hooks: Fix flaky test on MacOS
We have observed intermittent failures on
TestServer_PackObjectsHook_separateContext on our MacOS runners. The
error occurs ~10% of the time on MacOS, but has been completely
unreproducible on Linux.
This appears to be a long-standing issue with FreeBSD, dating back to
2005, which MacOS has inherited. Unix domain sockets that are closed
after a partial read may return ENOTCONN when read, instead of EPIPE as seen
on Linux. This is exactly the scenario performed in this test.
Using the original reproduction script provided in the linked bug
report, the ENOTCONN issue occurs ~10% of the time, matching Gitaly's
failure rate.
Given that this functionality works as expected on Linux and the OS
itself is what is non-deterministic, the simplest fix is to accept
either EPIPE or ENOTCONN when on MacOS. We are forced to check for
the expected error string instead of errors.Is(err, syscall.ENOTCONN)
as the syscall information is lost when the error is returned over gRPC to the test
program.
Closes #4806 (closed)