NETMOD Working Group K. Watsen Internet-Draft Watsen Networks Intended status: Best Current Practice A. Farrel Expires: December 22, 2019 Old Dog Consulting Q. Wu Huawei Technologies June 20, 2019 Handling Long Lines in Inclusions in Internet-Drafts and RFCs draft-ietf-netmod-artwork-folding-05 Abstract This document defines two strategies for handling long lines in width-bounded text content. One strategy is based on the historic use of a single backslash ('\') character to indicate where line- folding has occurred, with the continuation occurring with the first non-space (' ') character on the next line. The second strategy extends the first strategy by adding a second backslash character to identify where the continuation begins and thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on December 22, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. Watsen, et al. Expires December 22, 2019 [Page 1] Internet-Draft Handling Long Lines in Inclusions June 2019 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://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 Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Applicability Statement . . . . . . . . . . . . . . . . . . . 4 3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 4. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Automated Folding of Long Lines in Text Content . . . . . 4 4.2. Automated Reconstitution of the Original Text Content . . 5 5. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Not Recommended for Graphical Artwork . . . . . . . . . . 5 5.2. Doesn't Work as Well as Format-Specific Options . . . . . 5 6. Two Folding Strategies . . . . . . . . . . . . . . . . . . . 6 6.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . 6 6.2. Recommendation . . . . . . . . . . . . . . . . . . . . . 6 7. The Single Backslash Strategy ('\') . . . . . . . . . . . . . 6 7.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 6 7.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 7 7.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 7 7.2. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 7 7.2.1. Folding . . . . . . . . . . . . . . . . . . . . . . . 7 7.2.2. Unfolding . . . . . . . . . . . . . . . . . . . . . . 9 8. The Double Backslash Strategy ('\\') . . . . . . . . . . . . 9 8.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 9 8.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 9 8.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 10 8.2. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 10 8.2.1. Folding . . . . . . . . . . . . . . . . . . . . . . . 10 8.2.2. Unfolding . . . . . . . . . . . . . . . . . . . . . . 11 9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Example Showing Boundary Conditions . . . . . . . . . . . 12 9.1.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 12 9.1.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 13 9.2. Example Showing Multiple Wraps of a Single Line . . . . . 13 9.2.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 13 9.2.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 13 9.3. Example Showing Smart Folding . . . . . . . . . . . . . . 13 9.3.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 14 9.3.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 15 Watsen, et al. Expires December 22, 2019 [Page 2] Internet-Draft Handling Long Lines in Inclusions June 2019 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.2. Informative References . . . . . . . . . . . . . . . . . 16 Appendix A. POSIX Shell Script . . . . . . . . . . . . . . . . . 18 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 1. Introduction [RFC7994] sets out the requirements for plain-text RFCs and states that each line of an RFC (and hence of an Internet-Draft) must be limited to 72 characters followed by the character sequence that denotes an end-of-line (EOL). Internet-Drafts and RFCs often include example text or code fragments. Many times the example text or code exceeds the 72 character line-length limit. The `xml2rfc` utility does not attempt to wrap the content of such inclusions, simply issuing a warning whenever lines exceed 69 characters. According to the RFC Editor, there is currently no convention in place for how to handle long lines in such inclusions, other than advising authors to clearly indicate what manipulation has occurred. This document defines two strategies for handling long lines in width-bounded text content. One strategy is based on the historic use of a single backslash ('\') character to indicate where line- folding has occurred, with the continuation occurring with the first non-space (' ') character on the next line. The second strategy extends the first strategy by adding a second backslash character to identify where the continuation begins and thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content. The strategies defined in this document work on any text content, but are primarily intended for a structured sequence of lines, such as would be referenced by the element defined in Section 2.48 of [RFC7991], rather than for two-dimensional imagery, such as would be referenced by the element defined in Section 2.5 of [RFC7991]. Note that text files are represented as lines having their first character in column 1, and a line length of N where the last character is in the Nth column and is immediately followed by an end of line character sequence. Watsen, et al. Expires December 22, 2019 [Page 3] Internet-Draft Handling Long Lines in Inclusions June 2019 2. Applicability Statement The formats and algorithms defined in this document may be used in any context, whether for IETF documents or in other situations where structured folding is desired. Within the IETF, this work primarily targets the xml2rfc v3 element (Section 2.48 of [RFC7991]) and the xml2rfc v2 element (Section 2.5 of [RFC7749]) that, for lack of a better option, is currently used for both source code and artwork. This work may be also be used for the xml2rfc v3 element (Section 2.5 of [RFC7991]) but, as described in Section 5.1, it is generally not recommended. 3. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 4. Goals 4.1. Automated Folding of Long Lines in Text Content Automated folding of long lines is needed in order to support draft compilations that entail a) validation of source input files (e.g., XML, JSON, ABNF, ASN.1) and/or b) dynamic generation of output, using a tool that doesn't observe line lengths, that is stitched into the final document to be submitted. Generally, in order for tooling to be able to process input files, the files must be in their original/natural state, which may entail them having some long lines. Thus, these source files need to be modified before inclusion in the document in order to satisfy the line length limits. This modification SHOULD be automated to reduce effort and errors resulting from manual processing. Similarly, dynamically generated output (e.g., tree diagrams) must also be modified, if necessary, in order for the resulting document to satisfy the line length limits. When needed, this effort again SHOULD be automated to reduce effort and errors resulting from manual processing. Watsen, et al. Expires December 22, 2019 [Page 4] Internet-Draft Handling Long Lines in Inclusions June 2019 4.2. Automated Reconstitution of the Original Text Content Automated reconstitution of the exact original text content is needed to support validation of text-based content extracted from documents. For instance, already YANG [RFC7950] modules are extracted from Internet-Drafts and validated as part of the draft-submission process. Additionally, the desire to validate instance examples (i.e., XML/JSON documents) contained within Internet-Drafts has been discussed ([yang-doctors-thread]). 5. Limitations 5.1. Not Recommended for Graphical Artwork While the solution presented in this document works on any kind of text-based content, it is most useful on content that represents source code (XML, JSON, etc.) or, more generally, on content that has not been laid out in two dimensions (e.g., diagrams). Fundamentally, the issue is whether the text content remains readable once folded. Text content that is unpredictable is especially susceptible to looking bad when folded; falling into this category are most UML diagrams, YANG tree diagrams, and ASCII art in general. It is NOT RECOMMENDED to use the solution presented in this document on graphical artwork. 5.2. Doesn't Work as Well as Format-Specific Options The solution presented in this document works generically for all text-based content, as it only views content as plain text. However, various formats sometimes have built-in mechanisms that are better suited to prevent long lines. For instance, both the `pyang` and `yanglint` utilities have the command line option "--tree-line-length" that can be used to indicate a desired maximum line length for when generating tree diagrams [RFC8340]. In another example, some source formats (e.g., YANG [RFC7950]) allow any quoted string to be broken up into substrings separated by a concatenation character (e.g., '+'), any of which can be on a different line. It is RECOMMENDED that authors do as much as possible within the selected format to avoid long lines. Watsen, et al. Expires December 22, 2019 [Page 5] Internet-Draft Handling Long Lines in Inclusions June 2019 6. Two Folding Strategies This document defines two nearly identical strategies for folding text-based content. The Single Backslash Strategy ('\'): Uses a backslash ('\') character at the end of the line where folding occurs, and assumes that the continuation begins at the character that is not a space character (' ') on the following line. The Double Backslash Strategy ('\\'): Uses a backslash ('\') character at the end of the line where folding occurs, and assumes that the continuation begins after a second backslash ('\') character on the following line. 6.1. Comparison The first strategy produces more readable output, however it is significantly more likely to encounter unfoldable input (e.g., there exists a line anywhere in the input ending with a backslash character, or there exists a long line containing only space characters) and, for long lines that can be folded, automation implementations may encounter scenarios that will produce errors without special care. The second strategy produces less readable output, but is unlikely to encounter unfoldable input, there are no long lines that cannot be folded, and no special care is required for when folding a long line. 6.2. Recommendation It is RECOMMENDED for implementations to first attempt to fold content using the single backslash strategy and, only in the unlikely event that it cannot fold the input or the folding logic is unable to cope with a contingency occurring on the desired folding column, then fallback to the double backslash strategy. 7. The Single Backslash Strategy ('\') 7.1. Folded Structure Text content that has been folded as specified by this strategy MUST adhere to the following structure. Watsen, et al. Expires December 22, 2019 [Page 6] Internet-Draft Handling Long Lines in Inclusions June 2019 7.1.1. Header The header is two lines long. The first line is the following 45-character string that MAY be surrounded by any number of printable characters. This first line cannot itself be folded. NOTE: '\' line wrapping per BCP XX (RFC XXXX) [Note to RFC Editor: Please replace XX and XXXX with the numbers assigned to this document and delete this note. Please make this change in multiple places in this document.] The second line is a blank line. This line provides visual separation for readability. 7.1.2. Body The character encoding is the same as described in Section 2 of [RFC7994], except that, per [RFC7991], tab characters are prohibited. Lines that have a backslash ('\') occurring as the last character in a line are considered "folded". Really long lines may be folded multiple times. 7.2. Algorithm This section describes a process for folding and unfolding long lines when they are encountered in text content. The steps are complete, but implementations MAY achieve the same result in other ways. When a larger document contains multiple instances of text content that may need to be folded or unfolded, another process must insert/ extract the individual text content instances to/from the larger document prior to utilizing the algorithms described in this section. For example, the `xiax` utility [xiax] does this. 7.2.1. Folding Determine the desired maximum line length from input to the line- wrapping process, such as from a command line parameter. If no value is explicitly specified, the value "69" SHOULD be used. Watsen, et al. Expires December 22, 2019 [Page 7] Internet-Draft Handling Long Lines in Inclusions June 2019 Ensure that the desired maximum line length is not less than the minimum header, which is 45 characters. If the desired maximum line length is less than this minimum, exit (this text-based content cannot be folded). Scan the text content for horizontal tab characters. If any horizontal tab characters appear, either resolve them to space characters or exit, forcing the input provider to convert them to space characters themselves first. Scan the text content to ensure at least one line exceeds the desired maximum. If no line exceeds the desired maximum, exit (this text content does not need to be folded). Scan the text content to ensure no existing lines already end with a backslash ('\') character, as this would lead to an ambiguous result. If such a line is found, exit (this text content cannot be folded). If this text content needs to and can be folded, insert the header described in Section 7.1.1, ensuring that any additional printable characters surrounding the header does not result in a line exceeding the desired maximum. For each line in the text content, from top-to-bottom, if the line exceeds the desired maximum, then fold the line by: 1. Determine where the fold will occur. This location MUST be before or at the desired maximum column, and MUST NOT be chosen such that the character immediately after the fold is a space (' ') character. If no such location can be found, then exit (this text content cannot be folded) 2. At the location where the fold is to occur, insert a backslash ('\') character followed by the end of line character sequence. 3. On the following line, insert any number of space (' ') characters. The result of the previous operation is that the next line starts with an arbitrary number of space (' ') characters, followed by the character that was previously occupying the position where the fold occurred. Continue in this manner until reaching the end of the text content. Note that this algorithm naturally addresses the case where the remainder of a folded line is still longer than the desired maximum, and hence needs to be folded again, ad infinitum. Watsen, et al. Expires December 22, 2019 [Page 8] Internet-Draft Handling Long Lines in Inclusions June 2019 The process described in this section is illustrated by the "fold_it_1()" function in Appendix A. 7.2.2. Unfolding Scan the beginning of the text content for the header described in Section 7.1.1. If the header is not present, starting on the first line of the text content, exit (this text contents does not need to be unfolded). Remove the 2-line header from the text content. For each line in the text content, from top-to-bottom, if the line has a backslash ('\') character immediately followed by the end of line character sequence, then the line can be unfolded. Remove the backslash ('\') character, the end of line character sequence, and any leading space (' ') characters, which will bring up the next line. Then continue to scan each line in the text content starting with the current line (in case it was multiply folded). Continue in this manner until reaching the end of the text content. The process described in this section is illustrated by the "unfold_it_1()" function in Appendix A. 8. The Double Backslash Strategy ('\\') 8.1. Folded Structure Text content that has been folded as specified by this strategy MUST adhere to the following structure. 8.1.1. Header The header is two lines long. The first line is the following 46-character string that MAY be surrounded by any number of printable characters. This first line cannot itself be folded. NOTE: '\\' line wrapping per BCP XX (RFC XXXX) [Note to RFC Editor: Please replace XX and XXXX with the numbers assigned to this document and delete this note. Please make this change in multiple places in this document.] The second line is a blank line. This line provides visual separation for readability. Watsen, et al. Expires December 22, 2019 [Page 9] Internet-Draft Handling Long Lines in Inclusions June 2019 8.1.2. Body The character encoding is the same as described in Section 2 of [RFC7994], except that, per [RFC7991], tab characters are prohibited. Lines that have a backslash ('\') occurring as the last character in a line immediately followed by the end of line character sequence, when the subsequent line starts with a backslash ('\') as the first non-space (' ') character, are considered "folded". Really long lines may be folded multiple times. 8.2. Algorithm This section describes a process for folding and unfolding long lines when they are encountered in text content. The steps are complete, but implementations MAY achieve the same result in other ways. When a larger document contains multiple instances of text content that may need to be folded or unfolded, another process must insert/ extract the individual text content instances to/from the larger document prior to utilizing the algorithms described in this section. For example, the `xiax` utility [xiax] does this. 8.2.1. Folding Determine the desired maximum line length from input to the line- wrapping process, such as from a command line parameter. If no value is explicitly specified, the value "69" SHOULD be used. Ensure that the desired maximum line length is not less than the minimum header, which is 46 characters. If the desired maximum line length is less than this minimum, exit (this text-based content cannot be folded). Scan the text content for horizontal tab characters. If any horizontal tab characters appear, either resolve them to space characters or exit, forcing the input provider to convert them to space characters themselves first. Scan the text content to see if any line exceeds the desired maximum. If no line exceeds the desired maximum, exit (this text content does not need to be folded). Scan the text content to ensure no existing lines already end with a backslash ('\') character while the subsequent line starts with a Watsen, et al. Expires December 22, 2019 [Page 10] Internet-Draft Handling Long Lines in Inclusions June 2019 backslash ('\') character as the first non-space (' ') character, as this could lead to an ambiguous result. If such a line is found, and its width is less than the desired maximum, then it SHOULD be flagged for forced folding (folding even though unnecessary). If the folding implementation doesn't support forced foldings, it MUST exit. If this text content needs to and can be folded, insert the header described in Section 8.1.1, ensuring that any additional printable characters surrounding the header does not result in a line exceeding the desired maximum. For each line in the text content, from top-to-bottom, if the line exceeds the desired maximum, or requires a forced folding, then fold the line by: 1. Determine where the fold will occur. This location MUST be before or at the desired maximum column. 2. At the location where the fold is to occur, insert a first backslash ('\') character followed by the end of line character sequence. 3. On the following line, insert any number of space (' ') characters followed by a second backslash ('\') character. The result of the previous operation is that the next line starts with an arbitrary number of space (' ') characters, followed by a backslash ('\') character, immediately followed by the character that was previously occupying the position where the fold occurred. Continue in this manner until reaching the end of the text content. Note that this algorithm naturally addresses the case where the remainder of a folded line is still longer than the desired maximum, and hence needs to be folded again, ad infinitum. The process described in this section is illustrated by the "fold_it_2()" function in Appendix A. 8.2.2. Unfolding Scan the beginning of the text content for the header described in Section 8.1.1. If the header is not present, starting on the first line of the text content, exit (this text content does not need to be unfolded). Remove the 2-line header from the text content. Watsen, et al. Expires December 22, 2019 [Page 11] Internet-Draft Handling Long Lines in Inclusions June 2019 For each line in the text content, from top-to-bottom, if the line has a backslash ('\') character immediately followed by the end of line character sequence, and if the next line has a backslash ('\') character as the first non-space (' ') character, then the lines can be unfolded. Remove the first backslash ('\') character, the end of line character sequence, any leading space (' ') characters, and the second backslash ('\') character, which will bring up the next line. Then continue to scan each line in the text content starting with the current line (in case it was multiply folded). Continue in this manner until reaching the end of the text content. The process described in this section is illustrated by the "unfold_it_2()" function in Appendix A. 9. Examples The following self-documenting examples illustrate folded text-based content. The source text content cannot be presented here, as it would again be folded. Alas, only the results can be provided. 9.1. Example Showing Boundary Conditions This example illustrates boundary condition. The input contains seven lines, each line one character longer than the previous line. Numbers for counting purposes. The default desired maximum column value "69" is used. 9.1.1. Using '\' =========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) =========== 123456789012345678901234567890123456789012345678901234567890123456 1234567890123456789012345678901234567890123456789012345678901234567 12345678901234567890123456789012345678901234567890123456789012345678 123456789012345678901234567890123456789012345678901234567890123456789 12345678901234567890123456789012345678901234567890123456789012345678\ 90 12345678901234567890123456789012345678901234567890123456789012345678\ 901 12345678901234567890123456789012345678901234567890123456789012345678\ 9012 Watsen, et al. Expires December 22, 2019 [Page 12] Internet-Draft Handling Long Lines in Inclusions June 2019 9.1.2. Using '\\' ========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== 123456789012345678901234567890123456789012345678901234567890123456 1234567890123456789012345678901234567890123456789012345678901234567 12345678901234567890123456789012345678901234567890123456789012345678 123456789012345678901234567890123456789012345678901234567890123456789 12345678901234567890123456789012345678901234567890123456789012345678\ \90 12345678901234567890123456789012345678901234567890123456789012345678\ \901 12345678901234567890123456789012345678901234567890123456789012345678\ \9012 9.2. Example Showing Multiple Wraps of a Single Line This example illustrates what happens when very long line needs to be folded multiple times. The input contains one line containing 280 characters. Numbers for counting purposes. The default desired maximum column value "69" is used. 9.2.1. Using '\' =========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) =========== 12345678901234567890123456789012345678901234567890123456789012345678\ 90123456789012345678901234567890123456789012345678901234567890123456\ 78901234567890123456789012345678901234567890123456789012345678901234\ 56789012345678901234567890123456789012345678901234567890123456789012\ 34567890 9.2.2. Using '\\' ========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== 12345678901234567890123456789012345678901234567890123456789012345678\ \9012345678901234567890123456789012345678901234567890123456789012345\ \6789012345678901234567890123456789012345678901234567890123456789012\ \3456789012345678901234567890123456789012345678901234567890123456789\ \01234567890 9.3. Example Showing Smart Folding This example illustrates how readability can be improved via "smart" folding, whereby folding occurs at format-specific locations and format-specific indentations are used. Watsen, et al. Expires December 22, 2019 [Page 13] Internet-Draft Handling Long Lines in Inclusions June 2019 The text content was manually folded, since the script in the appendix does not implement smart folding. Note that the header is surrounded by different printable characters then shown in the script-generated examples. 9.3.1. Using '\' [NOTE: '\' line wrapping per BCP XX (RFC XXXX)] config-modules ietf-interfaces 2018-02-20 \ urn:ietf:params:xml:ns:yang:ietf-interfaces\ ... ... Below is the equivalent to the above, but it was folded using the script in the appendix. Watsen, et al. Expires December 22, 2019 [Page 14] Internet-Draft Handling Long Lines in Inclusions June 2019 =========== NOTE: '\' line wrapping per BCP XX (RFC XXXX) =========== config-modules ietf-interfaces 2018-02-20 urn:ietf:params:xml:ns:yang:ietf-interfaces ... ... 9.3.2. Using '\\' [NOTE: '\\' line wrapping per BCP XX (RFC XXXX)] config-modules ietf-interfaces 2018-02-20 \ \urn:ietf:params:xml:ns:yang:ietf-interfaces\ \ ... ... Below is the equivalent to the above, but it was folded using the script in the appendix. Watsen, et al. Expires December 22, 2019 [Page 15] Internet-Draft Handling Long Lines in Inclusions June 2019 ========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== config-modules ietf-interfaces 2018-02-20 urn:ietf:params:xml:ns:yang:ietf-interfaces ... ... 10. Security Considerations This BCP has no Security Considerations. 11. IANA Considerations This BCP has no IANA Considerations. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 12.2. Informative References [RFC7749] Reschke, J., "The "xml2rfc" Version 2 Vocabulary", RFC 7749, DOI 10.17487/RFC7749, February 2016, . Watsen, et al. Expires December 22, 2019 [Page 16] Internet-Draft Handling Long Lines in Inclusions June 2019 [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC7991] Hoffman, P., "The "xml2rfc" Version 3 Vocabulary", RFC 7991, DOI 10.17487/RFC7991, December 2016, . [RFC7994] Flanagan, H., "Requirements for Plain-Text RFCs", RFC 7994, DOI 10.17487/RFC7994, December 2016, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [xiax] "The `xiax` Python Package", . [yang-doctors-thread] "[yang-doctors] automating yang doctor reviews", . Watsen, et al. Expires December 22, 2019 [Page 17] Internet-Draft Handling Long Lines in Inclusions June 2019 Appendix A. POSIX Shell Script This non-normative appendix section includes a shell script that can both fold and unfold text content using both the single and double backslash strategies described in Section 7 and Section 8 respectively. This script is intended to be applied to a single text content instance. If it is desired to fold or unfold test content instances within a larger document (e.g., an Internet draft or RFC), then another tool must be used to extract the content from the larger document before utilizing this script. For readability purposes, this script forces the minimally supported line length to be eight characters longer than the raw header text defined in Section 7.1.1 and Section 8.1.1 so as to ensure that the header can be wrapped by a space (' ') character and three equal ('=') characters on each side of the raw header text. This script does not implement the "forced folding" logic described in Section 8.2.1. In such cases the script will exit with the message: Error: infile has a line ending with a '\\' character followed by a '\\' character as the first non-space character on the next line. This file cannot be folded. Shell-level end-of-line backslash ('\') characters have been purposely added to the script so as to ensure that the script is itself not folded in this document, thus simplify the ability to copy/paste the script for local use. As should be evident by the lack of the mandatory header described in Section 7.1.1, these backslashes do not designate a folded line, such as described in Section 7. #!/bin/bash --posix # must be `bash` (not `sh`) print_usage() { echo echo "Folds the text file, only if needed, at the specified" echo "column, according to BCP XX." echo echo "Usage: $0 [-s ] [-c ] [-r] -i " echo " -o " echo echo " -s: strategy to use, '1' or '2' (default: try 1, else 2)" Watsen, et al. Expires December 22, 2019 [Page 18] Internet-Draft Handling Long Lines in Inclusions June 2019 echo " -c: column to fold on (default: 69)" echo " -r: reverses the operation" echo " -i: the input filename" echo " -o: the output filename" echo " -d: show debug messages" echo " -q: quiet (suppress error messages)" echo " -h: show this message" echo echo "Exit status code: zero on success, non-zero otherwise." echo } # global vars, do not edit strategy=0 # auto debug=0 quiet=0 reversed=0 infile="" outfile="" maxcol=69 # default, may be overridden by param hdr_txt_1="NOTE: '\\' line wrapping per BCP XX (RFC XXXX)" hdr_txt_2="NOTE: '\\\\' line wrapping per BCP XX (RFC XXXX)" equal_chars="==============================================" space_chars=" " temp_dir="" fold_it_1() { # ensure input file doesn't contain the fold-sequence already pcregrep -M "\\\\\n" $infile >> /dev/null 2>&1 if [[ $? -eq 0 ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: infile $infile has a line ending with a '\\'" echo "character. This file cannot be folded using the '\\'" echo "strategy." echo fi return 1 fi # stash some vars testcol=`expr "$maxcol" + 1` foldcol=`expr "$maxcol" - 1` # for the inserted '\' char # ensure input file doesn't contain whitespace on the fold column grep "^.\{$foldcol\} " $infile >> /dev/null 2>&1 if [[ $? -eq 0 ]]; then if [[ $quiet -eq 0 ]]; then Watsen, et al. Expires December 22, 2019 [Page 19] Internet-Draft Handling Long Lines in Inclusions June 2019 echo echo "Error: infile has a space character occuring on the" echo "folding column. This file cannot be folded using the" echo "'\\' strategy." echo fi return 1 fi # center header text length=`expr ${#hdr_txt_1} + 2` left_sp=`expr \( "$maxcol" - "$length" \) / 2` right_sp=`expr "$maxcol" - "$length" - "$left_sp"` header=`printf "%.*s %s %.*s" "$left_sp" "$equal_chars"\ "$hdr_txt_1" "$right_sp" "$equal_chars"` # generate outfile echo "$header" > $outfile echo "" >> $outfile gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n/g"\ < $infile >> $outfile return 0 } fold_it_2() { if [ "$temp_dir" == "" ]; then temp_dir=`mktemp -d` fi # ensure input file doesn't contain the fold-sequence already pcregrep -M "\\\\\n[\ ]*\\\\" $infile >> /dev/null 2>&1 if [[ $? -eq 0 ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: infile has a line ending with a '\\' character" echo "followed by a '\\' character as the first non-space" echo "character on the next line. This file cannot be folded" echo "using the '\\\\' strategy." echo fi return 1 fi # center header text length=`expr ${#hdr_txt_2} + 2` left_sp=`expr \( "$maxcol" - "$length" \) / 2` right_sp=`expr "$maxcol" - "$length" - "$left_sp"` Watsen, et al. Expires December 22, 2019 [Page 20] Internet-Draft Handling Long Lines in Inclusions June 2019 header=`printf "%.*s %s %.*s" "$left_sp" "$equal_chars"\ "$hdr_txt_2" "$right_sp" "$equal_chars"` # fold using recursive passes ('g' used in fold_it_1 didn't work) if [ -z "$1" ]; then # init recursive env cp $infile $temp_dir/wip fi testcol=`expr "$maxcol" + 1` foldcol=`expr "$maxcol" - 1` # for the inserted '\' char gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n\\\\/" \ < $temp_dir/wip >> $temp_dir/wip2 diff $temp_dir/wip $temp_dir/wip2 > /dev/null 2>&1 if [ $? -eq 1 ]; then mv $temp_dir/wip2 $temp_dir/wip fold_it_2 "recursing" else echo "$header" > $outfile echo "" >> $outfile cat $temp_dir/wip2 >> $outfile rm -rf $temp_dir fi return 0 } fold_it() { # ensure input file doesn't contain a TAB grep $'\t' $infile >> /dev/null 2>&1 if [[ $? -eq 0 ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: infile contains a TAB character, which is" echo "not allowed." echo fi return 1 fi # check if file needs folding testcol=`expr "$maxcol" + 1` grep ".\{$testcol\}" $infile >> /dev/null 2>&1 if [ $? -ne 0 ]; then if [[ $debug -eq 1 ]]; then echo "nothing to do" fi cp $infile $outfile return -1 fi Watsen, et al. Expires December 22, 2019 [Page 21] Internet-Draft Handling Long Lines in Inclusions June 2019 if [[ $strategy -eq 1 ]]; then fold_it_1 return $? fi if [[ $strategy -eq 2 ]]; then fold_it_2 return $? fi quiet_sav=$quite quiet=1 fold_it_1 result=$? quiet=$quiet_sav if [[ $result -ne 0 ]]; then if [[ $debug -eq 1 ]]; then echo "Folding strategy 1 didn't succeed, trying strategy 2..." fi fold_it_2 return $? fi return 0 } unfold_it_1() { temp_dir=`mktemp -d` # output all but the first two lines (the header) to wip file awk "NR>2" $infile > $temp_dir/wip # unfold wip file gsed ":x; /.*\\\\$/N; s/\\\\\n[ ]*//; tx" $temp_dir/wip > $outfile # clean up and return rm -rf $temp_dir return 0 } unfold_it_2() { temp_dir=`mktemp -d` # output all but the first two lines (the header) to wip file awk "NR>2" $infile > $temp_dir/wip # unfold wip file gsed ":x; /.*\\\\$/N; s/\\\\\n[ ]*\\\\//; tx" $temp_dir/wip \ > $outfile # clean up and return Watsen, et al. Expires December 22, 2019 [Page 22] Internet-Draft Handling Long Lines in Inclusions June 2019 rm -rf $temp_dir return 0 } unfold_it() { # check if file needs unfolding line=`head -n 1 $infile` result=`echo $line | fgrep "$hdr_txt_1"` if [ $? -eq 0 ]; then unfold_it_1 return $? fi result=`echo $line | fgrep "$hdr_txt_2"` if [ $? -eq 0 ]; then unfold_it_2 return $? fi if [[ $debug -eq 1 ]]; then echo "nothing to do" fi cp $infile $outfile return -1 } process_input() { while [ "$1" != "" ]; do if [ "$1" == "-h" -o "$1" == "--help" ]; then print_usage exit 1 fi if [ "$1" == "-d" ]; then debug=1 fi if [ "$1" == "-q" ]; then quiet=1 fi if [ "$1" == "-s" ]; then strategy="$2" shift fi if [ "$1" == "-c" ]; then maxcol="$2" shift fi if [ "$1" == "-r" ]; then reversed=1 fi if [ "$1" == "-i" ]; then Watsen, et al. Expires December 22, 2019 [Page 23] Internet-Draft Handling Long Lines in Inclusions June 2019 infile="$2" shift fi if [ "$1" == "-o" ]; then outfile="$2" shift fi shift done if [[ -z "$infile" ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: infile parameter missing (use -h for help)" echo fi exit 1 fi if [[ -z "$outfile" ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: outfile parameter missing (use -h for help)" echo exit 1 fi fi if [[ ! -f "$infile" ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: specified file \"$infile\" is does not exist." echo exit 1 fi fi if [[ $strategy -eq 2 ]]; then min_supported=`expr ${#hdr_txt_2} + 8` else min_supported=`expr ${#hdr_txt_1} + 8` fi if [[ $maxcol -lt $min_supported ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: the folding column cannot be less than" echo "$min_supported." echo Watsen, et al. Expires December 22, 2019 [Page 24] Internet-Draft Handling Long Lines in Inclusions June 2019 fi exit 1 fi # this is only because the code otherwise runs out of equal_chars max_supported=`expr ${#equal_chars} + 1 + ${#hdr_txt_1} + 1\ + ${#equal_chars}` if [[ $maxcol -gt $max_supported ]]; then if [[ $quiet -eq 0 ]]; then echo echo "Error: the folding column cannot be more than" echo "$max_supported." echo fi exit 1 fi } main() { if [ "$#" == "0" ]; then print_usage exit 1 fi process_input $@ if [[ $reversed -eq 0 ]]; then fold_it code=$? else unfold_it code=$? fi exit $code } main "$@" Acknowledgements The authors thank the following folks for their various contributions (sorted by first name): Benoit Claise, Gianmarco Bruno, Italo Busi, Joel Jaeggli, Jonathan Hansford, Lou Berger, Martin Bjorklund, and Rob Wilton. Watsen, et al. Expires December 22, 2019 [Page 25] Internet-Draft Handling Long Lines in Inclusions June 2019 The authors additionally thank the RFC Editor for confirming that there is no set convention today for handling long lines in artwork/ sourcecode inclusions. Authors' Addresses Kent Watsen Watsen Networks EMail: kent+ietf@watsen.net Adrian Farrel Old Dog Consulting EMail: adrian@olddog.co.uk Qin Wu Huawei Technologies EMail: bill.wu@huawei.com Watsen, et al. Expires December 22, 2019 [Page 26]