Bug in network library, uncaught exception when dealing with ipv6 sockets

[Thomas Hartman]

There is an uncaught exception in the network library which is causing
my HAppS demo website

http://happstutorial.com

to crash every couple of days. This has affected other people using
HAppS as well, as described on postings to the HAppS users list.

The bug, and workarounds, is described at

http://code.google.com/p/happs/issues/detail?id=40

This message is to suggest a fix for the issue.

The problem seems to me to be localized in the following bit of code,
from -- http://hackage.haskell.org/packages/archive/network/2.2.0.1/doc/html/src/Network.html#accept

***************************

#if defined(IPV6_SOCKET_SUPPORT)
accept sock@(MkSocket _ AF_INET6 _ _ _) = do

 (sock', addr) <- Socket.accept sock

 (Just peer, _) <- getNameInfo [] True False addr


 handle <- socketToHandle sock' ReadWriteMode
 (PortNumber port) <- socketPort sock'


 return (handle, peer, port)

#endif
***************************

The problem is that getNameInfo can give rise to an IO exception,
which should be caught at the library level. An exception IS caught at
the library level when fetching peer for ipv4 packets, as follows.
Since the code can never crash when fetching peer for ipv4 packets, it
seems to me it shouldn't be allowed to crash when fetching peer for
ipv6 packets either.

ip v4 packet code:

***************************
accept sock@(MkSocket _ AF_INET _ _ _) = do
 ~(sock', (SockAddrInet port haddr)) <- Socket.accept sock
 peer <- catchIO
	  (do 	
	     (HostEntry peer _ _ _) <- getHostByAddr AF_INET haddr
	     return peer
	  )
	  (\e -> inet_ntoa haddr)
		-- if getHostByName fails, we fall back to the IP address
 handle <- socketToHandle sock' ReadWriteMode
 return (handle, peer, port)
***************************

My suggestion for fixing for ipv6  is as follows, basically having
similar error catching as for ipv4.

***************************

#if defined(IPV6_SOCKET_SUPPORT)
accept sock@(MkSocket _ AF_INET6 _ _ _) = do
 (sock', addr@((SockAddrInet port haddr) )) <- Socket.accept sock
 (Just peer, _) <- catchIO ( getNameInfo [] True False addr )
                           (\e -> do peerAsIp <- inet_ntoa haddr
                                     return (Just peerAsIp, undefined))


 handle <- socketToHandle sock' ReadWriteMode
 (PortNumber port) <- socketPort sock'
 return (handle, peer, port)
#endif

***************************

Des this seem reasonable?

Of course, please advise if I should repost this issue to the ghc
bugtracker, or similar.

Thanks also to Matt Elder for being very generous with his time in
helping me diagnose this. And also thanks to the others on the
above-linked HAppS bug thread.

Thomas.