[3.12] gh-144125: email: verify headers are sound in BytesGenerator

[miss-islington]

(cherry picked from commit 052e55e)

Co-authored-by: Seth Michael Larson seth@python.org
Co-authored-by: Denis Ledoux dle@odoo.com
Co-authored-by: Denis Ledoux 5822488+beledouxdenis@users.noreply.github.com
Co-authored-by: Petr Viktorin 302922+encukou@users.noreply.github.com
Co-authored-by: Bas Bloemsaat 1586868+basbloemsaat@users.noreply.github.com

• Issue: Encode newlines in headers when using ByteGenerator #144125

[pablogsal]

LGTM

[encukou]

@webknjaz Hmm. Is this failure familiar?
The UI doesn't show any info:

But the downloadable logs contain:

Job is waiting for a hosted runner to come online.

2026-01-26T17:03:37.2490000Z Evaluating build-windows.if
2026-01-26T17:03:37.2490000Z Evaluating: (success() && (fromJSON(needs.build-context.outputs.run-windows-tests)))
2026-01-26T17:03:37.2490000Z Expanded: (true && true)
2026-01-26T17:03:37.2490000Z Result: true
2026-01-26T17:03:37.2490000Z Evaluating build-windows.arm64_false.build.if
2026-01-26T17:03:37.2490000Z Evaluating: success()
2026-01-26T17:03:37.2490000Z Result: true
2026-01-26T17:03:38.9380000Z Requested labels: windows-2022
2026-01-26T17:03:38.9380000Z Job defined at: python/cpython/.github/workflows/reusable-windows.yml@refs/pull/144188/merge
2026-01-26T17:03:38.9380000Z Reusable workflow chain:
2026-01-26T17:03:38.9380000Z python/cpython/.github/workflows/build.yml@refs/pull/144188/merge (615364956b0ea0a8353c2c5623362d88b20b1f48)
2026-01-26T17:03:38.9380000Z -> python/cpython/.github/workflows/reusable-windows.yml@refs/pull/144188/merge (615364956b0ea0a8353c2c5623362d88b20b1f48)
2026-01-26T17:03:38.9380000Z Waiting for a runner to pick up this job...
2026-01-26T17:03:39.8610000Z Job is about to start running on the hosted runner: GitHub Actions 1000510261
2026-01-26T17:03:39.8610000Z Job is waiting for a hosted runner to come online.

2026-01-26T17:03:43.2883707Z ##[error]Could not find a part of the path 'D:\a'.

[webknjaz]

@encukou not sure but sound like a problem with their runners. I've restarted them in debug mode to see if that exposes anything else.

The cancellation behavior is rather weird — sounds like something in the jobs failed, then GHA went ahead to cancel them citing those same jobs as the reason for cancellation. Usually, jobs in matrices are marked as failed when they fail and if there's fail-fast, other jobs are marked as cancelled. Maybe, normal failed state cleanup timed out and GHA was cancelling those as well. But this is just a speculation..

[webknjaz]

Oh.. I didn't notice this is an old branch. It's probably a good idea to diff the CI infra with main. This is one of the reasons I insist on backporting all the CI changes into all the branches.

[webknjaz]

So merging #144036 30 minutes ago failed. It's the last commit on the branch. Yesterday, everything was fine, though (when Pablo merged the target branch into that PR). So this is new.

[webknjaz]

Looking at https://github.com/actions/runner-images?tab=readme-ov-file#available-images, the last windows-2022 runner rebuild was on Jan 19, it seems.

[webknjaz]

Trying to restart jobs one at a time with debugging on.

[webknjaz]

Looks like Win32 is the problem.

[webknjaz]

Weird.. I've seen each of those jobs crashing flakily. But mostly when they ran in parallel. Now that I've restarted each individually, they seem to be running fine. Definitely a platform problem...

[webknjaz]

@encukou it's probably a good idea to complain to GH support unless it self-heals.

---

I've downloaded the logs from https://github.com/python/cpython/actions/runs/21365488062/job/61510137519 (DEBUG RUN!)

And they've got something similar:

$ cat 1_Windows\ _\ build\ and\ test\ \(Win32\).txt
2026-01-26T18:39:28.6558234Z ##[debug]Starting: Windows / build and test (Win32)
2026-01-26T18:39:28.6630888Z ##[error]Could not find a part of the path 'D:\a'.
2026-01-26T18:39:28.6637136Z ##[debug]System.IO.DirectoryNotFoundException: Could not find a part of the path 'D:\a'.
2026-01-26T18:39:28.6638073Z ##[debug]   at System.IO.FileSystem.CreateDirectory(String fullPath, Byte[] securityDescriptor)
2026-01-26T18:39:28.6638844Z ##[debug]   at System.IO.Directory.CreateDirectory(String path)
2026-01-26T18:39:28.6639798Z ##[debug]   at GitHub.Runner.Worker.JobRunner.RunAsync(AgentJobRequestMessage message, CancellationToken jobRequestCancellationToken)
2026-01-26T18:39:28.6655833Z ##[debug]Finishing: Windows / build and test (Win32)

$ cat Windows\ _\ build\ and\ test\ \(Win32\)/system.txt
2026-01-26T18:39:25.2470000Z Requested labels: windows-2022
2026-01-26T18:39:25.2470000Z Job defined at: python/cpython/.github/workflows/reusable-windows.yml@refs/pull/144188/merge
2026-01-26T18:39:25.2470000Z Reusable workflow chain:
2026-01-26T18:39:25.2470000Z python/cpython/.github/workflows/build.yml@refs/pull/144188/merge (615364956b0ea0a8353c2c5623362d88b20b1f48)
2026-01-26T18:39:25.2470000Z -> python/cpython/.github/workflows/reusable-windows.yml@refs/pull/144188/merge (615364956b0ea0a8353c2c5623362d88b20b1f48)
2026-01-26T18:39:25.2470000Z Waiting for a runner to pick up this job...
2026-01-26T18:39:25.2450000Z Evaluating build-windows.if
2026-01-26T18:39:25.2450000Z Evaluating: (success() && (fromJSON(needs.build-context.outputs.run-windows-tests)))
2026-01-26T18:39:25.2450000Z Expanded: (true && true)
2026-01-26T18:39:25.2450000Z Result: true
2026-01-26T18:39:25.2450000Z Evaluating build-windows.Win32_false.build.if
2026-01-26T18:39:25.2450000Z Evaluating: success()
2026-01-26T18:39:25.2450000Z Result: true
2026-01-26T18:39:25.7450000Z Job is waiting for a hosted runner to come online.
2026-01-26T18:39:25.7450000Z Job is about to start running on the hosted runner: GitHub Actions 1000510807

This one has a trace in debug ^

The runner diagnostic logs don't have anything interesting and also seem to only have the alls-green job details with Ubuntu paths inside and nothing about Windows.

Attaching the logs for history: logs_55453059899.zip.

[encukou]

Thanks for the investigation!

it's probably a good idea to complain to GH support unless it self-heals.

I'll keep an eye out for this happening again.

[webknjaz]

So merging #144036 30 minutes ago failed. It's the last commit on the branch. Yesterday, everything was fine, though (when Pablo merged the target branch into that PR). So this is new.

I've just restarted the failing jobs on that commit and it they didn't crash immediately: https://github.com/python/cpython/actions/runs/21366922074. So I think it's safe to say the flaky behavior is gone for now.