net: simplify ListenMulticastUDP

R=rsc, iant, dave
CC=golang-dev
https://golang.org/cl/6999053

src/pkg/net/udpsock_posix.go

@@ -211,25 +211,22 @@ func ListenMulticastUDP(net string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, e
 		return nil, UnknownNetworkError(net)
 	}
 	if gaddr == nil || gaddr.IP == nil {
-		return nil, &OpError{"listenmulticast", net, nil, errMissingAddress}
+		return nil, &OpError{"listen", net, nil, errMissingAddress}
 	}
 	fd, err := internetSocket(net, gaddr.toAddr(), nil, noDeadline, syscall.SOCK_DGRAM, 0, "listen", sockaddrToUDP)
 	if err != nil {
 		return nil, err
 	}
 	c := newUDPConn(fd)
-	ip4 := gaddr.IP.To4()
-	if ip4 != nil {
-		err := listenIPv4MulticastUDP(c, ifi, ip4)
-		if err != nil {
+	if ip4 := gaddr.IP.To4(); ip4 != nil {
+		if err := listenIPv4MulticastUDP(c, ifi, ip4); err != nil {
 			c.Close()
-			return nil, err
+			return nil, &OpError{"listen", net, &IPAddr{IP: ip4}, err}
 		}
 	} else {
-		err := listenIPv6MulticastUDP(c, ifi, gaddr.IP)
-		if err != nil {
+		if err := listenIPv6MulticastUDP(c, ifi, gaddr.IP); err != nil {
 			c.Close()
-			return nil, err
+			return nil, &OpError{"listen", net, &IPAddr{IP: gaddr.IP}, err}
 		}
 	}
 	return c, nil
@@ -237,17 +234,14 @@ func ListenMulticastUDP(net string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, e
 
 func listenIPv4MulticastUDP(c *UDPConn, ifi *Interface, ip IP) error {
 	if ifi != nil {
-		err := setIPv4MulticastInterface(c.fd, ifi)
-		if err != nil {
+		if err := setIPv4MulticastInterface(c.fd, ifi); err != nil {
 			return err
 		}
 	}
-	err := setIPv4MulticastLoopback(c.fd, false)
-	if err != nil {
+	if err := setIPv4MulticastLoopback(c.fd, false); err != nil {
 		return err
 	}
-	err = joinIPv4GroupUDP(c, ifi, ip)
-	if err != nil {
+	if err := joinIPv4Group(c.fd, ifi, ip); err != nil {
 		return err
 	}
 	return nil
@@ -255,34 +249,15 @@ func listenIPv4MulticastUDP(c *UDPConn, ifi *Interface, ip IP) error {
 
 func listenIPv6MulticastUDP(c *UDPConn, ifi *Interface, ip IP) error {
 	if ifi != nil {
-		err := setIPv6MulticastInterface(c.fd, ifi)
-		if err != nil {
+		if err := setIPv6MulticastInterface(c.fd, ifi); err != nil {
 			return err
 		}
 	}
-	err := setIPv6MulticastLoopback(c.fd, false)
-	if err != nil {
+	if err := setIPv6MulticastLoopback(c.fd, false); err != nil {
 		return err
 	}
-	err = joinIPv6GroupUDP(c, ifi, ip)
-	if err != nil {
+	if err := joinIPv6Group(c.fd, ifi, ip); err != nil {
 		return err
 	}
 	return nil
 }
-
-func joinIPv4GroupUDP(c *UDPConn, ifi *Interface, ip IP) error {
-	err := joinIPv4Group(c.fd, ifi, ip)
-	if err != nil {
-		return &OpError{"joinipv4group", c.fd.net, &IPAddr{IP: ip}, err}
-	}
-	return nil
-}
-
-func joinIPv6GroupUDP(c *UDPConn, ifi *Interface, ip IP) error {
-	err := joinIPv6Group(c.fd, ifi, ip)
-	if err != nil {
-		return &OpError{"joinipv6group", c.fd.net, &IPAddr{IP: ip}, err}
-	}
-	return nil
-}