allow router to be started w/o capture/inject interface

useful for testing of the control plane

router/router.go

@@ -73,17 +73,24 @@ func NewRouter(iface *net.Interface, name PeerName, nickName string, password []
 
 func (router *Router) Start() {
 	// we need two pcap handles since they aren't thread-safe
-	pio, err := NewPcapIO(router.Iface.Name, router.BufSz)
-	checkFatal(err)
-	po, err := NewPcapO(router.Iface.Name)
-	checkFatal(err)
+	var pio PacketSourceSink
+	var po PacketSink
+	var err error
+	if router.Iface != nil {
+		pio, err = NewPcapIO(router.Iface.Name, router.BufSz)
+		checkFatal(err)
+		po, err = NewPcapO(router.Iface.Name)
+		checkFatal(err)
+	}
 	router.Ourself.Start()
 	router.Macs.Start()
 	router.Routes.Start()
 	router.ConnectionMaker.Start()
 	router.UDPListener = router.listenUDP(Port, po)
 	router.listenTCP(Port)
-	router.sniff(pio)
+	if pio != nil {
+		router.sniff(pio)
+	}
 }
 
 func (router *Router) UsingPassword() bool {
@@ -310,8 +317,10 @@ func (router *Router) handleUDPPacketFunc(dec *EthernetDecoder, sender *net.UDPA
 		if router.Macs.Enter(srcMac, srcPeer) {
 			log.Println("Discovered remote MAC", srcMac, "at", srcPeer.FullName())
 		}
-		router.LogFrame("Injecting", frame, &dec.eth)
-		checkWarn(po.WritePacket(frame))
+		if po != nil {
+			router.LogFrame("Injecting", frame, &dec.eth)
+			checkWarn(po.WritePacket(frame))
+		}
 
 		dstPeer, found = router.Macs.Lookup(dstMac)
 		if !found || dstPeer != router.Ourself.Peer {

weaver/main.go

@@ -49,7 +49,7 @@ func main() {
 	)
 
 	flag.BoolVar(&justVersion, "version", false, "print version and exit")
-	flag.StringVar(&ifaceName, "iface", "", "name of interface to read from")
+	flag.StringVar(&ifaceName, "iface", "", "name of interface to capture/inject from (disabled if left blank)")
 	flag.StringVar(&routerName, "name", "", "name of router (defaults to MAC)")
 	flag.StringVar(&nickName, "nickname", "", "nickname of peer (defaults to hostname)")
 	flag.StringVar(&password, "password", "", "network password")
@@ -77,13 +77,14 @@ func main() {
 	log.Println("Command line options:", options)
 	log.Println("Command line peers:", peers)
 
-	if ifaceName == "" {
-		fmt.Println("Missing required parameter 'iface'")
-		os.Exit(1)
-	}
-	iface, err := weavenet.EnsureInterface(ifaceName, wait)
-	if err != nil {
-		log.Fatal(err)
+	var err error
+
+	var iface *net.Interface
+	if ifaceName != "" {
+		iface, err = weavenet.EnsureInterface(ifaceName, wait)
+		if err != nil {
+			log.Fatal(err)
+		}
 	}
 
 	if routerName == "" {