Film at 11 Subject: Re: Film at 11 Subject: Godwin's law considered harmful (was: Film at 11) Subject: Godwin's law (was: Film at 11) C. H. Lindsey [Page 34] News Article Format August 2002 Subject: Re: Godwin's law (was: Film at 11) Subject: Re: Godwin's law 5.5. Newsgroups The Newsgroups-header's content specifies the newsgroup(s) in which the article is intended to appear. It is an inheritable header (4.2.5.2) which then becomes the default Newsgroups-header of any followup, unless a Followup-To-header is present to prescribe otherwise. Articles MUST NOT be passed between relaying agents or to serving agents unless the sending agent has been configured to supply and the receiving agent to receive at least one of the newsgroup- names in the Newsgroups-header. In order to allow newsgroup-names containing Non-ASCII characters, this section relies heavily on the provisions of the Unicode Standard. All references to "Unicode" mean [UNICODE 3.2] or any standard that supersedes it. That document contains guarantees of strict future upwards compatibility (e.g. no character will be removed or change classification). Implementors should be aware that currently unassigned code points (Unicode category Cn) may become valid characters in future versions of Unicode. Since the poster of an article might have access to a newer version of that standard, relaying and serving agents MUST accept such characters, but posting agents (and indeed all agents) MUST NOT generate them (though they might well follow up to newsgroup-names containing them). header =/ Newsgroups-header Newsgroups-header = "Newsgroups" ":" SP Newsgroups-content *( ";" other-parameter ) Newsgroups-content = [FWS] newsgroup-name *( [FWS] ng-delim [FWS] newsgroup-name ) [FWS] newsgroup-name = component *( "." component ) component = 1*component-grapheme ng-delim = "," component-grapheme = combiner-base *combiner-mark combiner-base = combiner-ASCII / combiner-extended combiner-ASCII = DIGIT / ALPHA / "+" / "-" / "_" combiner-extended = combiner-mark = NOTE: the excluded characters in a combiner-extended are control characters (Cc), format control characters (Cf), surrogates (Cs), marks (M*) and separators (Z*). In particular, this excludes all whitespace characters. To all intents and purposes, a component-grapheme is what a user might regard as a single "character" as displayed on his screen, though it might be transmitted as several actual characters (e.g. q-circumflex is two characters). Note also that, in some writing schemes, C. H. Lindsey [Page 35] News Article Format August 2002 several component-graphemes will merge into one visible object of variable size. Each component MUST be invariant under Unicode normalization NFKC (cf. the weaker normalization requirement for other headers in section 4.4.1 which specified no more than normalization NFC, and see also the explanatory NOTE in that section). NOTE: As a result of of this restriction, a name has only one valid form. Implementations can assume that a straight (case sensitive) comparison of characters or octets is sufficient to compare two newsgroup-names. The requirement that names be invariant under NFKC, rather than NFC, means that all characters with a "compatibility decomposition" are forbidden (Unicode provides the property "NFKC_NO" to make this test easier). The effect is to exclude variant forms of characters, such as superscripts and subscripts, wide and narrow forms, font variants, encircled forms, ligatures, and so on, as their use could cause confusion. There is insufficient experience in this area to determine whether this is the right long-term solution. Implementors should therefore be aware that a future version of this standard might reduce the requirement in the direction of NFC as opposed to NFKC. NOTE: An implementation is not required to apply NFKC, or any other normalization, to newsgroup-names. Only agencies that create new groups need to be careful to obey this restriction (7.2.1). However, if a posting agent neglects to normalize a newsgroup-name entered manually, this may lead to the user posting to a non-existent group without understanding why. Newsgroup-names containing non-ASCII characters MUST be encoded in UTF-8 and not according to [RFC 2047]. Components beginning with underline ("_") are reserved for use by future versions of this standard and MUST NOT occur in newsgroup- names (whether in Newsgroups-headers or in newgroup control messages (7.2.1)). However, such names MUST be accepted. Components beginning with "+" or "-" are reserved for use by implementations and MUST NOT occur in newsgroup-names (whether in Newsgroups-headers or in newgroup control messages). Implementors may assume that this rule will not change in any future version of this standard. NOTE: For example, implementors may safely use leading "+" and "-" to "escape" other entities within something that looks like a newsgroup-name. C. H. Lindsey [Page 36] News Article Format August 2002 Agencies responsible for the administration of particular hierarchies Ought to place additional restrictions on the characters they allow in newsgroup-names within those hierarchies (such as to accord with the languages commonly used within those hierarchies, or to avoid perceived ambiguities pertinent to those languages). Where there is no such specific policy, the following restrictions SHOULD be applied to newsgroup-names. NOTE: These restrictions are intended to reflect existing practice, with some additions to accommodate foreseeable enhancements, and are intended both to avoid certain technical difficulties and to avoid unnecessary confusion. It may well be that experience will allow future extensions to this standard to relax some or all of these restrictions. The specific restrictions (to be applied in the absence of established policies to the contrary) are: 1. The following characters are forbidden, subject to the comments and notes at the end of the list: characters in category Cn (Other, Not assigned) [1] characters in category Co (Other, Private Use) [2] characters in category Lt (Letter, Titlecase) [3] characters in category Lu (Letter, Uppercase) [3] characters in category Me (Mark, Enclosing) [4] characters in category Pd (Punctuation, Dash) [4][5] characters in category Pe (Punctuation, Close) [4] characters in category Pf (Punctuation, Final quote) [4] characters in category Pi (Punctuation, Initial quote) [4] characters in category Po (Punctuation, Other) [4] characters in category Ps (Punctuation, Open) [4] characters in category Sc (Symbol, Currency) [4] characters in category Sk (Symbol, Modifier) [4] characters in category Sm (Symbol, Math) [4][5] characters in category So (Symbol, Other) [4] [1] As new characters are added to Unicode, the code point moves from category Cn to some other category. As stated above, implementors should be prepared for this. [2] Specific private use characters can be used within a hierarchy or co-operating subnet that has agreed meanings for them. [3] Traditionally, newsgroup-names have been written in lowercase. Posting agents Ought Not to convert uppercase or titlecase characters to the corresponding lowercase forms except under the explicit instructions of the poster. [4] Traditionally newsgroup-names have only used letters, digits, and the three special characters "+", "-" and "_". These categories correspond to characters outside that set. C. H. Lindsey [Page 37] News Article Format August 2002 [5] Although the characters "+" and "-" are within categories Pd and Sm, they are not forbidden. 2. A component name is forbidden to consist entirely of digits. NOTE: This requirement was in [RFC 1036] but nevertheless several such groups have appeared in practice and implementors should be prepared for them. A common implementation technique uses each component as the name of a directory and uses numeric filenames for each article within a group. Such an implementation needs to be careful when this could cause a clash (e.g. between article 123 of group xxx.yyy and the directory for group xxx.yyy.123). 3. A component is limited to 30 component-graphemes and a newsgroup- name to 71 component-graphemes (counting also the '.'s separating the components). Whilst there is no longer any technical reason to limit the length of a component (formerly, it was limited to 14 octets) nor of a newsgroup-name, it should be noted that these names are also used in the newsgroups-line (7.2.1.2) where an overall policy limit applies and, moreover, excessively long names can be exceedingly inconvenient in practical use. Serving and relaying agents MUST accept any newsgroup-name that meets the above requirements, even if they violate one or more of the policy restrictions. Posting and injecting agents MAY reject articles containing newsgroup-names that do not meet these restrictions, and posting agents MAY attempt to correct them (but only with the explicit agreement of the poster for anything more than NFC or NFKC normalization). However, because of the large and changing tables required to do these checks and corrections throughout the whole of Unicode, this standard does not require them to do so. Rather, the onus is placed on those who create new newsgroups (7.2.1) to check the mandatory requirements, to consider the effects of relaxing the other restrictions, and to consider how all this may affect propagation of the group. Since future extensions to this standard and the Unicode standard, including a possible relaxation of the NFKC normalization, plus any relaxations of the default restrictions introduced by specific hierarchies might invalidate some such checks, warnings, and adjustments, implementations MUST incorporate means to disable them. NOTE: The newsgroup-name as encoded in UTF-8 should be regarded as the canonical form. Reading agents may convert it to whatever character set they are able to display and serving agents may possibly need to convert it to some form more suitable as a filename. Simple algorithms for both kinds of conversion are readily available. Observe that the syntax does not allow comments within the Newsgroups-header; this is to simplify processing by relaying and serving agents which have a requirement to process this header extremely rapidly. C. H. Lindsey [Page 38] News Article Format August 2002 The inclusion of folding white space within a Newsgroups-content is a newly introduced feature in this standard. It MUST be accepted by all conforming implementations (relaying agents, serving agents and reading agents). Posting agents should be aware that such postings may be rejected by overly-critical old-style relaying agents. When a sufficient number of relaying agents are in conformance, posting agents SHOULD generate such whitespace in the form of so as to keep the length of lines in the relevant headers (notably Newsgroups and Followup-To) to no more than than 79 characters (or other agreed policy limit - see 4.5). Before such critical mass occurs, injecting agents MAY reformat such headers by removing whitespace inserted by the posting agent, but relaying agents MUST NOT do so. Posters SHOULD use only the names of existing newsgroups in the Newsgroups-header. However, it is legitimate to cross-post to newsgroups which do not exist on the posting agent's host, provided that at least one of the newsgroups DOES exist there, and followup agents SHOULD accept this (posting agents MAY accept it, but Ought at least to alert the poster to the situation and request confirmation). Relaying agents MUST NOT rewrite Newsgroups-headers in any way, even if some or all of the newsgroups do not exist on the relaying agent's host. Serving agents MUST NOT create new newsgroups simply because an unrecognized newsgroup-name occurs in a Newsgroups-header (see 7.2.1 for the correct method of newsgroup creation). The Newsgroups-header is intended for use in Netnews articles rather than in email messages. It MAY be used in an email message to indicate that it is a copy also posted to the listed newsgroups, in which case the inclusion of a Posted-And-Mailed header (6.9) would also be appropriate. However, it SHOULD NOT be used in an email-only reply to a Netnews article (thus the "inheritable" property of this header applies only to followups to a newsgroup, and not to followups to the poster). Moreover, if a newsgroup-name contains any non-ASCII character, it may need to be encoded using the mechanism defined in section 5.5.2. See also the further discussion in section 8.8.1. 5.5.1. Forbidden newsgroup-names The following forms of newsgroup-name MUST NOT be used except for the specific purposes indicated: o Newsgroup-names having only one component. These are reserved for newsgroups whose propagation is restricted to a single host or local network, and for pseudo-newsgroups such as "poster" (which has special meaning in the Followup-To-header - see section 6.7), "junk" (often used by serving agents), and "control" (likewise); o Any newsgroup-name beginning with "control." (used as pseudo- newsgroups by many serving agents); o Any newsgroup-name containing the component "ctl" (likewise); o "to" or any newsgroup-name beginning with "to." (reserved for the ihave/sendme protocol described in section 7.4, and for test messages sent on an essentially point-to-point basis); o Any newsgroup-name beginning with "example." (reserved for C. H. Lindsey [Page 39] News Article Format August 2002 examples in this and other standards); o Any newsgroup-name containing the component "all" (because this is used as a wildcard in some implementations). A newsgroup-name SHOULD NOT appear more than once in the Newsgroups- header. The order of newsgroup-names in the Newsgroups-header is not significant, except for determining which moderator to send the article to if more than one of the groups is moderated (see 8.2). 5.5.2. Encoded newsgroup-names Where it is required to transport an article across some medium that cannot reliably convey the full 8 bits of each octet, such as when gatewaying it into Email (8.8.1), or when emailing it to a moderator or constructing the submission address of the moderator (8.2.2), it may be necessary to encode any newsgroup-name within a Newsgroups- or Followup-To-header that contains any non-ASCII character. For that purpose, the following algorithm is provided: 1. Initially, the newsgroup-name is in the form of a sequence of octets representing that name in the UTF-8 character set. 2. Each octet in the name in the range 0x80-FF is replaced by an "=" character (US-ASCII 61), followed by two characters representing that octet in hexadecimal, in which the hexadecimal digits "A" through "F" MUST be in uppercase. 3. Each octet in the name in the range 0x00-7F remains unaltered (and thus MUST NOT be replaced by its hexadecimal equivalent). NOTE: Observe that this algorithm provides a unique encoding for each newsgroup-name. Observe also that within the unaltered range 0x00-7F, only the octets 0x2B, 0x2D-2E, 0x30-39, 0x41-5A, 0x5F, and 0x61-7A can appear in a newsgroup-name. This standard provides no authority for the use of this algorithm other than in the context of newsgroup-names occurring within headers being conveyed by email. In particular, it MUST NOT be used within any article conveyed by the Netnews protocols and thus, if an email using it is subsequently returned to the Netnews environment, it MUST be decoded back into UTF-8. NOTE: Although the encoding defined by [RFC 2047] is available for use with other headers containing non-ASCII characters, the Newsgroups-header, being a structured header, is not one of the contexts permitted for its use (and moreover it would not produce a unique encoding nor cope well with newsgroup-names of excessive length). Therefore it SHOULD NOT be used within the Newsgroups-header. C. H. Lindsey [Page 40] News Article Format August 2002 5.6. Path The Path-header shows the route taken by a message since its entry into the Netnews system. It is a variant header (4.2.5.3), each agent that processes an article being required to add one (or more) entries to it. This is primarily to enable relaying agents to avoid sending articles to sites already known to have them, in particular the site they came from, and additionally to permit tracing the route articles take in moving over the network, and for gathering Usenet statistics. Finally the presence of a '%' path-delimiter in the Path-header can be used to identify an article injected in conformance with this standard. 5.6.1. Format header =/ Path-header Path-header = "Path" ":" SP Path-content *( ";" other-parameter ) Path-content = [FWS] *( path-identity [FWS] path-delimiter [FWS] ) tail-entry [FWS] path-identity = ( ALPHA / DIGIT ) *( ALPHA / DIGIT / "-" / "." / ":" / "_" ) path-delimiter = "/" / "?" / "%" / "," / "!" tail-entry = path-identity NOTE: A Path-content will inevitably contain at least one path- identity, except possibly in the case of a proto-article that has not yet been injected onto the network. NOTE: Observe that the syntax does not allow comments within the Path-header; this is to simplify processing by relaying and injecting agents which have a requirement to process this header extremely rapidly. A relaying agent SHOULD NOT pass an article to another relaying agent whose path-identity (or some known alias thereof) already appears in the Path-content. Since the comparison may be either case sensitive or case insensitive, relaying agents SHOULD NOT generate a name which differs from that of another site only in terms of case. A relaying agent MAY decline to accept an article if its own path- identity is already present in the Path-content or if the Path- content contains some path-identity whose articles the relaying agent does not want, as a matter of local policy. NOTE: This last facility is sometimes used to detect and decline control messages (notably cancel messages) which have been deliberately seeded with a path-identity to be "aliased out" by sites not wishing to act upon them. C. H. Lindsey [Page 41] News Article Format August 2002 5.6.2. Adding a path-identity to the Path-header When an injecting, relaying or serving agent receives an article, it MUST prepend its own path-identity followed by a path-delimiter to the beginning of the Path-content. In addition, it SHOULD then add CRLF and WSP if it would otherwise result in a line longer than 79 characters. The path-identity added MUST be unique to that agent. To this end it SHOULD be one of: 1. A fully qualified domain name (FQDN) associated (by the Internet DNS service [RFC 1034]) with an A record, which SHOULD identify the actual machine prepending this path-identity. Ideally, this FQDN should also be "mailable" (see below). 2. A fully qualified domain name (FQDN) associated (by the Internet DNS service) with an MX record, which MUST be "mailable". 3. An arbitrary name believed to be unique and registered at least with all sites immediately downstream from the given site. 4. An encoding of an IP address - or [RFC 2373] (the requirement to be able to use an is the reason for including ':' as an allowed character within a path- identity). The FQDN of an agent is "mailable" if the administrators of that agent can be reached by email using both of the forms "usenet@" and "news@", in conformity with [RFC 2142]. Of the above options, nos. 1 to 3 are much to be preferred, unless there are strong technical reasons dictating otherwise. In particular, the injecting agent's path-identity MUST, as a special case, be an FQDN as in option 1 or option 2, and MUST be mailable. Additionally, in the case of an injecting agent offering its services to the general public, its administrators MUST also be reachable using the form "abuse@" UNLESS a more specific complaints address has been specified in a Complaints-To-header (6.20). The injecting agent's path-identity MUST be followed by the special path-delimiter '%' which serves to separate the pre-injection and post-injection regions of the Path-content (see 5.6.3). In the case of a relaying or serving agent, the path-delimiter is chosen as follows. When such an agent receives an article, it MUST establish the identity of the source and compare it with the leftmost path-identity of the Path-content. If it matches, a '/' should be used as the path-delimiter when prepending the agent's own path- identity. If it does not match then the agent should prepend two entries to the Path-content; firstly the true established path- identity of the source followed by a '?' path-delimiter, and then, to the left of that, the agent's own path-identity followed by a '/' path-delimiter as usual. This prepending of two entries SHOULD NOT C. H. Lindsey [Page 42] News Article Format August 2002 be done if the provided and established identities match. Any method of establishing the identity of the source may be used (but see 5.6.5 below), with the consideration that, in the event of problems, the agent concerned may be called upon to justify it. NOTE: The use of the '%' path-delimiter marks the position of the injecting agent in the chain. In normal circumstances there should therefore be only one '%' path-delimiter present, and injecting agents MAY choose to reject proto-articles with a '%' already in them. If, for whatever reason, more than one '%' is found, then the path-identity in front of the leftmost '%' is to be regarded as the true injecting agent. 5.6.3. The tail-entry For historical reasons, the tail-entry (i.e. the rightmost entry in the Path-content) is regarded as a "user name", and therefore MUST NOT be interpreted as a site through which the article has already passed. Moreover, the Path-content as a whole is not an email address and MUST NOT be used to contact the poster. Posting and/or injecting agents MAY place any string here. When it is not an actual user name, the string "not-for-mail" is often used, but in fact a simple "x" would be sufficient. Often this field will be the only entry in the region (known as the pre-injection region) after the '%', although there may be entries corresponding to machines traversed between the posting agent and the injecting agent proper. In particular, injecting agents that receive articles from many sources MAY include information to establish the circumstances of the injection such as the identity of the source machine (especially if an Injector-Info-header (6.19) is not being provided). Any such inclusion SHOULD NOT conflict with any genuine site identifier. The '!' path-delimiter may be used freely within the pre-injection region, although '/' and '?' are also appropriate if used correctly. 5.6.4. Path-Delimiter Summary A summary of the various path-delimiters. The name immediately to the left of the path-delimiter is always that of the machine which added the path-delimiter. '/' The name immediately to the right is known to be the identity of the machine from which the article was received (either because the entry was made by that machine and we have verified it, or because we have added it ourselves). '?' The name immediately to the right is the claimed identity of the machine from which the article was received, but we were unable to verify it (and have prepended our own view of where it came from, and then a '/'). C. H. Lindsey [Page 43] News Article Format August 2002 '%' Everything to the right is the pre-injection region followed by the tail-entry. The name on the left is the FQDN of the injecting agent. The presence of two '%'s in a path indicates a double-injection (see 8.2.2). '!' The name immediately to the right is unverified. The presence of a '!' to the left of the '%' indicates that the identity to the left is that of an old-style system not conformant with this standard. ',' Reserved for future use, treat as '/'. Other Old software may possibly use other path-delimiters, which should be treated as '!'. But note in particular that ':', '-' and '_' are components of names, not path-delimiters, and FWS on its own MUST NOT be used as the sole path-delimiter. NOTE: Old Netnews relaying and injecting agents almost all delimit Path entries with a '!', and these entries are not verified. The presence of '%' indicates that the article was injected by software conforming to this standard, and the presence of '!' to the left of a '%' indicates that the message passed through systems developed prior to this standard. It is anticipated that relaying agents will reject articles in the old style once this new standard has been widely adopted. 5.6.5. Suggested Verification Methods It is preferable to verify the claimed path-identity against the source than to make routine use of the '?' path-delimiter, with consequential wasteful double-entry Path additions. If the incoming article arrives through some TCP/IP protocol such as NNTP, the IP address of the source will be known, and will likely already have been checked against a list of known FQDNs, IP addresses, or other registered aliases that the receiving site has agreed to peer with. Since the source host may have several IP addresses, checking the claimed FQDN or IP address against the source IP, or finding a suitable FQDN to report with a '?' path-delimiter, may involve several DNS lookups, following CNAME chains as required. Note that any reverse DNS lookup that is involved needs to be confirmed by a forward one. If the incoming article arrives through some other protocol, such as UUCP, that protocol MUST include a means of verifying the source site. In UUCP implementations, commonly each incoming connection has a unique login name and password, and that login name (or some alias registered for it) would be expected as the path-identity. C. H. Lindsey [Page 44] News Article Format August 2002 5.6.6. Example Path: foo.isp.example/ foo-server/bar.isp.example?10.123.12.2/old.site.example! barbaz/baz.isp.example%dialup123.baz.isp.example!x NOTE: That article was injected into the news stream by baz.isp.example (complaints may be addressed to abuse@baz.isp.example). The injector has taken care to record that it got it from dialup123.baz.isp.example. "x" is a dummy tail-entry, though sometimes a real userid is put there. The article was relayed, perhaps by UUCP, to the machine known, at least to its downstream, as "barbaz". Barbaz relayed it to old.site.example, which does not yet conform to this standard (hence the '!' path-delimiter). So one cannot be sure that it really came from barbaz. Old.site.example relayed it to a site claiming to have the IP address [10.123.12.2], and claiming (by using the '/' path- delimiter) to have verified that it came from old.site.example. [10.123.12.2] relayed it to "foo-server" which, not being convinced that it truly came from [10.123.12.2], did a reverse lookup on the actual source and concluded it was known as bar.isp.example (that is not to say that [10.123.12.2] was not a correct IP address for bar.isp.example, but simply that that connection could not be substantiated by foo-server). Observe that foo-server has now added two entries to the Path. "foo-server" is a locally significant name within the complex site of many machines run by foo.isp.example, so the latter should have no problem recognizing foo-server and using a '/' path-delimiter. Presumably foo.isp.example then delivered the article to its direct clients. It appears that foo.isp.example and old.site.example decided to fold the line, on the grounds that it seemed to be getting a little too long. 6. Optional Headers None of the headers appearing in this section is required to appear in every article but some of them are required in certain types of article, such as followups. Any header defined in this (or any other) standard MUST NOT appear more than once in an article unless specifically stated otherwise. Experimental headers (4.2.5.1) and headers defined by cooperating subnets are exempt from this requirement. See section 8 "Duties of Various Agents" for the full picture. C. H. Lindsey [Page 45] News Article Format August 2002 6.1. Reply-To The Reply-To-header specifies a reply address(es) to be used for personal replies for the poster(s) of the article when this is different from the poster's address(es) given in the From-header. The content syntax makes use of syntax defined in [RFC 2822], but subject to the revised definition of local-part given in section 5.2. header =/ Reply-To-header Reply-To-header = "Reply-To" ":" SP Reply-To-content Reply-To-content = address-list In the absence of Reply-To, the reply address(es) is the address(es) in the From-header. For this reason a Reply-To SHOULD NOT be included if it just duplicates the From-header. NOTE: Use of a Reply-To-header is preferable to including a similar request in the article body, because replying agents can take account of Reply-To automatically. 6.1.1. Examples Reply-To: John Smith Reply-To: John Smith , dave@isp.example Reply-To: John Smith ,andrew@isp.example, fred@site2.example 6.2. Sender The Sender-header specifies the mailbox of the person or entity which caused this article to be posted (and hence injected), if that person or entity is different from that given in the From-header or if more than one mailbox appears in the From-header. This header SHOULD NOT appear in an article unless the sender is different from the poster. This header is appropriate for use by automatic article posters. The content syntax makes use of syntax defined in [RFC 2822]. header =/ Sender-header Sender-header = "Sender" ":" SP Sender-content *( ";" other-parameter ) Sender-content = mailbox 6.3. Organization The Organization-header is a short phrase identifying the poster's organization. header =/ Organization-header Organization-header = "Organization" ":" SP Organization-content Organization-content= unstructured NOTE: Posting and injecting agents are discouraged from providing a default value for this header unless it is acceptable to all posters using those agents. Unless this header C. H. Lindsey [Page 46] News Article Format August 2002 contains useful information (including some indication of the posters physical location) posters are discouraged from including it. 6.4. Keywords The Keywords field contains a comma separated list of important words and phrases intended to describe some aspect of the content of the article. The content syntax makes use of syntax defined in [RFC 2822]. header =/ Keywords-header Keywords-header = "Keywords" ":" SP Keywords-content *( ";" other-parameter ) Keywords-content = phrase *( "," phrase ) NOTE: The list is comma separated, NOT space separated. NOTE: Contrary to the usage defined in [RFC 2822], this standard does not permit multiple occurrences of this header. 6.5. Summary The Summary-header is a short phrase summarizing the article's content. header =/ Summary-header Summary-header = "Summary" ":" SP Summary-content Summary-content = unstructured The summary should be terse. Authors Ought to avoid trying to cram their entire article into the headers; even the simplest query usually benefits from a sentence or two of elaboration and context, and not all reading agents display all headers. On the other hand the summary should give more detail than the Subject. 6.6. Distribution The Distribution-header is an inheritable header (see 4.2.5.2) which specifies geographical or organizational limits to an article's propagation. header =/ Distribution-header Distribution-header = "Distribution" ":" SP Distribution-content *( ";" other-parameter ) Distribution-content= distribution *( dist-delim distribution ) dist-delim = "," distribution = [FWS] distribution-name [FWS] distribution-name = ALPHA 1*distribution-rest distribution-rest = ALPHA / "+" / "-" / "_" NOTE: The use of ALPHA in the syntax ensures that distribution names are always in US-ASCII. C. H. Lindsey [Page 47] News Article Format August 2002 Articles MUST NOT be passed between relaying agents or to serving agents unless the sending agent has been configured to supply and the receiving agent to receive at least one of the distributions in the Distribution-header. Additionally, reading agents MAY also be configured so that unwanted distributions do not get displayed. NOTE: Although it would seem redundant to filter out unwanted distributions at both ends of a relaying link (and it is clearly more efficient to do so at the sending end), many sending sites have been reluctant, historically speaking, to apply such filters (except to ensure that distributions local to their own site or cooperating subnet did not escape); moreover they tended to configure their filters on an "all but those listed" basis, so that new and hitherto unheard of distributions would not be caught. Indeed many "hub" sites actually wanted to receive all possible distributions so that they could feed on to their clients in all possible geographical (or organizational) regions. Therefore, it is desirable to provide facilities for rejecting unwanted distributions at the receiving end. Indeed, it may be simpler to do so locally than to inform each sending site of what is required, especially in the case of specialized distributions (for example for control messages, such as cancels from certain issuers) which might need to be added at short notice. The possibility for reading agents to filter distributions has been provided for the same reason. Exceptionally, ALL relaying agents are deemed willing to supply or accept the distribution "world", and NO relaying agent should supply or accept the distribution "local". However, "world" SHOULD NEVER be mentioned explicitly since it is the default when the Distribution- header is absent entirely. "All" MUST NOT be used as a distribution-name. Distribution-names SHOULD contain at least three characters, except when they are two-letter country names as in [ISO 3166]. Distribution-names are case-insensitive (i.e. "US", "Us" and "us" all specify the same distribution). Posting agents Ought Not to provide a default Distribution-header without giving the poster an opportunity to override it. Followup agents SHOULD initially supply the same Distribution-header as found in the precursor. 6.7. Followup-To The Followup-To-header specifies which newsgroup(s) followups should be posted to. header =/ Followup-To-header Followup-To-header = "Followup-To" ":" SP Followup-To-content *( ";" other-parameter ) Followup-To-content = Newsgroups-content / [FWS] "poster" [FWS] C. H. Lindsey [Page 48] News Article Format August 2002 The syntax is the same as that of the Newsgroups-content, with the addition that the keyword "poster" is allowed. In the absence of a Followup-To-header, the default newsgroup(s) for a followup are those in the Newsgroups-header, and for this reason the Followup-To-header SHOULD NOT be included if it just duplicates the Newsgroups-header. A Followup-To-header consisting of the keyword "poster" indicates that the poster requests no followups to be sent in response to this article, only personal replies to the article's reply address. NOTE: A poster who wishes both a personal reply and a followup post should include an appropriate Mail-Copies-To-header (6.8). 6.8. Mail-Copies-To The Mail-Copies-To-header indicates whether or not the poster wishes to have followups to an article emailed in addition to being posted to Netnews and, if so, establishes the address to which they should be sent. The content syntax makes use of syntax defined in [RFC 2822], but subject to the revised definition of local-part given in section 5.2. header =/ Mail-Copies-To-header Mail-Copies-To-header = "Mail-Copies-To" ":" SP Mail-Copies-To-content Mail-Copies-To-content = copy-addr / [CFWS] ( "nobody" / "poster" ) [CFWS] copy-addr = address-list The keyword "nobody" indicates that the poster does not wish copies of any followup postings to be emailed. This indication is widely seen as a very strong wish, and is to be taken as the default when this header is absent. The keyword "poster" indicates that the poster wishes a copy of any followup postings to be emailed to him. Otherwise, this header contains a copy-addr to which the poster wishes a copy of any followup postings to be sent. NOTE: Some existing practice uses the keyword "never" in place of "nobody" and "always" in place of "poster". These usages are deprecated, but followup agents MAY observe them. The automatic actions of a followup agent in the various cases (subject to manual override by the user) are as follows: nobody (or when the header is absent) The followup agent SHOULD NOT, by default, email such a copy and Ought, especially when there is an explicit "nobody", to issue a warning and ask for confirmation if the user attempts to do so. C. H. Lindsey [Page 49] News Article Format August 2002 poster The followup agent Ought, by default, to email a copy, which MUST then be sent to the address(es) in the Reply-To-header, and in the absence of that to the address(es) in the From-header. copy-addr The followup agent Ought, by default, to email a copy, which MUST then be sent to the copy-addr. NOTE: This header is only relevant when posting followups to Netnews articles, and is to be ignored when sending pure email replies to the poster, which are handled as prescribed under the Reply-To-header (6.1). Whether or not this header will also find similar usage for replies to messages sent to mailing lists falls outside the scope of this standard. When emailing a copy, the followup agent SHOULD also include a "Posted-And-Mailed: yes" header (6.9). NOTE: In addition to the Posted-And-Mailed-header, some followup agents also include within the body a mention that the article is both posted and mailed, for the benefit of reading agents that do not normally show that header. 6.9. Posted-And-Mailed header =/ Posted-And-Mailed-header Posted-And-Mailed-header = "Posted-And-Mailed" ":" SP Posted-And-Mailed-content *( ";" other-parameter ) Posted-And-Mailed-content = [CFWS] ( "yes" / "no" ) [CFWS] This header, when used with the "yes" keyword, indicates that the article has been both posted to the specified newsgroups and emailed. It SHOULD be used when replying to the poster of an article to which this one is a followup (see the Mail-Copies-To-header in section 6.8) and it MAY be used when any article is also mailed to a recipient(s) identified in a To- and/or Cc-header that is also present. The "no" keyword is included for the sake of completeness; it MAY be used to indicate the opposite state, but is redundant insofar as it only describes the default state when this header is absent. This header, if present, MUST be included in both the posted and emailed versions of the article. The Newsgroups-header of the posted article SHOULD be included in the email version as recommended in section 5.5. All other headers defined in this standard (excluding variant headers) MUST be identical in both the posted and mailed versions of the article, except that headers containing UTF8-xtra- chars in the posted version MAY be encoded according to [RFC 2047] or [RFC 2231], or (in the case of a Newsgroups-header) to section 5.5.2, in the emailed version. In particular, the Message-ID-headers MUST be identical. The bodies MUST be identical in both, apart from a possible change of Content-Transfer-Encoding. C. H. Lindsey [Page 50] News Article Format August 2002 NOTE: This leaves open the question of whether a To- or a Cc- header should appear in the posted version. Naturally, a Bcc- header should not appear, except in a form which indicates that there are additional unspecified recipients. 6.10. References The References-header lists CFWS-separated message identifiers of precursors. The content syntax makes use of syntax defined in [RFC 2822], subject to the same revisions as in section 5.3. header =/ References-header References-header = "References" ":" SP References-content *( ";" other-parameter ) References-content = [CFWS] msg-id *( CFWS msg-id ) [CFWS] NOTE: This differs from the syntax of [RFC 2822] by requiring at least one CFWS between the msg-ids (a SP at this point was an [RFC 1036] requirement). A followup MUST have a References-header, and an article that is not a followup MUST NOT have a References-header. In a followup, if the precursor did not have a References-header, the followup's References-content MUST be formed by the message identifier of the precursor. A followup to an article which had a References-header MUST have a References-header containing the precursor's References- content (subject to trimming as described below) plus the precursor's message identifier appended to the end of the list (separated from it by CFWS). Followup agents SHOULD NOT trim message identifiers out of a References-header unless the number of message identifiers exceeds 21, at which time trimming SHOULD be done by removing sufficient identifiers starting with the second so as to bring the total down to 21 (but the first message identifier MUST NOT be trimmed). However, it would be wrong to assume that References-headers containing more than 21 message identifiers will not occur. 6.10.1. Examples References: References: References: <222@site1.example> <87tfbyv@site7.example> <67jimf@site666.example> References: 6.11. Expires The Expires-header specifies a date and time when the article is deemed to be no longer relevant and could usefully be removed ("expired"). The content syntax makes use of syntax defined in [RFC 2822]. C. H. Lindsey [Page 51] News Article Format August 2002 header =/ Expires-header Expires-header = "Expires" ":" SP Expires-content *( ";" other-parameter ) Expires-content = date-time An Expires-header should only be used in an article if the requested expiry time is earlier or later than the time typically to be expected for such articles. Local policy for each serving agent will dictate whether and when this header is obeyed and posters SHOULD NOT depend on it being completely followed. 6.12. Archive This optional header provides an indication of the poster's intent regarding preservation of the article in publicly accessible long- term or permanent storage. header =/ Archive-header Archive-header = "Archive" ":" SP Archive-content *( ";" ( Archive-parameter / other-parameter ) ) Archive-content = [CFWS] ("no" / "yes" ) [CFWS] Archive-parameter = The presence of an "Archive: no" header in an article indicates that the poster does not permit redistribution from publicly accessible long-term or permanent archives. The absence of this header, or an explicit "Archive: yes", indicates that the poster is willing for such redistribution to take place. The optional "filename" parameter can then be used to suggest a filename under which the article should be stored. Further extensions to this standard may provide additional parameters for administration of the archiving process. NOTE: This standard does not attempt to define the length of "long-term", since it is dependent on many factors, including the retention policies of individual sites, and the customs or policies established for particular newsgroups or hierarchies. NOTE: Posters are cautioned that some sites may not implement the "no" option of the Archive-header correctly. In some jurisdictions non-compliance with this header may constitute a breach of copyright or of other legal provisions. Moreover, even if this header prevents the poster's words from being archived publicly, it does nothing to prevent the archiving of a followup in which those words are quoted. 6.13. Control The Control-header marks the article as a control message, and specifies the desired actions (additional to the usual ones of storing and/or relaying the article). C. H. Lindsey [Page 52] News Article Format August 2002 header =/ Control-header Control-header = "Control" ":" SP Control-content *( ";" other-parameter ) Control-content = [CFWS] control-message [CFWS] control-message = However, the rule given above for control-message is incomplete. Further alternatives will be added incrementally as the various control-messages are introduced in section 7, or in extensions to this standard, using the "=/" notation defined in [RFC 2234]. For example, a typical CONTROL-message would be defined as follows: control-message =/ CONTROL-message CONTROL-message = "CONTROL" CONTROL-arguments CONTROL-arguments = where "CONTROL" is a "verb" which is (and MUST be) of the syntactic form of a token and CONTROL-arguments MUST be of the syntactic form of a CFWS-separated list of values (which may require the use of quoted-strings if any tspecials or non-ASCII characters are involved). The verb indicates what action should be taken, and the argument(s) (if any) supply details. In some cases, the body of the article may also contain details. An article with a Control-header MUST NOT also have a Supersedes- header. NOTE: The presence of a Subject-header starting with the string "cmsg " and followed by a Control-message MUST NOT be construed, in the absence of a proper Control-header, as a request to perform that control action (as may have occurred in some legacy software). See also section 5.4. 6.14. Approved The Approved-header indicates the mailing addresses (possibly including the full names) of the persons or entities approving the article for posting. header =/ Approved-header Approved-header = "Approved" ":" SP Approved-content *( ";" other-parameter ) Approved-content = From-content ; see 5.2 Each mailbox contained in the Approved-content MUST be that of one of the person(s) or entity(ies) in question, and one of those mailboxes MUST be that of the actual injector of the article. An Approved-header is required in all postings to moderated newsgroups. If this header is not present in such postings, then serving agents MUST (and relaying agents MAY) reject the article. C. H. Lindsey [Page 53] News Article Format August 2002 Please see section 8.2.2 for how injecting agents should treat postings to moderated groups that do not contain this header. An Approved-header is also required in certain control messages, to reduce the risks of accidental or unauthorized posting of same. NOTE: The presence of an Approved-header indicates that the person or entity identified claims to have the necessary authority to post the article in question, thus enabling sites that dispute that authority to refuse to accept or to act upon it. However, the mere presence of the header is insufficient to provide assurance that it indeed originated from that person or entity, and it is therefore desirable that it be included within some digital signature scheme (see 7.1), especially in the case of control messages (section 7). 6.15. Supersedes The Supersedes-header contains a message identifier specifying an article to be superseded upon the arrival of this one. The specified article MUST be treated as though a "cancel" control message had arrived for the article (but observe that a site MAY choose not to honour a "cancel" message, especially if its authenticity is in doubt). The content syntax makes use of syntax defined in [RFC 2822], subject to the same revisions as in 5.3. header =/ Supersedes-header Supersedes-header = "Supersedes" ":" SP Supersedes-content *( ";" other-parameter ) Supersedes-content = [CFWS] msg-id [CFWS] NOTE: There is no "c" in "Supersedes". NOTE: The Supersedes-header defined here has no connection with the Supersedes-header that sometimes appears in Email messages converted from X.400 according to [RFC 2156]; in particular, the syntax here permits only one msg-id in contrast to the multiple msg-ids in that Email version. Thus when an article contains a Supersedes-header, the old article mentioned SHOULD be withdrawn from circulation or access, as in a cancel message (7.3), and the new article inserted into the system as any other new article would have been. Whatever security or authentication checks are normally applied to a Control cancel message (or may be prescribed for such messages by some extension to this standard - see the remarks in 7.1 and 7.3) MUST also be applied to an article with a Supersedes-header. In the event of the failure of such checks, the article SHOULD be discarded, or at most stored as an ordinary article. C. H. Lindsey [Page 54] News Article Format August 2002 6.16. Xref The Xref-header is a variant header (4.2.5.3) which indicates where an article was filed by the last serving agent to process it. header =/ Xref-header Xref-header = "Xref" ":" SP Xref-content *( ";" other-parameter ) Xref-content = [CFWS] server-name 1*( CFWS location ) [CFWS] server-name = path-identity ; see 5.6.1 location = newsgroup-name ":" article-locator article-locator = 1*( %x21-27 / %x29-3A / %x3C-7E ) ; US-ASCII printable characters ; except '(' and ';' The server-name is included so that software can determine which serving agent generated the header. The locations specify what newsgroups the article was filed under (which may differ from those in the Newsgroups-header) and where it was filed under them. The exact form of an article-locator is implementation-specific. NOTE: The traditional form of an article-locator is a decimal number, with articles in each newsgroup numbered consecutively starting from 1. NNTP demands that such a model be provided, and much other software expects it, but it seems desirable to permit flexibility for unorthodox implementations. An agent inserting an Xref-header into an article MUST delete any previous Xref-header(s). A relaying agent MAY delete it before relaying, but otherwise it SHOULD be ignored by any relaying or serving agent receiving it. It is convenient, though not required, for a serving agent to use the same server-name in Xref-headers as the path-identity it uses in Path-headers (just so long as reading agents can distinguish it from other serving agents known to them). 6.17. Lines The Lines-header indicates the number of lines in the body of the article. header =/ Lines-header Lines-header = "Lines" ":" SP Lines-content *( ";" other-parameter ) Lines-content = [CFWS] 1*DIGIT [CFWS] The line count includes all body lines, including the signature if any, including empty lines (if any) at the beginning or end of the body, and including the whole of all MIME message and multipart parts contained in the body (the single empty separator line between the headers and the body is not part of the body). The "body" here is the body as found in the posted article as transmitted by the posting agent. C. H. Lindsey [Page 55] News Article Format August 2002 This header is to be regarded as obsolete, and it will likely be removed entirely in a future version of this standard. In the meantime, its use is deprecated. 6.18. User-Agent The User-Agent-header contains information about the user agent (typically a newsreader) generating the article, for statistical purposes and tracing of standards violations to specific software needing correction. Although not one of the mandatory headers, posting agents SHOULD normally include it. header =/ User-Agent-header User-Agent-header = "User-Agent" ":" SP User-Agent-content *( ";" other-parameter ) User-Agent-content = product-token *( CFWS product-token ) product-token = value [ "/" product-version ] ; see 4.1 product-version = value This header MAY contain multiple product-tokens identifying the agent and any subproducts which form a significant part of the posting agent, listed in order of their significance for identifying the application. Product-tokens should be short and to the point - they MUST NOT be used for information beyond the canonical name of the product and its version. Injecting agents MAY include product information for themselves (such as "INN/1.7.2"), but relaying and serving agents MUST NOT generate or modify this header to list themselves. NOTE: Variations from [RFC 2616] which describes a similar facility for the HTTP protocol: 1. use of arbitrary text or octets from character sets other than US-ASCII in a product-token may require the use of a quoted-string, 2. "{" and "}" are allowed in a value (product-token and product-version) in Netnews, 3. UTF-8 replaces ISO-8859-1 as charset assumption. NOTE: Comments should be restricted to information regarding the product named to their left such as platform information and should be concise. Use as an advertising medium (in the mundane sense) is discouraged. 6.18.1. Examples User-Agent: tin/1.2-PL2 User-Agent: tin/1.3-950621beta-PL0 (Unix) User-Agent: tin/unoff-1.3-BETA-970813 (UNIX) (Linux/2.0.30 (i486)) User-Agent: tin/pre-1.4-971106 (UNIX) (Linux/2.0.30 (i486)) User-Agent: Mozilla/4.02b7 (X11; I; en; HP-UX B.10.20 9000/712) User-Agent: Microsoft-Internet-News/4.70.1161 C. H. Lindsey [Page 56] News Article Format August 2002 User-Agent: Gnus/5.4.64 XEmacs/20.3beta17 ("Bucharest") User-Agent: Pluto/1.05h (RISC-OS/3.1) NewsHound/1.30 User-Agent: inn/1.7.2 User-Agent: telnet NOTE: This header supersedes the role performed redundantly by experimental headers such as X-Newsreader, X-Mailer, X-Posting- Agent, X-Http-User-Agent, and other headers previously used on Usenet for this purpose. Use of these experimental headers SHOULD be discontinued in favor of the single, standard User- Agent-header which can be used freely both in Netnews and Email (except that non-ASCII characters would be inappropriate in email). 6.19. Injector-Info The Injector-Info-header SHOULD be added to each article by the injecting agent in order to provide information as to how that article entered the Netnews system and to assist in tracing its true origin. header =/ Injector-Info-header Injector-Info-header = "Injector-Info" ":" SP Injector-Info-content *( ";" ( Injector-Info-parameter / other-parameter ) ) Injector-Info-content = [CFWS] path-identity [CFWS] Injector-Info-parameter = posting-host-parameter / posting-account-parameter / posting-sender-parameter / posting-logging-parameter / posting-date-parameter ; for {USENET}-parameters see 4.1 posting-host-parameter = host-value = dot-atom / [ dot-atom ":" ] ( IPv4address / IPv6address ); see [RFC 2373] posting-account-parameter = posting-sender-parameter = sender-value = mailbox / "verified" posting-logging-parameter = posting-date-parameter = C. H. Lindsey [Page 57] News Article Format August 2002 An Injector-Info-header MUST NOT be added to an article by any agent other than an injecting agent. Any Injector-Info-header present when an article arrives at an injecting agent MUST be removed. In particular if, for some exceptional reason (8.2.2), an article gets injected twice, the Injector-Info-header will always relate to the second injection. The path-identity MUST be the same as the path-identity prepended to the Path-header by that same injecting agent which, following section 5.6.2, MUST therefore be a fully qualified domain name (FQDN) mailable address. Although comments and folding of white space are permitted throughout the Injector-Info-content specification, it is RECOMMENDED that folding is not used within any parameter (but only before or after the ";" separating those parameters), and that comments are only used following the last parameter. It is also RECOMMENDED that such parameters as are present are included in the order in which they have been defined in the syntax above. An injecting agent SHOULD use a consistent form of this header for all articles emanating from the same or similar origins. NOTE: The effect of those recommendations is to facilitate the recognition of articles arising from certain designated origins (as in the so-called "killfiles" which are available in some reading agents). Observe that the order within the syntax has been chosen to place last those parameters which are most likely to change between successive articles posted from the same origin. NOTE: To comply with the overall "attribute = value" syntax of parameters, any value containing an IPv6address, a date-time, a mailbox, any UTF8-xtra-char, or any CFWS MUST be quoted using s (the quoting is optional in other cases). NOTE: This header is intended to replace various currently-used but nowhere-documented headers such as "NNTP-Posting-Host", "NNTP-Posting-Date" and "X-Trace". These headers are now deprecated, and any of them present when an article arrives at an injecting agent SHOULD also be removed as above. 6.19.1. Usage of Injector-Info-parameters The purpose of these parameters is to enable the injecting agent to make assertions about the origin of the article, in fulfilment of its responsibilities towards the rest of the network as set out in section 8.2. These assertions can then be utilized as follows: 1. To enable the administrator of the injecting agent to respond to complaints and queries concerning the article. For this purpose, the parameters included SHOULD be sufficient to enable the administrator to identify its true origin (which parameters are best suited to this purpose will vary with the nature of the injecting site and of its relationship to the posters who use it - C. H. Lindsey [Page 58] News Article Format August 2002 there is no benefit in including parameters which contribute nothing to this aim). An administrator MAY, with those parameters where the syntax so allows, use cryptic notations interpretable only by himself if he considers it appropriate to protect the privacy of that origin. 2. To enable relaying, serving and reading agents to recognize articles from origins which they might wish to reject, divert, or otherwise handle specially, for reasons of site policy. 3. To enable the timely identification of spews of articles arising from a common origin. An injecting agent MUST NOT include any Injector-Info-parameter unless it has positive evidence of its correctness. An injecting agent MAY include other-parameters with x-token attributes which will assist in identifying the origin of the article. NOTE: Administrators of injecting agents can choose which selection of the following parameters best enables them to fulfil their responsibilities. Some of these parameters identify the source of the article explicitly whereas others do so indirectly, thus affording more privacy to posters who value their anonymity, but also making harder the tracking of malicious disruption of the network, especially so if the administrators choose not to cooperate. There is thus a balance to be struck between the needs of privacy on the one hand and the good order of Usenet on the other, and administrators need to be aware of this when formulating their policies. 6.19.1.1. The posting-host-parameter If a dot-atom is present, it MUST be a FQDN identifying the specific host from which the injecting agent received the article. Alternatively, an IP address (IPv4address or IPv6address) identifies that host. If both forms are present, then they MUST identify the same host, or at least have done so at the time the article was injected. NOTE: It is commonly the case that this parameter identifies a dial-up point-of-presence, in which case a posting-account or logging-data may need to be consulted to find the true origin of the article. 6.19.1.2. The posting-account-parameter This parameter identifies the source from which the injecting agent received the article. It SHOULD be in a cryptic notation understandable only by the administrator of the injecting agent, but it MUST be such that a given source gives rise to the same posting- account, at least in the short term. If the injecting agent is unable to meet that obligation, then it should use a posting-logging- parameter instead. C. H. Lindsey [Page 59] News Article Format August 2002 6.19.1.3. The posting-sender-parameter This parameter identifies the mailbox of the verified sender of the article (alternatively, it uses the token "verified" to indicate that at least any addr-spec in the Sender-header of the article, or in the From-header if the Sender-header is absent, is correct). NOTE: An injecting agent is unlikely to be able to make use of this parameter except in cases where it is running on a machine which is aware of the user-space in which the posting agent is operating. This parameter should be used in preference to a posting-account-parameter in such situations. 6.19.1.4. The posting-logging-parameter This parameter contains information (typically a session number or other non-persistent means of identifying a posting account) which will enable the true origin of the article to be determined by reference to logging information kept by the injecting agent. 6.19.1.5. The posting-date-parameter This parameter identifies the time at which the article was injected (as distinct from the Date-header, which indicates when it was written). 6.19.2. Example Injector-Info: news2.isp.net; posting-host=modem-15.pop.isp.net; posting-account=client0002623; logging-data=2427; posting-date="Wed, 2 Aug 2000 20:05:33 -0100 (BST)" 6.20. Complaints-To The Complaints-To-header is added to an article by an injecting agent in order to indicate the mailbox to which complaints concerning the poster of the article may be sent. header =/ Complaints-To-header Complaints-To-header = "Complaints-To" ":" SP Complaints-To-content Complaints-To-content = address-list A Complaints-To-header MUST NOT be added to an article by any agent other than an injecting agent. Any Complaints-To-header present when an article arrives at an injecting agent MUST be removed. In particular if, for some exceptional reason (8.2.2), an article gets injected twice, the Complaints-To-header will always relate to the second injection. C. H. Lindsey [Page 60] News Article Format August 2002 The specified mailbox is for sending complaints concerning the behaviour of the poster of the article; it SHOULD NOT be used for matters concerning propagation, protocol problems, etc. which should be addressed to "usenet@" or "news@" the path-identity which was prepended to the Path-header by the injecting agent, in accordance with section 5.6.2. In the absence of this header, complaints concerning a poster's behaviour MAY be addressed to "abuse@" that path-identity (although section 5.6.2 provides no obligation for that address to be mailable at an injecting agent that is not provided for the use of the general public). 6.21. MIME headers 6.21.1. Syntax The following headers may be used within articles conforming to this standard. MIME-Version: [RFC 2045] Content-Type: [RFC 2045],[RFC 2046] Content-Transfer-Encoding: [RFC 2045] Content-ID: [RFC 2045] Content-Description: [RFC 2045] Content-Disposition: [RFC 2183] Content-Location: [RFC 2557] Content-MD5: [RFC 1864] The RFCs listed are deemed to be incorporated into this standard to the extent necessary to facilitate their usage within Netnews, subject to the revised syntax of parameter given in this standard (which permits UTF-xtra-chars to appear within quoted-strings used as values), and subject to curtailment of that usage as described in the following sections. Moreover, extensions to those standards registered in accordance with [RFC 2048] are also available for use within Netnews, as indeed is any other header in the Content-* series which has a sensible interpretation within Netnews. Insofar as the syntax for these headers, as given in those RFCs does not specify precisely where whitespace and comments may occur (whether in the form of WSP, FWS or CFWS), the usage defined in this standard, and failing that in [RFC 2822], and failing that in [RFC 822] MUST be followed. In particular, there MUST NOT be any WSP between a header-name and the following colon and there MUST be a SP following that colon. 6.21.2. Content-Type The Content-Type: "text/plain" is the default type for any news article, but the recommendations and limits on line lengths set out in section 4.5 Ought to be observed. The acceptability of other subtypes of Content-Type: "text" (such as "text/html") is a matter of policy (see 1.1), and posters Ought Not to use them unless established policy or custom in the particular C. H. Lindsey [Page 61] News Article Format August 2002 hierarchies or groups involved so allows. Moreover, even in those cases, for the benefit of readers who see it only in its transmitted form, the material SHOULD be "pretty-printed" (for example by restricting its line length as above and by keeping sequences which control its layout or style separate from the meaningful text). In the same way, Content-Types requiring special processing for their display, such as "application", "image", "audio", "video" and "multipart/related" are discouraged except in groups specifically intended (by policy or custom) to include them. Exceptionally, those application types defined in [RFC 1847] and [RFC 3156] for use within "multipart/signed" articles, and the type "application/pgp-keys" (or other similar types containing digital certificates) may be used freely. Reading agents SHOULD NOT, unless explicitly configured otherwise, act automatically on Application types which could change the state of that agent (e.g. by writing or modifying files), except in the case of those prescribed for use in control messages (7.2.1.2 and 7.2.4.1). 6.21.2.1. Message/partial The Content-Type "message/partial" MAY be used to split a long news article into several smaller ones. NOTE: This Content-Type is not recommended for textual articles because the Content-Type, and in particular the charset, of the complete article cannot be determined by examination of the second and subsequent parts, and hence it is not possible to read them as separate articles (except when they are written in pure US-ASCII). Moreover, for full compliance with [RFC 2046] it would be necessary to use the "quoted-printable" encoding to ensure the material was 7bit-safe. In any case, breaking such long texts into several parts is usually unnecessary, since modern transport agents should have no difficulty in handling articles of arbitrary length. On the other hand, "message/partial" may be useful for binaries of excessive length, since reading of the individual parts on their own is not required and they would likely be encoded in a manner that was 7bit-safe. IF this Content-Type is used, then the "id" parameter SHOULD be in the form of a unique message identifier (but different from that in the Message-ID-header of any of the parts). The second and subsequent parts SHOULD contain References-headers referring to all the previous parts, thus enabling reading agents with threading capabilities to present them in the correct order. Reading agents MAY then provide a facility to recombine the parts into a single article (but this standard does not require them to do so). C. H. Lindsey [Page 62] News Article Format August 2002 6.21.2.2. Message/rfc822 The Content-Type "message/rfc822" should be used for the encapsulation (whether as part of another news article or, more usually, as part of an email message) of complete news articles which have already been posted to Netnews and which are for the information of the recipient, and do not constitute a request to repost them (refer to 6.21.6.2 for the now obsolete "message/news" formerly intended for this purpose). In the case where such an encapsulated news article has Content- Transfer-Encoding "8bit" or where its headers contain any UTF8-xtra- chars (2.4.2), it might not be possible to transport it by email without some prior transformations, although there should be few problems if the email transport supports 8BITMIME [RFC 2821]. The problems that arise are similar to those encountered by an outgoing gateway, and therefore the advice on transformations given in section 8.8.1 should be followed. It may be necessary to reverse such transformations at the far end if certain forms of digital signatures have been employed in the article. 6.21.2.3. Message/external-body The Content-Type "message/external-body" could be appropriate for texts which it would be uneconomic (in view of the likely readership) to distribute to the entire network. 6.21.2.4. Multipart types The Content-Types "multipart/mixed", "multipart/parallel" and "multipart/signed" may be used freely in news articles. However, except where policy or custom so allows, the Content-Type: "multipart/alternative" SHOULD NOT be used, on account of the extra bandwidth consumed and the difficulty of quoting in followups, but reading agents MUST accept it. The Content-Type: "multipart/digest" is commended for any article composed of multiple messages more conveniently viewed as separate entities, thus enabling reading agents to move rapidly between them. The "boundary" should be composed of 28 hyphens (US-ASCII 45) (which makes each boundary delimiter 30 hyphens, or 32 for the final one) so as to enable reading agents which currently support the digest usage described in [RFC 1153] to continue to operate correctly. NOTE: The various recommendations given above regarding the usage of particular Content-Types apply also to the individual parts of these multiparts. 6.21.3. Content-Transfer-Encoding "Content-Transfer-Encoding: 7bit" is sufficient for article bodies (or parts of multiparts) written in pure US-ASCII (or most other material representable in 7 bits). Posting agents SHOULD specify "Content-Transfer-Encoding: 8bit" for all other cases unless there C. H. Lindsey [Page 63] News Article Format August 2002 are pressing reasons to do otherwise. They MAY use "8bit" encoding even when "7bit" encoding would have sufficed. Examples of such pressing reasons are the following: 1. The content type implies that the content is (or may be) "8bit- unsafe"; i.e. it may contain octets equivalent to the US-ASCII characters CR or LF (other than in the combination CRLF) or NUL. In that case one of the Content-Transfer-Encodings "base64" or "quoted-printable" MUST be used, and reading agents MUST be able to handle both of them. Encoding "binary" MUST NOT be used (except in cooperating subnets with alternative transport arrangements) because this standard does not mandate a transport mechanism that could support it. NOTE: If a future extension to the MIME standards were to provide a more compact encoding of binary suited to transport over an 8bit channel, it could be considered as an alternative to base64 once it had gained widespread acceptance. 2. It is often the case that "application" Content-Types are textual in nature, and intelligible to humans as well as to machines, and where this state can be recognized by the posting agent (either through knowledge of the particular application type or by testing) the material SHOULD NOT be treated as 8bit-unsafe; this has the added benefit, where the posting agent uses other than CRLF for line endings internally, of automatically ensuring that line endings are processed correctly during transport. If, on the other hand, the posting agent recognizes that the material is not textual, or cannot reasonably determine it to be so, then the material MUST be encoded as for 8bit-unsafe (however, in that case, it is the responsibility of the agent generating the material to ensure that lines endings, if any, are represented correctly). NOTE: All the application types defined by this standard, namely "application/news-transmission", "application/news-groupinfo" and "application/news-checkgroups" are textual, and indeed designed for human reading. 3. Although the "text" Content-Types should normally be encoded as 8bit (or 7bit), if the character set specified by the "charset=" parameter can include the 3 disallowed octets, then the material MUST be encoded as for 8bit-unsafe. This is most likely to arise in the case of 16-bit character sets such as UTF-16 ([UNICODE 3.2] or [ISO/IEC 10646]). In addition, where it is known that the material is subsequently to be gatewayed from Netnews to Email (8.8), the encoding "quoted-printable" MAY be used (otherwise the gateway might have to re-encode it itself). 4. Some protocols REQUIRE the use of a particular Content-Transfer- Encoding. In particular, the authentication protocol based on OpenPGP defined in [RFC 3156] mandates the use of one of the encodings "quoted-printable" or "base64". Whilst posters might be C. H. Lindsey [Page 64] News Article Format August 2002 tempted to risk the use of "8bit" or "7bit" encodings (and indeed the referenced standard recommends that signed messages using those encodings be accepted and interpreted), they should be warned that differences in the treatment of trailing whitespace between OpenPGP [RFC 2440] and earlier versions of PGP may render signatures written with the one unverifiable by the other; and, moreover, Usenet articles are very likely to include trailing whitespace in the form of a personal signature (4.3.2). 5. The Content-Type message/partial [RFC 2046] is required to use encoding "7bit" (the encapsulated complete message may itself use encoding "quoted-printable" or "base64", but that information is only conveyed along with the first of the partial parts). NOTE: Although there would actually be no problem using encoding "8bit" in a pure Netnews (as opposed to Email) environment, this standard discourages (see 6.21.2.1) the use of "message/partial" except for binary material, which will likely be encoded to pass through "7bit" in any case. Injecting and relaying agents MUST NOT change the encoding of articles passed to them. Gateways SHOULD NOT change the encoding unless absolutely necessary. 6.21.4. Character Sets In principle, any character set may be specified in the "charset=" parameter of a content type. However, only those character sets (and the corresponding parts of UTF-8) should be used which are appropriate for the customary language(s) of the hierarchy or newsgroup concerned (whose readers could be expected to possess agents capable of displaying them). 6.21.5. Content Disposition Reading agents Ought to honour any Content-Disposition-header that is provided (in particular, they Ought to display any part of a multipart for which the disposition is "inline", possibly distinguished from adjacent parts by some suitable separator). In the absence of such a header, the body of an article or any part of a multipart with Content-Type "text" Ought to be displayed inline. Followup agents which quote parts of a precursor (see 4.3.2) Ought initially to include all parts of the precursor that were displayed inline, as if they were a single part. 6.21.6. Definition of some new Content-Types This standard defines (or redefines) several new Content-Types, which require to be registered with IANA as provided for in [RFC 2048]. For "application/news-groupinfo" see 7.2.1.2, for "application/news- checkgroups" see 7.2.4.1, and for "application/news-transmission" see the following section. C. H. Lindsey [Page 65] News Article Format August 2002 6.21.6.1. Application/news-transmission The Content-Type "application/news-transmission" is intended for the encapsulation of complete news articles where the intention is that the recipient should then inject them into Netnews. This Application type provides one of the methods for mailing articles to moderators (see 8.2.2) and it is also the preferred method when sending to an email-to-news gateway (see 8.8.1). NOTE: The benefit of such encapsulation is that it removes possible conflict between news and email headers and it provides a convenient way of "tunnelling" a news article through a transport medium that does not support 8bit characters. The MIME content type definition of "application/news-transmission" is: MIME type name: application MIME subtype name: news-transmission Required parameters: none Optional parameters: usage=moderate usage=inject usage=relay Encoding considerations: A transfer-encoding (such as Quoted- Printable or Base64) different from that of the article transmitted MAY be supplied (perhaps en route) to ensure correct transmission over some 7bit transport medium. Security considerations: A news article may be a "control message", which could have effects on the recipient host's system beyond just storage of the article. However, such control messages also occur in normal news flow, so most hosts will already be suitably defended against undesired effects. Published specification: [USEFOR] Body part: A complete article or proto-article, ready for injection into Netnews, or a batch of such articles. NOTE: It is likely that the recipient of an "application/news- transmission" will be a specialized gateway (e.g. a moderator's submission address) able to accept articles with only one of the three usage parameters "moderate", "inject" and "relay", hence the reason why they are optional, being redundant in most situations. Nevertheless, they MAY be used to signify the originator's intention with regard to the transmission, so removing any possible doubt. When the parameter "relay" is used, or implied, the body part MAY be a batch of articles to be transmitted together, in which case the following syntax MUST be used. C. H. Lindsey [Page 66] News Article Format August 2002 batch = 1*( batch-header article ) batch-header = "#!" SP rnews SP article-size CRLF rnews = %x72.6E.65.77.73 ; case sensitive "rnews" article-size = 1*DIGIT Thus a batch is a sequence of articles, each prefixed by a header line that includes its size. The article-size is a decimal count of the octets in the article, counting each CRLF as one octet regardless of how it is actually represented. NOTE: Despite the similarity of this format to an executable UNIX script, it is EXTREMELY unwise to feed such a batch into a command interpreter in anticipation of it running a command named "rnews"; the security implications of so doing would be disastrous. 6.21.6.2. Message/news obsoleted The Content-Type "message/news", as previously registered with IANA, is hereby declared obsolete. It was never widely implemented, and its default treatment as "application/octet-stream" by agents that did not recognize it was counter productive. The Content-Type "message/rfc822" SHOULD be used in its place, as already described above. 6.22. Obsolete Headers Persons writing new agents SHOULD ignore any former meanings of the following headers: Also-Control See-Also Article-Names Article-Updates 7. Control Messages The following sections document the control messages. "Message" is used herein as a synonym for "article" unless context indicates otherwise. The Newsgroups-header of each control message SHOULD include the newsgroup-name(s) for the group(s) affected (i.e. groups to be created, modified or removed, or containing articles to be canceled). This is to ensure that the message propagates to all sites which receive (or would receive) that group(s). It MAY include other newsgroup-names so as to improve propagation (but this practice may cause the control message to propagate also to places where it is unwanted, or even cause it not to propagate where it should, so it should not be used without good reason). The descriptions below set out REQUIREMENTS to be followed by sites that receive control messages and choose to honour them. However, nothing in these descriptions should be taken as overriding the right C. H. Lindsey [Page 67] News Article Format August 2002 of any such site, in accordance with its local policy, to deny any particular control message, or to refer it to an administrator for approval (either as a class or on a case-by-case basis). In particular, sites Ought to deny messages not issued by the appropriate administrative agencies, and therefore SHOULD take such steps as are reasonably practicable to validate their authenticity (see, for example, section 7.1 below). Relaying Agents MUST propagate even control messages that they do not recognize. In the following sections, each type of control message is defined syntactically by defining its verb, its arguments, and possibly its body. 7.1. Digital Signature of Headers It is most desirable that group control messages (7.2) in particular be authenticated by incorporating them within some digital signature scheme that encompasses other headers closely associated with them (including at least the Approved-, Message-ID- and Date-headers). At the time of writing, this is usually done by means of a protocol known as "PGPverify" ([PGPVERIFY]), and continued usage of this is encouraged at least as an interim measure. However, PGPverify is not considered suitable for standardization in its present form, for various technical reasons. It is therefore expected that an early extension to this standard will provide a robust and general purpose digital authentication mechanism with applicability to all situations requiring protection against malicious use of, or interference with, headers. That extension would also address other Netnews security issues. 7.2. Group Control Messages "Group control messages" are the sub-class of control messages that request some update to the configuration of the groups known to a serving agent, namely "newgroup". "rmgroup", "mvgroup" and "checkgroups", plus any others created by extensions to this standard. All of the group control messages MUST have an Approved-header (6.14). Moreover, in those hierarchies where appropriate administrative agencies exist (see 1.1), group control messages Ought Not to be issued except as authorized by those agencies. 7.2.1. The 'newgroup' Control Message control-message =/ Newgroup-message Newgroup-message = "newgroup" Newgroup-arguments Newgroup-arguments = CFWS newsgroup-name [ CFWS newgroup-flag ] newgroup-flag = "moderated" C. H. Lindsey [Page 68] News Article Format August 2002 The "newgroup" control message requests that the specified group be created or changed. If the request is honoured, or if the group already exists on the serving agent, and if the newgroup-flag "moderated" is present, then the group MUST be marked as moderated, and vice versa. "Moderated" is the only such flag defined by this standard; other flags MAY be defined for use in cooperating subnets, but newgroup messages containing them MUST NOT be acted on outside of those subnets. NOTE: Specifically, some alternative flags such as "y" and "m", which are sent and recognized by some current software, are NOT part of this standard. Moreover, some existing implementations treat any flag other than "moderated" as indicating an unmoderated newsgroup. Both of these usages are contrary to this standard and control messages with such non-standard flags should be ignored. The message body comprises or includes an "application/news- groupinfo" (7.2.1.2) part containing machine- and human-readable information about the group. It is REQUIRED that the newsgroup-name conforms to all requirements set out in section 5.5. This includes the restrictions as to the permitted characters, and the requirement that they be invariant under NFKC normalization. It is essential that those who issue newgroup messages are aware of their responsibility to enforce this requirement, since some of those conditions are hard to enforce mechanically. Additionally, the newsgroup-name Ought to conform to whatever policies have been established by the administrative agency, if any, for that hierarchy. Serving agents SHOULD, insofar as they are conveniently able to detect them, reject all newgroup messages not meeting those requirements. The newgroup command is also used to update the newsgroups-line or the moderation status of a group. 7.2.1.1. The Body of the 'newgroup' Control Message The body of the newgroup message contains the following subparts, preferably in the order shown: 1. An "application/news-groupinfo" part (7.2.1.2) containing the name and newsgroups-line of the group(s). This part MUST be present. 2. Other parts containing useful information about the background of the newgroup message (typically of type "text/plain"). 3. Parts containing initial articles for the newsgroup. See section 7.2.1.3 for details. C. H. Lindsey [Page 69] News Article Format August 2002 In the event that there is only the single (i.e. application/news- groupinfo) subpart present, it will suffice to include a "Content- Type: application/news-groupinfo" amongst the headers of the control message. Otherwise, a "Content-Type: multipart/mixed" header will be needed, and each separate part will then need its own Content-Type- header. 7.2.1.2. Application/news-groupinfo The "application/news-groupinfo" body part contains brief information about a newsgroup, i.e. the group's name, it's newsgroup-description and the moderation-flag. NOTE: The presence of the newsgroups-tag "For your newsgroups file:" is intended to make the whole newgroup message compatible with current practice as described in [Son-of-1036]. The MIME content type definition of "application/news-groupinfo" is: MIME type name: application MIME subtype name: news-groupinfo Required parameters: none Disposition: by default, inline Encoding considerations: "7bit" or "8bit" is sufficient and MUST be used to maintain compatibility. Security considerations: this type MUST NOT be used except as part of a control message for the creation or modification of a Netnews newsgroup Published specification: [USEFOR] The content of the "application/news-groupinfo" body part is defined as: groupinfo-body = [ newsgroups-tag CRLF ] newsgroups-line CRLF newsgroups-tag = %x46.6F.72 SP %x79.6F.75.72 SP %x6E.65.77.73.67.72.6F.75.70.73 SP %x66.69.6C.65.3A ; case sensitive ; "For your newsgroups file:" newsgroups-line = newsgroup-name [ 1*HTAB newsgroup-description ] [ 1*WSP moderation-flag ] newsgroup-description = utext *( *WSP utext ) moderation-flag = %x28.4D.6F.64.65.72.61.74.65.64.29 ; case sensitive "(Moderated)" The newsgroup-description MUST NOT contain any occurrence of the string "(Moderated)" within it. The whole groupinfo-body is intended to be interpreted as a text written in the UTF-8 character set. C. H. Lindsey [Page 70] News Article Format August 2002 The "application/news-groupinfo" is used in conjunction with the "newgroup" (7.2.1) and "mvgroup" (7.2.3) control messages. The newsgroup-name in the newsgroups-line MUST agree with the newsgroup- name in the "newgroup" or "mvgroup" control message. The Content- Type "application/news-groupinfo" MUST NOT be used except as a part of such control messages. Although optional, the newsgroups-tag SHOULD be included until such time as this standard has been widely adopted, to ensure compatibility with present practice. Moderated newsgroups MUST be marked by appending the case sensitive text " (Moderated)" at the end. It is NOT recommended that the moderator's email address be included in the newsgroup-description as has sometimes been done. Although, in accordance with [RFC 2822] and section 4.5 of this standard, a newsgroups-line could have a maximum length of 998 octets, as a matter of policy a far lower limit, expressed in characters, Ought to be set. The current convention is to limit its length so that the newsgroup-name, the HTAB(s) (interpreted as 8- character tabs that takes one at least to column 24) and the newsgroup-description (excluding any moderation-flag) fit into 79 characters. However, this standard does not seek to enforce any such rule, and reading agents SHOULD therefore enable a newsgroups-line of any length to be displayed, e.g. by wrapping it as required. NOTE: The newsgroups-line is intended to provide a brief description of the newsgroup, written in the UTF-8 character set. Since newsgroup-names are required to be expressed in UTF-8 when they appear in headers, and since [NNTP] requires the use of UTF-8 when such a description is transmitted by the LIST NEWSGROUPS command, it would also be convenient for serving agents that keep a "newsgroups" file to store them in that form, so as to avoid unnecessary conversions. [If, at the time of publication of this standard, [NNTP] is still [RFC 977], that NOTE will need to be changed to indicate that "it is expected that a future extension of [RFC 977] will require ...".] 7.2.1.3. Initial Articles Some subparts of a "newgroup" or "mvgroup" control message MAY contain an initial set of articles to be posted to the affected newsgroup(s) as soon as it has been created or modified. These parts are identified by having the Content-Type "application/news- transmission", possibly with the parameter "usage=inject". The body of each such part should be a complete proto-article, ready for posting. This feature is intended for the posting of charters, initial FAQs and the like to the newly formed group(s). The Newsgroups-header of the proto-article MUST include the newsgroup-name of the newly created or modified group. It MAY include other newsgroup-names. If the proto-article includes a Message-ID- header, the message identifier in it MUST be different from that of any existing article and from that of the control message as a whole. Alternatively such a message identifier MAY be derived by the C. H. Lindsey [Page 71] News Article Format August 2002 injecting agent when the proto-article is posted. The proto-article SHOULD include the header "Distribution: local". The proto-article SHOULD be injected at the serving agent that processes the control message AFTER the newsgroup in question has been created or modified. It MUST NOT be injected if the newsgroup is not, in fact, created (for whatever reason). It MUST NOT be submitted to any relaying agent for transmission beyond the serving agent(s) upon which the newsgroup creation has just been effected (in other words, it is to be treated as having a "Distribution: local" header, whether such a header is actually present or not). NOTE: It is not precluded that the proto-article is itself a control message or other type of special article, to be activated only upon creation of the new newsgroup. However, except as might arise from that possibility, any "application/news-transmission" within some nested "multipart/*" structure within the proto-article is not to be activated. 7.2.1.4. Example A "newgroup" with its charter: From: "example.all Administrator" Newsgroups: example.admin.info,example.admin.announce Date: 27 Feb 2002 12:50:22 +0200 Subject: cmsg newgroup example.admin.info moderated Approved: admin@noc.example Control: newgroup example.admin.info moderated Message-ID: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="nxtprt" Content-Transfer-Encoding: 8bit This is a MIME control message. --nxtprt Content-Type: application/news-groupinfo For your newsgroups file: example.admin.info About the example.* groups (Moderated) --nxtprt Content-Type: application/news-transmission Newsgroups: example.admin.info From: "example.all Administrator" Subject: Charter for example.admin.info Message-ID: Distribution: local Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit The group example.admin.info contains regularly posted C. H. Lindsey [Page 72] News Article Format August 2002 information on the example.* hierarchy. --nxtprt-- 7.2.2. The 'rmgroup' Control Message control-message =/ Rmgroup-message Rmgroup-message = "rmgroup" Rmgroup-arguments Rmgroup-arguments = CFWS newsgroup-name The "rmgroup" control message requests that the specified group be removed from the list of valid groups. The Content-Type of the body is unspecified; it MAY contain anything, usually an explanatory text. NOTE: It is entirely proper for a serving agent to retain the group until all the articles in it have expired, provided that it ceases to accept new articles. 7.2.2.1. Example Plain "rmgroup": From: "example.all Administrator" Newsgroups: example.admin.obsolete, example.admin.announce Date: 4 Apr 2002 22:04 -0900 (PST) Subject: cmsg rmgroup example.admin.obsolete Message-ID: Approved: admin@noc.example Control: rmgroup example.admin.obsolete The group example.admin.obsolete is obsolete. Please remove it from your system. 7.2.3. The 'mvgroup' Control Message control-message =/ Mvgroup-message Mvgroup-message = "mvgroup" Mvgroup-arguments Mvgroup-arguments = CFWS newsgroup-name CFWS newsgroup-name [ CFWS newgroup-flag ] The "mvgroup" control message requests that the group specified by the first (old-)newsgroup-name be moved to that specified by the second (new-)newsgroup-name. Thus it is broadly equivalent to a "newgroup" control message for the second group followed by a "rmgroup" control message for the first group. The second (new-)newsgroup-name MUST conform to all requirements prescribed for the newsgroup-name of a "newgroup" control message (7.2.1) and Ought, similarly, to conform to any established policies of the hierarchy. The message body contains an "application/news- groupinfo" part (7.2.1.2) containing machine- and human-readable information about the new group, and possibly other subparts as for a "newgroup" control message. The information conveyed in the "application/news-groupinfo" body part, notably its newsgroups-line C. H. Lindsey [Page 73] News Article Format August 2002 (7.2.1.2), is applied to the new group. When this message is received, the new group is created (if it does not exist already) as for a "newgroup" control message, and MUST in any case be made moderated if a newgroup-flag "moderated" is present, and vice versa. At the same time, arrangements SHOULD be made to remove the old group (as with a "rmgroup" control message), but only after a suitable overlap period to allow the network to adjust to the new arrangement. At the same time as a serving agent acts upon this message, all injecting agents associated with that serving agent SHOULD inhibit the posting of new articles to the old group (preferably with some indication to the poster that the new group should have been used). Relaying agents, however, MUST continue to propagate such articles during the overlap period. NOTE: It is to be expected that different serving agents will act on this message at different points of time, users of the old group will have to become accustomed to the new arrangement, and followups to already established threads will likely continue under the old group. Therefore, there needs to be an overlap period during which articles may continue to be accepted by relaying and serving agents in either group. This standard does not specify any standard period of overlap (though it would be expected to be expressed in days rather than in months). The inhibition of injection of new articles to the old group may seem draconian, but it is the surest way to prevent the changeover from dragging on indefinitely. Since the "mvgroup" control message is newly introduced in this standard and may not be widely implemented initially, it SHOULD be followed shortly afterwards by a corresponding "newgroup" control message; and again, after a reasonable overlap period, it MUST be followed by a "rmgroup" control message for the old group. In order to facilitate a smooth changeover, serving agents MAY arrange to service requests for access to the old group by providing access to the new group, which would then contain, or appear to contain, all articles posted to either group (including, ideally, the pre-changeover articles from the old one). Nevertheless, if this feature is implemented, the articles themselves, as supplied to reading agents, MUST NOT be altered in any way (and, in particular, their Newsgroups-headers MUST contain exactly those newsgroups present when they were injected). On the other hand, the Xref-header MAY contain entries for either group (or even both). NOTE: Some serving agents that use an "active" file permit an entry of the form "oldgroup xxx yyy =newgroup", which enables any articles arriving for oldgroup to be diverted to newgroup, thus providing a simple implementation of this feature. However, it is known that not all current serving agents will find implementation so easy (especially in the short term) which is why it is not mandated by this standard. Nevertheless, its C. H. Lindsey [Page 74] News Article Format August 2002 eventual implementation in all serving agents is to be considered highly desirable. On the other hand, it is recognized that this feature would likely not be implementable if the new group was already in existence with existing articles in it. This situation should not normally arise except when there is already some confusion as to which groups are, or are not, supposed to exist in that hierarchy. Note that the "mvgroup" control message is not really intended to be used for merging two existing groups. 7.2.3.1. Example From: "example.all Administrator" Newsgroups: example.oldgroup,example.newgroup,example.admin.announce Date: 30 Apr 2002 22:04 -0500 (EST) Subject: cmsg mvgroup example.oldgroup example.newgroup moderated Message-ID: Approved: admin@noc.example Control: mvgroup example.oldgroup example.newgroup moderated MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=nxt --nxt Content-Type: application/news-groupinfo For your newsgroups file: example.newgroup The new replacement group (Moderated) --nxt The moderated group example.oldgroup is replaced by example.newgroup. Please update your configuration, and please, if possible, arrange to file articles arriving for example.oldgroup as if they were in example.newgroup. --nxt-- 7.2.4. The 'checkgroups' Control Message The "checkgroups" control message contains a list of all the valid groups in a complete hierarchy. control-message =/ Checkgroup-message Checkgroup-message = "checkgroups" Checkgroup-arguments Checkgroup-arguments= [ chkscope ] [ chksernr ] chkscope = 1*( CFWS ["!"] newsgroup-name ) chksernr = CFWS "#" 1*DIGIT A "checkgroups" message applies to any (sub-)hierarchy with a prefix listed in the chkscope parameter, provided that the rightmost matching newsgroup-name in the list is not immediately preceded by a "!". If no chkscope parameter is given, it applies to all hierarchies for which group statements appear in the message. C. H. Lindsey [Page 75] News Article Format August 2002 NOTE: Some existing software does not support the "chkscope" parameter. Thus a "checkgroups" message SHOULD also contain the groups of other subhierarchies the sender is not responsible for. "New" software MUST ignore groups which do not fall within the chkscope parameter of the "checkgroups" message. The chksernr parameter is a serial number, which can be any positive integer (e.g. just numbered or the date in YYYYMMDD). It SHOULD increase by an arbitrary value with every change to the group list and MUST NOT ever decrease. NOTE: This was added to circumvent security problems in situations where the Date-header cannot be authenticated. Example: Control: checkgroups de !de.alt #248 which includes the whole of the 'de.*' hierarchy, with the exception of its 'de.alt.*' sub-hierarchy. The body of the message has the Content-Type "application/news- checkgroups". It asserts that the newsgroups it lists are the only newsgroups in the specified hierarchies. NOTE: The checkgroups message is intended to synchronize the list of newsgroups stored by a serving agent, and their newsgroup-descriptions, with the lists stored by other serving agents throughout the network. However, it might be inadvisable for the serving agent actually to create or delete any newsgroups without first obtaining the approval of its administrators for such proposed actions. 7.2.4.1. Application/news-checkgroups The "application/news-checkgroups" body part contains a complete list of all the newsgroups in a hierarchy, their newsgroup-descriptions and their moderation status. The MIME content type definition of "application/news-checkgroups" is: MIME type name: application MIME subtype name: news-checkgroups Required parameters: none Disposition: by default, inline Encoding considerations: "7bit" or "8bit" is sufficient and MUST be used to maintain compatibility. Security considerations: this type MUST NOT be used except as part of a checkgroups control message The content of the "application/news-checkgroups" body part is defined as: C. H. Lindsey [Page 76] News Article Format August 2002 checkgroups-body = *( valid-group CRLF ) valid-group = newsgroups-line ; see 7.2.1.2 The whole checkgroups-body is intended to be interpreted as a text written in the UTF-8 character set. The "application/news-checkgroups" content type is used in conjunction with the "checkgroups" control message (7.2.4). NOTE: The possibility of removing a complete hierarchy by means of an "invalidation" line beginning with a '!' is no longer provided by this standard. The intent of the feature was widely misunderstood and it was misused more often than it was used correctly. The same effect, if required, can now be obtained by the use of an appropriate chkscope argument in conjunction with an empty checkgroups-body. 7.3. Cancel The cancel message requests that a target article be "canceled" i.e. be withdrawn from circulation or access. A cancel message may be issued in the following circumstances. 1. The poster of an article (or, more specifically, any entity mentioned in the From-header or the Sender-header, whether or not that entity was the actual poster) is always entitled to issue a cancel message for that article, and serving agents SHOULD honour such requests. Posting agents SHOULD facilitate the issuing of cancel messages by posters fulfilling these criteria. 2. The agent which injected the article onto the network (more specifically, the entity identified by the path-identity in front of the leftmost '%' delimiter in the Path-header (5.6) or in the Injector-Info-header (6.19) and, where appropriate, the moderator (more specifically, any entity mentioned in the Approved-header) is always entitled to issue a cancel message for that article, and serving agents SHOULD honour such requests. 3. Other entities MAY be entitled to issue a cancel message for that article, in circumstances where established policy for any hierarchy or group in the Newsgroup-header, or established custom within Usenet, so allows (such policies and customs are not defined by this standard). Such cancel messages MUST include an Approved-header identifying the responsible entity. Serving agents MAY honour such requests, but SHOULD first take steps to verify their appropriateness. control-message =/ Cancel-message Cancel-message = "cancel" Cancel-arguments Cancel-arguments = CFWS msg-id [CFWS] The argument identifies the article to be cancelled by its message identifier. The body SHOULD contain an indication of why the cancellation was requested. The cancel message SHOULD be posted to C. H. Lindsey [Page 77] News Article Format August 2002 the same newsgroup, with the same distribution, as the article it is attempting to cancel. A serving agent that elects to honour a cancel message SHOULD make the article unavailable for relaying or serving (perhaps by deleting it completely). If the target article is unavailable, and the acceptability of the cancel message cannot be established without it, activation of the cancel message SHOULD be delayed until the target article has been seen. See also sections 8.3 and 8.4. NOTE: It is expected that the security extension envisaged in section 7.1 will make more detailed provisions for establishing whether honouring a particular cancel message is in order. In particular, it is likely that there will be provision for the digital signature of 3rd party cancels. NOTE: The former requirement [RFC 1036] that the From and/or Sender-headers of the cancel message should match those of the original article has been removed from this standard, since it only encouraged cancel issuers to conceal their true identity, and it was not usually checked or enforced by canceling software. Therefore, both the From and/or Sender-headers and any Approved-header should now relate to the entity responsible for issuing the cancel message. 7.4. Ihave, sendme The "ihave" and "sendme" control messages implement a crude batched predecessor of the NNTP [NNTP] protocol. They are largely obsolete on the Internet, but still see use in conjunction with some transport protocols such as UUCP, especially for backup feeds that normally are active only when a primary feed path has failed. There is no requirement for relaying agents that do not support such transport protocols to implement them. NOTE: The ihave and sendme messages defined here have ABSOLUTELY NOTHING TO DO WITH NNTP, despite similarities of terminology. The two messages share the same syntax: control-message =/ Ihave-message Ihave-message = "ihave" Ihave-arguments Ihave-arguments = relayer-name control-message =/ Sendme-message Sendme-message = "sendme" Sendme-arguments Sendme-arguments = Ihave-arguments relayer-name = path-identity ; see 5.6.1 ihave-body = *( msg-id CRLF ) sendme-body = ihave-body The body of the message consists of a list of msg-ids, one per line. [RFC 1036] also permitted the list of msg-ids to appear in the Ihave- or Sendme-arguments with the syntax C. H. Lindsey [Page 78] News Article Format August 2002 Ihave-arguments = [FWS] *( msg-id FWS ) [relayer-name] but this form SHOULD NOT now be used, though relaying agents MAY recognize and process it for backward compatibility. The ihave message states that the named relaying agent has received articles with the specified message identifiers, which may be of interest to the relaying agents receiving the ihave message. The sendme message requests that the agent receiving it send the articles having the specified message identifiers to the named relaying agent. These control messages are normally sent essentially as point-to- point messages, by using newsgroup-names in the Newsgroups-header of the form "to." followed by one (or possibly more) components in the form of a relayer-name (see section 5.5.1 which forbids "to" as the first component of a newsgroup-name). The control message SHOULD then be delivered ONLY to the relaying agent(s) identified by that relayer-name, and any relaying agent receiving such a message which includes its own relayer-name MUST NOT propagate it further. Each pair of relaying agent(s) sending and receiving these messages MUST be immediate neighbors, exchanging news directly with each other. Each relaying agent advertises its new arrivals to the other using ihave messages, and each uses sendme messages to request the articles it lacks. To reduce overhead, ihave and sendme messages SHOULD be sent relatively infrequently and SHOULD contain reasonable numbers of message IDs. If ihave and sendme are being used to implement a backup feed, it may be desirable to insert a delay between reception of an ihave and generation of a sendme, so that a slightly slow primary feed will not cause large numbers of articles to be requested unnecessarily via sendme. 7.5. Obsolete control messages. The following control messages are declared obsolete by this standard: sendsys version whogets senduuname 8. Duties of Various Agents The following section sets out the duties of various agents involved in the creation, relaying and serving of Usenet articles. In this section, the word "trusted", as applied to the source of some article, means that an agent processing that article has verified, by some means, the identity of that source (which may be another agent or a poster). C. H. Lindsey [Page 79] News Article Format August 2002 NOTE: In many implementations, a single agent may perform various combinations of the injecting, relaying and serving functions. Its duties are then the union of the various duties concerned. 8.1. General principles to be followed There are two important principles that news implementors (and administrators) need to keep in mind. The first is the well-known Internet Robustness Principle: Be liberal in what you accept, and conservative in what you send. However, in the case of news there is an even more important principle, derived from a much older code of practice, the Hippocratic Oath (we may thus call this the Hippocratic Principle): First, do no harm. It is VITAL to realize that decisions which might be merely suboptimal in a smaller context can become devastating mistakes when amplified by the actions of thousands of hosts within a few minutes. In the case of gateways, the primary corollary to this is: Cause no loops. 8.2. Duties of an Injecting Agent An Injecting Agent is responsible for taking a proto-article from a posting agent and either forwarding it to a moderator or injecting it into the relaying system for access by readers. As such, an injecting agent is considered responsible for ensuring that any article it injects conforms with the rules of this standard and the policies of any newsgroups or hierarchies that the article is posted to. It is also expected to bear some responsibility towards the rest of the network for the behaviour of its posters (and provision is therefore made for it to be easily contactable by email). To this end injecting agents MAY cancel articles which they have previously injected (see 7.3). 8.2.1. Proto-articles A proto-article is one that has been created by a posting agent and has not yet been injected into the news system by an injecting agent. It SHOULD NOT be propagated in that form to other than injecting agents. A proto-article has the same format as a normal article except that some of the following mandatory headers MAY be omitted: Message-Id-header, Date-header, Path-header (and even From-header if the particular injecting agent can derive that information from other C. H. Lindsey [Page 80] News Article Format August 2002 sources). These headers MUST NOT contain invalid values; they MUST either be correct or not present at all. A proto-article SHOULD NOT contain the '%' path-delimiter in any Path-header, except in the rare cases where an article gets injected twice. It MAY contain path-identities with other path-delimiters in the pre-injection portion of the Path-header (5.6.3). 8.2.2. Procedure to be followed by Injecting Agents A injecting agent receives proto-articles from posting and followup agents. It verifies them, adds headers where required and then either forwards them to a moderator or injects them by passing them to serving or relaying agents. If an injecting agent receives an otherwise valid article that has already been injected it SHOULD either act as if it is a relaying agent or else pass the article on to a relaying agent completely unaltered. Exceptionally, it MAY reinject the article, perhaps as a part of some complex gatewaying process (in which case it will add a second '%' path-delimiter to the Path-header). It MUST NOT forward an already injected article to a moderator. An injecting agent processes articles as follows: 1. It MUST remove any Injector-Info- or Complaints-To-header already present (though it might be useful to copy them to suitable X- headers). It SHOULD likewise remove any NNTP-Posting-Host or other undocumented tracing header. 2. It SHOULD verify that the article is from a trusted source. However, it MAY allow articles in which headers contain "forged" email addresses, that is, addresses which are not valid for the known and trusted source, especially if they end in ".invalid". 3. It MUST reject any article whose Date-header is more than 24 hours into the past or into the future (cf. 5.1). 4. It MUST reject any article that does not have the correct mandatory headers for a proto-article (5 and 8.2.1) present, or which contains any header that does not have legal contents. In particular, it MUST reject any article whose Newsgroups-header or Followup-To-header contains an encoded newsgroup-name (5.5.2); alternatively, it MAY decode those newsgroup-names and continue (this being a useful service for moderators using that injecting agent, see 8.7). It SHOULD reject any article which contains any header deprecated for Netnews (4.2.1). 5. If the article is rejected (for reasons given above, or for other formatting errors or matters of site policy) the posting agent SHOULD be informed (such as via an NNTP 44x response code) that posting has failed and the article MUST NOT then be processed further. C. H. Lindsey [Page 81] News Article Format August 2002 6. The Message-ID and Date-headers (and their contents) MUST be added when not already present. 7. A Path-header with a tail-entry (5.6.3) MUST be correctly added if not already present (except that it SHOULD NOT be added if the article is to be forwarded to a moderator). 8. The path-identity of the injecting agent with a '%' path-delimiter (5.6.2) MUST be prepended to the Path-header; moreover, that path-identity MUST be an FQDN mailable address (5.6.2). 9 An Injector-Info-header (6.19) SHOULD be added, identifying the trusted source of the article, and a suitable Complaints-To-header (6.20) MAY be added (except that these two headers SHOULD NOT be added if the article is to be forwarded to a moderator). 10.The injecting agent MUST NOT alter the body of the article in any way. It MAY add other headers not already provided by the poster, but SHOULD NOT alter, delete, or reorder any existing header, with the specific exception of "tracing" headers such as Injector-Info and Complaints-To, which are to be removed as already mentioned. NOTE: The addition of non-mandatory headers by the injecting agent may alter the posting agent's preferred presentation of information. In particular, adding a Sender-header that exposes a sender's mailbox has privacy implications; where the main or only purpose for doing so is as tracing information, it is preferable to use instead one of the options provided for the Injector-Info header (6.19.1). 11.If the Newsgroups-header contains no moderated groups, or if it contains an Approved-header, the injecting agent forwards the article to one or more relaying or serving agents. 12.Otherwise, when the Newsgroups-header contains one or more moderated groups and the article does NOT contain an Approved- header, the injecting agent MUST forward it to the moderator of the first (leftmost) moderated group listed in the Newsgroups- header via email. There are two possibilities for doing this: (a) The complete article is encapsulated (headers and all) within the email, preferably using the Content-Type "application/news-transmission" (6.21.6.1) with any usage parameter set to "moderate". Moreover, there SHOULD NOT be more than one encapsulated article within the one email. This method has the advantage of removing any possible conflict between Netnews and Email headers, or of changes to those headers during transport through email (and in particular, it ensures that any UTF8-xtra-chars within those headers will pass safely through any email transport even if it is 8bit-unsafe). C. H. Lindsey [Page 82] News Article Format August 2002 (b) The article is sent as an email as it stands, with the addition of such extra headers (e.g. a To-header) as are necessary for an email. Since the article is, in effect, being gatewayed into Email, the provisions of section 8.8.1 apply. In particular, if the headers contain any UTF8-xtra- chars, it may be necessary to apply encodings, specifically the encoding defined in section 5.5.2 in the case of the article's Newsgroups- and Followup-To-headers. Although both of these methods have seen use in the past, the preponderance of current usage on Usenet has been for method (b) and many moderators are ill-prepared to deal with method (a). Therefore, method (a) SHOULD NOT be used until such time as the majority of moderators are able to accept it. 13.This standard does not prescribe how the email address of the moderator is to be determined, that being a matter of policy to be arranged by the agency responsible for the oversight of each hierarchy. Nevertheless, there do exist various agents worldwide which provide the service of forwarding to moderators, and the address to use with them is obtained as follows: (a) Each '.' in the newsgroup-name is replaced with a '-'. (b) If the newsgroup-name contains any UTF8-xtra-char, it is encoded as described in section 5.5.2. (c) The result of these operations is used as the local-part of the mailbox of the agent. For example, articles intended for "news.announce.important" would be emailed to "news- announce-important@forwardingagent.example". 8.3. Duties of a Relaying Agent A Relaying Agent accepts injected articles from injecting and other relaying agents and passes them on to relaying or serving agents according to mutually agreed policy. Relaying agents SHOULD accept articles ONLY from trusted agents. A relaying agent processes articles as follows: 1. It MUST verify the leftmost entry in the Path-header and then prepend its own path-identity with a '/' path-delimiter, and possibly also the verified path-identity of its source with a '?' path-delimiter (5.6.2). 2. It MUST reject any article whose Date-header is stale (see 5.1). 3. It MUST reject any article that does not have the correct mandatory headers (section 5) present with legal contents. 4. It SHOULD reject any article whose optional headers (section 6) do not have legal contents. C. H. Lindsey [Page 83] News Article Format August 2002 5. It SHOULD reject any article that has already been sent to it (a database of message identifiers of recent messages is usually kept and matched against). 6. It SHOULD reject any article that matches an already received cancel message (or an equivalent Supersedes-header) issued by its poster or by some other trusted entity. 7. It MAY reject any article without an Approved-header posted to newsgroups known to be moderated (this practice is strongly recommended, but the information necessary to do it may not be available to all agents). 8. It then passes articles which match mutually agreed criteria on to neighbouring relaying and serving agents. However, it SHOULD NOT forward articles to sites whose path-identity is already in the Path-header. NOTE: It is usual for relaying and serving agents to restrict the Newsgroups, Distributions, age and size of articles that they wish to receive. If the article is rejected as being invalid, unwanted or unacceptable due to site policy, the agent that passed the article to the relaying agent SHOULD be informed (such as via an NNTP 43x response code) that relaying failed. In order to prevent a large number of error messages being sent to one location, relaying agents MUST NOT inform any other external entity that an article was not relayed UNLESS that external entity has explicitly requested that it be informed of such errors. NOTE: In order to prevent overloading, relaying agents should not routinely query an external entity (such as a DNS-server) in order to verify an article (though a local cache of the required information might usefully be consulted). Relaying agents MUST NOT alter, delete or rearrange any part of an article expect for headers designated as variant (4.2.5.3). 8.4. Duties of a Serving Agent A Serving Agent takes an article from a relaying or injecting agent and files it in a "news database". It also provides an interface for reading agents to access the news database. This database is normally indexed by newsgroup with articles in each newsgroup identified by an article-locater (usually in the form of a decimal number - see 6.16). NOTE: Since control messages are often of interest, but should not be displayed as normal articles in regular newsgroups, it is common for serving agents to make them available in a pseudo- newsgroup named "control" or in a pseudo-newsgroup in a sub- hierarchy under "control." (e.g. "control.cancel"). C. H. Lindsey [Page 84] News Article Format August 2002 A serving agent processes articles as follows: 1. It MUST verify the leftmost entry in the Path-header and then prepend its own path-identity with a '/' path-delimiter, and possibly also the verified path-identity of its source with a '?' path-delimiter (5.6.2). 2. It MUST reject any article whose Date-header is stale (see 5.1). 3. It MUST reject any article that does not have the correct mandatory headers (section 5) present, or which contains any header that does not have legal contents. 4. It SHOULD reject any article that has already been sent to it (a database of message identifiers of recent messages is usually kept and matched against). 5. It SHOULD reject any article that matches an already received cancel message (or an equivalent Supersedes-header) issued by its poster or by some other trusted entity. 6. It MUST reject any article without an Approved-header posted to any moderated newsgroup which it is configured to receive, and it MAY reject such articles for any newsgroup it knows be moderated. 7. It MUST remove any Xref-header (6.16) from each article. It then MAY (and usually will) generate a fresh Xref-header. 8. Finally, it stores the article in its news database. 8.5. Duties of a Posting Agent A Posting Agent is used to assist the poster in creating a valid proto-article and forwarding it to an injecting agent. Postings agents SHOULD ensure that proto-articles they create are valid news articles according to this standard and other applicable policies. Posting agents meant for use by ordinary posters SHOULD reject any attempt to post an article which cancels or Supersedes another article of which the poster is not the author. 8.6. Duties of a Followup Agent A Followup Agent is a special case of a posting agent and as such is bound by all the posting agent's requirements plus additional ones. Followup agents MUST create valid followups, in particular by providing correctly adjusted forms of those headers described as inheritable (4.2.5.2), notably the Newsgroups-header (5.5), the Subject-header (5.4) and the References-header (6.10), and they Ought to observe appropriate quoting conventions in the body (see 4.3.2). C. H. Lindsey [Page 85] News Article Format August 2002 Followup agents SHOULD initialize the Newsgroups-header from the precursor's Followup-To-header, if present, when preparing a followup; however posters MAY then change this before posting if they wish. Followup agents MUST NOT attempt to send email to any address ending in ".invalid". Followup agents SHOULD NOT email copies of the followup to the poster of the precursor unless this has been explicitly requested by means of a Mail-Copies-To-header (6.8), but they SHOULD include a Posted-And-Mailed-header (6.9) whenever a copy is so emailed. 8.7. Duties of a Moderator A Moderator receives news articles by email, decides whether to accept them and, if so, either injects them into the news stream or forwards them to further moderators. A moderator processes an article, as submitted to any newsgroup that he moderates, as follows: 1. He decides, on the basis of whatever moderation policy applies to his group, whether to accept or reject the article. He MAY do this manually, or else partially or wholly with the aid of appropriate software for whose operation he is then responsible. He MAY modify the article if that is in accordance with the applicable moderation policy (and in particular he MAY remove redundant headers and add Comments and other informational headers). He MAY inform the poster as to whether the article has been accepted or rejected. If the article is rejected, then it fails for all the newsgroups for which it was intended (in particular the moderator SHOULD NOT resubmit the article, with a reduced Newsgroups-header, to any remaining groups, especially if this will break any authentication checks present in the article). If the article is accepted, the moderator proceeds with the following steps. 2. The Date-header SHOULD be retained, except that if it is stale (5.1) for reasons understood by the moderator (e.g. delays in the moderation process) he MAY substitute the current date (but must then take responsibility for any loops that ensue). Any variant headers (4.2.5.3) MUST be removed, except that a Path-header MAY be truncated to only its pre-injection region (5.6.3). Any Injector-Info-header (6.19) or Complaints-To-header (6.20) MUST be removed. 3. He adds an Approved-header (6.14) containing a mailbox identifying himself (or, if the article already contains an Approved-header from another moderator, he adds that identifying information to it). He MAY also include that Approved-header within some digital signature scheme (see 7.1). C. H. Lindsey [Page 86] News Article Format August 2002 4. If the Newsgroups-header contains further moderated newsgroups for which approval has not already been given, he forwards the article to the moderator of the leftmost such group (which, if this standard has been followed correctly, will always be the group immediately to the right of the group(s) for which he is responsible). However, he MUST NOT alter the order in which the newsgroups are listed in the Newsgroups-header. 5. Otherwise, he causes the article to be injected, having first decoded any encoded newsgroup-name (5.5.2), unless his injecting agent offers that service (8.2.2), and having observed all the duties of a posting agent (8.5). NOTE: This standard does not prescribe how the moderator or moderation policy for each newsgroup is established; rather it assumes that whatever agencies are responsible for the relevant network or hierarchy (1.1) will have made appropriate arrangements in that regard. Articles will be received by the moderator either encapsulated as an object of Content-Type application/news-transmission (8.2.2) (or possibly encapsulated but without an explicit Content-Type-header), or else directly as an email already containing all the headers appropriate for a Netnews article (see 8.2.2) in which case he needs to be aware of the Duties of an Incoming Gateway (8.8.2) (and, in particular, he SHOULD adopt the Message-ID- and Date-headers of the email message, though he SHOULD NOT add any Sender-header). Moderators SHOULD be prepared to accept articles in either format. 8.8. Duties of a Gateway A Gateway transforms an article into the native message format of another medium, or translates the messages of another medium into news articles. Encapsulation of a news article into a message of MIME type application/news-transmission, or the subsequent undoing of that encapsulation, is not gatewaying, since it involves no transformation of the article. There are two basic types of gateway, the Outgoing Gateway that transforms a news article into a different type of message, and the Incoming Gateway that transforms a message from another medium into a news article and injects it into a news system. These are handled separately below. The primary dictat for a gateway is: Above all, prevent loops. Transformation of an article into another medium stands a very high chance of discarding or interfering with the protection inherent in the news system against duplicate articles. The most common problem caused by gateways is "spews," gateway loops that cause previously posted articles to be reinjected repeatedly into Usenet. To prevent this, a gateway MUST take precautions against loops, as detailed C. H. Lindsey [Page 87] News Article Format August 2002 below. If bidirectional gatewaying (both an incoming and an outgoing gateway) is being set up between Netnews and some other medium, the incoming and outgoing gateways SHOULD be coordinated to avoid reinjection of gated articles. Circular gatewaying (gatewaying a message into another medium and then back into Netnews) SHOULD NOT be done; encapsulation of the article SHOULD be used instead where this is necessary. A second general principal of gatewaying is that the transformations applied to the message SHOULD be as minimal as possible while still accomplishing the gatewaying. Every change made by a gateway potentially breaks a property of one of the media or loses information, and therefore only those transformations made necessary by the differences between the media should be applied. It is worth noting that safe bidirectional gatewaying between a mailing list and a newsgroup is far easier if the newsgroup is moderated. Posts to the moderated group and submissions to the mailing list can then go through a single point that does the necessary gatewaying and then sends the message out to both the newsgroup and the mailing list at the same time, eliminating most of the possibility of loops. Bidirectional gatewaying between a mailing list and an unmoderated newsgroup, in contrast, is difficult to do correctly and is far more fragile. Newsgroups intended to be bidirectionally gated to a mailing list SHOULD therefore be moderated where possible, even if the moderator is a simple gateway and injecting agent that correctly handles crossposting to other moderated groups and otherwise passes all traffic. 8.8.1. Duties of an Outgoing Gateway From the perspective of Netnews, an outgoing gateway is just a special type of reading agent. The exact nature of what the outgoing gateway will need to do to articles depends on the medium to which the articles are being gated. The operation of the outgoing gateway is only subject to additional constraints in the presence of one or more corresponding incoming gateways back from that medium to Netnews, since this opens the possibility of loops. Where the format of the news article is incompatible with that of the target medium, it may be necessary to apply transformations. It is not the purpose of this standard to set requirements to be followed by implementors of outgoing gateways. Those implementors are in the best position to know the capabilities of the systems to which the article is to be sent, the purposes for which it is being sent, and the extent to which those purposes will be vitiated if the content of some header is mutilated en route, or fails to display correctly upon arrival; this is a matter for their judgement. Nevertheless, it is useful to draw attention to a few transformations C. H. Lindsey [Page 88] News Article Format August 2002 which such implementors might find useful. o Transporting headers containing non-ASCII characters without first encoding them is contrary to the current Email standards [RFC 2821] and [RFC 2822]. This applies both to the top-level headers of the email, and also to headers contained within any embedded message or multipart Content-Types (and so recursively). However, it is well known that most mail transport agents will in fact convey these characters intact, especially for non-top-level headers in the case of transports which support the 8BITMIME extension, and it is to be expected that the prevalence of this ability will increase in the future (and may even be compliant with future versions of the Email standards). Moreover, many mail user agents will also display such characters correctly, or at least adequately. Therefore, some implementors of gateways may consider it an acceptable risk not to transform these headers in any way, especially in the case of the lower-level ones. NOTE: It is not the purpose of this standard either to condemn or to condone behaviours which may be non-compliant with other standards. That is a matter for those implementors. o Where an implementor considers the risk too high for the top-level headers, encapsulating the whole article as a message/rfc822 (6.21.2.2) may make it less likely to be mutilated during transport, especially where 8BITMIME is supported. Alternatively, encapsulating as an application/news-transmission (6.21.6.1) will guarantee correct transmission in all cases and is the method of choice where the intent is to gateway it back into Netnews later on. o To ensure full compliance with the Email standards it is necessary to encode words containing UTF8-xtra-chars according to [RFC 2047] (but only where permitted by that standard, i.e. within phrases and unstructured headers, although many user agents will display this encoding correctly in other contexts also). Likewise, within parameters the proper encoding is that defined in [RFC 2231]. In both cases, it is preferable to encode using the charset UTF-8, although it might be wise first to confirm that that is indeed the charset which had been used (see 4.4.1). o In the case of newsgroup-names, as found in Newsgroups-headers, Followup-To-headers and some Control-headers, [RFC 2047] is not applicable (even though some mail reading agents might nevertheless display it correctly). Therefore, it is necessary to use the encoding described in section 5.5.2. Even if it is not decoded at the far end, it is preferable to display such an encoded form than to display nothing at all. Note, however, that such encoded newsgroup-names MUST be restored to their canonical form before reinjection into any Netnews system. In general, the following practices are recommended for all outgoing gateways, regardless of whether there is known to be a related incoming gateway, both as a precautionary measure and as a guideline to quality of implementation. C. H. Lindsey [Page 89] News Article Format August 2002 1. The message identifier of the news article should be preserved if at all possible, preferably as or within the corresponding unique identifier of the other medium, but if not at least as a comment in the message. This helps greatly with preventing loops. 2. The Date of the news article should also be preserved if possible, for similar reasons. 3. The message should be tagged in some way so as to prevent its reinjection into Netnews. This may be impossible to do without knowledge of potential incoming gateways, but it is better to try to provide some indication even if not successful; at the least, a human-readable indication that the article should not be gated back to Netnews can help locate a human problem. 4. Netnews control messages should not be gated to another medium unless they would somehow be meaningful in that medium. 8.8.2. Duties of an Incoming Gateway The incoming gateway has the serious responsibility of ensuring that all of the requirements of this standard are met by the articles that it forms. In addition to its special duties as a gateway, it bears all of the duties and responsibilities of an injecting agent as well, and additionally has the same responsibility of a relaying agent to reject articles that it has already gatewayed. An incoming gateway MUST NOT gate the same message twice. It may not be possible to ensure this in the face of mangling or modification of the message, but at the very least a gateway, when given a copy of a message it has already gated identical except for trace headers (like Received in Email or Path in Netnews) MUST NOT gate the message again. An incoming gateway SHOULD take precautions against having this rule bypassed by modifications of the message that can be anticipated. News articles prepared by gateways MUST be legal news articles. In particular, they MUST include all of the mandatory headers, MUST fully conform to the restrictions on said headers, and SHOULD exclude any deprecated headers (4.2.1). This often requires that a gateway function not only as a relaying agent, but also partly as a posting agent, aiding in the synthesis of a conforming article from non- conforming input. Incoming gateways MUST NOT pass control messages (articles containing a Control- or Supersedes-header) without removing or renaming that header. Gateways MAY, however, generate their own cancel messages, under the general allowance for injecting agents to cancel their own messages (7.3). If a gateway receives a message that it can determine is a valid equivalent of a cancel message in the medium it is gatewaying, it SHOULD discard that message without gatewaying it, generate a corresponding cancel message of its own, and inject that cancel message. C. H. Lindsey [Page 90] News Article Format August 2002 Incoming gateways MUST NOT inject control messages other than cancels. Encapsulation SHOULD be used instead of gatewaying, when direct posting is not possible or desirable. NOTE: It is not unheard of for mail-to-news gateways to be used to post control messages, but encapsulation should be used for these cases instead. Gateways by their very nature are particularly prone to loops. Spews of normal articles are bad enough; spews of control messages with special significance to the news system, possibly resulting in high processing load or even email sent for every message received, are catastrophic. It is far preferable to construct a system specifically for posting control messages that can do appropriate consistency checks and authentication of the originator of the message. If there is a message identifier that fills a role similar to that of the Message-ID-header in news, it SHOULD be used in the formation of the message identifier of the news article, perhaps with transformations required to meet the uniqueness requirement of Netnews and with the removal of any comments so as to comply with the syntax in section 5.3. Such transformations SHOULD be designed so that two messages with the same identifier generate the same Message-ID-header. NOTE: Message identifiers play a central role in the prevention of duplicates, and their correct use by gateways will do much to prevent loops. Netnews does, however, require that message identifiers be unique, and therefore message identifiers from other media may not be suitable for use without modification. A balance must be struck by the gateway between preserving information used to prevent loops and generating unique message identifiers. Exceptionally, if there are multiple incoming gateways for a particular set of messages, each to a different newsgroup(s), each one SHOULD generate a message identifier unique to that gateway. Each incoming gateway nonetheless MUST ensure that it does not gate the same message twice. NOTE: Consider the example of two gateways of a given mailing list into the world-wide Usenet newsgroups, both of which preserve the email message identifier. Each newsgroup may then receive a portion of the messages (different sites seeing different portions). In these cases, where there is no one "official" gateway, some other method of generating message identifiers has to be used to avoid collisions. It would obviously be preferable for there to be only one gateway which crossposts, but this may not be possible to coordinate. If no date information is available, the gateway MAY supply a Date- header with the gateway's current date. If only partial information is available (e.g. date but not time), this SHOULD be fleshed out to a full Date-header by adding default values rather than discarding this information. Only in very exceptional circumstances should Date C. H. Lindsey [Page 91] News Article Format August 2002 information be discarded, as it plays an important role in preventing reinjection of old messages. An incoming gateway MUST add a Sender-header to the news article it forms containing the mailbox of the administrator of the gateway. Problems with the gateway may be reported to this mailbox. The display-name portion of this mailbox SHOULD indicate that the entity responsible for injection of the message is a gateway. If the original message already had a Sender-header, it SHOULD be renamed so that its contents can be preserved. 8.8.3. Example To illustrate the type of precautions that should be taken against loops, here is an example of the measures taken by one particular combination of mail-to-news and news-to-mail gateways at Stanford University designed to handle bidirectional gatewaying between mailing lists and unmoderated groups. 1. The news-to-mail gateway preserves the message identifier of the news article in the generated email message. The mail-to-news gateway likewise preserves the email message identifier provided that it is syntactically valid for Netnews. This allows the news system's built-in suppression of duplicates to serve as the first line of defense against loops. 2. The news-to-mail gateway adds an X-Gateway-header to all messages it generates. The mail-to-news gateway discards any incoming messages containing this header. This is robust against mailing list managers that replace the message identifier, and against any number of email hops, provided that the other message headers are preserved. 3. The mail-to-news gateway inserts the host name from which it received the email message in the pre-injection region of the Path (5.6.3). The news-to-mail gateway refuses to gateway any message that contains the list server name in the pre-injection region of its Path-header. This is robust against any amount of munging of the message headers by the mailing list, provided that the email only goes through one hop. 4. The mail-to-news gateway is designed never to generate bounces to the envelope sender. Instead, articles that are rejected by the news server (for reasons not warranting silent discarding of the message) result in a bounce message sent to an errors address known not to forward to any mailing lists, so that they can be handled by the news administrators. These precautions have proven effective in practice at preventing loops for this particular application (bidirectional gatewaying between mailing lists and locally distributed newsgroups where both gateways can be designed together). General gatewaying to world-wide newsgroups poses additional difficulties; one must be very wary of strange configurations, such as a newsgroup gated to a mailing list C. H. Lindsey [Page 92] News Article Format August 2002 which is in turn gated to a different newsgroup. 9. Security and Related Considerations There is no security. Don't fool yourself. Usenet is a prime example of an Internet Adhocratic-Anarchy; that is, an environment in which trust forms the basis of all agreements. It works. 9.1. Leakage Articles which are intended to have restricted distribution are dependent on the goodwill of every site receiving them. The "Archive: no" header (6.12) is available as a signal to automated archivers not to file an article, but that cannot be guaranteed. The Distribution-header makes provision for articles which should not be propagated beyond a cooperating subnet. The key security word here is "cooperating". When a machine is not configured properly, it may become uncooperative and tend to distribute all articles. The flooding algorithm is extremely good at finding any path by which articles can leave a subnet with supposedly restrictive boundaries, and substantial administrative effort is required to avoid this. Organizations wishing to control such leakage are strongly advised to designate a small number of official gateways to handle all news exchange with the outside world (however, making such gateways too restrictive can also encourage the setting up of unofficial paths which can be exceedingly hard to track down). The sendme control message (7.4), insofar as it is still used, can be used to request articles with a given message identifier, even one that is not supposed to be supplied to the requestor. 9.2. Attacks 9.2.1. Denial of Service The proper functioning of individual newsgroups can be disrupted by the massive posting of "noise" articles, by the repeated posting of identical or near identical articles, by posting followups unrelated to their precursors, or which quote their precursors in full with the addition of minimal extra material (especially if this process is iterated), and by crossposting to, or setting followups to, totally unrelated newsgroups. Many have argued that "spam", massively multiposted (and to a lesser extent massively crossposted) articles, usually for advertising purposes, also constitutes a DoS attack in its own regard. This may be so. Such articles intended to deny service, or other articles of an inflammatory nature, may also have their From or Reply-To addresses set to valid but incorrect email addresses, thus causing large volumes of email to descend on the true owners of those addresses. C. H. Lindsey [Page 93] News Article Format August 2002 Similar effects could be caused by any email header which could cause every reading agent receiving it to take some externally visible action. For example, the Disposition-Notification-To-header defined in [RFC 2298] could cause huge numbers of acknowledgements to be emailed to an unsuspecting third party (for which reason [RFC 2298] declares that that header SHOULD NOT be used in Netnews). It is a violation of this standard for a poster to use as his address a mailbox which he is not entitled to use. Even addresses with an invalid local-part but a valid domain can cause disruption to the administrators of such domains. Posters who wish to remain anonymous or to prevent automated harvesting of their addresses, but who do not care to take the additional precautions of using more sophisticated anonymity measures, should avoid that violation by the use of addresses ending in the ".invalid" top-level-domain (see 5.2). A malicious poster may also prevent his article being seen at a particular site by preloading that site into the Path-header (5.6.1) and may thus prevent the true owner of a forged From or Reply-To address from ever seeing it. A malicious complainer may submit a modified copy of an article (e.g. with an altered Injector-Info-header) to the administrator of an injecting agent in an attempt to discredit the author of that article and even to have his posting privileges removed. Administrators should therefore obtain a genuine copy of the article from their own serving agent before taking such precipitate action. Administrative agencies with responsibility for establishing policies in particular hierarchies can and should set bounds upon the behaviour that is considered acceptable within those hierarchies (for example by promulgating charters for individual newsgroups, and other codes of conduct). Whilst this standard places an onus upon injecting agents to bear responsibility for the misdemeanours of their posters (which includes non-adherence to established policies of the relevant hierarchies as provided in section 8.2), and to provide assistance to the rest of the network by making proper use of the Injector-Info- (6.19) and Complaints-To- (6.20) headers, it makes no provision for enforcement, which may in consequence be patchy. Nevertheless, injecting sites which persistently fail to honour their responsibilities or to comply with generally accepted standards of behaviour are likely to find themselves blacklisted, with their articles refused propagation and even subject to cancellation, and other relaying sites would be well advised to withdraw peering arrangements from them. 9.2.2. Compromise of System Integrity The posting of unauthorized (as determined by the policies of the relevant hierarchy) control messages can cause unwanted newsgroups to be created, or wanted ones removed, from serving agents. Administrators of such agents SHOULD therefore take steps to verify the authenticity of such control messages, either by manual C. H. Lindsey [Page 94] News Article Format August 2002 inspection (particularly of the Approved-header) or by checking any digital signatures that may be provided (see 7.1). In addition, they SHOULD periodically compare the newsgroups carried against any regularly issued checkgroups messages, or against lists maintained by trusted servers and accessed by out-of-band protocols such as FTP or HTTP. Malicious cancel messages (7.3) can cause valid articles to be removed from serving agents. Administrators of such agents SHOULD therefore take steps to verify that they originated from the (apparent) poster, the injector or the moderator of the article, or that in other cases they came from a place that is trusted to work within established policies and customs. Such steps SHOULD include the checking of any digital signatures, or other security devices, that may be provided (see 7.1). Articles containing Supersedes- headers (6.15) are effectively cancel messages, and SHOULD be subject to the same checks. Currently, many sites choose to ignore all cancel messages on account of the difficulty of conducting such checks. Improperly configured serving agents can allow articles posted to moderated groups onto the net without first being approved by the moderator. Injecting agents SHOULD verify that moderated articles were received from one of the entities given in their Approved- headers and/or check any digital signatures that may be provided (see 7.1). The filename parameter of the Archive-header (6.12) can be used to attempt to store archived articles in inappropriate locations. Archiving sites should be suspicious of absolute filename parameters, as opposed to those relative to some location of the archiver's choosing. There may be weaknesses in particular implementations that are subject to malicious exploitation. In particular, it has not been unknown for complete shell scripts to be included within Control- headers. Implementors need to be aware of this. Reading agents should be chary of acting automatically upon MIME objects with an "application" Content-Type that could change the state of that agent, except in contexts where such applications are specifically expected (see 6.21). Even the Content-Type "text/html" could have unexpected side effects on account of embedded objects, especially embedded executable code or URLs that invoke non-news protocols such as HTTP [RFC 2616]. It is therefore generally recommended that reading agents do not enable the execution of such code (since it is extremely unlikely to have a valid application within Netnews) and that they only honour URLs referring to other parts of the same article. Non-printable characters embedded in article bodies may have surprising effects on printers or terminals, notably by reconfiguring them in undesirable ways which may become apparent only after the reading agent has terminated. C. H. Lindsey [Page 95] News Article Format August 2002 9.3. Liability There is a presumption that a poster who sends an article to Usenet intends it to be stored on a multitude of serving agents, and has therefore given permission for it to be copied to that extent. Nevertheless, Usenet is not exempt from the Copyright laws, and it should not be assumed that permission has been given for the article to be copied outside of Usenet, nor for its permanent archiving contrary to any Archive-header that may be present. Posters also need to be aware that they are responsible if they breach Copyright, Libel, Harassment or other restrictions relating to material that they post, and that they may possibly find themselves liable for such breaches in jurisdictions far from their own. Serving agents may also be liable in some jurisdictions, especially if the breach has been explicitly drawn to their attention. Users who are concerned about such matters should seek advice from competent legal authorities. 10. IANA Considerations IANA is requested to register the following media types, described elsewhere in this standard for use with the Content-Type-header, in the IETF tree in accordance with the procedures set out in [RFC 2048]. application/news-transmission (6.21.6.1) application/news-groupinfo (7.2.1.2) application/news-checkgroups (7.2.4.1) IANA is also requested to change the status of the following media type to "OBSOLETE". message/news (6.21.6.2) NOTE: "Application/news-transmission" is an update, with clarification and additional optional parameters, to an existing registration. "Message/rfc822" should now be used in place of the obsoleted "message/news". 11. References [ANSI X3.4] "American National Standard for Information Systems - Coded Character Sets - 7-Bit American National Standard Code for Information Interchange (7-Bit ASCII)", ANSI X3.4, 1986. [ISO 3166] "Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes", ISO 3166, 1997. [ISO 8859] International Standard - Information Processing - 8-bit Single-Byte Coded Graphic Character Sets. Part 1: Latin alphabet No. 1, ISO 8859-1, 1987. Part 2: Latin alphabet No. 2, C. H. Lindsey [Page 96] News Article Format August 2002 ISO 8859-2, 1987. Part 3: Latin alphabet No. 3, ISO 8859-3, 1988. Part 4: Latin alphabet No. 4, ISO 8859-4, 1988. Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988. Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987. Part 7: Latin/Greek alphabet, ISO 8859-7, 1987. Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988. [ISO/IEC 10646] "International Standard - Information technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane", ISO/IEC 10646- 1:2000, 2000. [NNTP] S. Barber, "Network News Transport Protocol", draft-ietf- nntpext-base-*.txt. [PGPVERIFY] David Lawrence, . [RFC 1034] P. Mockapetris, "Domain Names - Concepts and Facilities", RFC 1034, November 1987. [RFC 1036] M. Horton and R. Adams, "Standard for Interchange of USENET Messages", RFC 1036, December 1987. [RFC 1153] F. Wancho, "Digest Message Format", RFC 1153, April 1990. [RFC 1847] J. Galvin, S. Murphy, S. Crocker, and N. Freed, "Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, October 1995. [RFC 1864] J. Myers and M. Rose, "The Content-MD5 Header Field", RFC 1864, October 1995. [RFC 2045] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC 2046] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC 2047] K. Moore, "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047, November 1996. [RFC 2048] N. Freed, J. Klensin, and J. Postel, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", RFC 2048, November 1996. [RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC 2142] D. Crocker, "Mailbox Names for Common Services, Roles and Functions", RFC 2142, May 1997. C. H. Lindsey [Page 97] News Article Format August 2002 [RFC 2156] S. Kille, "MIXER (Mime Internet X.400 Enhanced Relay): Mapping between X.400 and RFC 822/MIME", RFC 2156, January 1998. [RFC 2183] R. Troost, S. Dorner, and K.Moore, "Communicating Presentation Information in Internet Messages: The Content- Disposition Header Field", RFC 2183, August 1997. [RFC 2231] N. Freed and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2231, November 1997. [RFC 2234] D. Crocker and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [RFC 2279] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [RFC 2279bis] F. Yergeau, "UTF-8, a transformation format of ISO 10646", draft-yergeau-rfc2279bis-00.txt, April 2002. [RFC 2298] R. Fajman, "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998. [RFC 2373] R. Hinden and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [RFC 2440] J. Callas, L. Donnerhacke, H. Finney, and R. Thayer, "OpenPGP Message Format", RFC 2440, November 1998. [RFC 2557] J. Palme, A. Hopmann, and N. Shelness, "MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)", RFC 2557, March 1999. [RFC 2606] D. Eastlake and A. Panitz, "Reserved Top Level DNS Names", RFC 2606, June 1999. [RFC 2616] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC 2821] John C. Klensin and Dawn P. Mann, "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC 2822] P. Resnick, "Internet Message Format", RFC 2822, April 2001. [RFC 3156] M. Elkins, D. Del Torto, R. Levien, and T. Roessler, "MIME Security with OpenPGP", RFC 3156, August 2001. [RFC 822] D. Crocker, "Standard for the Format of ARPA Internet Text Messages.", STD 11, RFC 822, August 1982. [RFC 850] Mark R. Horton, "Standard for interchange of Usenet messages", RFC 850, June 1983. C. H. Lindsey [Page 98] News Article Format August 2002 [RFC 976] Mark R. Horton, "UUCP mail interchange format standard", RFC 976, February 1986. [Son-of-1036] Henry Spencer, "News article format and transmission", , June 1994. [UNICODE 3.0] The Unicode Consortium, "The Unicode Standard - Version 3.0", Addison-Wesley, 2000. [UNICODE 3.1] The Unicode Consortium, "The Unicode Standard - Version 3.1, being an amendment to [UNICODE 3.0]", Unicode Standard Annex #27 , 2001. [UNICODE 3.2] The Unicode Consortium, "The Unicode Standard - Version 3.2, being an amendment to [UNICODE 3.1]", Unicode Standard Annex #28 , 2002. [USEFOR] This Standard. 12. Acknowledgements The editor wishes to thank the following members of the IETF Usenet Format Working Group who made significant contributions to this endeavour (however, inclusion in this list does not imply that a person approves of everything contained herein). Per Abrahamsen Brian Kelly Peter Alfredsen Evan Kirshenbaum Russ Allbery Brad Knowles Greg Andruk Kent Landfield Ralph Babel David C. Lawrence Stan Barber Bruce Lilly Dave Barr Simon Lyall Ian Bell Todd Michel McComb G. James Berigan Denis McKeon Terje Bless Seymour J. Metz Seth Breidbart John Moreno Buddha Buck Chris Newman Forrest J. Cavalier III Dirk Nimmich Evan Champion Paul Overell Maurizio Codogno Jacob Palme Don Croyle Brian Palmer Matt Curtin Pete Resnick Bill Davidsen Jon Ribbens Ian Davis Dan Ritter Jean-Marc Desperrier Thomas Roessler Martin J. Duerst Doug Royer Claus Andre Faerber Frederic Senis Clive D.W. Feather Erland Sommarskog David Formosa Henry Spencer Marty Fouts John Stanley Benjamin Franz Brad Templeton Andrew Gierth Florian Weimer C. H. Lindsey [Page 99] News Article Format August 2002 Jonathan Grobe Curt Welch Thomas Gschwind Curtis Whalen Kai Henningsen Leonid Yegoshin Lars Magne Ingebrigtsen Jamie Zawinski 13. Contact Address Editor Charles. H. Lindsey 5 Clerewood Avenue Heald Green Cheadle Cheshire SK8 3JU United Kingdom Phone: +44 161 436 6131 Email: chl@clw.cs.man.ac.uk [ Working group chair David Barr Digital Island Email: barr@visi.com ] Comments on this draft should preferably be sent to the mailing list of the Usenet Format Working Group at usenet-format@landfield.com. This draft expires six months after the date of publication (see Page 1) (i.e. in Feb 2003). Appendix A.1 - A-News Article Format The obsolete "A News" article format consisted of exactly five lines of header information, followed by the body. For example: Aeagle.642 news.misc cbosgd!mhuxj!mhuxt!eagle!jerry Fri Nov 19 16:14:55 1982 Usenet Etiquette - Please Read body body body The first line consisted of an "A" followed by an article ID (analogous to a message ID and used for similar purposes). The second line was the list of newsgroups. The third line was the path. The fourth was the date, in the format above (all fields fixed width), resembling an Internet date but not quite the same. The fifth C. H. Lindsey [Page 100] News Article Format August 2002 was the subject. This format is documented for archeological purposes only. Articles MUST NOT be generated in this format. Appendix A.2 - Early B-News Article Format The obsolete pseudo-Internet article format, used briefly during the transition between the A News format and the modern format, followed the general outline of a MAIL message but with some non-standard headers. For example: From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz) Newsgroups: news.misc Title: Usenet Etiquette -- Please Read Article-I.D.: eagle.642 Posted: Fri Nov 19 16:14:55 1982 Received: Fri Nov 19 16:59:30 1982 Expires: Mon Jan 1 00:00:00 1990 body body body The From-header contained the information now found in the Path- header, plus possibly the full name now typically found in the From- header. The Title-header contained what is now the Subject-content. The Posted-header contained what is now the Date-content. The Article-I.D.-header contained an article ID, analogous to a message ID and used for similar purposes. The Newsgroups- and Expires-headers were approximately as now. The Received-header contained the date when the latest relaying agent to process the article first saw it. All dates were in the above format, with all fields fixed width, resembling an Internet date but not quite the same. This format is documented for archeological purposes only. Articles MUST NOT be generated in this format. Appendix A.3 - Obsolete Headers Early versions of news software following the modern format sometimes generated headers like the following: Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP Posting-Version: version B 2.10 2/13/83; site eagle.UUCP Date-Received: Friday, 19-Nov-82 16:59:30 EST Relay-Version contained version information about the relaying agent that last processed the article. Posting-Version contained version information about the posting agent that posted the article. Date- Received contained the date when the last relaying agent to process the article first saw it (in a slightly nonstandard format). C. H. Lindsey [Page 101] News Article Format August 2002 In addition, this present standard obsoletes certain headers defined in [Son-of-1036] (see 6.22): Also-Control: cancel <9urrt98y53@site.example> See-Also: Article-Names: comp.foo:charter Article-Updates: Also-Control indicated a control message that was also intended to be filed as a normal article. See-Also listed related articles, but without the specific relationship with followups that pertains to the References-header. Article-Names indicated some special significance of that article in relation to the indicated newsgroup. Article- Updates indicated that an earlier article was updated, without at the same time being superseded. These headers are documented for archeological purposes only. Articles containing these headers MUST NOT be generated. Appendix A.4 - Obsolete Control Messages This present standard obsoletes certain control messages defined in [RFC 1036] (see 7.5), all of which had the effect of requesting a description of a relaying or serving agent's software, or its peering arrangements with neighbouring sites, to be emailed to the article's reply address. Whilst of some utility when Usenet was much smaller than it is now, they had become no more than a tool for the malicious sending of mailbombs. Moreover, many organizations now consider information about their internal connectivity to be confidential. version sendsys whogets senduuname "Version" requested details of the transport software in use at a site. "Sendsys" requested the full list of newsgroups taken, and the peering arrangements. "Who gets" was similar, but restricted to a named newsgroup. "Senduuname" resembled "sendsys" but restricted to the list of peers connected by UUCP. Historically, a checkgroups body consisting of one or two lines, the first of the form "-n newsgroup", caused check-groups to apply to only that single newsgroup. Historically, an article posted to a newsgroup whose name had exactly three components of which the third was "ctl" signified that article was to be taken as a control message. The Subject-header specified the actions, in the same way the Control-header does now. These forms are documented for archeological purposes only; they MUST NO LONGER be used. C. H. Lindsey [Page 102] News Article Format August 2002 Appendix B - Collected Syntax Appendix B.1 - Characters, Atoms and Folding In the following syntactic rules, numbers in the left hand margin indicate rules taken from other documents, specifically: 2 from [RFC 2822] with the exception of those elements described therein as "obsolete"; 3 from [RFC 2373]; 4 from [RFC 2234]; 5 from [RFC 2045]. Where the number is followed by an asterisk ('*'), it indicates that the rule in question has been modified for the purposes of this standard. 4 ALPHA = %x41-5A / ; A-Z %x61-7A ; a-z 2 CFWS = *([FWS] comment) ( ([FWS] comment) / FWS ) 4 CR = %x0D ; carriage return 4 CRLF = CR LF 4 DIGIT = %x30-39 ; 0-9 4 DQUOTE = %d34 ; quote mark 2 FWS = ([*WSP CRLF] 1*WSP); folding whitespace 4 HEXDIG = DIGIT / "A" / "B" / "C" / "D" / "E" / "F" 4 HTAB = %x09 ; horizontal tab 4 LF = %x0A ; line feed 2 NO-WS-CTL = %d1-8 / ; US-ASCII control characters %d11 / ; which do not include the %d12 / ; carriage return, line feed, %d14-31 / ; and whitespace characters %d127 4 SP = %x20 ; space 4 WSP = SP / HTAB ; whitespace characters UTF8-xtra-2-head = %xC2-DF UTF8-xtra-3-head = %xE0 %xA0-BF / %xE1-EC %x80-BF / %xED %x80-9F / %xEE-EF %x80-BF UTF8-xtra-4-head = %xF0 %x90-BF / %xF1-F7 %x80-BF UTF8-xtra-5-head = %xF8 %x88-BF / %xF9-FB %x80-BF UTF8-xtra-6-head = %xFC %x84-BF / %xFD %x80-BF UTF8-xtra-char = UTF8-xtra-2-head 1( UTF8-xtra-tail ) / UTF8-xtra-3-head 1( UTF8-xtra-tail ) / UTF8-xtra-4-head 2( UTF8-xtra-tail ) / UTF8-xtra-5-head 3( UTF8-xtra-tail ) / UTF8-xtra-6-head 4( UTF8-xtra-tail ) UTF8-xtra-tail = %x80-BF C. H. Lindsey [Page 103] News Article Format August 2002 2 atext = ALPHA / DIGIT / "!" / "#" / ; Any character except "$" / "%" / ; controls, SP, and specials. "&" / "'" / ; Used for atoms "*" / "+" / "-" / "/" / "=" / "?" / "^" / "_" / "`" / "{" / "|" / "}" / "~" 2 atom = [CFWS] 1*atext [CFWS] 2 ccontent = ctext / quoted-pair / comment 2 comment = "(" *([FWS] ccontent) [FWS] ")" 2* ctext = NO-WS-CTL / ; all of except %d33-39 / ; SP, HTAB, "(", ")" %d42-91 / ; and "\" %d93-126 / UTF8-xtra-char 2 dcontent = dtext / quoted-pair 2 dot-atom = [CFWS] dot-atom-text [CFWS] 2 dot-atom-text = 1*atext *( "." 1*atext ) 2 dtext = NO-WS-CTL / ; Non white space controls %d33-90 / ; The rest of the US-ASCII %d94-126 ; characters not including ; "[", "]", or " 2 phrase = 1*word 2 qcontent = qtext / quoted-pair 2* qtext = NO-WS-CTL / ; all of except %d33 / ; SP, HTAB, "\" and DQUOTE %d35-91 / %d93-126 / UTF8-xtra-char 2 quoted-pair = "\" text 2 quoted-string = [CFWS] DQUOTE *( [FWS] qcontent ) [FWS] DQUOTE [CFWS] 2 specials = "(" / ")" / ; Special characters used in "<" / ">" / ; other parts of the syntax "[" / "]" / ":" / ";" / "@" / "\" / "," / "." / DQUOTE strict-qcontent = strict-qtext / strict-quoted-pair strict-quoted-pair = "\" strict-text strict-quoted-string = [CFWS] DQUOTE *( [FWS] strict-qcontent ) [FWS] DQUOTE [CFWS] strict-qtext = NO-WS-CTL / ; qtext restricted to %d33 / ; US-ASCII %d35-91 / %d93-126 C. H. Lindsey [Page 104] News Article Format August 2002 strict-text = %d1-9 / ; text restricted to %d11-12 / ; US-ASCII %d14-127 2* text = %d1-9 / ; all UTF-8 characters except %d11-12 / ; US-ASCII NUL, CR and LF %d14-127 / UTF8-xtra-char 5 tspecials = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" / DQUOTE / "/" / "[" / "]" / "?" / "=" 2* unstructured = 1*( [FWS] utext ) [FWS] 2* utext = NO-WS-CTL / ; Non white space controls %d33-126 / ; The rest of US-ASCII UTF8-xtra-char 2 word = atom / quoted-string Appendix B.2 - Basic Forms 2 addr-spec = local-part "@" domain 2 address = mailbox / group 2 address-list = address *( "," address ) 2 angle-addr = [CFWS] "<" addr-spec ">" [CFWS] article = 1*( header CRLF ) separator body 5* attribute = [CFWS] token [CFWS] body = *( *998text CRLF ) 2 display-name = phrase 2 date = day month year 2 date-time = [ day-of-week "," ] date FWS time [CFWS] 2 day = [FWS] 1*2DIGIT 2 day-name = "Mon" / "Tue" / "Wed" / "Thu" / "Fri" / "Sat" / "Sun" 2 day-of-week = [FWS] day-name 2 domain = dot-atom / domain-literal 2 domain-literal = [CFWS] "[" *([FWS] dcontent) [FWS] "]" [CFWS] 2 group = display-name ":" [ mailbox-list / CFWS ] ";" [CFWS] header-name = 1*name-character *( "-" 1*name-character ) 2 hour = 2DIGIT 2* local-part = dot-atom / strict-quoted-string 2 mailbox = name-addr / addr-spec 2 mailbox-list = mailbox *( "," mailbox ) 2 minute = 2DIGIT 2 month = FWS month-name FWS 2 month-name = "Jan" / "Feb" / "Mar" / "Apr" / "May" / "Jun" / "Jul" / "Aug" / "Sep" / "Oct" / "Nov" / "Dec" 2 name-addr = [display-name] angle-addr name-character = ALPHA / DIGIT other-header = header-name ":" 1*SP other-content other-content = other-parameter = 5 parameter = attribute "=" value 2 second = 2DIGIT C. H. Lindsey [Page 105] News Article Format August 2002 separator = CRLF 2 time = time-of-day FWS zone 2 time-of-day = hour ":" minute [ ":" second ] 5 token = 1* 5 value = [CFWS] token [CFWS] / quoted-string 5* x-token = "x-" token 2 year = 4*DIGIT 2* zone = (( "+" / "-" ) 4DIGIT) / "UT" / "GMT" Appendix B.3 - Headers Appendix B.3.1 - Header outlines header = other-header / Date-header / From-header / Message-ID-header / Subject-header / Newsgroups-header / Path-header / Reply-To-header / Sender-header / Organization-header / Keywords-header / Summary-header / Distribution-header / Followup-To-header / Mail-Copies-To-header / Posted-And-Mailed-header / References-header / Expires-header / Archive-header / Control-header / Approved-header / Supersedes-header / Xref-header / Lines-header / User-Agent-header / Injector-Info-header / Complaints-To-header Approved-content = From-content Approved-header = "Approved" ":" SP Approved-content *( ";" other-parameter ) Archive-content = [CFWS] ("no" / "yes" ) [CFWS] Archive-header = "Archive" ":" SP Archive-content *( ";" ( Archive-parameter / other-parameter ) ) Archive-parameter = Complaints-To-content= address-list Complaints-To-header = "Complaints-To" ":" SP Complaints-To-content Control-content = [CFWS] control-message [CFWS] C. H. Lindsey [Page 106] News Article Format August 2002 Control-header = "Control" ":" SP Control-content *( ";" other-parameter ) Date-content = date-time Date-header = "Date" ":" SP Date-content *( ";" other-parameter ) Distribution-content = distribution *( dist-delim distribution ) Distribution-header = "Distribution" ":" SP Distribution-content *( ";" other-parameter ) Expires-content = date-time Expires-header = "Expires" ":" SP Expires-content *( ";" other-parameter ) Followup-To-content = Newsgroups-content / [FWS] "poster" [FWS] Followup-To-header = "Followup-To" ":" SP Followup-To-content *( ";" other-parameter ) From-content = mailbox-list From-header = "From" ":" SP From-content Injector-Info-content= [CFWS] path-identity [CFWS] Injector-Info-header = "Injector-Info" ":" SP Injector-Info-content *( ";" ( Injector-Info-parameter / other-parameter ) ) Injector-Info-parameter = posting-host-parameter / posting-account-parameter / posting-sender-parameter / posting-logging-parameter / posting-date-parameter Keywords-content = phrase *( "," phrase ) Keywords-header = "Keywords" ":" SP Keywords-content *( ";" other-parameter ) Lines-content = [CFWS] 1*DIGIT [CFWS] Lines-header = "Lines" ":" SP Lines-content *( ";" other-parameter ) Mail-Copies-To-content = copy-addr / [CFWS] ( "nobody" / "poster" ) [CFWS] Mail-Copies-To-header= "Mail-Copies-To" ":" SP Mail-Copies-To-content Message-ID-content = [FWS] msg-id [FWS] Message-ID-header = "Message-ID" ":" SP Message-ID-content *( ";" other-parameter ) Newsgroups-content = [FWS] newsgroup-name *( [FWS] ng-delim [FWS] newsgroup-name ) [FWS] Newsgroups-header = "Newsgroups" ":" SP Newsgroups-content *( ";" other-parameter ) Organization-content = unstructured Organization-header = "Organization" ":" SP Organization-content Path-content = [FWS] *( path-identity [FWS] path-delimiter [FWS] ) tail-entry [FWS] Path-header = "Path" ":" SP Path-content *( ";" other-parameter ) Posted-And-Mailed-content = [CFWS] ( "yes" / "no" ) [CFWS] C. H. Lindsey [Page 107] News Article Format August 2002 Posted-And-Mailed-header = "Posted-And-Mailed" ":" SP Posted-And-Mailed-content *( ";" other-parameter ) References-content = [CFWS] msg-id *( CFWS msg-id ) [CFWS] References-header = "References" ":" SP References-content *( ";" other-parameter ) Reply-To-content = address-list Reply-To-header = "Reply-To" ":" SP Reply-To-content Sender-content = mailbox Sender-header = "Sender" ":" SP Sender-content *( ";" other-parameter ) Subject-content = [ [FWS] back-reference ] pure-subject Subject-header = "Subject" ":" SP Subject-content Summary-content = unstructured Summary-header = "Summary" ":" SP Summary-content Supersedes-content = [CFWS] msg-id [CFWS] Supersedes-header = "Supersedes" ":" SP Supersedes-content *( ";" other-parameter ) User-Agent-content = product-token *( CFWS product-token ) User-Agent-header = "User-Agent" ":" SP User-Agent-content *( ";" other-parameter ) Xref-content = [CFWS] server-name 1*( CFWS location ) [CFWS] Xref-header = "Xref" ":" SP Xref-content *( ";" other-parameter ) Appendix B.3.2 - Control-message outlines control-message = / Newgroup-message / Rmgroup-message / Mvgroup-message / Checkgroup-message / Cancel-message / Ihave-message / Sendme-message Cancel-arguments = CFWS msg-id [CFWS] Cancel-message = "cancel" Cancel-arguments Checkgroup-arguments = [ chkscope ] [ chksernr ] Checkgroup-message = "checkgroups" Checkgroup-arguments Ihave-arguments = relayer-name Ihave-message = "ihave" Ihave-arguments Mvgroup-arguments = CFWS newsgroup-name CFWS newsgroup-name [ CFWS newgroup-flag ] Mvgroup-message = "mvgroup" Mvgroup-arguments Newgroup-arguments = CFWS newsgroup-name [ CFWS newgroup-flag ] Newgroup-message = "newgroup" Newgroup-arguments Rmgroup-arguments = CFWS newsgroup-name Rmgroup-message = "rmgroup" Rmgroup-arguments Sendme-arguments = Ihave-arguments Sendme-message = "sendme" Sendme-arguments C. H. Lindsey [Page 108] News Article Format August 2002 Appendix B.3.3 - Other header rules article-locator = 1*( %x21-27 / %x29-3A / %x3C-7E ) ; US-ASCII printable characters ; except'(' and ';' article-size = 1*DIGIT back-reference = %x52.65.3A.20 ; which is a case-sensitive "Re: " batch = 1*( batch-header article ) batch-header = "#!" SP rnews SP article-size CRLF checkgroups-body = *( valid-group CRLF ) chkscope = 1*( CFWS ["!"] newsgroup-name ) chksernr = CFWS "#" 1*DIGIT combiner-ASCII = DIGIT / ALPHA / "+" / "-" / "_" combiner-base = combiner-ASCII / combiner-extended combiner-extended = combiner-mark = component = 1*component-grapheme component-grapheme = combiner-base *combiner-mark copy-addr = address-list dist-delim = "," distribution = [FWS] distribution-name [FWS] distribution-name = ALPHA 1*distribution-rest distribution-rest = ALPHA / "+" / "-" / "_" groupinfo-body = [ newsgroups-tag CRLF ] newsgroups-line CRLF 3 hex4 = 1*4HEXDIG 3 hexpart = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ] 3 hexseq = hex4 *( ":" hex4 ) host-value = dot-atom / [ dot-atom ":" ] ( IPv4address / IPv6address ) ; see [RFC 2373] 2 id-left = dot-atom-text / no-fold-quote 2 id-right = dot-atom-text / no-fold-literal ihave-body = *( msg-id CRLF ) 3 IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT 3 IPv6address = hexpart [ ":" IPv4address ] location = newsgroup-name ":" article-locator moderation-flag = %x28.4D.6F.64.65.72.61.74.65.64.29 ; case sensitive "(Moderated)" 2* msg-id = "<" id-left "@" id-right ">" newgroup-flag = "moderated" newsgroup-description = utext *( *WSP utext ) newsgroup-name = component *( "." component ) newsgroups-line = newsgroup-name [ 1*HTAB newsgroup-description ] [ 1*WSP moderation-flag ] C. H. Lindsey [Page 109] News Article Format August 2002 newsgroups-tag = %x46.6F.72 SP %x79.6F.75.72 SP %x6E.65.77.73.67.72.6F.75.70.73 SP %x66.69.6C.65.3A ; case sensitive ; "For your newsgroups file:" ng-delim = "," 2* no-fold-literal = "[" *( dtext / "\[" / "\]" / "\\" ) "]" 2* no-fold-quote = DQUOTE *( strict-qtext / "\\" / "\" DQUOTE ) qspecial *( strict-qtext / "\\" / "\" DQUOTE ) DQUOTE path-delimiter = "/" / "?" / "%" / "," / "!" path-identity = ( ALPHA / DIGIT ) *( ALPHA / DIGIT / "-" / "." / ":" / "_" ) posting-account-parameter = posting-date-parameter = posting-host-parameter = posting-logging-parameter = posting-sender-parameter = product-token = value [ "/" product-version ] product-version = value pure-subject = unstructured qspecial = "(" / ")" / ; same as specials except "<" / ">" / ; "\" and DQUOTE quoted "[" / "]" / ":" / ";" / "@" / "\\" / "," / "." / "\" DQUOTE relayer-name = path-identity rnews = %x72.6E.65.77.73 ; case sensitive "rnews" sender-value = mailbox / "verified" sendme-body = ihave-body server-name = path-identity tail-entry = path-identity valid-group = newsgroups-line Appendix C - Notices C. H. Lindsey [Page 110] News Article Format August 2002 Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. C. H. Lindsey [Page 111]