| NETMOD Working Group | K. Watsen |
| Internet-Draft | Watsen Networks |
| Intended status: Best Current Practice | Q. Wu |
| Expires: September 11, 2019 | Huawei Technologies |
| A. Farrel | |
| Old Dog Consulting | |
| B. Claise | |
| Cisco Systems, Inc. | |
| March 10, 2019 |
Handling Long Lines in Inclusions in Internet-Drafts and RFCs
draft-ietf-netmod-artwork-folding-01
This document introduces a simple and yet time-proven strategy for handling long lines in inclusions in drafts using a backslash ('\') character where line-folding has occurred. The strategy works on any text-based content, but is primarily intended for a structured sequence of lines, such as would be referenced by the <sourcecode> element defined in Section 2.48 of RFC 7991, rather than for two-dimensional imagery, such as would be referenced by the <artwork> element defined in Section 2.5 of RFC 7991. The approach produces consistent results, regardless of the content, that is both self-documenting and enables automated reconstitution of the original content.
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 September 11, 2019.
Copyright (c) 2019 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 (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.
[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. In order to render the formatting of such text it is usually presented as a figure using the "<sourcecode>" element in the source XML. Many times the example text or code exceeds the 72 character line-length limit and 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, other than advising authors to clearly indicate what manipulation has occurred.
This document introduces a simple and yet time-proven strategy for handling long lines in inclusions in drafts using a backslash ('\') character where line-folding has occurred. The strategy works on any text based inclusion, but is primarily intended for a structured sequence of lines, such as would be referenced by the <sourcecode> element defined in Section 2.48 of [RFC7991], rather than for two-dimensional imagery, such as would be referenced by the <artwork> element defined in Section 2.5 of [RFC7991]. The approach produces consistent results, regardless of the content, that is both self-documenting and enables automated reconstitution of the original content.
Note that text files are represent 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.
The format and algorithm 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 is primarily targeted to xml2rfc v3 <sourcecode> element (Section 2.48 of [RFC7991]) and xml2rfc v2 <artwork> 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 <artwork> element (Section 2.5 of [RFC7991]) but, as described in Section 5.1, it is generally not recommended.
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.
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 include 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 effort.
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 effort.
Automated reconstitution of the original content is needed to support validation of artwork extracted from documents. YANG [RFC7950] modules are already extracted from Internet-Drafts and validated as part of the draft-submission process. Additionally, there has been some discussion regarding needing to do the same for instance examples (i.e., XML/JSON documents) contained within Internet-Drafts ([yang-doctors-thread]). Thus, it SHOULD be possible to mechanically reconstitute the original text content in order to satisfy tooling input parsers.
While the solution presented in this document will work 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.
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.
In yet another example, some languages allow factoring blocks 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.
It is RECOMMENDED that authors do as much as possible within the selected format to avoid long lines.
Text content that has been folded as specified by this document MUST contain the following structure.
The header is two lines long.
NOTE: '\\' line wrapping per BCP XX (RFC XXXX)
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 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.
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.
This section describes the processes for folding and unfolding long lines when they are encountered in a single instance of text content. It is assumed that another process inserts/extracts the individual text content instances to/from an Internet-Draft or RFC. For example, the `xiax` utility [xiax] does just this.
Determine the desired maximum line length from input to the automated 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 when the subsequent line starts with a backslash ('\') character as the first non-space (' ') 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 as described in Section 6.1.
For each line in the text content, from top-to-bottom, if the line exceeds the desired maximum, then fold the line at the desired maximum column by 1) inserting the character backslash ('\') character at the maximum column, 2) inserting the end of line character sequence, inserting any number of space (' ') characters, and 4) inserting a further backslash ('\') character.
The result of this 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 in the maximum column.
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()" function in Appendix A.
Authors may choose to fold text examples and source code by hand to produce a text content that is more pleasant for a human reader but which can still be automatically unfolded (as described in Section 7.2) to produce single lines that are longer than the maximum document line length.
For example, an author may choose to make the fold at convenient gaps between words such that the backslash is placed in a lower column number than the text content's maximum column value.
Additionally, an author may choose to indent the start of a continuation line by inserting space characters before the line continuation marker backslash character.
Manual folding may also help handle the cases that cannot be automatically folded as described in Section 7.
Authors MUST produce a result that adheres to the structure described in Section 6.
All unfolding is assumed to be automated although a reader will mentally perform the act of unfolding the text to understand the true nature of the original text content.
Scan the beginning of the text content for the header described in Section 6.1. If the header is not present, starting on the first line of the text content, exit (this artwork 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, 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()" function in Appendix A.
The following self-documenting examples illustrate folded text-based content.
The source text content cannot be presented here, as it would again need to be folded. Alas, only the result can be provided.
The examples in Sections 8.1 through 8.4 were automatically folded on column 69, the default value. Section 8.5 shows an example of manual folding.
This example illustrates a boundary condition test using numbers for counting purposes. The input contains 5 lines, each line one character longer than the previous.
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 if the first non-space character of the next line is a '\' character, as that would lead to an ambiguous result.
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== 123456789012345678901234567890123456789012345678901234567890123456 1234567890123456789012345678901234567890123456789012345678901234567 12345678901234567890123456789012345678901234567890123456789012345678 123456789012345678901234567890123456789012345678901234567890123456789 12345678901234567890123456789012345678901234567890123456789012345678\ \90 12345678901234567890123456789012345678901234567890123456789012345678\ \901 12345678901234567890123456789012345678901234567890123456789012345678\ \9012
This example illustrates one very long line (280 characters).
Any printable character (including ' ' and '\') can be used as a substitute for any number.
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== 12345678901234567890123456789012345678901234567890123456789012345678\ \9012345678901234567890123456789012345678901234567890123456789012345\ \6789012345678901234567890123456789012345678901234567890123456789012\ \3456789012345678901234567890123456789012345678901234567890123456789\ \01234567890
This example has a '\' character in the wrapping column. The native text includes the sequence "fish\fowl" with the '\' character occurring on the 69th column.
string1="The quick brown dog jumps over the lazy dog which is a fish\ \\fowl as appropriate"
This example has whitespace spanning the wrapping column. The native input contains 15 space (' ') characters between "like" and "white".
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =========== Sometimes our strings include multiple spaces such as "We like \ \ white space."
This example was manually wrapped to cause the folding to occur after each term, putting each term on its own line. Indentation is used to additionally improve readability. Also note that the mandatory header is surrounded by different printable characters than shown in the other examples.
===== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) =====
<yang-library
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<module-set>
<name>config-modules</name>
<module>
<name>ietf-interfaces</name>
<revision>2018-02-20</revision>
<namespace>\
\urn:ietf:params:xml:ns:yang:ietf-interfaces\
\</namespace>
</module>
<module>
<name>ietf-ip</name>
<revision>2018-02-22</revision>
<namespace>\
\urn:ietf:params:xml:ns:yang:ietf-ip\
\</namespace>
</module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>\
\urn:ietf:params:xml:ns:yang:ietf-yang-types\
\</namespace>
</import-only-module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>\
\urn:ietf:params:xml:ns:yang:ietf-inet-types\
\</namespace>
</import-only-module>
</module-set>
<schema>
<name>config-schema</name>
<module-set>config-modules</module-set>
</schema>
<schema>
<name>state-schema</name>
<module-set>config-modules</module-set>
<module-set>state-modules</module-set>
</schema>
<datastore>
<name>ds:startup</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:running</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:operational</name>
<schema>state-schema</schema>
</datastore>
<content-id>75a43df9bd56b92aacc156a2958fbe12312fb285</content-id>
</yang-library>
The manual folding produces a more readable result than the following equivalent folding that contains no indentation.
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) ===========
<yang-library
xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-library"
xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
<module-set>
<name>config-modules</name>
<module>
<name>ietf-interfaces</name>
<revision>2018-02-20</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-interfaces</namesp\
\ace>
</module>
<module>
<name>ietf-ip</name>
<revision>2018-02-22</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-ip</namespace>
</module>
<import-only-module>
<name>ietf-yang-types</name>
<revision>2013-07-15</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-yang-types</namesp\
\ace>
</import-only-module>
<import-only-module>
<name>ietf-inet-types</name>
<revision>2013-07-15</revision>
<namespace>urn:ietf:params:xml:ns:yang:ietf-inet-types</namesp\
\ace>
</import-only-module>
</module-set>
<schema>
<name>config-schema</name>
<module-set>config-modules</module-set>
</schema>
<schema>
<name>state-schema</name>
<module-set>config-modules</module-set>
<module-set>state-modules</module-set>
</schema>
<datastore>
<name>ds:startup</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:running</name>
<schema>config-schema</schema>
</datastore>
<datastore>
<name>ds:operational</name>
<schema>state-schema</schema>
</datastore>
<content-id>75a43df9bd56b92aacc156a2958fbe12312fb285</content-id>
</yang-library>
This BCP has no Security Considerations.
This BCP has no IANA Considerations.
| [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. |
| [RFC7749] | Reschke, J., "The "xml2rfc" Version 2 Vocabulary", RFC 7749, DOI 10.17487/RFC7749, February 2016. |
| [RFC7950] | Bjorklund, M., "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, "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" |
This non-normative appendix section includes a shell script that can both fold and unfold text content. Note that this script is applied only to single text content instances.
#!/bin/bash
print_usage() {
echo
echo "Folds the text file, only if needed, at the specified"
echo "column, according to BCP XX."
echo
echo "Usage: $0 [-c <col>] [-r] -i <infile> -o <outfile>"
echo
echo " -c: column to fold on (default: 69)"
echo " -r: reverses the operation"
echo " -i: the input filename"
echo " -o: the output filename"
echo " -d: show debug messages"
echo " -h: show this message"
echo
echo "Exit status code: zero on success, non-zero otherwise."
echo
}
# global vars, do not edit
debug=0
reversed=0
infile=""
outfile=""
maxcol=69 # default, may be overridden by param
hdr_txt="NOTE: '\\\\' line wrapping per BCP XX (RFC XXXX)"
equal_chars="=============================================="
space_chars=" "
fold_it() {
# since upcomming tests are >= (not >)
testcol=`expr "$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 $outfile
return -1
fi
foldcol=`expr "$maxcol" - 1` # for the inserted '\' char
# ensure input file doesn't contain a TAB
grep $'\t' $infile >> /dev/null 2>&1
if [ $? -eq 0 ]; then
echo
echo "Error: infile contains a TAB character, which is not"
echo "allowed."
echo
return 1
fi
# ensure input file doesn't contain the fold-sequence already
pcregrep -M "\\\\\n[\ ]*\\\\" $infile >> /dev/null 2>&1
if [ $? -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"
echo " folded."
echo
return 1
fi
# center header text
length=`expr ${#hdr_txt} + 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" "$right_sp" "$equal_chars"`
# fold using recursive passes ('g' didn't work)
if [ -z "$1" ]; then
# init recursive env
cp $infile /tmp/wip
fi
gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n\\\\/" < /tmp/wip\
>> /tmp/wip2
diff /tmp/wip /tmp/wip2 > /dev/null 2>&1
if [ $? -eq 1 ]; then
mv /tmp/wip2 /tmp/wip
fold_it "recursing"
else
echo "$header" > $outfile
echo "" >> $outfile
cat /tmp/wip2 >> $outfile
rm /tmp/wip*
fi
## following two lines represent a non-functional variant to the
## recursive logic presented in the block above. It used to work
## before the '\' on the next line was added to the format (i.e.,
## the trailing '\\\\' in the substitution below), but now there
## is an off-by-one error. Leaving here in case anyone can fix it.
#echo "$header" > $outfile
#echo "" >> $outfile
#gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n\\\\/g"\
< $infile >> $outfile
return 0
}
unfold_it() {
# check if file needs unfolding
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 -1
fi
# output all but the first two lines (the header) to wip (work
# in progress) file
awk "NR>2" $infile > /tmp/wip
# unfold wip file
gsed ":x; /.*\\\\\$/N; s/\\\\\n[ ]*\\\\//; 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
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=`expr ${#hdr_txt} + 8`
if [ $maxcol -lt $min_supported ]; then
echo
echo "Error: the folding column cannot be less than"
echo "$min_supported"
echo
exit 1
fi
max_supported=`expr ${#equal_chars} + 1 + ${#hdr_txt} + 1\
+ ${#equal_chars}`
if [ $maxcol -gt $max_supported ]; then
echo
echo "Error: the folding column cannot be more than"
echo "$max_supported"
echo
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 $code
}
main "$@"
The authors thank the following folks for their various contributions (sorted by first name): Gianmarco Bruno, Italo Busi, Jonathan Hansford, Joel Jaeggli, Lou Berger, Martin Bjorklund, Italo Busi, 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/sourcecode inclusions.