net: make LocalAddr on multicast UDPConn return a listening address

The package go.net/ipv4 allows to exist a single UDP listener
that join multiple different group addresses. That means that
LocalAddr on multicast UDPConn returns a first joined group
address is not desirable.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6822108

diff --git a/src/pkg/net/multicast_posix_test.go b/src/pkg/net/multicast_posix_test.go
index 3767a6bc17844fe5b3dd2b27378d776ecf7ee343..d4a8a35627dd937977dacd1d8f9f96f55cffa6d8 100644 (file)
--- a/src/pkg/net/multicast_posix_test.go
+++ b/src/pkg/net/multicast_posix_test.go
@@ -118,16 +118,29 @@ func TestSimpleMulticastListener(t *testing.T) {
 
 func checkMulticastListener(t *testing.T, err error, c *UDPConn, gaddr *UDPAddr) {
        if !multicastRIBContains(t, gaddr.IP) {
-               t.Fatalf("%q not found in RIB", gaddr.String())
+               t.Errorf("%q not found in RIB", gaddr.String())
+               return
+       }
+       la := c.LocalAddr()
+       if la == nil {
+               t.Error("LocalAddr failed")
+               return
        }
-       if c.LocalAddr().String() != gaddr.String() {
-               t.Fatalf("LocalAddr returns %q, expected %q", c.LocalAddr().String(), gaddr.String())
+       if a, ok := la.(*UDPAddr); !ok || a.Port == 0 {
+               t.Errorf("got %v; expected a proper address with non-zero port number", la)
+               return
        }
 }
 
 func checkSimpleMulticastListener(t *testing.T, err error, c *UDPConn, gaddr *UDPAddr) {
-       if c.LocalAddr().String() != gaddr.String() {
-               t.Fatalf("LocalAddr returns %q, expected %q", c.LocalAddr().String(), gaddr.String())
+       la := c.LocalAddr()
+       if la == nil {
+               t.Error("LocalAddr failed")
+               return
+       }
+       if a, ok := la.(*UDPAddr); !ok || a.Port == 0 {
+               t.Errorf("got %v; expected a proper address with non-zero port number", la)
+               return
        }
 }
 

diff --git a/src/pkg/net/sock_posix.go b/src/pkg/net/sock_posix.go
index a3354eacb1b68875abfcca3a63e6bcb4a7947e5c..78417fd2ee7f95547ec09a05b55102167fc6410b 100644 (file)
--- a/src/pkg/net/sock_posix.go
+++ b/src/pkg/net/sock_posix.go
@@ -33,13 +33,19 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
                return nil, err
        }
 
-       var blsa syscall.Sockaddr
        if ulsa != nil {
-               if blsa, err = listenerSockaddr(s, f, ulsa, toAddr); err != nil {
+               // We provide a socket that listens to a wildcard
+               // address with reusable UDP port when the given ulsa
+               // is an appropriate UDP multicast address prefix.
+               // This makes it possible for a single UDP listener
+               // to join multiple different group addresses, for
+               // multiple UDP listeners that listen on the same UDP
+               // port to join the same group address.
+               if ulsa, err = listenerSockaddr(s, f, ulsa, toAddr); err != nil {
                        closesocket(s)
                        return nil, err
                }
-               if err = syscall.Bind(s, blsa); err != nil {
+               if err = syscall.Bind(s, ulsa); err != nil {
                        closesocket(s)
                        return nil, err
                }
@@ -64,12 +70,7 @@ func socket(net string, f, t, p int, ipv6only bool, ulsa, ursa syscall.Sockaddr,
        }
 
        lsa, _ := syscall.Getsockname(s)
-       var laddr Addr
-       if ulsa != nil && blsa != ulsa {
-               laddr = toAddr(ulsa)
-       } else {
-               laddr = toAddr(lsa)
-       }
+       laddr := toAddr(lsa)
        rsa, _ := syscall.Getpeername(s)
        raddr := toAddr(rsa)
        fd.setAddr(laddr, raddr)