Correct HTTPU serving to not require an interface for multicast.

cmd/example_httpu_serving/example_httpu_serving.go

@@ -2,24 +2,19 @@ package main
 
 import (
 	"log"
-	"net"
 	"net/http"
 
 	"github.com/huin/goupnp/httpu"
 )
 
 func main() {
-	eth0, err := net.InterfaceByName("eth0")
-	if err != nil {
-		log.Fatal(err)
-	}
 	srv := httpu.Server{
 		Addr:      "239.255.255.250:1900",
-		Interface: eth0,
+		Multicast: true,
 		Handler: httpu.HandlerFunc(func(r *http.Request) {
 			log.Printf("Got %s %s message from %v: %v", r.Method, r.URL.Path, r.RemoteAddr, r.Header)
 		}),
 	}
-	err = srv.ListenAndServe()
+	err := srv.ListenAndServe()
 	log.Printf("Serving failed with error: %v", err)
 }

httpu/serve.go

@@ -36,13 +36,15 @@ func (f HandlerFunc) ServeMessage(r *http.Request) {
 // A Server defines parameters for running an HTTPU server.
 type Server struct {
 	Addr            string         // UDP address to listen on
-	Interface       *net.Interface // Network interface to listen on
+	Multicast       bool           // Should listen for multicast?
+	Interface       *net.Interface // Network interface to listen on for multicast, nil for default multicast interface
 	Handler         Handler        // handler to invoke
 	MaxMessageBytes int            // maximum number of bytes to read from a packet, DefaultMaxMessageBytes if 0
 }
 
-// ListenAndServe listens on the UDP network address srv.Addr. If srv.Interface
-// != nil, then a multicast UDP listener will be used on the given interface.
+// ListenAndServe listens on the UDP network address srv.Addr. If srv.Multicast
+// is true, then a multicast UDP listener will be used on srv.Interface (or
+// default interface if nil).
 func (srv *Server) ListenAndServe() error {
 	var err error
 
@@ -52,7 +54,7 @@ func (srv *Server) ListenAndServe() error {
 	}
 
 	var conn net.PacketConn
-	if srv.Interface != nil {
+	if srv.Multicast {
 		if conn, err = net.ListenMulticastUDP("udp", srv.Interface, addr); err != nil {
 			return err
 		}