Tests fail with "OSError: AF_UNIX path too long" because socket paths exceed max length (107 bytes)

[cjntaylor]

Splitting apart into a separate PR

Unix socket tests were failing with OSError: AF_UNIX path too long. The paths generated by pytest's tmp_path_factory fixture on macOS exceed the system max socket path length.

On macOS, the unix socket path length limit is 107 bytes; the base temp directory of /private/var/folders combined with the subdirectories added by tmp_path_factory generates paths regularly exceeding this limit by 10+ bytes. Linux also has this limit (108 bytes), but because it's almost always rooted at /tmp or /var/tmp it's unlikely to trigger this error. These limits are discussed more here: python/cpython#93852

A simple workaround was to use tempdir.TemporaryDirectory for socket paths. Even on macOS, these paths are short enough that they shouldn't trigger this error, while still using standard tempdir conventions/locations.

I'm unsure why these path lengths aren't an issue on the macOS CI instances; it's very odd they're not. The only major difference I can find is that I'm running Ventura (macOS 13) vs the CI's Monterey (macOS 12); otherwise my pytest version matches up exactly. I also don't see anything in the pytest commit history indicating a change to how tmp_path_factory locations are generated.

[agronholm]

Out of curiosity, what kinds of paths are you getting from tmp_path_factory?

[cjntaylor]

Out of curiosity, what kinds of paths are you getting from tmp_path_factory?

They look like this:

/private/var/folders/0w/hxs339xd1jx78kt6gpy0b8_w0000gp/T/pytest-of-cjntaylor/pytest-80/unix50/socket
/private/var/folders/0w/hxs339xd1jx78kt6gpy0b8_w0000gp/T/pytest-of-cjntaylor/pytest-80/unix51/socket
/private/var/folders/0w/hxs339xd1jx78kt6gpy0b8_w0000gp/T/pytest-of-cjntaylor/pytest-80/unix52/socket
/private/var/folders/0w/hxs339xd1jx78kt6gpy0b8_w0000gp/T/pytest-of-cjntaylor/pytest-80/unix53/socket

These are short enough to not throw AF_UNIX errors. I must have run the tests enough to increase the counts enough to push the path past 107 bytes. Explains why the CI works - it's tearing down it's temp folder each run so those counts will never get that high

Up to you if you still think this is an issue; it's a little close for comfort for me but the average person would probably not run into it 🤷‍♂️

[agronholm]

Looks uncomfortably close to the limit still.