Handle request processes exits that get sent exit signal

[hubertlepicki]

When a web request is being processes by Cowboy, and the request handling process get sent exit signal (as in with exit/2), it seems like the process is silently crashing without reporting anything to the logger.

It looks like Cowboy handles exits of these processes here using try/catch clause:

https://github.com/ninenines/cowboy/blob/master/src/cowboy_stream_h.erl#L289-L300

But it does only work if process exits on it's own. When it is being sent exit signal, it's not.

This is because the process is not trapping exits, and even that wouldn't catch all signals, i.e. kill wouldn't get detected.

I have to detect these exits, and I am currently doing that by setting up a monitor.

I am just wondering if that is not something Cowboy would want to be doing internally? Since it catches exits of these processes if they exit with exit/1, maybe it makes sense to add functionality to catch abnormal exits when these processes are sent a signal with exit/2 too?

[essen]

What you linked to is only to add the stacktrace to exit reasons. The actual handling is at https://github.com/ninenines/cowboy/blob/master/src/cowboy_stream_h.erl#L127-L156

You are correct that it's missing a more general clause.

[hubertlepicki]

Right, so it's probably missing the clause of

info(StreamID, Exit={'EXIT', Pid, Reason})

Want me to give it a shot with a PR?

[essen]

Sure.

[hubertlepicki]

I have created a PR. There's at least one issue with it (silencing crashes in tests that I don't know how to do properly). Other than that it seems to resolve the issue at least on my app.

[essen]

Done for Cowboy 2.13. Closing, thanks!!

[hubertlepicki]

Awesome @essen this is still relevant to me so I'll pass that on to the team that's currently monitoring this with custom implementation. Thank you so much!