warp terminates silently

[agrafix]

On a system I've observed that a web server application written using warp sometimes terminates with exit code 0 for 'no reason'. After some debugging, I noticed that it ran out of file descriptors. The problem lies here:

wai/warp/Network/Wai/Handler/Warp/Run.hs

Lines 224 to 253 in c6a542c

	acceptLoop = do
	-- Allow async exceptions before receiving the next connection maker.
	allowInterrupt
	-- acceptNewConnection will try to receive the next incoming
	-- request. It returns a /connection maker/, not a connection,
	-- since in some circumstances creating a working connection
	-- from a raw socket may be an expensive operation, and this
	-- expensive work should not be performed in the main event
	-- loop. An example of something expensive would be TLS
	-- negotiation.
	mx <- acceptNewConnection
	case mx of
	Nothing -> return ()
	Just (mkConn, addr) -> do
	fork set mkConn addr app counter ii0
	acceptLoop
	acceptNewConnection = do
	ex <- try getConnMaker
	case ex of
	Right x -> return $ Just x
	Left e -> do
	let eConnAborted = getErrno eCONNABORTED
	getErrno (Errno cInt) = cInt
	if ioe_errno e == Just eConnAborted
	then acceptNewConnection
	else do
	settingsOnException set Nothing $ toException e
	return Nothing

. With the default configuration, the exception is NOT logged and the runLoop simply terminates. I think it should always log the expection in default configuration if the server terminates. (Maybe even rethrow?)

[snoyberg]

Reading through that code, shouldn't settingsOnException be able to print the exception?

[agrafix]

Yes, but I think the default defaultOnException with defaultShouldDisplayException misses the out of file descriptors exceptions and thus does not print it

[snoyberg]

Here's the relevant code:

https://www.stackage.org/haddock/lts-7.14/warp-3.2.9/src/Network.Wai.Handler.Warp.Settings.html#defaultShouldDisplayException

Which of those clauses is catching the out of file descriptors exception?