Independent Submission K. Murchison Internet-Draft Carnegie Mellon University Intended status: Standards Track January 21, 2010 Expires: July 25, 2010 Network News Transfer Protocol (NNTP) Extension for Compression draft-murchison-nntp-compress-00.txt Abstract This memo defines an extension to the Network News Transport Protocol (NNTP) to allow a connection to be effectively and efficiently compressed. Murchison Expires July 25, 2010 [Page 1] Internet-Draft NNTP Extension for Compression January 2010 Issues to be addressed o What 2xx code should we use when compression is activated? 20x, 28x, 29x? o Should failure to activate compression result in a 4xx or 5xx code? o Do we need a special error code for an unknown compression algorithm? o Should we have separate 5xx codes when TLS compression is already active vs. when NNTP COMPRESS is already active? o Do we setup an IANA registery of supported compression algorithms? I don't think we need/want more than DEFLATE. o The text referring to attachments needs work. Should we discuss yEnc and/or uuencode? I'm not sure the text regarding binary form even applies to NNTP. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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. This Internet-Draft will expire on July 25, 2010. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the Murchison Expires July 25, 2010 [Page 2] Internet-Draft NNTP Extension for Compression January 2010 document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Conventions Used in this Document . . . . . . . . . . . . 4 2. The COMPRESS Extension . . . . . . . . . . . . . . . . . . . . 6 2.1. Advertising the COMPRESS Extension . . . . . . . . . . . . 6 2.2. COMPRESS Command . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2.2. Description . . . . . . . . . . . . . . . . . . . . . 7 2.2.3. Examples . . . . . . . . . . . . . . . . . . . . . . . 8 3. Compression Efficiency . . . . . . . . . . . . . . . . . . . . 10 4. Augmented BNF Syntax for the COMPRESS Extension . . . . . . . 12 4.1. Commands . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Capability entries . . . . . . . . . . . . . . . . . . . . 12 5. Summary of Response Codes . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 18 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19 Murchison Expires July 25, 2010 [Page 3] Internet-Draft NNTP Extension for Compression January 2010 1. Introduction The goal of COMPRESS is to reduce the bandwidth usage of NNTP. Compared to PPP compression [RFC1962] and modem-based compression ([MNP] and [V42bis]), COMPRESS offers greater compression efficiency. COMPRESS can be used together with Transport Security Layer (TLS) [RFC5246], Simple Authentication and Security layer (SASL) encryption [RFC4422], Virtual Private Networks (VPNs), etc. Compared to TLS compression [RFC3749], COMPRESS has the following advantages: o COMPRESS can be implemented easily both by NNTP servers and clients. o NNTP COMPRESS benefits from an intimate knowledge of the NNTP protocol's state machine, allowing for dynamic and aggressive optimization of the underlying compression algorithm's parameters. and the following disadvantages: o When the TLS layer implements compression, any protocol using that layer can transparently benefit from that compression (e.g., SMTP and NNTP). COMPRESS is specific to NNTP. In order to increase interoperability, it is desirable to have as few different compression algorithms as possible, so this document specifies only one. The DEFLATE algorithm (defined in [RFC1951]) is standard, widely available and fairly efficient, so it is the only algorithm defined by this document. In order to increase interoperability, NNTP servers that advertise this extension SHOULD also support the TLS DEFLATE compression mechanism as defined in [RFC3749]. NNTP clients MAY use either COMPRESS or TLS compression, however, if the client and server support both, it is RECOMMENDED that the client choose TLS compression. 1.1. Conventions Used in this Document The notational conventions used in this document are the same as those in [RFC3977] and any term not defined in this document has the same meaning as in that one. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Murchison Expires July 25, 2010 [Page 4] Internet-Draft NNTP Extension for Compression January 2010 In the examples, commands from the client are indicated with [C], and responses from the server are indicated with [S]. Murchison Expires July 25, 2010 [Page 5] Internet-Draft NNTP Extension for Compression January 2010 2. The COMPRESS Extension The COMPRESS extension is used to enable compression of an NNTP connection. This extension provides a new COMPRESS command and has capability label COMPRESS. 2.1. Advertising the COMPRESS Extension A server supporting the COMPRESS command as defined in this document will advertise the "COMPRESS" capability label in response to the CAPABILITIES command ([RFC3977] Section 5.2). This capability MAY be advertised both before and after any use of the MODE READER command ([RFC3977] section 5.3), with the same semantics. The COMPRESS capability label contains a whitespace-separated list of available compression algorithms. This document defines one compression algorithm: DEFLATE. At least one compression algorithm MUST be supported in order to advertise the COMPRESS extension. Future extensions may add additional compression algorithms to this capability. Unrecognized algorithms MUST be ignored by the client. Example: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] READER [S] IHAVE [S] COMPRESS DEFLATE [S] LIST ACTIVE NEWSGROUPS [S] . 2.2. COMPRESS Command 2.2.1. Usage This command MUST NOT be pipelined. Murchison Expires July 25, 2010 [Page 6] Internet-Draft NNTP Extension for Compression January 2010 Syntax COMPRESS algorithm Responses 291 Compression active 403 Unable to activate compression 502 Command unavailable [1] [1] If a compression layer is already active, COMPRESS is not a valid command (see Section 2.2). Parameters algorithm = Name of compression algorithm: "DEFLATE" 2.2.2. Description The COMPRESS command instructs the server to use the named compression algorithm ("DEFLATE" is the only one defined) for all commands and/or responses after COMPRESS. The client MUST NOT send any further commands until it has seen the result of COMPRESS. If the server is unable to activate compression for any reason (e.g., a server configuration or resource problem), the server MUST reject the COMPRESS command with a 403 response. Otherwise, the server issues a 291 response and the compression layer takes effect for both client and server immediately following the CRLF of the success reply. Both the client and the server MUST know if there is a compression layer active. A client MUST NOT attempt to activate compression (via either the COMPRESS or STARTTLS [RFC4642] commands) if a compression layer is already active. A server MUST NOT return the COMPRESS or STARTTLS capability labels in response to a CAPABILITIES command received after a compression layer is active, and a server MUST reply with a 502 response code if a COMPRESS or STARTTLS command is received while a compression layer is already active. For DEFLATE (as for many other compression mechanisms), the compressor can trade speed against quality. When decompressing there isn't much of a tradeoff. Consequently, the client and server are both free to pick the best reasonable rate of compression for the data they send. When COMPRESS is combined with TLS [RFC5246] or SASL [RFC4422] security layers, the sending order of the three extensions MUST be first COMPRESS, then SASL, and finally TLS. That is, before data is Murchison Expires July 25, 2010 [Page 7] Internet-Draft NNTP Extension for Compression January 2010 transmitted it is first compressed. Second, if a SASL security layer has been negotiated, the compressed data is then signed and/or encrypted accordingly. Third, if a TLS security layer has been negotiated, the data from the previous step is signed and/or encrypted accordingly. When receiving data, the processing order MUST be reversed. This ensures that before sending, data is compressed before it is encrypted, independent of the order in which the client issues COMPRESS, AUTHINFO SASL, and STARTTLS. 2.2.3. Examples Example of layering TLS and NNTP compression: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] STARTTLS [S] AUTHINFO [S] COMPRESS DEFLATE [S] . [C] STARTTLS [S] 382 Continue with TLS negotiation [TLS negotiation without compression occurs here] [Following successful negotiation, all traffic is encrypted] [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] AUTHINFO USER [S] COMPRESS DEFLATE [S] . [C] AUTHINFO USER fred [S] 381 Enter passphrase [C] AUTHINFO PASS flintstone [S] 281 Authentication accepted [C] COMPRESS DEFLATE [S] 291 Compression active [From this point on, all traffic is compresssed before being encrypted] Example of a server failing to activate compression: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] COMPRESS DEFLATE [S] . [C] COMPRESS DEFLATE [S] 403 Unable to activate compression Murchison Expires July 25, 2010 [Page 8] Internet-Draft NNTP Extension for Compression January 2010 Examples of a server refusing to compress twice: [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] STARTTLS [S] COMPRESS DEFLATE [S] . [C] STARTTLS [S] 382 Continue with TLS negotiation [TLS negotiation with compression occurs here] [Following successful negotiation, all traffic is protected by TLS] [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] . [C] COMPRESS DEFLATE [S] 502 Compression already active via TLS [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] STARTTLS [S] COMPRESS DEFLATE [S] . [C] COMPRESS DEFLATE [S] 291 Compression active [C] CAPABILITIES [S] 101 Capability list: [S] VERSION 2 [S] . [C] STARTTLS [S] 502 DEFLATE compression already active Murchison Expires July 25, 2010 [Page 9] Internet-Draft NNTP Extension for Compression January 2010 3. Compression Efficiency This section is informative, not normative. NNTP poses some unusual problems for a compression layer. Upstream is fairly simple. Most NNTP clients send the same few commands again and again, so any compression algorithm that can exploit repetition works efficiently. The POST and IHAVE commands are an exception; clients that send many POST/IHAVE commands may want to surround large multi-line data blocks with flushes in the same way as is recommended for servers later in this section. Downstream has the unusual property that several kinds of data are sent, confusing all dictionary-based compression algorithms. One type is NNTP responses. These are highly compressible; zlib using its least CPU-intensive setting compresses typical responses to 25-40% of their original size. Another type is article headers. These are equally compressible, and benefit from using the same dictionary as the NNTP responses. A third type is article body text. Text is usually fairly short and includes much ASCII, so the same compression dictionary will do a good job here, too. When multiple messages in the same thread are read at the same time, quoted lines etc. can often be compressed almost to zero. Finally, attachments (non-text article bodies) are transmitted, either in binary form or encoded with base-64. When attachments are retrieved in binary form, DEFLATE may be able to compress them, but the format of the attachment is usually not NNTP- like, so the dictionary built while compressing NNTP does not help. The compressor has to adapt its dictionary from NNTP to the attachment's format, and then back. A few file formats aren't compressible at all using deflate, e.g., .gz, .zip, and .jpg files. When attachments are retrieved in base-64 form, the same problems apply, but the base-64 encoding adds another problem. 8-bit compression algorithms such as deflate work well on 8-bit file formats, however base-64 turns a file into something resembling 6-bit bytes, hiding most of the 8-bit file format from the compressor. When using the zlib library (see [RFC1951]), the functions deflateInit2(), deflate(), inflateInit2(), and inflate() suffice to implement this extension. The windowBits value must be in the range Murchison Expires July 25, 2010 [Page 10] Internet-Draft NNTP Extension for Compression January 2010 -8 to -15, or else deflateInit2() uses the wrong format. deflateParams() can be used to improve compression rate and resource use. The Z_FULL_FLUSH argument to deflate() can be used to clear the dictionary (the receiving peer does not need to do anything). A server can improve downstream compression if it hints to the compressor that the data type is about to change strongly, e.g., by sending a Z_FULL_FLUSH at the start and end of large non-text multi- line data blocks (before and after 'content-lines' in the definition of 'multi-line-data-block' in [RFC3977] Section 9.8). Small multi- line data blocks are best left alone. A possible boundary is 5k. A server can improve the CPU efficiency both of the server and the client if it adjusts the compression level (e.g., using the deflateParams() function in zlib) at these points, to avoid trying to compress incompressible attachments. A very simple strategy is to change the level to 0 at the start of a multi-line data block provided the first two bytes are either 0x1F 0x8B (as in deflate- compressed files) or 0xFF 0xD8 (JPEG), and to keep it at 1-5 the rest of the time. More complex strategies are possible. Murchison Expires July 25, 2010 [Page 11] Internet-Draft NNTP Extension for Compression January 2010 4. Augmented BNF Syntax for the COMPRESS Extension This section describes the syntax of the COMPRESS extension using ABNF [RFC5234]. It extends the syntax in Section 9 of [RFC3977], and non-terminals not defined in this document are defined there. The [RFC3977] ABNF should be imported first before attempting to validate these rules. 4.1. Commands This syntax extends the non-terminal "command", which represents an NNTP command. command =/ compress-command compress-command = "COMPRESS" WS compress-alg compress-alg = "DEFLATE" 4.2. Capability entries This syntax extends the non-terminal "capability-entry", which represents a capability that may be advertised by the server. capability-entry =/ compress-capability compress-capability = "COMPRESS" *(WS compress-alg) Murchison Expires July 25, 2010 [Page 12] Internet-Draft NNTP Extension for Compression January 2010 5. Summary of Response Codes This section contains a list of each new response code defined in this document and indicates whether it is multi-line, which commands can generate it, what arguments it has, and what its meaning is. Response code 291 Generated by: COMPRESS Meaning: Compression layer activated Murchison Expires July 25, 2010 [Page 13] Internet-Draft NNTP Extension for Compression January 2010 6. Security Considerations As for TLS compression [RFC3749]. Murchison Expires July 25, 2010 [Page 14] Internet-Draft NNTP Extension for Compression January 2010 7. IANA Considerations This section gives a formal definition of the COMPRESS extension as required by Section 3.3.3 of [RFC3977] for the IANA registry. o The COMPRESS extension allows an NNTP connection to be effectively and efficiently compressed. o The capability label for this extension is "COMPRESS", whose arguments list the available compression algorithms. o This extension defines one new command, COMPRESS, whose behavior, arguments, and responses are defined in Section 2.2. o This extension does not associate any new responses with pre- existing NNTP commands. o This extension does affect the overall behavior of both server and client, in that after successful use of the COMPRESS command, all communication is transmitted in a compressed format. o This extension does not affect the maximum length of commands or initial response lines. o This extension does not alter pipelining, but the COMPRESS command cannot be pipelined o Use of this extension does alter the capabilities list; once the COMPRESS command has been used successfully, the COMPRESS capability can no longer be advertised by CAPABILITIES. Additionally, the STARTTLS and MODE-READER capabilities MUST NOT be advertised after successful execution of the COMPRESS command. o This extension does not cause any pre-existing command to produce a 401, 480, or 483 response. o This extension is unaffected by any use of the MODE READER command, however the MODE READER command MUST NOT be used in the same session following a successful execution of the COMPRESS command. o The STARTTLS command MUST NOT be used in the same session following a successful execution of the COMPRESS command. o Published Specification: This document. o Contact for Further Information: Author of this document. Murchison Expires July 25, 2010 [Page 15] Internet-Draft NNTP Extension for Compression January 2010 o Change Controller: IESG . Murchison Expires July 25, 2010 [Page 16] Internet-Draft NNTP Extension for Compression January 2010 8. References 8.1. Normative References [RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification version 1.3", RFC 1951, May 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3977] Feather, C., "Network News Transfer Protocol (NNTP)", RFC 3977, October 2006. [RFC4642] Murchison, K., Vinocur, J., and C. Newman, "Using Transport Layer Security (TLS) with Network News Transfer Protocol (NNTP)", RFC 4642, October 2006. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 8.2. Informative References [MNP] Held, G., "The Complete Modem Reference", Second Edition, Wiley Professional Computing, May 1994. [RFC1962] Rand, D. and K. Fox, "The PPP Compression Control Protocol (CCP)", RFC 1962, June 1996. [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol Compression Methods", RFC 3749, May 2004. [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC4643] Vinocur, J. and K. Murchison, "Network News Transfer Protocol (NNTP) Extension for Authentication", RFC 4643, October 2006. [RFC4978] Gulbrandsen, A., "The IMAP COMPRESS Extension", RFC 4978, August 2007. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [V42bis] International Telecommunications Union, "Data compression procedures for data circuit-terminating equipment (DCE) using error correction procedures", ITU-T Recommendation V.42bis, January 1990. Murchison Expires July 25, 2010 [Page 17] Internet-Draft NNTP Extension for Compression January 2010 Appendix A. Acknowledgements This document draws heavily on ideas in [RFC4978] by Arnt Gulbrandsen and a large portion of this text was borrowed from that specification. Murchison Expires July 25, 2010 [Page 18] Internet-Draft NNTP Extension for Compression January 2010 Author's Address Kenneth Murchison Carnegie Mellon University 5000 Forbes Avenue Cyert Hall 285 Pittsburgh, PA 15213 US Phone: +1 412 268 2638 Email: murch@andrew.cmu.edu Murchison Expires July 25, 2010 [Page 19]