Re: Network problem with ghc on WinXP

29 Jan 2004


      Works like a charm now :)
Thank you for the insight.
Robin.
...
Hi there,
looks like a network byte-order vs host byte-order gotcha.
Never use the PortNum constructor, but declare 'portnum'
to have type PortNumber and simply drop the use of PortNum
in your code alltogether. Alternatively, use intToPortNumber
to translate between Int and PortNumber.
hth
--sigbjorn
----- Original Message ----- 
From: "robin abraham" 
To: 
Sent: Wednesday, January 28, 2004 21:57
Subject: Network problem with ghc on WinXP
...
Hi,
I have ghc-6.0.1 on WinXP and Solaris. I have a simple echo server
(server.hs
given below) and client (client.hs given below) and I encounter the
following:
1) server.hs compiled and running on Solaris:
   a) client.hs (Solaris) can connect.
   b) client.hs (WinXP) cannot connect.
   c) telnet (WinXP) can connect.
   d) telnet (Solaris) can connect.
   e) Scan of port 3000 shows server is listening.
2) server.hs compiled and running on WinXP:
   a) client.hs (Solaris) cannot connect.
   b) client.hs (WinXP) can connect.
   c) telnet (WinXP) cannot connect.
   d) telnet (Solaris) cannot connect.
   e) Scan of ports does not show server.
Basically, when the server is running on WinXP, only the Haskell program
client.hs (also running on the same WinXP machine) can "converse" with it
through the socket connection. To verify this, I wrote a client in C# -
from the
WinXP machine, it can connect to server running on my Solaris machine but
not to
server on the same WinXP machine.
Why isn't the server program on WinXP not behaving itself? Any
help/guidance
would be highly appreciated.
Thank you.
Robin.
-- server.hs
module Main where
import SocketPrim
import Concurrent
import System (getArgs,exitFailure)
import Exception(finally)
import MVar
import IO
server_sock :: IO (Socket)
server_sock = do
    s <- socket AF_INET Stream 6
    setSocketOption s ReuseAddr 1
    bindSocket s (SockAddrInet (PortNum portnum) iNADDR_ANY)
    listen s 2
    return s
echo_server :: Socket -> IO ()
echo_server s = do
    (s', clientAddr) <- accept s
    h <- socketToHandle s' ReadWriteMode
    proc <- read_data s' 0
    putStrLn ("server processed "++(show proc)++" bytes")
    sClose s'
    where
        read_data sock totalbytes = do
            str <- recv sock 18
            putStrLn ("Server recv: " ++ str)
            if ((length str) >= 18)
                then do
                    putStrLn ("Server read: " ++ str)
                    writ <- send sock str
                    putStrLn ("Server wrote: " ++ str)
                    read_data sock $! (totalbytes+(length $! str))
                else do
                    putStrLn ("server read: " ++ str)
                    return totalbytes
message     = "Hello there sailor"
portnum     = 3000
main = withSocketsDo $ do {
    ~[n] <- getArgs;
    ssock <- server_sock;
    s <- myForkIO (echo_server ssock);
    join s;
    putStrLn "join s";
    }
myForkIO :: IO () -> IO (MVar ())
myForkIO io = do
    mvar <- newEmptyMVar
    forkIO (io `finally` putMVar mvar ())
    return mvar
join :: MVar () -> IO ()
join mvar = readMVar mvar
-- end of server.hs
-- ***********************************************
-- client.hs
module Main where
import SocketPrim
import Concurrent
import System (getArgs,exitFailure)
import Exception(finally)
import MVar
import IO
local       = "128.193.39.108"
message     = "Hello there sailor"
portnum     = 3000
client_sock = do
    s <- socket AF_INET Stream 6
    ia <- inet_addr local
    connect s (SockAddrInet (PortNum portnum) ia)
    return s
echo_client n = do
    s <- client_sock
    drop <- server_echo s n
    sClose s
    where
        server_echo sock n = if n > 0
            then do
                send sock message
                putStrLn ("Client wrote: " ++ message)
                str <- recv sock 19
                if (str /= message)
                    then do
                        putStrLn ("Client read error: " ++ str)
                        exitFailure
                    else do
                        putStrLn ("Client read success")
                        server_echo sock (n-1)
            else do
                putStrLn "Client read nil"
                return []
main = withSocketsDo $ do
    ~[n] <- getArgs
    c <- myForkIO (echo_client (read n::Int))
    join c
    putStrLn "join c"
myForkIO :: IO () -> IO (MVar ())
myForkIO io = do
    mvar <- newEmptyMVar
    forkIO (io `finally` putMVar mvar ())
    return mvar
join :: MVar () -> IO ()
join mvar = readMVar mvar
-- end of client.hs