[PATCH] Revert "parser: Ensure whitespace is stripped for long headers"
dja at axtens.net
Tue May 14 16:11:25 AEST 2019
This reverts commit 841f966b8d54b2f51ab1c498eed6e5391f2546a9.
In July 2018, we received a report of OzLabs patchwork mangling
emails that have subjects containing words with internal commas,
like "Insert DT binding for foo,bar" (#197).
Stephen took a look and came up with the comment this reverts. Quoting
the commit message:
RFC2822 states that long headers can be wrapped using CRLF followed by
WSP . For example:
Subject: Foo bar,
Should be parsed as:
As it turns out, this is not the case. Journey with me to
section 2.2.3 of RFC 2822:
2.2.3. Long Header Fields
Each header field is logically a single line of characters comprising
the field name, the colon, and the field body. For convenience
however, and to deal with the 998/78 character limitations per line,
the field body portion of a header field can be split into a multiple
line representation; this is called "folding". The general rule is
that wherever this standard allows for folding white space (not
simply WSP characters), a CRLF may be inserted before any WSP. For
example, the header field:
Subject: This is a test
can be represented as:
is a test
So the issue with the example in the reverted commit is that
there is no folding white space in "bar,baz", so it's not valid
to split it.
These are valid:
Subject: Foo bar,baz
but splitting "bar,baz" into "bar,\n baz" is not valid.
What then is correct unfolding behaviour? Quoting the RFC again:
The process of moving from this folded multiple-line representation
of a header field to its single line representation is called
"unfolding". Unfolding is accomplished by simply removing any CRLF
that is immediately followed by WSP. Each header field should be
treated in its unfolded form for further syntactic and semantic
In other words, the unfolding rule requires you to strip the CRLF,
but it does not permit you to strip the WSP. Indeed, if "bar,\n baz"
is received, the correct unfolding is "bar, baz".
If you do strip the WSP, you end up mashing words together, such
as in https://patchwork.ozlabs.org/patch/1097852/
So revert the commit, restoring original behaviour, but keep a
corrected version of the test.
This presents a big question though: how did Rob's email up with
a mangled subject line?
To answer this question, you end up having to learn about OzLabs
Patchwork and how it differs from Patchwork the project.
OzLabs Patchwork (patchwork.ozlabs.org) is an installation of
Patchwork. Part of what makes it so useful for so many projects is
a little intervening layer that can massage some mail to make it
end up in the right project. Email that lands in the device tree
project is an example of email that goes through this process.
I only learned about this today and I haven't looked in any detail
at precisely what is done to the mail. The script is not part of the
This intervening filter is a Python script that runs - and this
is an important detail - in Python 2.7.
Ignoring all the details, the filter basically operates in a pipe
between the mail program and patchwork's parsemail, like
(mail from system) | filter.py | parsemail
At it's very simplest, filter.py acts as follows:
mail = email.parse_from_file(sys.stdin)
Fascinatingly, if you take Rob's email from #197 and put it through
this process, you can see that it is getting mangled:
Subject: [PATCH v2 3/4] dt-bindings: sound: wm8994: document wlf,csnaddr-pd property
Subject: [PATCH v2 3/4] dt-bindings: sound: wm8994: document wlf,
You can see that python27 has incorrectly wrapped the header, breaking
where there is not a foldable space. Python3 does not have this issue.
- part of the magic of OzLabs PW is a filter to make sure mail gets
to the right place. This isn't part of the Patchwork project and
so is usually invisible to patchwork developers.
- the filter is written in python27. The email module in py27 has
a bug that incorrectly breaks subjects around commas within words.
- patchwork correctly unfolds those broken subjects with a space
after the comma.
- thr extra space was interpreted as a bug in patchwork, leading to
a misinterpretation of the spec to strip out the whitespace that
was believed to be in error.
- that broke other wrapped subjects.
To solve this, revert the commit and I'll work with jk to get the
filter script into py3 compatibility. (Given that py27 sunsets in
~7mo, trying to fix it is not worth it.)
patchwork/parser.py | 1 -
patchwork/tests/test_parser.py | 2 +-
releasenotes/notes/issue-197-4f7594db1e4c9887.yaml | 9 +++++----
3 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/patchwork/parser.py b/patchwork/parser.py
index 712780a498c4..91e9920c8782 100644
@@ -47,7 +47,6 @@ class DuplicateMailError(Exception):
- value = ''.join(re.split(r'\n\s+', value))
whitespace_re = re.compile(r'\s+')
return whitespace_re.sub(' ', value).strip()
diff --git a/patchwork/tests/test_parser.py b/patchwork/tests/test_parser.py
index ddbcf5b15a19..f18220298078 100644
@@ -838,7 +838,7 @@ class SubjectTest(TestCase):
self.assertEqual(clean_subject("[PATCH] meep \n meep"),
('meep meep', ))
self.assertEqual(clean_subject("[PATCH] meep,\n meep"),
- ('meep,meep', ))
+ ('meep, meep', ))
self.assertEqual(clean_subject('[PATCH RFC] meep'),
('[RFC] meep', ['RFC']))
diff --git a/releasenotes/notes/issue-197-4f7594db1e4c9887.yaml b/releasenotes/notes/issue-197-4f7594db1e4c9887.yaml
index 2777fbc2f85b..41b86c064b8a 100644
@@ -1,7 +1,8 @@
- Long headers can be wrapped using CRLF followed by WSP (whitespace). This
- whitespace was not being stripped, resulting in errant whitespace being
- saved for the patch subject. This is resolved though existing patches and
- cover letters will need to be updated manually.
+ Long headers can be wrapped using CRLF followed by WSP (whitespace). There
+ was an incorrect fix that would lead to whitespace being stripped where it
+ shouldn't be, resulting in words being stuck together (likethis). This is
+ resolved, though existing patches and cover letters will need to be
+ updated manually.
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