gh-148192: Fix Generator._make_boundary behavior with CRLF line endings. by henryivesjones · Pull Request #148193 · python/cpython

henryivesjones · 2026-04-07T02:21:26Z

The Generator._make_boundary regex does not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending.

Issue: #148192

Issue: email.generator.Generator does not correctly identify a boundary phrase when using CRLF line endings. #148192

The Generator._make_boundary regex does not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending.

python-cla-bot · 2026-04-07T02:21:37Z

All commit authors signed the Contributor License Agreement.

henryivesjones · 2026-04-07T03:21:30Z

The failing test seems to just be flaky? I ran just that one test 4 times and 2 passed and 2 failed.

cpython % ./python.exe -m test -j 14 test_perf_profiler
Raised RLIMIT_NOFILE: 256 -> 1024
Using random seed: 1400475968
0:00:00 load avg: 4.26 Run 1 test in parallel using 1 worker process
0:00:00 load avg: 4.26 [1/1] test_perf_profiler passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 394 ms
Total tests: run=14 skipped=5
Total test files: run=1/1
Result: SUCCESS
cpython % ./python.exe -m test -j 14 test_perf_profiler
Raised RLIMIT_NOFILE: 256 -> 1024
Using random seed: 1646608690
0:00:00 load avg: 4.26 Run 1 test in parallel using 1 worker process
0:00:00 load avg: 4.26 [1/1/1] test_perf_profiler failed (1 failure)
test test_perf_profiler failed -- Traceback (most recent call last):
  File "/Users/hjones/git/forks/cpython/Lib/test/test_perf_profiler.py", line 145, in test_trampoline_works_with_forks
    self.assertEqual(process.returncode, 0)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 11 != 0


== Tests result: FAILURE ==

1 test failed:
    test_perf_profiler

Total duration: 393 ms
Total tests: run=14 failures=1 skipped=5
Total test files: run=1/1 failed=1
Result: FAILURE
cpython % ./python.exe -m test -j 14 test_perf_profiler
Raised RLIMIT_NOFILE: 256 -> 1024
Using random seed: 2888117323
0:00:00 load avg: 3.52 Run 1 test in parallel using 1 worker process
0:00:00 load avg: 3.52 [1/1/1] test_perf_profiler failed (1 failure)
test test_perf_profiler failed -- Traceback (most recent call last):
  File "/Users/hjones/git/forks/cpython/Lib/test/test_perf_profiler.py", line 145, in test_trampoline_works_with_forks
    self.assertEqual(process.returncode, 0)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 11 != 0


== Tests result: FAILURE ==

1 test failed:
    test_perf_profiler

Total duration: 388 ms
Total tests: run=14 failures=1 skipped=5
Total test files: run=1/1 failed=1
Result: FAILURE
cpython % ./python.exe -m test -j 14 test_perf_profiler
Raised RLIMIT_NOFILE: 256 -> 1024
Using random seed: 164762511
0:00:00 load avg: 3.52 Run 1 test in parallel using 1 worker process
0:00:00 load avg: 3.52 [1/1] test_perf_profiler passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 388 ms
Total tests: run=14 skipped=5
Total test files: run=1/1
Result: SUCCESS

bitdancer · 2026-04-11T14:33:35Z

Lib/test/test_email/test_generator.py

+            msg = MIMEMultipart()
+            msg.attach(MIMEText(boundary_in_part))
+            self.genclass(self.ioclass()).flatten(msg, linesep=linesep)
+            # .0 is appended if the boundary was found.


Let's be verbose and enhance this comment a bit to make things clearer. How about "Generator checks the message content for the string it is about to use as a boundary ('token' in this test) and when it finds it in our attachment appends .0 to make the boundary it uses unique."

bitdancer · 2026-04-11T14:33:36Z

Misc/NEWS.d/next/Library/2026-04-07-14-13-40.gh-issue-148192.34AUYQ.rst

@@ -0,0 +1,2 @@
+``email.generator.Generator._make_boundary`` now correctly finds the
+boundary when using CRLF linesep.


This description more about the bugfix implementation than the bug. How about "could fail to detect a duplicate boundary string if linesep was not \n. It now correctly detects boundary strings when linesep is \r\n as well."

And, having written that, it occurs to me we could have the same bug if linesep were set to something exotic. Which shouldn't be a problem in practice, but then, neither is this bug ;) I'm sure non-standard linesep would reveal lots of other bugs in the code in that regard as well, though, so let's just ignore that potential issue.

bedevere-app · 2026-04-11T14:33:53Z

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

…enerator-crlf-boundary

henryivesjones · 2026-04-13T22:11:30Z

I have made the requested changes; please review again

bedevere-app · 2026-04-13T22:11:37Z

Thanks for making the requested changes!

@bitdancer: please review the changes made to this pull request.

miss-islington-app · 2026-04-14T13:11:05Z

Thanks @henryivesjones for the PR, and @bitdancer for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

miss-islington-app · 2026-04-14T13:11:07Z

Thanks @henryivesjones for the PR, and @bitdancer for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

… endings. (pythonGH-148193) The Generator._make_boundary regex did not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending. (cherry picked from commit 4af46b4) Co-authored-by: Henry Jones <44321887+henryivesjones@users.noreply.github.com>

bedevere-app · 2026-04-14T13:11:14Z

GH-148549 is a backport of this pull request to the 3.13 branch.

… endings. (pythonGH-148193) The Generator._make_boundary regex did not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending. (cherry picked from commit 4af46b4) Co-authored-by: Henry Jones <44321887+henryivesjones@users.noreply.github.com>

bedevere-app · 2026-04-14T13:11:18Z

GH-148550 is a backport of this pull request to the 3.14 branch.

…e endings. (GH-148193) (#148550) The Generator._make_boundary regex did not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending. (cherry picked from commit 4af46b4) Co-authored-by: Henry Jones <44321887+henryivesjones@users.noreply.github.com>

…e endings. (GH-148193) (#148549) The Generator._make_boundary regex did not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending. (cherry picked from commit 4af46b4) Co-authored-by: Henry Jones <44321887+henryivesjones@users.noreply.github.com>

Fix Generator._make_boundary behavior with CRLF line endings.

2dfdcb6

The Generator._make_boundary regex does not match on boundary phrases correctly when using CRLF line endings due to re.MULTILINE not considering \r\n as a line ending.

henryivesjones requested a review from a team as a code owner April 7, 2026 02:21

bedevere-app bot added the awaiting review label Apr 7, 2026

bedevere-app bot mentioned this pull request Apr 7, 2026

email.generator.Generator does not correctly identify a boundary phrase when using CRLF line endings. #148192

Closed

remove :func: on blurb

540b8d9

bitdancer requested changes Apr 11, 2026

View reviewed changes

bedevere-app bot added awaiting changes and removed awaiting review labels Apr 11, 2026

henryivesjones added 2 commits April 14, 2026 08:18

Update comments/blurb

5727398

Merge branch 'main' of https://github.com/python/cpython into email-g…

e1c6a13

…enerator-crlf-boundary

henryivesjones force-pushed the email-generator-crlf-boundary branch from 848427a to e1c6a13 Compare April 13, 2026 20:34

bedevere-app bot removed the awaiting changes label Apr 13, 2026

henryivesjones requested a review from bitdancer April 13, 2026 22:11

bedevere-app bot added the awaiting change review label Apr 13, 2026

bitdancer approved these changes Apr 14, 2026

View reviewed changes

bedevere-app bot added awaiting merge and removed awaiting change review labels Apr 14, 2026

bitdancer merged commit 4af46b4 into python:main Apr 14, 2026
59 of 62 checks passed

bedevere-app bot removed the awaiting merge label Apr 14, 2026

bitdancer added needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes labels Apr 14, 2026

bedevere-app bot removed the needs backport to 3.13 bugs and security fixes label Apr 14, 2026

bedevere-app bot removed the needs backport to 3.14 bugs and security fixes label Apr 14, 2026

		@@ -0,0 +1,2 @@
		``email.generator.Generator._make_boundary`` now correctly finds the
		boundary when using CRLF linesep.

Uh oh!

Conversation

henryivesjones commented Apr 7, 2026 • edited by bedevere-app bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

python-cla-bot bot commented Apr 7, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

henryivesjones commented Apr 7, 2026

Uh oh!

bitdancer Apr 11, 2026

Choose a reason for hiding this comment

Uh oh!

henryivesjones Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

bitdancer Apr 11, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

henryivesjones Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

bedevere-app bot commented Apr 11, 2026

Uh oh!

henryivesjones commented Apr 13, 2026

Uh oh!

bedevere-app bot commented Apr 13, 2026

Uh oh!

Uh oh!

miss-islington-app bot commented Apr 14, 2026

Uh oh!

miss-islington-app bot commented Apr 14, 2026

Uh oh!

bedevere-app bot commented Apr 14, 2026

Uh oh!

bedevere-app bot commented Apr 14, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

henryivesjones commented Apr 7, 2026 •

edited by bedevere-app bot

Loading

python-cla-bot bot commented Apr 7, 2026 •

edited

Loading

bitdancer Apr 11, 2026 •

edited

Loading