prototype of server and client successfully communicating via unconnected Datagram sockets

Hash2Pub/democlient.hs

@@ -0,0 +1,26 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import Network.Socket hiding (send, sendTo, recv, recvFrom)
+import Network.Socket.ByteString
+import Control.Monad (forever)
+import System.IO (
+        IOMode (ReadWriteMode)
+                 )
+import qualified Data.ByteString as BS
+import qualified Data.ByteString.UTF8 as BSU
+
+main = do
+    sock <- socket AF_INET6 Datagram defaultProtocol
+    -- lookup destination to get a SockAddr
+    let hints = defaultHints { addrFamily = AF_INET6, addrSocketType = Datagram}
+    destAddr <- addrAddress . head <$> getAddrInfo (Just hints) (Just "::1") (Just "7331")
+    forever $ do
+        inp <- getLine
+        sendTo sock (BSU.fromString inp) destAddr
+        print "Yeah, sent sth."
+        -- important: as the socket is unconnected, it also accepts replies from a different source port
+        (msg, fromAddr) <- recvFrom sock 65535
+        putStrLn $ "Woop, received " ++ show msg ++ " from " ++ show fromAddr
+    return ()

Hash2Pub/demoserver.hs

@@ -9,12 +9,12 @@ import Control.Exception
 import Control.Monad (forever)
 import System.IO (
         IOMode (ReadWriteMode)
-        , hPutStrLn
                  )
 import qualified Data.ByteString as BS
 
 main = do
     sock <- socket AF_INET6 Datagram defaultProtocol
+    -- lookup destination to get a SockAddr
     let hints = defaultHints { addrFamily = AF_INET6, addrSocketType = Datagram}
     serverAddr <- addrAddress . head <$> getAddrInfo (Just hints) (Just "::1") (Just "7331")
     print serverAddr
@@ -28,6 +28,7 @@ serveReceive :: (BS.ByteString, SockAddr) -> Socket -> IO ()
 serveReceive (msg, fromAddr) sendSocket = do
     print sendSocket
     putStrLn $ "Got message " ++ show msg ++ " from " ++ show fromAddr
+    -- important: as new socket sends from a different port, the receiving client must use an unconnected socket!
     sentBytes <- sendTo sendSocket ("Hi, thx for " `BS.append` msg) fromAddr
     putStrLn $ "sent response of " ++ show sentBytes ++ "bytes"
     return ()