Handling Long Lines in Artwork in Drafts
draft-kwatsen-netmod-artwork-folding-04

Abstract

This document introduces a simple and yet time-proven strategy for handling long lines in artwork in drafts using a backslash ('\') character where line-folding has occurred. The strategy works on any text based artwork, producing consistent results regardless the artwork content. Using a per-artwork header, the strategy is both self-documenting and enables automated reconstitution of the original artwork.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on December 24, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Requirements Language
• 3. Goals
• 3.1. Automated folding of long lines in artwork
• 3.2. Automated reconstitution of original artwork
• 4. Limitations
• 4.1. Doesn't work well on graphical artwork
• 4.2. Doesn't work as well as format-specific options
• 5. Solution
• 5.1. Header
• 5.2. Folding
• 5.3. Unfolding
• 5.4. Example
• 6. Security Considerations
• 7. IANA Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Appendix A. POSIX Shell Script
• Acknowledgements
• Authors' Addresses

1. Introduction

Internet drafts many times contain artwork that exceed the 72 character limit specified by RFC 7994 [RFC7994]. The "xml2rfc" utility, in an effort to maintain clean formatting, issues a warning whenever artwork lines exceed 69 characters. According to RFC Editor, there is currently no convention in place for how to handle long lines, other than clearly indicating that some manipulation has occurred.

This document introduces a simple and yet time-proven strategy for handling long lines using a backslash ('\') character where line-folding has occurred. The strategy works on any text based artwork, producing consistent results regardless the artwork content. Using a per-artwork header, the strategy is both self-documenting and enables automated reconstitution of the original artwork.

2. 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.

3. Goals

3.1. Automated folding of long lines in artwork

Automated folding of long lines is needed in order to support draft compilations that entail a) validation of source input files (e.g., YANG, XML, JSON, ABNF, ASN.1) and/or b) dynamic generation of output (e.g., tree diagrams) that are stitched into the final draft 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 include having some long lines. Thus, these source files need to be modified before inclusion in the draft in order to satisfy the line length limits. This modification SHOULD be automated to reduce effort and errors resulting from manual effort.

Similarly, dynamically generated output (e.g., tree diagrams) must also be modified, if necessary, in order for the resulting I-D to satisfy the line length limits. When needed, this effort again SHOULD be automated to reduce effort and errors resulting from manual effort.

3.2. Automated reconstitution of original artwork

Automated reconstitution of the original artwork is needed to support validation of artwork extracted from drafts. Already YANG modules are extracted from drafts and validated as part of the draft-submission process. Additionally, there has been some discussion regarding needing to do the same for examples contained within drafts ([yang-doctors-list]). Thus, it SHOULD be possible to mechanically reconstitute artwork in order to satisfy the tooling input parsers.

4. Limitations

4.1. Doesn't work well on graphical artwork

While the solution presented in this document will work on any kind of text-based artwork, it is most useful on artwork that represents sourcecode (e.g., YANG, XML, JSON, etc.) or, more generally, on artwork that has not been laid out in two dimensions (e.g., diagrams).

The issue regards the readability of the folded artwork in the draft. Artwork that is unpredictable is especially susceptible is looking bad when folded; falling into this category are most UML diagrams. Artwork that is somewhat structured (e.g., YANG tree diagrams [RFC8340]) fair better when folded, as the eyes seem to be able to still see the vertical lines, even when they are interrupted.

It is thus NOT RECOMMENDED to use the solution presented in this document on graphical artwork.

4.2. Doesn't work as well as format-specific options

The solution presented in this document works generically for all artwork, as it only views artwork as plain text. However, various formats sometimes have mechanisms that can be used to prevent long lines.

For instance, some source formats allow any quoted string to be broken up into substrings separated by a concatenation character ('+'), any of which can by on a different line.

In another example, some languages allow factoring out chucks of code out into "functions" or "groupings". Using such call outs is especially helpful when in some deeply-nested code, as it typically resets the indentation back to the first column.

As such, it is RECOMMENDED that authors do as much as possible within the selected format to avoid long lines.

5. Solution

The following two sections provide the folding and unfolding algorithms that MUST be implemented to align with this BCP.

5.1. Header

Any artwork that has been folded as specificed by this document MUST contain the header described in this section.

The header is two lines long.

The first line is the following 53-character string that has been padded with roughly equal numbers of equal ('=') characters to reach the artwork's maximum line length. This line is self-describing in three ways: use of '\' character, identification of BCP/RFC, and identification of what the maximum line length is for the artwork. Following is the mimimal header string (53-characters):

=== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ===

The second line is a blank line. This line provides visual seperation for the readability.

5.2. Folding

Scan the artwork to see if any line exceeds the desired maximum. If no line exceeds the desired maximum, exit (this artwork does not need to be folded).

Ensure that the desired maximum is not less than then minumum header, which is 53 characters. If the desired maximum is less than this minimum, exit (this artwork can not be folded).

Scan the artwork to ensure no existing lines already end with a '\' character on the desired maximum column, as this would be lead to an ambiguous result. If such a line is found, exit (this artwork cannot be folded).

For each line in the artwork, from top-to-bottom, if the line exceeds the desired maximum, then fold the line at the desired maximum column by inserting the string "\\n" (backlash followed by line return) at the column before the maximum column. Note that the column before needs to be used in order to enable the '\' character to be placed on the desired maximum column. The result of this operation is that the character that was on the maximum colomn is now the first character of the next line.

Continue in this manner until reaching the end of the artwork. 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.

5.3. Unfolding

Scan the beginning of the artwork for the header described in Section 5.1. If the header is not present, starting on the first line of the artwork, exit (this artwork does not need to be unfolded).

Caluculate the folding-column used from the length of the provided header.

Remove the 2-line header from the artwork.

For each line in the artwork, from top-to-bottom, if the line has a '\' on the folding-column followed by a '\n' character, then remove both the '\' and '\n' characters, which will bring up the next line, and then scan the remainder of the line to see if it again has a '\' after folding-column characters followed by a '\n' character, and so on.

Continue in this manner until reaching the end of the artwork.

5.4. Example

The following self-documenting example illustrates the result of the folding algorithm running over a specific artwork input.

The specific input used cannot be presented here, as it would again need to be folded. Alas, only the result can be provided.

Some things to note about the following example:

• This artwork is exactly 69 characters wide, the widest possible before `xml2rfc` starts to issue warnings.
• The line having the 'x' character on the 69th column would've been illegal input had the '\' been used.

INSERT_TEXT_FROM_FILE(refs/folding-needed.txt.folded)

6. Security Considerations

This BCP has no Security Considerations.

7. IANA Considerations

This BCP has no IANA Considerations.

8. References

8.1. Normative References

8.2. Informative References

Appendix A. POSIX Shell Script

This non-normative appendix section includes a shell script that can both fold and unfold artwork based on the solution presented in this document.

For folding:
  gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n/g"

For unfolding:
  gsed ":x; /[^\t]\\{$foldcol\\}\\\\\$/N; s/\\\\\n/\t/; tx; s/\t//g"

As a testament for the simplicity of this solution, note that at the core of the script are the following two one-liners:

Disclaimer: this script has the limitation of disallowing the input file from containing any TAB ('\t') characters.

=====START SCRIPT=====

INSERT_TEXT_FROM_FILE(fold-artwork.sh)

=====END SCRIPT=====

Acknowledgements

The authors thank the RFC Editor for confirming that there are no set convention today for handling long lines in artwork.

Authors' Addresses