net/http: nil pointer dereference panic for httputil.ReverseProxy users [1.22 backport]

[gopherbot]

@neild requested issue #53808 to be considered for backport to the next 1.22 minor release.

@gopherbot please open backport issues. This causes panics for ReverseProxy users, with no workaround.

[dmitshur]

We've discussed this candidate and are currently leaning towards rejection: this is an issue that has existed since at least Go 1.18, with difficulty in reliably reproducing it and not many users running into it. It appears the workaround of restarting the server when it does happen is working, even if it's suboptimal.

We should reconsider if a case can be made that this fix is low risk (i.e., the chance of it introducing a new, different bug is very low) and high reward, otherwise let's leave the fix to be available in Go 1.23.

[mdempsky]

Rejected as won't fix. @dmitshur mentions this caused a test to become flaky.