From 64ac7745fec17dafe1c75a38f2999d43bba0e76e Mon Sep 17 00:00:00 2001
From: David Wragg <david@wragg.org>
Date: Mon, 25 May 2015 21:38:55 +0100
Subject: [PATCH] Don't inspect the DF flag earlier than we need to

---
 router/forwarder.go  |  5 +++++
 router/local_peer.go | 16 ++++++++--------
 router/router.go     | 13 +++++--------
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/router/forwarder.go b/router/forwarder.go
index da727034..cab1c0ff 100644
--- a/router/forwarder.go
+++ b/router/forwarder.go
@@ -77,6 +77,11 @@ func (conn *LocalConnection) Forward(df bool, frame *ForwardedFrame, dec *Ethern
 		conn.Log("Cannot forward frame yet - awaiting contact")
 		return nil
 	}
+
+	if dec != nil {
+		df = dec.DF()
+	}
+
 	// We could use non-blocking channel sends here, i.e. drop frames
 	// on the floor when the forwarder is busy. This would allow our
 	// caller - the capturing loop in the router - to read frames more
diff --git a/router/local_peer.go b/router/local_peer.go
index 3be1e7b5..930fbf1b 100644
--- a/router/local_peer.go
+++ b/router/local_peer.go
@@ -28,15 +28,15 @@ func NewLocalPeer(name PeerName, nickName string, router *Router) *LocalPeer {
 	return peer
 }
 
-func (peer *LocalPeer) Forward(dstPeer *Peer, df bool, frame []byte, dec *EthernetDecoder) error {
-	return peer.Relay(peer.Peer, dstPeer, df, frame, dec)
+func (peer *LocalPeer) Forward(dstPeer *Peer, frame []byte, dec *EthernetDecoder) error {
+	return peer.Relay(peer.Peer, dstPeer, frame, dec)
 }
 
-func (peer *LocalPeer) Broadcast(df bool, frame []byte, dec *EthernetDecoder) {
-	peer.RelayBroadcast(peer.Peer, df, frame, dec)
+func (peer *LocalPeer) Broadcast(frame []byte, dec *EthernetDecoder) {
+	peer.RelayBroadcast(peer.Peer, frame, dec)
 }
 
-func (peer *LocalPeer) Relay(srcPeer, dstPeer *Peer, df bool, frame []byte, dec *EthernetDecoder) error {
+func (peer *LocalPeer) Relay(srcPeer, dstPeer *Peer, frame []byte, dec *EthernetDecoder) error {
 	relayPeerName, found := peer.router.Routes.Unicast(dstPeer.Name)
 	if !found {
 		// Not necessarily an error as there could be a race with the
@@ -50,20 +50,20 @@ func (peer *LocalPeer) Relay(srcPeer, dstPeer *Peer, df bool, frame []byte, dec
 		log.Println("Unable to find connection to relay peer", relayPeerName)
 		return nil
 	}
-	return conn.(*LocalConnection).Forward(df, &ForwardedFrame{
+	return conn.(*LocalConnection).Forward(false, &ForwardedFrame{
 		srcPeer: srcPeer,
 		dstPeer: dstPeer,
 		frame:   frame},
 		dec)
 }
 
-func (peer *LocalPeer) RelayBroadcast(srcPeer *Peer, df bool, frame []byte, dec *EthernetDecoder) {
+func (peer *LocalPeer) RelayBroadcast(srcPeer *Peer, frame []byte, dec *EthernetDecoder) {
 	nextHops := peer.router.Routes.Broadcast(srcPeer.Name)
 	if len(nextHops) == 0 {
 		return
 	}
 	for _, conn := range peer.ConnectionsTo(nextHops) {
-		err := conn.(*LocalConnection).Forward(df, &ForwardedFrame{
+		err := conn.(*LocalConnection).Forward(false, &ForwardedFrame{
 			srcPeer: srcPeer,
 			dstPeer: conn.Remote(),
 			frame:   frame},
diff --git a/router/router.go b/router/router.go
index 67d7b239..a85d1fb1 100644
--- a/router/router.go
+++ b/router/router.go
@@ -169,7 +169,6 @@ func (router *Router) handleCapturedPacket(frameData []byte, dec *EthernetDecode
 	if found && dstPeer == router.Ourself.Peer {
 		return
 	}
-	df := dec.DF()
 	router.LogFrame("Forwarding", frameData, dec)
 
 	// at this point we are handing over the frame to forwarders, so
@@ -182,11 +181,11 @@ func (router *Router) handleCapturedPacket(frameData []byte, dec *EthernetDecode
 	// If we don't know which peer corresponds to the dest MAC,
 	// broadcast it.
 	if !found {
-		router.Ourself.Broadcast(df, frameCopy, dec)
+		router.Ourself.Broadcast(frameCopy, dec)
 		return
 	}
 
-	err := router.Ourself.Forward(dstPeer, df, frameCopy, dec)
+	err := router.Ourself.Forward(dstPeer, frameCopy, dec)
 	if ftbe, ok := err.(FrameTooBigError); ok {
 		err = dec.sendICMPFragNeeded(ftbe.EPMTU, po.WritePacket)
 	}
@@ -312,15 +311,13 @@ func (router *Router) handleUDPPacketFunc(relayConn *LocalConnection, dec *Ether
 			return
 		}
 
-		df := dec.DF()
-
 		if dstPeer != router.Ourself.Peer {
 			// it's not for us, we're just relaying it
 			router.LogFrame("Relaying", frame, dec)
-			err := router.Ourself.Relay(srcPeer, dstPeer, df, frame, dec)
+			err := router.Ourself.Relay(srcPeer, dstPeer, frame, dec)
 			if ftbe, ok := err.(FrameTooBigError); ok {
 				err = dec.sendICMPFragNeeded(ftbe.EPMTU, func(icmpFrame []byte) error {
-					return router.Ourself.Forward(srcPeer, false, icmpFrame, nil)
+					return router.Ourself.Forward(srcPeer, icmpFrame, nil)
 				})
 			}
 
@@ -342,7 +339,7 @@ func (router *Router) handleUDPPacketFunc(relayConn *LocalConnection, dec *Ether
 		dstPeer, found = router.Macs.Lookup(dstMac)
 		if !found || dstPeer != router.Ourself.Peer {
 			router.LogFrame("Relaying broadcast", frame, dec)
-			router.Ourself.RelayBroadcast(srcPeer, df, frame, dec)
+			router.Ourself.RelayBroadcast(srcPeer, frame, dec)
 		}
 	}
 }