When WSGIRequestHandler catches socket.error it silences all other OSErrors in Python 3

[davidism]

Reported at pallets/flask#1995. WSGIRequestHander.run_wsgi catches socket.error to silence client disconnects. In Python 2 this was fine, because socket.error was unique. In Python 3, socket.error is OSError, so any OSError or subclass (IOError, etc.) is also silenced.

Possible solution is to check if e.errno is a disconnect-related error and bubble the error up otherwise. Or catch a more specific error such as ConnectionError in Python 3.

This only affects Werkzeug's dev server, other WSGI servers like Gunicorn do not exhibit this behavior.

[mitsuhiko]

I feel like we had this before. I thought we fixed this somewhere already.

[davidism]

It was reported against Flask and we discussed it there, but it's a bug against Werkzeug so I moved it here. Maybe that's what you're remembering? pallets/flask#1995

[aaossa]

Can I work on this? If so, any suggestion/advice to begin with that consideration?

[untitaker]

@aaossa I'm not sure what you mean with "that consideration". One possible approach to this issue is described in the OP

[aaossa]

With "that consideration" I meant the suggestion/advice I was asking for. I'll give it a try.

[aaossa]

I have a possible solution here, should I create a test? @untitaker

[davidism]

I haven't looked at this in a while, but type(e) is socket.error is the same issue we're talking about here: it's not a distinct error on py3. This looks like it just moved the check around, it didn't change the logic.

[aaossa]

I though that the problem was using except (socket.error ... because it uses isinstance instead of type and that caused the problems in error handling, because isinstance check subclasses and type does not.

EDIT: I tried the example from the original issue and worked without problems, but I haven't tested with a "pure" socket.error.

[davidism]

isinstance is the same as type is in this case, because socket.error = OSError.

[aaossa]

Then maybe use something like:

# (Not valid syntax)
except socket.timeout, _:
    # ...
except socket.error, exc:
    print("Caught exception socket.error : " + str(exc))

and check the error code (using errno) like this should work? I'm trying to find the errno for socket.error

[davidism]

That's what I said at the top. Also, you're using really old syntax for catching errors there.