net, syscall: add IPv4 multicast helpers for windows

Also re-enable simple IPv4 multicast testing on windows.

R=alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/5605048

src/pkg/net/multicast_test.go

@@ -86,7 +86,7 @@ func TestListenMulticastUDP(t *testing.T) {
 
 func TestSimpleListenMulticastUDP(t *testing.T) {
 	switch runtime.GOOS {
-	case "plan9", "windows":
+	case "plan9":
 		return
 	}
 

src/pkg/net/sockoptip_windows.go

@@ -7,6 +7,7 @@
 package net
 
 import (
+	"os"
 	"syscall"
 )
 
@@ -16,8 +17,19 @@ func ipv4MulticastInterface(fd *netFD) (*Interface, error) {
 }
 
 func setIPv4MulticastInterface(fd *netFD, ifi *Interface) error {
-	// TODO: Implement this
-	return syscall.EWINDOWS
+	ip, err := interfaceToIPv4Addr(ifi)
+	if err != nil {
+		return os.NewSyscallError("setsockopt", err)
+	}
+	var x [4]byte
+	copy(x[:], ip.To4())
+	fd.incref()
+	defer fd.decref()
+	err = syscall.SetsockoptInet4Addr(fd.sysfd, syscall.IPPROTO_IP, syscall.IP_MULTICAST_IF, x)
+	if err != nil {
+		return os.NewSyscallError("setsockopt", err)
+	}
+	return nil
 }
 
 func ipv4MulticastTTL(fd *netFD) (int, error) {
@@ -26,8 +38,14 @@ func ipv4MulticastTTL(fd *netFD) (int, error) {
 }
 
 func setIPv4MulticastTTL(fd *netFD, v int) error {
-	// TODO: Implement this
-	return syscall.EWINDOWS
+	fd.incref()
+	defer fd.decref()
+	err := syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_IP, syscall.IP_MULTICAST_TTL, v)
+	if err != nil {
+		return os.NewSyscallError("setsockopt", err)
+	}
+	return nil
+
 }
 
 func ipv4MulticastLoopback(fd *netFD) (bool, error) {
@@ -36,8 +54,14 @@ func ipv4MulticastLoopback(fd *netFD) (bool, error) {
 }
 
 func setIPv4MulticastLoopback(fd *netFD, v bool) error {
-	// TODO: Implement this
-	return syscall.EWINDOWS
+	fd.incref()
+	defer fd.decref()
+	err := syscall.SetsockoptInt(fd.sysfd, syscall.IPPROTO_IP, syscall.IP_MULTICAST_LOOP, boolint(v))
+	if err != nil {
+		return os.NewSyscallError("setsockopt", err)
+	}
+	return nil
+
 }
 
 func ipv4ReceiveInterface(fd *netFD) (bool, error) {

src/pkg/syscall/syscall_windows.go

@@ -657,6 +657,9 @@ type IPv6Mreq struct {
 
 func GetsockoptInt(fd Handle, level, opt int) (int, error)              { return -1, EWINDOWS }
 func SetsockoptLinger(fd Handle, level, opt int, l *Linger) (err error) { return EWINDOWS }
+func SetsockoptInet4Addr(fd Handle, level, opt int, value [4]byte) (err error) {
+	return Setsockopt(fd, int32(level), int32(opt), (*byte)(unsafe.Pointer(&value[0])), 4)
+}
 func SetsockoptIPMreq(fd Handle, level, opt int, mreq *IPMreq) (err error) {
 	return Setsockopt(fd, int32(level), int32(opt), (*byte)(unsafe.Pointer(mreq)), int32(unsafe.Sizeof(*mreq)))
 }

src/pkg/syscall/ztypes_windows.go

@@ -389,8 +389,13 @@ const (
 	SO_SNDBUF                = 0x1001
 	SO_UPDATE_ACCEPT_CONTEXT = 0x700b
 
+	// cf. http://support.microsoft.com/default.aspx?scid=kb;en-us;257460
+
 	IP_TOS             = 0x3
 	IP_TTL             = 0x4
+	IP_MULTICAST_IF    = 0x9
+	IP_MULTICAST_TTL   = 0xa
+	IP_MULTICAST_LOOP  = 0xb
 	IP_ADD_MEMBERSHIP  = 0xc
 	IP_DROP_MEMBERSHIP = 0xd