Safer socket

[kazu-yamamoto]

socket closes the file descriptor on exception.
This should fix #166 in master.

[eborden]

I like the improvement in readability of moving the ifdefs to where.

[eborden]

Should these be closing and throwing? Otherwise socket will return a Socket that has already been closed and file descriptor re-use by the OS could lead to us accidentally sending to an unknown socket.

[eborden]

Actually reuse is not an issue here since close changes it to -1, but is above with using vanilla c_close.

[eborden]

Won't this result in a Socket with a closed file descriptor within its IORef?

[eborden]

Woops, ignore the issues above. onException is fine here, since it isn't catching anything, but just a flavor of bracket.

[eborden]

Actually I'm not sure. onException is defined as:

onException :: IO a -> IO b -> IO a
onException io what = io `catch` \e -> do _ <- what
                                          throwIO (e :: SomeException)

Is that sufficient to prevent async exceptions from causing file descriptors leaking? It seems we might want to utilize bracketOnError to ensure masking and do something like:

    bracketOnError create c_close $ \fd -> do
        setNonBlock fd
        s <- mkSocket fd
        unsetIPv6Only s
        return s
  where
    create =
        c_stype <- modifyFlag <$> packSocketTypeOrThrow "socket" stype
        throwSocketErrorIfMinus1Retry "Network.Socket.socket" $
                  c_socket (packFamily family) c_stype protocol

[kazu-yamamoto]

@eborden My code is safe only for synchronous exceptions while your code is safe even for asynchronous exceptions! Also, close is not necessary to close Socket since it is not managed by the IO manager yet. No deadlock here.

OK. I will adopt your code. Thank you for your suggestion!

[kazu-yamamoto]

Rebased and merged.