added pair listener thread

Assistant/Threads/PairListener.hs

@@ -0,0 +1,50 @@
+{- git-annex assistant thread to listen for incoming pairing traffic
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Assistant.Threads.PairListener where
+
+import Assistant.Common
+import Assistant.Pairing
+import Assistant.ThreadedMonad
+import Assistant.DaemonStatus
+import Assistant.Alert
+import Utility.Verifiable
+
+import Network.Multicast
+import Network.Socket
+
+thisThread :: ThreadName
+thisThread = "PairListener"
+
+pairListenerThread :: ThreadState -> DaemonStatusHandle -> NamedThread
+pairListenerThread st dstatus = thread $ withSocketsDo $ do
+	sock <- multicastReceiver (multicastAddress $ IPv4Addr undefined) pairingPort
+	forever $ do
+		msg <- getmsg sock []
+		dispatch $ readish msg
+	where
+		thread = NamedThread thisThread
+
+		getmsg sock c = do
+			(msg, n, _) <- recvFrom sock chunksz
+			if n < chunksz
+				then return $ c ++ msg
+				else getmsg sock $ c ++ msg
+			where
+				chunksz = 1024
+
+		dispatch Nothing = noop
+		dispatch (Just (PairReqM (PairReq r))) = void $ do
+			let pairdata = verifiableVal r
+			let repo = remoteUserName pairdata ++ "@" ++
+				fromMaybe (showAddr $ remoteAddress pairdata)
+					(remoteHostName pairdata)
+			let msg = repo ++ " is sending a pair request."
+			{- Pair request alerts from the same host combine,
+			 - so repeated requests do not add additional alerts. -}
+			addAlert dstatus $ pairRequestAlert repo msg
+		dispatch (Just (PairAckM _)) = noop -- TODO