hGetContents puts the handle in semi-closed state and reads until there is nothing left to read. Hence you have a deadlock. Use hGetLine in "cli".

Sylvain

2014-05-21 9:15 GMT+02:00 yang.zhao <hckjsnzf@gmail.com>:

omg, i test it on Windows, it's ok now. GHC is 7.6.3.
i really don't konw why this happen..

but there is another question on Windows

main = withSocketsDo $ do
    s <- listenOn $ PortNumber $ fromIntegral port
    putStrLn "Listening..."
    (h, _, _) <- accept s
    putStrLn "After accept"
    sline <- hGetLine h

    putStrLn $ "get line from handle"++sline
    hPutStrLn h "xxxx...."
    putStrLn "send first done"
   
    --second recv
    slinea <- hGetLine h
    putStrLn $ "get line from handle"++slinea

    hPutStrLn h "yyyy....."
    putStrLn "send second done"

    threadDelay 1000000
--
cli:

main = withSocketsDo $ do
    h <- connectTo "127.0.0.1" $ PortNumber $ fromIntegral port
    putStrLn "After connect"

    hPutStrLn h "xxx"
    putStrLn "put first to handle done"

    bs <- hGetContents h
    putStrLn "read from handle done "
    putStrLn bs

    --second send
    hPutStrLn h "yyy"
    putStrLn "put second to handle done"
    bfs <- hGetContents h

    putStrLn "read from handle done "
    putStrLn bs
 

the second send and recv is blocking...
server's output:
Listening...
After accept
get line from handlexxx
send first done

client's output:
After connect
put first to handle done
read from handle done
xxx....


..... T_T

2014-05-21 14:10 GMT+08:00 yang.zhao <hckjsnzf@gmail.com>:

Here's my new code:

$ cat serv.hs

import Control.Concurrent
import System.IO
import Network

port :: Int
port = 1234

main :: IO ()
main = withSocketsDo $ do
    s <- listenOn $ PortNumber $ fromIntegral port

    putStrLn "Listening..."

    (h, _, _) <- accept s

    putStrLn "After accept"
    sline <- hGetLine h
    putStrLn "get line from handle"

    hPutStrLn h sline
    putStrLn $ "send "++sline
    threadDelay 1000000

    hClose h
    sClose s

--------
$ cat clie.hs

import System.IO
import Network

port :: Int
port = 1234

main :: IO ()
main = withSocketsDo $ do

    h <- connectTo "127.0.0.1" $ PortNumber $ fromIntegral port
    putStrLn "After connect"
    hPutStrLn h "hello"
    putStrLn "put hello to handle done"
    bs <- hGetContents h
    putStrLn "read from handle done"
    putStrLn bs
    hClose h


===
one terminal, run ./serv, then run ./clie in another terminal. Output is :

$ ./serv
Listening...
After accept

$ ./clie
After connect
put hello to handle done
read from handle done


it seems that client has read from then handle, but donesn't read anything, then block.
and server donesn't receive anything, still wait for something...

ghc version is 7.4.1, because of this?..

2014-05-21 13:57 GMT+08:00 Bob Ippolito <bob@redivi.com>:

Not sure why you're having issues, I just tried it on GHC 7.6.3 on Fedora 20 and it worked fine there as well (both with runhaskell or compiled with -O).

I might start adding putStrLn statements to the code to see where it's unexpectedly blocking, or perhaps use 127.0.0.1 instead of "localhost" in case the issue is a DNS misconfiguration.

On Tue, May 20, 2014 at 10:51 PM, yang.zhao <hckjsnzf@gmail.com> wrote:

thanks for your replay.
i run the two program in two different teriminal for sure.

it works for you?
but why can't run well on my computer.

make me creazy....

2014-05-21 13:47 GMT+08:00 Bob Ippolito <bob@redivi.com>:

How precisely are you trying to run the client? Are you typing it in to the same terminal? If so, then the client is never actually started, because when you type ./cli the input is going to ./serv and not the shell. Try running the client in a separate terminal.

It works for me here on Mac OS X 10.9.2 with GHC 7.8.2.

On Tue, May 20, 2014 at 10:42 PM, yang.zhao <hckjsnzf@gmail.com> wrote:

hi guys,
I'm newbie, just begin to learn Haskell.
now i write a very simple server and client .

Server:
import Control.Concurrent 
import System.IO          
import Network            
                          
port :: Int               
port = 1234               
                          
main :: IO ()             
main = withSocketsDo $ do 
    s <- listenOn $ PortNumber $ fromIntegral port
    (h, _, _) <- accept s 
                          
    sline <- hGetLine h   
    hPutStrLn h sline     
    putStrLn $ "send "++sline
    threadDelay 1000000   
                          
    hClose h              
    sClose s

Client :
import System.IO
import Network
 
port :: Int
port = 1234
 
main :: IO ()
main = withSocketsDo $ do
    h <- connectTo "localhost" $ PortNumber $ fromIntegral port
    hPutStrLn h "hello"
    bs <- hGetContents h
    putStrLn bs
    hClose h
 

And, it doesn't work now . I run ./serv , then run ./cli , they will block all the time.
but,  when i run ./serv, and telnet localhost 1234 in another terminal, it works fine.
so i don't know what's the wrong with my code.
anybody can tell me about my problem?

os is Debian 7,  haskell-platform  2012.2.0.0

thanks a lot!!!
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