capture and inject on the same pcap handle

...since there's no need to have separate handles

Also, make router.Start() perform all startup, including starting a
sniffer goroutine. The main goroutine is now kept alive by the signal
handling loop.

router.go

@@ -39,10 +39,12 @@ func (router *Router) UsingPassword() bool {
 }
 
 func (router *Router) Start() {
+	handle := router.createPCap(true, 65535, router.BufSz)
 	router.ConnectionMaker = StartConnectionMaker(router)
 	router.Topology = StartTopology(router)
-	router.UDPListener = router.listenUDP(Port)
+	router.UDPListener = router.listenUDP(Port, handle)
 	router.listenTCP(Port)
+	router.sniff(handle)
 }
 
 func (router *Router) Status() string {
@@ -56,12 +58,9 @@ func (router *Router) Status() string {
 	return buf.String()
 }
 
-func (router *Router) Sniff() {
+func (router *Router) sniff(handle *pcap.Handle) {
 	log.Println("Sniffing traffic on", router.Iface)
 
-	handle := router.createPCap(true, 65535, router.BufSz)
-	defer handle.Close()
-
 	dec := NewEthernetDecoder()
 
 	localAddrs, err := router.Iface.Addrs()
@@ -72,12 +71,15 @@ func (router *Router) Sniff() {
 	if router.Macs.Enter(mac, router.Ourself) {
 		log.Println("Discovered our MAC", mac)
 	}
-	for {
-		pkt, _, err := handle.ReadPacketData()
-		checkFatal(err)
-		router.LogFrame("Sniffed", pkt, nil)
-		checkWarn(router.handleCapturedPacket(pkt, dec, checkFrameTooBig))
-	}
+	go func() {
+		defer handle.Close()
+		for {
+			pkt, _, err := handle.ReadPacketData()
+			checkFatal(err)
+			router.LogFrame("Sniffed", pkt, nil)
+			checkWarn(router.handleCapturedPacket(pkt, dec, checkFrameTooBig))
+		}
+	}()
 }
 
 func (router *Router) handleCapturedPacket(frameData []byte, dec *EthernetDecoder, checkFrameTooBig func(error) error) error {
@@ -144,7 +146,7 @@ func (router *Router) acceptTCP(tcpConn *net.TCPConn) {
 	NewLocalConnection(connRemote, UnknownPeerName, tcpConn, nil, router)
 }
 
-func (router *Router) listenUDP(localPort int) *net.UDPConn {
+	func (router *Router) listenUDP(localPort int, handle *pcap.Handle) *net.UDPConn {
 	localAddr, err := net.ResolveUDPAddr("udp4", fmt.Sprint(":", localPort))
 	checkFatal(err)
 	conn, err := net.ListenUDP("udp4", localAddr)
@@ -156,13 +158,12 @@ func (router *Router) listenUDP(localPort int) *net.UDPConn {
 	// This one makes sure all packets we send out do not have DF set on them.
 	err = syscall.SetsockoptInt(fd, syscall.IPPROTO_IP, syscall.IP_MTU_DISCOVER, syscall.IP_PMTUDISC_DONT)
 	checkFatal(err)
-	go router.udpReader(conn)
+	go router.udpReader(conn, handle)
 	return conn
 }
 
-func (router *Router) udpReader(conn *net.UDPConn) {
+func (router *Router) udpReader(conn *net.UDPConn, handle *pcap.Handle) {
 	defer conn.Close()
-	handle := router.createPCap(false, 0, 0)
 	dec := NewEthernetDecoder()
 	handleUDPPacket := router.handleUDPPacketFunc(dec, handle)
 	buf := make([]byte, MaxUDPPacketSize)

weave/main.go

@@ -115,7 +115,6 @@ func main() {
 
 	router := weave.NewRouter(iface, ourName, []byte(password), connLimit, bufSz*1024*1024, logFrame)
 	router.Start()
-	startSignalHandlers(router)
 	for _, peer := range peers {
 		targetPeer := peer
 		go func() {
@@ -124,23 +123,21 @@ func main() {
 			}
 		}()
 	}
-	router.Sniff()
+	handleSignals(router)
 }
 
-func startSignalHandlers(router *weave.Router) {
+func handleSignals(router *weave.Router) {
 	sigs := make(chan os.Signal, 1)
 	signal.Notify(sigs, syscall.SIGQUIT, syscall.SIGUSR1)
 	buf := make([]byte, 1<<20)
-	go func() {
-		for {
-			sig := <-sigs
-			switch sig {
-			case syscall.SIGQUIT:
-				runtime.Stack(buf, true)
-				log.Printf("=== received SIGQUIT ===\n*** goroutine dump...\n%s\n*** end\n", buf)
-			case syscall.SIGUSR1:
-				log.Printf("=== received SIGUSR1 ===\n*** status...\n%s\n*** end\n", router.Status())
-			}
+	for {
+		sig := <-sigs
+		switch sig {
+		case syscall.SIGQUIT:
+			runtime.Stack(buf, true)
+			log.Printf("=== received SIGQUIT ===\n*** goroutine dump...\n%s\n*** end\n", buf)
+		case syscall.SIGUSR1:
+			log.Printf("=== received SIGUSR1 ===\n*** status...\n%s\n*** end\n", router.Status())
 		}
-	}()
+	}
 }