Re: Network.Socket endian problem?

13 Dec 2006

      Rich Neswold wrote:
...
On 12/13/06, Thorkil Naur  wrote:
...
I am not an expert on sockets, but I have both a Linux installation
and a PPC
Mac OS X 10.4 with both ghc-6.4.1 and ghc-6.6. So if you allow me some
additional details (such as complete program texts), perhaps I can
perform
some useful experiments under your conductance.
I can reproduce it with the following:
...
module Main
   where
import Control.Exception
import Network.Socket
import System.IO
allocSocket :: IO Socket
allocSocket =
    do { s <- socket AF_INET Datagram 0
       ; handle (\e -> sClose s >> throwIO e) $
                do { connect s (SockAddrInet 6802 0x7f000001)
                   ; return s
                   }
       }
main :: IO ()
main = withSocketsDo $ do { s <- allocSocket
                          ; getChar
                          ; sClose s
                          }
If you run the program on OSX, you can check the bound address while
it's waiting for a keystroke. Type "netstat -an -f inet | grep 6802"
to see. I get:
udp4       0      0  127.0.0.1.61704        127.0.0.1.6802
which is correct. When I run this program on Linux/i386, I get:
udp        0      0 (anonymized):33412    1.0.0.127:6802
ESTABLISHED
(I removed my IP address.) The second bound address, however, is
wrong: the octets are in the wrong order. Notice, though, that the
port number is correct!
Thanks for looking into this!
It does expect the address to be in network byte order instead of host
byte order, which is usually done using htons and htonl. This seems to
do what you want (running SUSE 10.1 on an Intel box):

{-# OPTIONS -fglasgow-exts #-}

module Main
   where

import Control.Exception
import Network.Socket
import System.IO
import Data.Word(Word32)

foreign import ccall unsafe "htonl" htonl :: Word32 -> Word32

allocSocket :: IO Socket
allocSocket =
    do { s <- socket AF_INET Datagram 0
       ; handle (\e -> sClose s >> throwIO e) $
                do { connect s (SockAddrInet 6802 (htonl 0x7f000001))
                   ; return s
                   }
       }

main :: IO ()
main = withSocketsDo $ do { s <- allocSocket
                          ; getChar
                          ; sClose s
                          }

The main change is with importing "htonl" to convert to the right byte
ordering (the other is adding the OPTIONS comment). I'm not that
familiar with GHC yet, so maybe there is something that does this that
is also available outside this module that I'm unaware of. It seems that
iNADDR_ANY uses this internally to get the proper address format. It
also looks like 6802 is converted into a PortNumber behind the scenes,
which involves using htons, making it correct on both machines.

Mark

Re: Network.Socket endian problem?

Mark Hills