NETMOD Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Best Current Practice A. Farrel
Expires: October 8, 2019 Old Dog Consulting
Q. Wu
Huawei Technologies
April 6, 2019
Handling Long Lines in Inclusions in Internet-Drafts and RFCs
draft-ietf-netmod-artwork-folding-02
Abstract
This document defines a simple and yet time-proven strategy for
handling long lines in inclusions in internet drafts and RFCs using a
backslash ('\') character to indicate where line-folding has
occurred. The strategy works on any text-based content, but is
primarily intended for a structured sequence of lines rather than for
two-dimensional imagery. The approach produces consistent results,
regardless of the content, that is both self-documenting and enables
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 October 8, 2019.
Copyright Notice
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
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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 . . . . . . . . . . . . . . . . . . . 3
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 . . 4
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 . . . . . . . . . . . . . . . . . . . 5
6.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . 6
6.2. Recommendation . . . . . . . . . . . . . . . . . . . . . 6
7. The Single Backslash Strategy ('\') . . . . . . . . . . . . . 6
7.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 6
7.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 6
7.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2.1. Folding . . . . . . . . . . . . . . . . . . . . . . . 7
7.2.2. Unfolding . . . . . . . . . . . . . . . . . . . . . . 8
8. The Double Backslash Strategy ('\\') . . . . . . . . . . . . 9
8.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 9
8.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 9
8.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 9
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 '\\' . . . . . . . . . . . . . . . . . . . . . 12
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 '\' . . . . . . . . . . . . . . . . . . . . . . 13
9.3.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
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12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. POSIX Shell Script . . . . . . . . . . . . . . . . . 17
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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 introduces a simple and yet time-proven strategy for
handling long lines using a backslash ('\') character to indicate
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 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.
2. Applicability Statement
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 primarily targets the xml2rfc v3
<sourcecode> element (Section 2.48 of [RFC7991]) and the 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.
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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.
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.
4.2. Automated Reconstitution of the Original Text Content
Automated reconstitution of the original content is needed to support
validation of text-based inclusions 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 also validate
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
utilize such tooling.
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5. Limitations
5.1. Not Recommended for Graphical Artwork
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.
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.
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.
6. Two Folding Strategies
This document defines two nearly identical strategies for folding
text-based content.
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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 first non-
whitespace 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
is exists a line anywhere in the input ending with a backslash
character, or there exists a long line containing only space and
backslash characters) and, for long lines that can be folded,
automation implementations are likely to 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.
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)
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[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 the process 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 this.
7.2.1. Folding
Folding is assumed to be automated although authors may perform the
folding steps manually.
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).
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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 precede a
space (' ') character.
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.
The process described in this section is illustrated by the
"fold_it_1()" function in Appendix A.
7.2.2. Unfolding
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 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.
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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.
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.
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8.2. Algorithm
This section describes the process 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 this.
8.2.1. Folding
Folding is assumed to be automated, although authors may perform the
folding steps manually.
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 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 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
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
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, then fold the line by:
1. Determine where the fold will occur. This location MUST be
before or at the desired maximum column.
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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
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 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.
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.
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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
9.1.2. Using '\\'
========== NOTE: '\\' line wrapping per BCP XX (RFC XXXX) ===========
123456789012345678901234567890123456789012345678901234567890123456
1234567890123456789012345678901234567890123456789012345678901234567
12345678901234567890123456789012345678901234567890123456789012345678
123456789012345678901234567890123456789012345678901234567890123456789
12345678901234567890123456789012345678901234567890123456789012345678\
\90
12345678901234567890123456789012345678901234567890123456789012345678\
\901
12345678901234567890123456789012345678901234567890123456789012345678\
\9012
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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.
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 '\'
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[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-set>
...
</yang-library>
Below is the equivalent to the above, but it was folded using the
script in the appendix.
=========== 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-set>
...
</yang-library>
9.3.2. Using '\\'
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[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-set>
...
</yang-library>
Below is the equivalent to the above, but it was folded using the
script in the appendix.
========== 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-set>
...
</yang-library>
10. Security Considerations
This BCP has no Security Considerations.
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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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
12.2. Informative References
[RFC7749] Reschke, J., "The "xml2rfc" Version 2 Vocabulary",
RFC 7749, DOI 10.17487/RFC7749, February 2016,
<https://www.rfc-editor.org/info/rfc7749>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[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>.
[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>.
[xiax] "The `xiax` Python Package",
<https://pypi.org/project/xiax/>.
[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 text content. Note that this script is applied
only to single text content instances.
#!/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 <strategy>] [-c <col>] [-r] -i <infile>"
echo " -o <outfile>"
echo
echo " -s: strategy to use, '1' or '2' (default: try 1, else 2)"
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
strategy=0 # auto
debug=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=" "
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
echo
echo "Error1: infile $infile has a line ending with a '\\'"
echo "character. This file cannot be folded."
echo
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return 1
fi
# stash some vars
testcol=`expr "$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
echo
echo "Error: infile has a space character occuring after the"
echo "folding column. This file cannot be folded."
echo
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() {
# ensure input file doesn't contain the fold-sequence already
pcregrep -M "\\\\\n[\ ]*\\\\" $infile >> /dev/null 2>&1
if [ $? -eq 0 ]; then
echo
echo "Error2: 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
return 1
fi
# center header text
length=`expr ${#hdr_txt_2} + 2`
left_sp=`expr \( "$maxcol" - "$length" \) / 2`
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right_sp=`expr "$maxcol" - "$length" - "$left_sp"`
header=`printf "%.*s %s %.*s" "$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 $infile /tmp/wip
fi
testcol=`expr "$maxcol" + 1`
foldcol=`expr "$maxcol" - 1` # for the inserted '\' char
gsed "/.\{$testcol\}/s/\(.\{$foldcol\}\)/\1\\\\\n\\\\/" < /tmp/wip\
>> /tmp/wip2
diff /tmp/wip /tmp/wip2 > /dev/null 2>&1
if [ $? -eq 1 ]; then
mv /tmp/wip2 /tmp/wip
fold_it_2 "recursing"
else
echo "$header" > $outfile
echo "" >> $outfile
cat /tmp/wip2 >> $outfile
rm /tmp/wip*
fi
return 0
}
fold_it() {
# ensure input file doesn't contain a TAB
grep $'\t' $infile >> /dev/null 2>&1
if [ $? -eq 0 ]; then
echo
echo "Error: infile contains a TAB character, which is not"
echo "allowed."
echo
return 1
fi
# check if file needs folding
testcol=`expr "$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
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if [[ $strategy -eq 1 ]]; then
fold_it_1
return $?
fi
if [[ $strategy -eq 2 ]]; then
fold_it_2
return $?
fi
fold_it_1
if [ $? -ne 0 ]; then
fold_it_2
return $?
fi
return 0
}
unfold_it_1() {
# output all but the first two lines (the header) to wip file
awk "NR>2" $infile > /tmp/wip
# unfold wip file
gsed ":x; /.*\\\\$/N; s/\\\\\n[ ]*//; tx" /tmp/wip > $outfile
# clean up and return
rm /tmp/wip
return 0
}
unfold_it_2() {
# output all but the first two lines (the header) to wip file
awk "NR>2" $infile > /tmp/wip
# unfold wip file
gsed ":x; /.*\\\\$/N; s/\\\\\n[ ]*\\\\//; tx" /tmp/wip > $outfile
# clean up and return
rm /tmp/wip
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
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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" == "-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
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
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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
if [[ $strategy -eq 2 ]]; then
min_supported=`expr ${#hdr_txt_2} + 8`
else
min_supported=`expr ${#hdr_txt_1} + 8`
fi
if [ $maxcol -lt $min_supported ]; then
echo
echo "Error: the folding column cannot be less than"
echo "$min_supported."
echo
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 $max_supported ]; then
echo
echo "Error: the folding column cannot be more than"
echo "$max_supported."
echo
exit 1
fi
}
main() {
if [ "$#" == "0" ]; then
print_usage
exit 1
fi
process_input $@
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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.
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
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