fix laziness problem in git relaying

The switch to hGetMetered subtly changed the laziness of how DATA was
read, and broke git protocol relaying. Fix by sending received data to
the git process's stdin immediately, which ensures that the lazy
bytestring is all read from the peer before going on to process the next
message from the peer.

P2P/IO.hs

@@ -167,7 +167,7 @@ runRelay runner (RelayHandle hout) (RelayHandle hin) = bracket setup cleanup go
   where
 	setup = do
 		v <- newEmptyMVar
-		void $ async $ relayFeeder runner v
+		void $ async $ relayFeeder runner v hin
 		void $ async $ relayReader v hout
 		return v
 	
@@ -175,7 +175,7 @@ runRelay runner (RelayHandle hout) (RelayHandle hin) = bracket setup cleanup go
 		hClose hin
 		hClose hout
 	
-	go v = relayHelper runner v hin
+	go v = relayHelper runner v
 
 runRelayService :: P2PConnection -> RunProto IO -> Service -> IO (Maybe ())
 runRelayService conn runner service = bracket setup cleanup go
@@ -195,7 +195,7 @@ runRelayService conn runner service = bracket setup cleanup go
 			, std_in = CreatePipe
 			}
 		v <- newEmptyMVar
-		void $ async $ relayFeeder runner v
+		void $ async $ relayFeeder runner v hin
 		void $ async $ relayReader v hout
 		waiter <- async $ waitexit v pid
 		return (v, waiter, hin, hout, pid)
@@ -206,8 +206,8 @@ runRelayService conn runner service = bracket setup cleanup go
 		cancel waiter
 		void $ waitForProcess pid
 
-	go (v, _, hin, _, _) = do
-		r <- relayHelper runner v hin
+	go (v, _, _, _, _) = do
+		r <- relayHelper runner v
 		case r of
 			Nothing -> return Nothing
 			Just exitcode -> runner $ net $ relayToPeer (RelayDone exitcode)
@@ -215,16 +215,12 @@ runRelayService conn runner service = bracket setup cleanup go
 	waitexit v pid = putMVar v . RelayDone =<< waitForProcess pid
 
 -- Processes RelayData as it is put into the MVar.
-relayHelper :: RunProto IO -> MVar RelayData -> Handle -> IO (Maybe ExitCode)
-relayHelper runner v hin = loop
+relayHelper :: RunProto IO -> MVar RelayData -> IO (Maybe ExitCode)
+relayHelper runner v = loop
   where
 	loop = do
 		d <- takeMVar v
 		case d of
-			RelayFromPeer b -> do
-				L.hPut hin b
-				hFlush hin
-				loop
 			RelayToPeer b -> do
 				r <- runner $ net $ relayToPeer (RelayToPeer b)
 				case r of
@@ -233,21 +229,25 @@ relayHelper runner v hin = loop
 			RelayDone exitcode -> do
 				_ <- runner $ net $ relayToPeer (RelayDone exitcode)
 				return (Just exitcode)
+			RelayFromPeer _ -> loop -- not handled here
 
--- Takes input from the peer, and puts it into the MVar for processing.
+-- Takes input from the peer, and sends it to the relay process's stdin.
 -- Repeats until the peer tells it it's done or hangs up.
-relayFeeder :: RunProto IO -> MVar RelayData -> IO ()
-relayFeeder runner v = loop
+relayFeeder :: RunProto IO -> MVar RelayData -> Handle -> IO ()
+relayFeeder runner v hin = loop
   where
 	loop = do
 		mrd <- runner $ net relayFromPeer
 		case mrd of
-			Nothing -> putMVar v (RelayDone (ExitFailure 1))
-			Just rd -> do
-				putMVar v rd
-				case rd of
-					RelayDone _ -> return ()
-					_ -> loop
+			Nothing ->
+				putMVar v (RelayDone (ExitFailure 1))
+			Just (RelayDone exitcode) ->
+				putMVar v (RelayDone exitcode)
+			Just (RelayFromPeer b) -> do
+				L.hPut hin b
+				hFlush hin
+				loop
+			Just (RelayToPeer _) -> loop -- not handled here
 
 -- Reads input from the Handle and puts it into the MVar for relaying to
 -- the peer. Continues until EOF on the Handle.