Simple unix domain sockets server - haskell

Question

I'm new to trying to program with Unix sockets, and struggling to get a simple server working. I'd like this to stay running and print messages it receives, but instead it prints the first message and exits. Depends on network, and bytestring.
module Main where
import Network.Socket hiding (send, sendTo, recv, recvFrom)
import Network.Socket.ByteString
import qualified Data.ByteString.Char8 as C
import Control.Monad
main :: IO ()
main = withSocketsDo $ do
sock <- socket AF_UNIX Stream 0 -- and try UDP?
bind sock (SockAddrUnix "/tmp/test_sock.ipc")
listen sock maxListenQueue -- TODO is maxListenQueue what we want?
(conn, _) <- accept sock
talk conn
close conn
close sock
putStrLn "DONE"
where
talk :: Socket -> IO ()
talk conn =
do msg <- recv conn 1024
unless (C.null msg) $ do
C.putStrLn msg
talk conn
I'm testing with socat, which I also don't really know how to use:
echo "FOOOOO" | socat - UNIX-CONNECT:/tmp/test_sock.ipc
Any pointers on the haskell code, and what I might be misunderstanding about unix sockets would be helpful.
EDIT Using Datagram instead of Stream I'm able to get more or less what I want:
main :: IO ()
main = withSocketsDo $ do
sock <- socket AF_UNIX Datagram 0 -- and try UDP?
bind sock (SockAddrUnix "/tmp/test_sock.ipc")
-- for Datagram:
talk sock
close sock
putStrLn "DONE"
where
talk :: Socket -> IO ()
talk conn =
do msg <- recv conn 1024
unless (C.null msg) $ do
C.putStrLn msg
talk conn
And I can test successfully with:
echo "FOOOOO" | socat - UNIX-SENDTO:/tmp/test_sock.ipc
I think I'm interested in datagram sockets anyway, but I'll leave this open if anyone wants to explain things to me.

Answer 1

Your code only runs "accept" once, so it can only handle one connection. If you want to handle multiple connections, the "accept" part has to be repeated, not just the "recv" part.
module Main where
import Network.Socket hiding (send, sendTo, recv, recvFrom)
import Network.Socket.ByteString
import qualified Data.ByteString.Char8 as C
import Control.Monad
main :: IO ()
main = withSocketsDo $ do
sock <- socket AF_UNIX Stream 0 -- and try UDP?
bind sock (SockAddrUnix "/tmp/test_sock.ipc")
listen sock maxListenQueue -- TODO is maxListenQueue what we want?
go sock
close conn
close sock
putStrLn "DONE"
where
go sock = do
(conn,_) <- accept sock
talk conn
go sock
talk :: Socket -> IO ()
talk conn =
do msg <- recv conn 1024
unless (C.null msg) $ do
C.putStrLn msg
talk conn