simplify setting up the network connection

main.go

@@ -28,16 +28,11 @@ func parseOpts() (options, error) {
 }
 
 func run(opt options) error {
-	conn, err := packet.ListenPort(opt.Port)
+	conn, err := packet.Listen(opt.Group, opt.Port, opt.Ifs...)
 	if err != nil {
 		return err
 	}
 	defer conn.Close()
-	for _, iface := range opt.Ifs {
-		if err = conn.JoinGroup(iface, opt.Group); err != nil {
-			return err
-		}
-	}
 
 	buf := [4096]byte{}
 	var s tlv.PacketDecoder

packet/packet.go

@@ -18,6 +18,19 @@ type Conn struct {
 	v6pc *ipv6.PacketConn
 }
 
+func Listen(group string, port uint16, ifaces ...string) (Conn, error) {
+	conn, err := ListenPort(port)
+	if err != nil {
+		return Conn{}, err
+	}
+	for _, iface := range ifaces {
+		if err = conn.JoinGroup(iface, group); err != nil {
+			conn.Close()
+			return Conn{}, err
+		}
+	}
+	return conn, nil
+}
 func ListenPort(port uint16) (Conn, error) {
 	var c Conn
 
@@ -27,7 +40,9 @@ func ListenPort(port uint16) (Conn, error) {
 	}
 	c.v6pc = ipv6.NewPacketConn(uc)
 
-	return c, c.v6pc.SetControlMessage(ipv6.FlagDst, true)
+	return c, c.v6pc.SetControlMessage(
+		ipv6.FlagDst|ipv6.FlagTrafficClass|ipv6.FlagHopLimit|ipv6.FlagPathMTU,
+		true)
 }
 
 func (c Conn) Close() error {