net, syscall: return source address in Recvmsg

R=rsc
CC=golang-dev
https://golang.org/cl/3766042

src/pkg/net/fd.go

@@ -417,7 +417,7 @@ func (fd *netFD) ReadMsg(p []byte, oob []byte) (n, oobn, flags int, sa syscall.S
 	var oserr os.Error
 	for {
 		var errno int
-		n, oobn, flags, errno = syscall.Recvmsg(fd.sysfd, p, oob, sa, 0)
+		n, oobn, flags, sa, errno = syscall.Recvmsg(fd.sysfd, p, oob, 0)
 		if errno == syscall.EAGAIN && fd.rdeadline >= 0 {
 			pollserver.WaitRead(fd)
 			continue

src/pkg/syscall/syscall_bsd.go

@@ -485,8 +485,8 @@ func Futimes(fd int, tv []Timeval) (errno int) {
 
 //sys	fcntl(fd int, cmd int, arg int) (val int, errno int)
 
-func Recvmsg(fd int, p, oob []byte, from Sockaddr, flags int) (n, oobn int, recvflags int, errno int) {
-	return 0, 0, 0, EAFNOSUPPORT
+func Recvmsg(fd int, p, oob []byte, flags int) (n, oobn int, recvflags int, from Sockaddr, errno int) {
+	return 0, 0, 0, nil, EAFNOSUPPORT
 }
 
 func Sendmsg(fd int, p, oob []byte, to Sockaddr, flags int) (errno int) {

src/pkg/syscall/syscall_linux.go

@@ -450,7 +450,7 @@ func Sendto(fd int, p []byte, flags int, to Sockaddr) (errno int) {
 	return sendto(fd, p, flags, ptr, n)
 }
 
-func Recvmsg(fd int, p, oob []byte, from Sockaddr, flags int) (n, oobn int, recvflags int, errno int) {
+func Recvmsg(fd int, p, oob []byte, flags int) (n, oobn int, recvflags int, from Sockaddr, errno int) {
 	var msg Msghdr
 	var rsa RawSockaddrAny
 	msg.Name = (*byte)(unsafe.Pointer(&rsa))
@@ -477,6 +477,10 @@ func Recvmsg(fd int, p, oob []byte, from Sockaddr, flags int) (n, oobn int, recv
 	}
 	oobn = int(msg.Controllen)
 	recvflags = int(msg.Flags)
+	// source address is only specified if the socket is unconnected
+	if rsa.Addr.Family != 0 {
+		from, errno = anyToSockaddr(&rsa)
+	}
 	return
 }