move some logic from TunAdapter.reader into a new function, TunAdapter.readerPacketHandler

src/tuntap/iface.go

@@ -110,12 +110,24 @@ func (tun *TunAdapter) writer() error {
 	}
 }
 
-func (tun *TunAdapter) reader() error {
+// Run in a separate goroutine by the reader
-	recvd := make([]byte, 65535+tun_ETHER_HEADER_LENGTH)
+// Does all of the per-packet ICMP checks, passes packets to the right Conn worker
-	toWorker := make(chan []byte, 32)
+func (tun *TunAdapter) readerPacketHandler(ch chan []byte) {
-	defer close(toWorker)
+	for recvd := range ch {
-	go func() {
+		// If it's a TAP adapter, update the buffer slice so that we no longer
-		for bs := range toWorker {
+		// include the ethernet headers
+		offset := 0
+		if tun.iface.IsTAP() {
+			// Set our offset to beyond the ethernet headers
+			offset = tun_ETHER_HEADER_LENGTH
+			// Check first of all that we can go beyond the ethernet headers
+			if len(recvd) <= offset {
+				continue
+			}
+		}
+		// Offset the buffer from now on so that we can ignore ethernet frames if
+		// they are present
+		bs := recvd[offset:]
 		// If we detect an ICMP packet then hand it to the ICMPv6 module
 		if bs[6] == 58 {
 			// Found an ICMPv6 packet - we need to make sure to give ICMPv6 the full
@@ -127,6 +139,8 @@ func (tun *TunAdapter) reader() error {
 				continue
 			}
 		}
+		// Shift forward to avoid leaking bytes off the front of the slide when we eventually store it
+		bs = append(recvd[:0], bs...)
 		// From the IP header, work out what our source and destination addresses
 		// and node IDs are. We will need these in order to work out where to send
 		// the packet
@@ -218,12 +232,11 @@ func (tun *TunAdapter) reader() error {
 				panic("Given empty dstNodeID and dstNodeIDMask - this shouldn't happen")
 			}
 			// Dial to the remote node
-				packet := bs
 			go func() {
 				// FIXME just spitting out a goroutine to do this is kind of ugly and means we drop packets until the dial finishes
 				tun.mutex.Lock()
 				_, known := tun.dials[*dstNodeID]
-					tun.dials[*dstNodeID] = append(tun.dials[*dstNodeID], packet)
+				tun.dials[*dstNodeID] = append(tun.dials[*dstNodeID], bs)
 				for len(tun.dials[*dstNodeID]) > 32 {
 					util.PutBytes(tun.dials[*dstNodeID][0])
 					tun.dials[*dstNodeID] = tun.dials[*dstNodeID][1:]
@@ -261,15 +274,20 @@ func (tun *TunAdapter) reader() error {
 		}
 		// If we have a connection now, try writing to it
 		if isIn && session != nil {
-				packet := bs
 			select {
-				case session.send <- packet:
+			case session.send <- bs:
 			default:
-					util.PutBytes(packet)
+				util.PutBytes(bs)
 			}
 		}
 	}
-	}()
+}
+
+func (tun *TunAdapter) reader() error {
+	recvd := make([]byte, 65535+tun_ETHER_HEADER_LENGTH)
+	toWorker := make(chan []byte, 32)
+	defer close(toWorker)
+	go tun.readerPacketHandler(toWorker)
 	for {
 		// Wait for a packet to be delivered to us through the TUN/TAP adapter
 		n, err := tun.iface.Read(recvd)
@@ -282,20 +300,7 @@ func (tun *TunAdapter) reader() error {
 		if n == 0 {
 			continue
 		}
-		// If it's a TAP adapter, update the buffer slice so that we no longer
+		bs := append(util.GetBytes(), recvd[:n]...)
-		// include the ethernet headers
-		offset := 0
-		if tun.iface.IsTAP() {
-			// Set our offset to beyond the ethernet headers
-			offset = tun_ETHER_HEADER_LENGTH
-			// Check first of all that we can go beyond the ethernet headers
-			if len(recvd) <= offset {
-				continue
-			}
-		}
-		// Offset the buffer from now on so that we can ignore ethernet frames if
-		// they are present
-		bs := append(util.GetBytes(), recvd[offset:offset+n]...)
 		toWorker <- bs
 	}
 }