Handling Long Lines in Artwork in Drafts
draft-kwatsen-netmod-artwork-folding-06

NETMOD Working Group                                           K. Watsen
Internet-Draft                                          Juniper Networks
Intended status: Best Current Practice                             Q. Wu
Expires: December 28, 2018                           Huawei Technologies
                                                               A. Farrel
                                                        Juniper Networks
                                                               B. Claise
                                                     Cisco Systems, Inc.
                                                           June 26, 2018

                Handling Long Lines in Artwork in Drafts
                draft-kwatsen-netmod-artwork-folding-06

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   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 28, 2018.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Automated folding of long lines in artwork  . . . . . . .   3
     3.2.  Automated reconstitution of original artwork  . . . . . .   3
   4.  Limitations . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Doesn't work well on graphical artwork  . . . . . . . . .   4
     4.2.  Doesn't work as well as format-specific options . . . . .   4
   5.  Folded Structure  . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Header  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  Body  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Folding . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Unfolding . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  POSIX Shell Script . . . . . . . . . . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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

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   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-thread]).  Thus, it SHOULD be possible to mechanically
   reconstitute artwork in order to satisfy the tooling input parsers.

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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 (YANG, XML, JSON, etc.) or, more generally, on artwork
   that has not been laid out in two dimensions (e.g., diagrams).

   Fundamentally, the issue is whether the artwork remains readable once
   folded.  Artwork that is unpredictable is especially susceptible to
   looking bad when folded; falling into this category are most UML
   diagrams.  Artwork that is somewhat structured (e.g., YANG tree
   diagrams [RFC8340]) fairs better when folded, as the eyes seem to be
   able to still see the vertical lines, even when they are interrupted.

   It is 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 built-in 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 chunks of code
   into call outs, such as functions.  Using such call outs is
   especially helpful when in some deeply-nested code, as they typically
   reset 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.  Folded Structure

   Artwork that has been folded as specified by this document MUST
   contain the following structure.

5.1.  Header

   The header is two lines long.

   The first line is an N-character string:

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

   where N is the column on which folding occurred (the minimal value is
   53, the length of the string above) padded with roughly equivalent
   number of equal ('=') characters on both sides of the string to reach
   the artwork's maximum line length.

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

5.2.  Body

   The character encoding is the same as described in Section 2 of
   [RFC7994], except that, per [RFC7991], tab ('\t') characters are
   prohibited.

   The backslash ('\') character may appear anywhere in the artwork,
   including at the end of any line.

   Lines that have a backslash occurring on the artwork's maximum column
   value (N) followed by the '\n' character are considered "folded".

   A really long line may be folded multiple times.

   Folded lines are continued on the next line on column 0.

6.  Algorithm

6.1.  Folding

   Determine the desired maximum line length from input.  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 53 characters.  If the desired maximum line
   length is less than this minimum, exit (this artwork can not be
   folded).

   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).

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

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   Scan the artwork to ensure the horizontal tab character '\t' does not
   appear.  If any horizontal tab character appears, 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 column 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.

6.2.  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).

   Calculate 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.

7.  Example

   The following self-documenting example illustrates a folded document.

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

   This artwork was folded on column 69, the default value.

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

   # Boundary condition tests using numbers for counting purposes.
   #
   # Any printable character (including ' ' and '\') can be used
   # as a substitute for any number, except for on the 4th row,
   # the trailing '9' is not allowed to be a '\' character, as
   # that leads to an ambiguous result.
   123456789012345678901234567890123456789012345678901234567890123456
   1234567890123456789012345678901234567890123456789012345678901234567
   12345678901234567890123456789012345678901234567890123456789012345678
   123456789012345678901234567890123456789012345678901234567890123456789
   12345678901234567890123456789012345678901234567890123456789012345678\
   90
   12345678901234567890123456789012345678901234567890123456789012345678\
   901

   # One very long line (280 characters)
   #
   # Any printable character (including ' ' and '\') can be used
   # as a substitute for any number, except the 69th character
   # is  not allowed to be a '\' character, as that leads to an
   # ambiguous result.
   12345678901234567890123456789012345678901234567890123456789012345678\
   90123456789012345678901234567890123456789012345678901234567890123456\
   78901234567890123456789012345678901234567890123456789012345678901234\
   56789012345678901234567890123456789012345678901234567890123456789012\
   34567890

8.  Security Considerations

   This BCP has no Security Considerations.

9.  IANA Considerations

   This BCP has no IANA Considerations.

10.  References

10.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC7991]  Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
              RFC 7991, DOI 10.17487/RFC7991, December 2016,
              <https://www.rfc-editor.org/info/rfc7991>.

   [RFC7994]  Flanagan, H., "Requirements for Plain-Text RFCs",
              RFC 7994, DOI 10.17487/RFC7994, December 2016,
              <https://www.rfc-editor.org/info/rfc7994>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative References

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [yang-doctors-thread]
              "[yang-doctors] automating yang doctor reviews",
              <https://mailarchive.ietf.org/arch/msg/yang-doctors/
              DCfBqgfZPAD7afzeDFlQ1Xm2X3g>.

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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.

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

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

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

   Disclaimer: this script has the limitation of disallowing the input
   file from containing any HTAB ('\t') characters.  It does not, for
   instance, make an attempt to convert an HTAB character to a fixed
   number of SPACE (' ') characters.

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

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

   #!/bin/bash
   #
   # the only reason why /bin/sh isn't being used
   # is because "echo -n" is broken on the Mac.

   print_usage() {
     echo
     echo "Folds the text file, only if needed, at the specified"
     echo "column, according to BCP XX."
     echo
     echo "Usage: $0 [-c <col>] [-r] -i <infile> -o <outfile>"
     echo
     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 "  -h: show this message"
     echo
     echo "Exit status code: zero on success, non-zero otherwise."
     echo
   }

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   # global vars, do not edit
   debug=0
   reversed=0
   infile=""
   outfile=""
   maxcol=69  # default, may be overridden by param
   hdr_txt="=== NOTE: '\' line wrapping per BCP XX (RFC XXXX) ==="
   equal_chars="==========================================="

   fold_it() {
     # since upcomming tests are >= (not >)
     testcol=`expr "$maxcol" + 1`

     # check if file needs folding
     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 0
     fi

     foldcol=`expr "$maxcol" - 1` # for the inserted '\' char

     # ensure file doesn't have any '\' char on $maxcol already
     #  - as this would lead to false positives...
     grep "^.\{$foldcol\}\\\\$" $infile >> /dev/null 2>&1
     if [ $? -eq 0 ]; then
       echo
       echo "Error: infile has a '\\\' on colomn $maxcol already."
       echo
       exit 1
     fi

     # calculate '=' character-filled header
     length=${#hdr_txt}
     left_sp=`expr \( "$maxcol" - "$length" \) / 2`
     right_sp=`expr "$maxcol" - "$length" - "$left_sp"`
     header=`printf "%.*s%s%.*s" "$left_sp" "$equal_chars" "$hdr_txt" "\
   $right_sp"  "$equal_chars"`

     # generate outfile and return
     echo -ne "$header\n\n" > $outfile
     gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n/g" < $infile >> \
   $outfile
     return 0
   }

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   unfold_it() {
     # check if it looks like a BCP XX header
     line=`head -n 1 $infile | fgrep "$hdr_txt"`
     if [ $? -ne 0 ]; then
       if [[ $debug -eq 1 ]]; then
         echo "nothing to do"
       fi
       cp $infile $outfile
       return 0
     fi

     # determine what maxcol value was used
     maxcol=${#line}

     # output all but the first two lines (the header) to wip (work in \
   progress) file
     awk "NR>2" $infile > /tmp/wip

     # unfold wip file
     foldcol=`expr "$maxcol" - 1` # for the inserted '\' char
     gsed ":x; /[^\t]\\{$foldcol\\}\\\\\$/N; s/\\\\\n/\t/; tx; s/\t//g"\
    /tmp/wip > $outfile

     # clean up and return
     rm /tmp/wip
     return 0
   }

   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" == "-c" ]; then
         maxcol="$2"
         shift
       fi
       if [ "$1" == "-r" ]; then
         reversed=1
       fi
       if [ "$1" == "-i" ]; then
         infile="$2"
         shift

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       fi
       if [ "$1" == "-o" ]; then
         outfile="$2"
         shift
       fi
       shift
     done

     if [ -z "$infile" ]; then
       echo
       echo "Error: infile parameter missing (use -h for help)"
       echo
       exit 1
     fi

     if [ -z "$outfile" ]; then
       echo
       echo "Error: outfile parameter missing (use -h for help)"
       echo
       exit 1
     fi

     if [ ! -f "$infile" ]; then
       echo
       echo "Error: specified file \"$infile\" is does not exist."
       echo
       exit 1
     fi

     min_supported=${#hdr_txt}
     if [ $maxcol -lt $min_supported ]; then
       echo
       echo "Error: the folding column cannot be less than $min_support\
   ed"
       echo
       exit 1
     fi

     max_supported=`expr ${#equal_chars} + ${#hdr_txt} + ${#equal_chars\
   }`
     if [ $maxcol -gt $max_supported ]; then
       echo
       echo "Error: the folding column cannot be more than $max_support\
   ed"
       echo
       exit 1
     fi

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   }

   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 "$@"

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

Acknowledgements

   The authors thank the following folks for their various contributions
   (sorted by first name): Martin Bjorklund, Jonathan Hansford, and Rob
   Wilton.

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

Authors' Addresses

   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net

   Qin Wu
   Huawei Technologies

   EMail: bill.wu@huawei.com

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   Adrian Farrel
   Juniper Networks

   EMail: afarrel@juniper.net

   Benoit Claise
   Cisco Systems, Inc.

   EMail: bclaise@cisco.com

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