NETMOD Working Group K. Watsen
Internet-Draft Watsen Networks
Intended status: Best Current Practice A. Farrel
Expires: March 1, 2020 Old Dog Consulting
Q. Wu
Huawei Technologies
August 29, 2019
Handling Long Lines in Inclusions in Internet-Drafts and RFCs
draft-ietf-netmod-artwork-folding-09
Abstract
This document defines two strategies for handling long lines in
width-bounded text content. One strategy is based on the historic
use of a single backslash ('\') character to indicate where line-
folding has occurred, with the continuation occurring with the first
non-space (' ') character on the next line. The second strategy
extends the first strategy by adding a second backslash character to
identify where the continuation begins and thereby able to handle
cases not supported by the first strategy. Both strategies use a
self-describing header enabling automated reconstitution of the
original content.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 1, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Automated Folding of Long Lines in Text Content . . . . . 4
4.2. Automated Reconstitution of the Original Text Content . . 5
5. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Not Recommended for Graphical Artwork . . . . . . . . . . 5
5.2. Doesn't Work as Well as Format-Specific Options . . . . . 5
6. Two Folding Strategies . . . . . . . . . . . . . . . . . . . 6
6.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . 6
6.2. Recommendation . . . . . . . . . . . . . . . . . . . . . 6
7. The Single Backslash Strategy ('\') . . . . . . . . . . . . . 6
7.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 6
7.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 6
7.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 7
7.2.1. Folding . . . . . . . . . . . . . . . . . . . . . . . 7
7.2.2. Unfolding . . . . . . . . . . . . . . . . . . . . . . 9
8. The Double Backslash Strategy ('\\') . . . . . . . . . . . . 9
8.1. Folded Structure . . . . . . . . . . . . . . . . . . . . 9
8.1.1. Header . . . . . . . . . . . . . . . . . . . . . . . 9
8.1.2. Body . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2.1. Folding . . . . . . . . . . . . . . . . . . . . . . . 10
8.2.2. Unfolding . . . . . . . . . . . . . . . . . . . . . . 12
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Example Showing Boundary Conditions . . . . . . . . . . . 12
9.1.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 12
9.1.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 13
9.2. Example Showing Multiple Wraps of a Single Line . . . . . 13
9.2.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 13
9.2.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 14
9.3. Example Showing "Smart" Folding . . . . . . . . . . . . . 14
9.3.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 14
9.3.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 15
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9.4. Example Showing "Forced" Folding . . . . . . . . . . . . 16
9.4.1. Using '\' . . . . . . . . . . . . . . . . . . . . . . 17
9.4.2. Using '\\' . . . . . . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 17
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. POSIX Shell Script: rfcfold . . . . . . . . . . . . 20
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
[RFC7994] sets out the requirements for plain-text RFCs and states
that each line of an RFC (and hence of an Internet-Draft) must be
limited to 72 characters followed by the character sequence that
denotes an end-of-line (EOL).
Internet-Drafts and RFCs often include example text or code
fragments. Many times the example text or code exceeds the 72
character line-length limit. The `xml2rfc` utility does not attempt
to wrap the content of such inclusions, simply issuing a warning
whenever lines exceed 69 characters. According to the RFC Editor,
there is currently no convention in place for how to handle long
lines in such inclusions, other than advising authors to clearly
indicate what manipulation has occurred.
This document defines two strategies for handling long lines in
width-bounded text content. One strategy is based on the historic
use of a single backslash ('\') character to indicate where line-
folding has occurred, with the continuation occurring with the first
non-space (' ') character on the next line. The second strategy
extends the first strategy by adding a second backslash character to
identify where the continuation begins and thereby able to handle
cases not supported by the first strategy. Both strategies use a
self-describing header enabling automated reconstitution of the
original content.
The strategies defined in this document work on any text content, but
are primarily intended for a structured sequence of lines, such as
would be referenced by the <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].
Note that text files are represented as lines having their first
character in column 1, and a line length of N where the last
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character is in the Nth column and is immediately followed by an end
of line character sequence.
2. Applicability Statement
The formats and algorithms defined in this document may be used in
any context, whether for IETF documents or in other situations where
structured folding is desired.
Within the IETF, this work primarily targets the xml2rfc v3
<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.
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. This work should also be
automated to reduce effort and errors resulting from manual
processing.
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4.2. Automated Reconstitution of the Original Text Content
Automated reconstitution of the exact original text content is needed
to support validation of text-based content extracted from documents.
For instance, already YANG [RFC7950] modules are extracted from
Internet-Drafts and validated as part of the draft-submission
process. Additionally, the desire to validate instance examples
(i.e., XML/JSON documents) contained within Internet-Drafts has been
discussed ([yang-doctors-thread]).
5. Limitations
5.1. Not Recommended for Graphical Artwork
While the solution presented in this document works on any kind of
text-based content, it is most useful on content that represents
source code (XML, JSON, etc.) or, more generally, on content that has
not been laid out in two dimensions (e.g., diagrams).
Fundamentally, the issue is whether the text content remains readable
once folded. Text content that is unpredictable is especially
susceptible to looking bad when folded; falling into this category
are most UML diagrams, YANG tree diagrams, and ASCII art in general.
It is NOT RECOMMENDED to use the solution presented in this document
on graphical artwork.
5.2. Doesn't Work as Well as Format-Specific Options
The solution presented in this document works generically for all
text-based content, as it only views content as plain text. However,
various formats sometimes have built-in mechanisms that are better
suited to prevent long lines.
For instance, both the `pyang` [pyang] and `yanglint` [yanglint]
utilities have the command line option "--tree-line-length" that can
be used to indicate a desired maximum line length for when generating
tree diagrams [RFC8340].
In another example, some source formats (e.g., YANG [RFC7950]) allow
any quoted string to be broken up into substrings separated by a
concatenation character (e.g., '+'), any of which can be on a
different line.
It is RECOMMENDED that authors do as much as possible within the
selected format to avoid long lines.
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6. Two Folding Strategies
This document defines two nearly identical strategies for folding
text-based content.
The Single Backslash Strategy ('\'): Uses a backslash ('\')
character at the end of the line where folding occurs, and
assumes that the continuation begins at the first character
that is not a space character (' ') on the following line.
The Double Backslash Strategy ('\\'): Uses a backslash ('\')
character at the end of the line where folding occurs, and
assumes that the continuation begins after a second backslash
('\') character on the following line.
6.1. Comparison
The first strategy produces more readable output, however it is
significantly more likely to encounter unfoldable input (e.g., a long
line containing only space characters) and, for long lines that can
be folded, automation implementations may encounter scenarios that
will produce errors without special care.
The second strategy produces less readable output, but is unlikely to
encounter unfoldable input, there are no long lines that cannot be
folded, and no special care is required for when folding a long line.
6.2. Recommendation
It is RECOMMENDED for implementations to first attempt to fold
content using the single backslash strategy and, only in the unlikely
event that it cannot fold the input or the folding logic is unable to
cope with a contingency occurring on the desired folding column, then
fallback to the double backslash strategy.
7. The Single Backslash Strategy ('\')
7.1. Folded Structure
Text content that has been folded as specified by this strategy MUST
adhere to the following structure.
7.1.1. Header
The header is two lines long.
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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 XXX (RFC XXXX)
[Note to RFC Editor: Please replace XXX 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 empty line, containing only the end-of-line
character sequence. This line provides visual separation for
readability.
7.1.2. Body
The character encoding is the same as described in Section 2 of
[RFC7994], except that, per [RFC7991], tab characters are prohibited.
Lines that have a backslash ('\') occurring as the last character in
a line are considered "folded".
Really long lines may be folded multiple times.
7.2. Algorithm
This section describes a process for folding and unfolding long lines
when they are encountered in text content.
The steps are complete, but implementations MAY achieve the same
result in other ways.
When a larger document contains multiple instances of text content
that may need to be folded or unfolded, another process must insert/
extract the individual text content instances to/from the larger
document prior to utilizing the algorithms described in this section.
For example, the `xiax` utility [xiax] does this.
7.2.1. Folding
Determine the desired maximum line length from input to the line-
wrapping process, such as from a command line parameter. If no value
is explicitly specified, the value "69" SHOULD be used.
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).
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Scan the text content for horizontal tab characters. If any
horizontal tab characters appear, either resolve them to space
characters or exit, forcing the input provider to convert them to
space characters themselves first.
Scan the text content to ensure at least one line exceeds the desired
maximum. If no line exceeds the desired maximum, exit (this text
content does not need to be folded).
Scan the text content to ensure no existing lines already end with a
backslash ('\') character, as this could lead to an ambiguous result.
If such a line is found, and its width is less than the desired
maximum, then it SHOULD be flagged for forced folding (folding even
though unnecessary). If the folding implementation doesn't support
forced foldings, it MUST exit.
If this text content needs to and can be folded, insert the header
described in Section 7.1.1, ensuring that any additional printable
characters surrounding the header do not result in a line exceeding
the desired maximum.
For each line in the text content, from top-to-bottom, if the line
exceeds the desired maximum, or requires a forced folding, then fold
the line by:
1. Determine where the fold will occur. This location MUST be
before or at the desired maximum column, and MUST NOT be chosen
such that the character immediately after the fold is a space ('
') character. For forced foldings, the location is between the
'\' and the end of line sequence. If no such location can be
found, then exit (this text content cannot be folded).
2. At the location where the fold is to occur, insert a backslash
('\') character followed by the end of line character sequence.
3. On the following line, insert any number of space (' ')
characters.
The result of the previous operation is that the next line starts
with an arbitrary number of space (' ') characters, followed by the
character that was previously occupying the position where the fold
occurred.
Continue in this manner until reaching the end of the text content.
Note that this algorithm naturally addresses the case where the
remainder of a folded line is still longer than the desired maximum,
and hence needs to be folded again, ad infinitum.
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The process described in this section is illustrated by the
"fold_it_1()" function in Appendix A.
7.2.2. Unfolding
Scan the beginning of the text content for the header described in
Section 7.1.1. If the header is not present, starting on the first
line of the text content, exit (this text contents does not need to
be unfolded).
Remove the 2-line header from the text content.
For each line in the text content, from top-to-bottom, if the line
has a backslash ('\') character immediately followed by the end of
line character sequence, then the line can be unfolded. Remove the
backslash ('\') character, the end of line character sequence, and
any leading space (' ') characters, which will bring up the next
line. Then continue to scan each line in the text content starting
with the current line (in case it was multiply folded).
Continue in this manner until reaching the end of the text content.
The process described in this section is illustrated by the
"unfold_it_1()" function in Appendix A.
8. The Double Backslash Strategy ('\\')
8.1. Folded Structure
Text content that has been folded as specified by this strategy MUST
adhere to the following structure.
8.1.1. Header
The header is two lines long.
The first line is the following 47-character string that MAY be
surrounded by any number of printable characters. This first line
cannot itself be folded.
NOTE: '\\' line wrapping per BCP XXX (RFC XXXX)
[Note to RFC Editor: Please replace XXX and XXXX with the numbers
assigned to this document and delete this note. Please make this
change in multiple places in this document.]
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The second line is a empty line, containing only the end-of-line
character sequence. 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.
8.2. Algorithm
This section describes a process for folding and unfolding long lines
when they are encountered in text content.
The steps are complete, but implementations MAY achieve the same
result in other ways.
When a larger document contains multiple instances of text content
that may need to be folded or unfolded, another process must insert/
extract the individual text content instances to/from the larger
document prior to utilizing the algorithms described in this section.
For example, the `xiax` utility [xiax] does this.
8.2.1. Folding
Determine the desired maximum line length from input to the line-
wrapping process, such as from a command line parameter. If no value
is explicitly specified, the value "69" SHOULD be used.
Ensure that the desired maximum line length is not less than the
minimum header, which is 47 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.
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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 could lead to an ambiguous result. If such a line is found, and
its width is less than the desired maximum, then it SHOULD be flagged
for forced folding (folding even though unnecessary). If the folding
implementation doesn't support forced foldings, it MUST exit.
If this text content needs to and can be folded, insert the header
described in Section 8.1.1, ensuring that any additional printable
characters surrounding the header do not result in a line exceeding
the desired maximum.
For each line in the text content, from top-to-bottom, if the line
exceeds the desired maximum, or requires a forced folding, then fold
the line by:
1. Determine where the fold will occur. This location MUST be
before or at the desired maximum column. For forced foldings,
the location is between the '\' and the end of line sequence on
the first line.
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.
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8.2.2. Unfolding
Scan the beginning of the text content for the header described in
Section 8.1.1. If the header is not present, starting on the first
line of the text content, exit (this text content does not need to be
unfolded).
Remove the 2-line header from the text content.
For each line in the text content, from top-to-bottom, if the line
has a backslash ('\') character immediately followed by the end of
line character sequence, and if the next line has a backslash ('\')
character as the first non-space (' ') character, then the lines can
be unfolded. Remove the first backslash ('\') character, the end of
line character sequence, any leading space (' ') characters, and the
second backslash ('\') character, which will bring up the next line.
Then continue to scan each line in the text content starting with the
current line (in case it was multiply folded).
Continue in this manner until reaching the end of the text content.
The process described in this section is illustrated by the
"unfold_it_2()" function in Appendix A.
9. Examples
The following self-documenting examples illustrate folded text-based
content.
The source text content cannot be presented here, as it would again
be folded. Alas, only the results can be provided.
9.1. Example Showing Boundary Conditions
This example illustrates boundary condition. The input contains
seven lines, each line one character longer than the previous line.
Numbers for counting purposes. The default desired maximum column
value "69" is used.
9.1.1. Using '\'
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========== NOTE: '\' line wrapping per BCP XXX (RFC XXXX) ===========
123456789012345678901234567890123456789012345678901234567890123456
1234567890123456789012345678901234567890123456789012345678901234567
12345678901234567890123456789012345678901234567890123456789012345678
123456789012345678901234567890123456789012345678901234567890123456789
12345678901234567890123456789012345678901234567890123456789012345678\
90
12345678901234567890123456789012345678901234567890123456789012345678\
901
12345678901234567890123456789012345678901234567890123456789012345678\
9012
9.1.2. Using '\\'
========== NOTE: '\\' line wrapping per BCP XXX (RFC XXXX) ==========
123456789012345678901234567890123456789012345678901234567890123456
1234567890123456789012345678901234567890123456789012345678901234567
12345678901234567890123456789012345678901234567890123456789012345678
123456789012345678901234567890123456789012345678901234567890123456789
12345678901234567890123456789012345678901234567890123456789012345678\
\90
12345678901234567890123456789012345678901234567890123456789012345678\
\901
12345678901234567890123456789012345678901234567890123456789012345678\
\9012
9.2. Example Showing Multiple Wraps of a Single Line
This example illustrates what happens when very long line needs to be
folded multiple times. The input contains one line containing 280
characters. Numbers for counting purposes. The default desired
maximum column value "69" is used.
9.2.1. Using '\'
========== NOTE: '\' line wrapping per BCP XXX (RFC XXXX) ===========
12345678901234567890123456789012345678901234567890123456789012345678\
90123456789012345678901234567890123456789012345678901234567890123456\
78901234567890123456789012345678901234567890123456789012345678901234\
56789012345678901234567890123456789012345678901234567890123456789012\
34567890
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9.2.2. Using '\\'
========== NOTE: '\\' line wrapping per BCP XXX (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 headers are surrounded by different printable
characters than shown in the script-generated examples.
9.3.1. Using '\'
[NOTE: '\' line wrapping per BCP XXX (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.
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========== NOTE: '\' line wrapping per BCP XXX (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 '\\'
[NOTE: '\\' line wrapping per BCP XXX (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.
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========== NOTE: '\\' line wrapping per BCP XXX (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>
9.4. Example Showing "Forced" Folding
This example illustrates how invalid sequences in lines that do not
have to be folded can be handled via forced folding, whereby the
folding occurs even though unnecessary.
The following line exceeds a 68-char max, thus demands folding
123456789012345678901234567890123456789012345678901234567890123456789
This line ends with a backslash \
This line ends with a backslash \
\ This line begins with a backslash
Following is an indented 3x3 block of backslashes:
\\\
\\\
\\\
The samples below were manually folded, since the script in the
appendix does not implement forced folding.
Note that the headers are prefixed by a pound ('#') character, rather
than surrounded by equal ('=') characters as shown in the script-
generated examples.
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9.4.1. Using '\'
# NOTE: '\' line wrapping per BCP XXX (RFC XXXX)
The following line exceeds a 68-char max, thus demands folding
1234567890123456789012345678901234567890123456789012345678901234567\
89
This line ends with a backslash \\
This line ends with a backslash \\
\ This line begins with a backslash
Following is an indented 3x3 block of backslashes:
\\\\
\\\\
\\\
9.4.2. Using '\\'
# NOTE: '\\' line wrapping per BCP XXX (RFC XXXX)
The following line exceeds a 68-char max, thus demands folding
1234567890123456789012345678901234567890123456789012345678901234567\
\89
This line ends with a backslash \
This line ends with a backslash \\
\
\ This line begins with a backslash
Following is an indented 3x3 block of backslashes:
\\\\
\
\\\\
\
\\\
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
[pyang] "An extensible YANG (RFC 6020/7950) validator.",
<https://pypi.org/project/pyang/>.
[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/>.
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[yang-doctors-thread]
"[yang-doctors] automating yang doctor reviews",
<https://mailarchive.ietf.org/arch/msg/yang-doctors/
DCfBqgfZPAD7afzeDFlQ1Xm2X3g>.
[yanglint]
"A feature-rich tool for validation and conversion of the
schemas and YANG modeled data.",
<https://github.com/CESNET/libyang#yanglint>.
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Appendix A. POSIX Shell Script: rfcfold
This non-normative appendix section includes a shell script that can
both fold and unfold text content using both the single and double
backslash strategies described in Section 7 and Section 8
respectively.
This script is intended to be applied to a single text content
instance. If it is desired to fold or unfold text content instances
within a larger document (e.g., an Internet draft or RFC), then
another tool must be used to extract the content from the larger
document before utilizing this script.
For readability purposes, this script forces the minimally supported
line length to be eight characters longer than the raw header text
defined in Section 7.1.1 and Section 8.1.1 so as to ensure that the
header can be wrapped by a space (' ') character and three equal
('=') characters on each side of the raw header text.
This script does not implement the whitespace-avoidance logic
described in Section 7.2.1. In such case, the script will exit with
one of the following message:
Error: infile has a space character occuring on the
folding column. This file cannot be folded using the
'\' strategy.
While this script can unfold input that contains forced foldings, it
unable to fold files that would require forced foldings. Forced
folding is described in Section 7.2.1 and Section 8.2.1. When being
asked to fold a file that would require forced folding, the script
will instead exit with one of the following messages:
Error: infile has a line ending with a '\' character.
This file cannot be folded using the '\' strategy without
there being false positives produced in the unfolding
(i.e., this script does not attempt to proactively
force-fold such lines, as described in RFC XXXX).
Error: infile has a line ending with a '\' character
followed by a '\' character as the first non-space
character on the next line. This script cannot fold
this file using '\\' strategy without there being
false positives produced in the unfolding (i.e., this
script does not attempt to proactively force-fold such
lines, as described in RFC XXXX).
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Shell-level end-of-line backslash ('\') characters have been
purposely added to the script so as to ensure that the script is
itself not folded in this document, thus simplify the ability to
copy/paste the script for local use. As should be evident by the
lack of the mandatory header described in Section 7.1.1, these
backslashes do not designate a folded line, such as described in
Section 7.
<CODE BEGINS>
#!/bin/bash --posix
# This script may need some adjustments to work on a given system.
# For instance, the utilities `pcregrep` and `gsed` may need to
# be installed. Also, please be advised that `bash` (not `sh`)
# must be used.
# Copyright (c) 2019 IETF Trust, Kent Watsen, and Erik Auerswald.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#
# * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following
# disclaimer in the documentation and/or other materials
# provided with the distribution.
#
# * Neither the name of Internet Society, IETF or IETF Trust, nor
# the names of specific contributors, may be used to endorse or
# promote products derived from this software without specific
# prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
# STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
print_usage() {
printf "\n"
printf "Folds or unfolds the input text file according to BCP XXX"
printf " (RFC XXXX).\n"
printf "\n"
printf "Usage: rfcfold [-s <strategy>] [-c <col>] [-r] -i <infile>"
printf " -o <outfile>\n"
printf "\n"
printf " -s: strategy to use, '1' or '2' (default: try 1,"
printf " else 2)\n"
printf " -c: column to fold on (default: 69)\n"
printf " -r: reverses the operation\n"
printf " -i: the input filename\n"
printf " -o: the output filename\n"
printf " -d: show debug messages\n"
printf " -q: quiet (suppress error messages)\n"
printf " -h: show this message\n"
printf "\n"
printf "Exit status code: 1 on error, 0 on success, -1 on no-op.\n"
printf "\n"
}
# global vars, do not edit
strategy=0 # auto
debug=0
quiet=0
reversed=0
infile=""
outfile=""
maxcol=69 # default, may be overridden by param
hdr_txt_1="NOTE: '\\' line wrapping per BCP XXX (RFC XXXX)"
hdr_txt_2="NOTE: '\\\\' line wrapping per BCP XXX (RFC XXXX)"
equal_chars="======================================================="
space_chars=" "
temp_dir=""
# determine name of [g]sed binary
type gsed > /dev/null 2>&1 && SED=gsed || SED=sed
# warn if a non-GNU sed utility is used
"$SED" --version < /dev/null 2> /dev/null \
| grep GNU >/dev/null 2>&1 || \
echo 'Warning: not using GNU `sed` (likely cause if an error occurs)'
# verify the availability of pcregrep
type pcregrep > /dev/null 2>&1 || {
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printf '\nError: missing utility `pcregrep`\n'
exit 1
}
cleanup() {
rm -rf "$temp_dir"
}
trap 'cleanup' EXIT
fold_it_1() {
# ensure input file doesn't contain the fold-sequence already
pcregrep -M "\\\\\n" $infile >> /dev/null 2>&1
if [[ $? -eq 0 ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: infile $infile has a line ending with a '\\'"
echo "character. This file cannot be folded using the '\\'"
echo "strategy without there being false positives produced"
echo "in the unfolding (i.e., this script does not attempt"
echo "to proactively force-fold such lines, as described"
echo "in RFC XXXX)."
echo
fi
return 1
fi
# where to fold
foldcol=`expr "$maxcol" - 1` # for the inserted '\' char
# ensure input file doesn't contain whitespace on the fold column
grep "^.\{$foldcol\} " $infile >> /dev/null 2>&1
if [[ $? -eq 0 ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: infile has a space character occuring on the"
echo "folding column. This file cannot be folded using the"
echo "'\\' strategy."
echo
fi
return 1
fi
# center header text
length=`expr ${#hdr_txt_1} + 2`
left_sp=`expr \( "$maxcol" - "$length" \) / 2`
right_sp=`expr "$maxcol" - "$length" - "$left_sp"`
header=`printf "%.*s %s %.*s" "$left_sp" "$equal_chars"\
"$hdr_txt_1" "$right_sp" "$equal_chars"`
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# generate outfile
echo "$header" > $outfile
echo "" >> $outfile
"$SED" 's/\(.\{'"$foldcol"'\}\)\(..\)/\1\\\n\2/;t M;b;:M;P;D;'\
< $infile >> $outfile 2>/dev/null
if [[ $? -ne 0 ]]; then
return 1
fi
return 0
}
fold_it_2() {
# where to fold
foldcol=`expr "$maxcol" - 1` # for the inserted '\' char
# ensure input file doesn't contain the fold-sequence already
pcregrep -M "\\\\\n[\ ]*\\\\" $infile >> /dev/null 2>&1
if [[ $? -eq 0 ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: infile has a line ending with a '\\' character"
echo "followed by a '\\' character as the first non-space"
echo "character on the next line. This script cannot fold"
echo "this file using '\\\\' strategy without there being"
echo "false positives produced in the unfolding (i.e., this"
echo "script does not attempt to proactively force-fold such"
echo "lines, as described in RFC XXXX)."
echo
fi
return 1
fi
# center header text
length=`expr ${#hdr_txt_2} + 2`
left_sp=`expr \( "$maxcol" - "$length" \) / 2`
right_sp=`expr "$maxcol" - "$length" - "$left_sp"`
header=`printf "%.*s %s %.*s" "$left_sp" "$equal_chars"\
"$hdr_txt_2" "$right_sp" "$equal_chars"`
# generate outfile
echo "$header" > $outfile
echo "" >> $outfile
"$SED" 's/\(.\{'"$foldcol"'\}\)\(..\)/\1\\\n\\\2/;t M;b;:M;P;D;'\
< $infile >> $outfile 2>/dev/null
if [[ $? -ne 0 ]]; then
return 1
fi
return 0
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}
fold_it() {
# ensure input file doesn't contain a TAB
grep $'\t' $infile >> /dev/null 2>&1
if [[ $? -eq 0 ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: infile contains a TAB character, which is"
echo "not allowed."
echo
fi
return 1
fi
# check if file needs folding
testcol=`expr "$maxcol" + 1`
grep ".\{$testcol\}" $infile >> /dev/null 2>&1
if [ $? -ne 0 ]; then
if [[ $debug -eq 1 ]]; then
echo "nothing to do"
fi
cp $infile $outfile
return -1
fi
if [[ $strategy -eq 1 ]]; then
fold_it_1
return $?
fi
if [[ $strategy -eq 2 ]]; then
fold_it_2
return $?
fi
quiet_sav=$quiet
quiet=1
fold_it_1
result=$?
quiet=$quiet_sav
if [[ $result -ne 0 ]]; then
if [[ $debug -eq 1 ]]; then
echo "Folding strategy 1 didn't succeed, trying strategy 2..."
fi
fold_it_2
return $?
fi
return 0
}
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unfold_it_1() {
temp_dir=`mktemp -d`
# output all but the first two lines (the header) to wip file
awk "NR>2" $infile > $temp_dir/wip
# unfold wip file
"$SED" '{H;$!d};x;s/^\n//;s/\\\n *//g' $temp_dir/wip > $outfile
return 0
}
unfold_it_2() {
temp_dir=`mktemp -d`
# output all but the first two lines (the header) to wip file
awk "NR>2" $infile > $temp_dir/wip
# unfold wip file
"$SED" '{H;$!d};x;s/^\n//;s/\\\n *\\//g' $temp_dir/wip > $outfile
return 0
}
unfold_it() {
# check if file needs unfolding
line=`head -n 1 $infile`
line2=`$SED -n '2p' $infile`
result=`echo $line | fgrep "$hdr_txt_1"`
if [ $? -eq 0 ]; then
if [ -n "$line2" ]; then
if [[ $quiet -eq 0 ]]; then
echo "Error: the second line is not empty."
fi
return 1
fi
unfold_it_1
return $?
fi
result=`echo $line | fgrep "$hdr_txt_2"`
if [ $? -eq 0 ]; then
if [ -n "$line2" ]; then
if [[ $quiet -eq 0 ]]; then
echo "Error: the second line is not empty."
fi
return 1
fi
unfold_it_2
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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 0
fi
if [ "$1" == "-d" ]; then
debug=1
fi
if [ "$1" == "-q" ]; then
quiet=1
fi
if [ "$1" == "-s" ]; then
strategy="$2"
shift
fi
if [ "$1" == "-c" ]; then
maxcol="$2"
shift
fi
if [ "$1" == "-r" ]; then
reversed=1
fi
if [ "$1" == "-i" ]; then
infile="$2"
shift
fi
if [ "$1" == "-o" ]; then
outfile="$2"
shift
fi
shift
done
if [[ -z "$infile" ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: infile parameter missing (use -h for help)"
echo
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fi
exit 1
fi
if [[ -z "$outfile" ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: outfile parameter missing (use -h for help)"
echo
exit 1
fi
fi
if [[ ! -f "$infile" ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: specified file \"$infile\" is does not exist."
echo
exit 1
fi
fi
if [[ $strategy -eq 2 ]]; then
min_supported=`expr ${#hdr_txt_2} + 8`
else
min_supported=`expr ${#hdr_txt_1} + 8`
fi
if [[ $maxcol -lt $min_supported ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: the folding column cannot be less than"
echo "$min_supported."
echo
fi
exit 1
fi
# this is only because the code otherwise runs out of equal_chars
max_supported=`expr ${#equal_chars} + 1 + ${#hdr_txt_1} + 1\
+ ${#equal_chars}`
if [[ $maxcol -gt $max_supported ]]; then
if [[ $quiet -eq 0 ]]; then
echo
echo "Error: the folding column cannot be more than"
echo "$max_supported."
echo
fi
exit 1
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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 $code
}
main "$@"
<CODE ENDS>
Acknowledgements
The authors thank the RFC Editor for confirming that there was
previously no set convention for handling long lines in sourcecode
inclusions, thus instigating this work.
The authors thank the following folks for their various contributions
while producing this document (sorted by first name): Benoit Claise,
Erik Auerswald, Gianmarco Bruno, Italo Busi, Joel Jaeggli, Jonathan
Hansford, Lou Berger, Martin Bjorklund, and Rob Wilton.
Special acknowledgement to Erik Auerswald for his contributions to
the `rfcfold` script, especially for greatly improving the `sed` one-
liners used therein.
Authors' Addresses
Kent Watsen
Watsen Networks
EMail: kent+ietf@watsen.net
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Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
Qin Wu
Huawei Technologies
EMail: bill.wu@huawei.com
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