net: fix Dial(":80") on Windows

Windows sockets allow bind to 0.0.0.0:80 but not connect to it.
To make Listen(":80") / Dial(":80") work as documented on Windows,
connect to 127.0.0.1 or ::1 (depending on network) in place of 0.0.0.0.

Fixes #6290.

Change-Id: Ia27537067276871648546678fbe0f1b8478329fe
Reviewed-on: https://go-review.googlesource.com/32101
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

src/net/dial_test.go

@@ -55,6 +55,23 @@ func TestProhibitionaryDialArg(t *testing.T) {
 	}
 }
 
+func TestDialLocal(t *testing.T) {
+	ln, err := newLocalListener("tcp")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+	_, port, err := SplitHostPort(ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	c, err := Dial("tcp", JoinHostPort("", port))
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.Close()
+}
+
 func TestDialTimeoutFDLeak(t *testing.T) {
 	switch runtime.GOOS {
 	case "plan9":

src/net/iprawsock_posix.go

@@ -50,6 +50,10 @@ func (a *IPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, 0, a.Zone)
 }
 
+func (a *IPAddr) toLocal(net string) sockaddr {
+	return &IPAddr{loopbackIP(net), a.Zone}
+}
+
 func (c *IPConn) readFrom(b []byte) (int, *IPAddr, error) {
 	// TODO(cw,rsc): consider using readv if we know the family
 	// type to avoid the header trim/copy

src/net/ipsock.go

@@ -251,3 +251,10 @@ func (r *Resolver) internetAddrList(ctx context.Context, net, addr string) (addr
 	}
 	return filterAddrList(filter, ips, inetaddr)
 }
+
+func loopbackIP(net string) IP {
+	if net != "" && net[len(net)-1] == '6' {
+		return IPv6loopback
+	}
+	return IP{127, 0, 0, 1}
+}

src/net/ipsock_posix.go

@@ -154,6 +154,9 @@ func favoriteAddrFamily(net string, laddr, raddr sockaddr, mode string) (family
 
 // Internet sockets (TCP, UDP, IP)
 func internetSocket(ctx context.Context, net string, laddr, raddr sockaddr, sotype, proto int, mode string) (fd *netFD, err error) {
+	if (runtime.GOOS == "windows" || runtime.GOOS == "openbsd" || runtime.GOOS == "nacl") && mode == "dial" && raddr.isWildcard() {
+		raddr = raddr.toLocal(net)
+	}
 	family, ipv6only := favoriteAddrFamily(net, laddr, raddr, mode)
 	return socket(ctx, net, family, sotype, proto, ipv6only, laddr, raddr)
 }

src/net/sock_posix.go

@@ -30,6 +30,9 @@ type sockaddr interface {
 	// interface. It returns a nil interface when the address is
 	// nil.
 	sockaddr(family int) (syscall.Sockaddr, error)
+
+	// toLocal maps the zero address to a local system address (127.0.0.1 or ::1)
+	toLocal(net string) sockaddr
 }
 
 // socket returns a network file descriptor that is ready for

src/net/tcpsock_posix.go

@@ -40,6 +40,10 @@ func (a *TCPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
 }
 
+func (a *TCPAddr) toLocal(net string) sockaddr {
+	return &TCPAddr{loopbackIP(net), a.Port, a.Zone}
+}
+
 func (c *TCPConn) readFrom(r io.Reader) (int64, error) {
 	if n, err, handled := sendFile(c.fd, r); handled {
 		return n, err

src/net/udpsock_posix.go

@@ -38,6 +38,10 @@ func (a *UDPAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return ipToSockaddr(family, a.IP, a.Port, a.Zone)
 }
 
+func (a *UDPAddr) toLocal(net string) sockaddr {
+	return &UDPAddr{loopbackIP(net), a.Port, a.Zone}
+}
+
 func (c *UDPConn) readFrom(b []byte) (int, *UDPAddr, error) {
 	var addr *UDPAddr
 	n, sa, err := c.fd.readFrom(b)

src/net/unixsock_posix.go

@@ -94,6 +94,10 @@ func (a *UnixAddr) sockaddr(family int) (syscall.Sockaddr, error) {
 	return &syscall.SockaddrUnix{Name: a.Name}, nil
 }
 
+func (a *UnixAddr) toLocal(net string) sockaddr {
+	return a
+}
+
 func (c *UnixConn) readFrom(b []byte) (int, *UnixAddr, error) {
 	var addr *UnixAddr
 	n, sa, err := c.fd.readFrom(b)