net/http: TestClientCallsCloseOnlyOnce failures with "host has failed to respond" on Windows

[bcmills]

--- FAIL: TestClientCallsCloseOnlyOnce (21.04s)
    client_test.go:2063: dial tcp 127.0.0.1:51357: connectex: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
FAIL
FAIL	net/http	25.262s

greplogs --dashboard -md -l -e '(?m)FAIL: TestClientCallsCloseOnlyOnce.*\n.*host has failed to respond'

2021-11-05T22:03:24-035963c/windows-arm64-10
2020-12-23T02:10:51-b0b0d98/windows-arm-zx2c4

CC @neild

[neild]

cc @bufflig

This test creates 50 HTTP client connections, in sequence, to the same server. The error seems to indicate that one of them failed. I don't know what might cause this, but the fact that the failure has happened once in a year and only on Windows makes this hard to diagnose; I suspect it's an issue on the builder, but I don't know what. Something applying a rate limit to connection attempts?

Given the rarity of the failure, this is probably not a priority.

[bufflig]

I wonder if the fact that it happens on both arm 32 and 64 bit is significant? I agree that it seems really hard to diagnose when it happens this rarely. I can attempt to get it to happen with brute force running on my parallels VM, but I can not leave any guarantees of success.

[bcmills]

If the cause isn't easy to spot, I suggest that we give it a while to look for more occurrences. (I agree with Damien that this doesn't seem worth prioritizing at the moment.)