windows: add Recvfrom and Sendto implementations

Added the missing `Sendto` and `Recvfrom` syscalls for Windows.
Fixes golang/go#7170

Change-Id: I794b4f631fad424400fec85ccecc3a3b3abe5465
GitHub-Last-Rev: 39ebe92
GitHub-Pull-Request: #46
Reviewed-on: https://go-review.googlesource.com/c/sys/+/208321
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: maltalex

windows/syscall_windows.go

@@ -701,6 +701,8 @@ const socket_error = uintptr(^uint32(0))
 //sys	WSACleanup() (err error) [failretval==socket_error] = ws2_32.WSACleanup
 //sys	WSAIoctl(s Handle, iocc uint32, inbuf *byte, cbif uint32, outbuf *byte, cbob uint32, cbbr *uint32, overlapped *Overlapped, completionRoutine uintptr) (err error) [failretval==socket_error] = ws2_32.WSAIoctl
 //sys	socket(af int32, typ int32, protocol int32) (handle Handle, err error) [failretval==InvalidHandle] = ws2_32.socket
+//sys	sendto(s Handle, buf []byte, flags int, to unsafe.Pointer, tolen int32) (err error) [failretval==socket_error] = ws2_32.sendto
+//sys	recvfrom(s Handle, buf []byte, flags int, from *RawSockaddrAny, fromlen *int) (n int, err error) [failretval==-1] = ws2_32.recvfrom
 //sys	Setsockopt(s Handle, level int32, optname int32, optval *byte, optlen int32) (err error) [failretval==socket_error] = ws2_32.setsockopt
 //sys	Getsockopt(s Handle, level int32, optname int32, optval *byte, optlen *int32) (err error) [failretval==socket_error] = ws2_32.getsockopt
 //sys	bind(s Handle, name unsafe.Pointer, namelen int32) (err error) [failretval==socket_error] = ws2_32.bind
@@ -1129,10 +1131,26 @@ func NsecToTimespec(nsec int64) (ts Timespec) {
 // TODO(brainman): fix all needed for net
 
 func Accept(fd Handle) (nfd Handle, sa Sockaddr, err error) { return 0, nil, syscall.EWINDOWS }
+
 func Recvfrom(fd Handle, p []byte, flags int) (n int, from Sockaddr, err error) {
-	return 0, nil, syscall.EWINDOWS
+	var rsa RawSockaddrAny
+	l := int(unsafe.Sizeof(rsa))
+	n, err = recvfrom(fd, p, flags, &rsa, &l)
+	if err != nil {
+		return
+	}
+	from, err = rsa.Sockaddr()
+	return
 }
-func Sendto(fd Handle, p []byte, flags int, to Sockaddr) (err error)       { return syscall.EWINDOWS }
+
+func Sendto(fd Handle, p []byte, flags int, to Sockaddr) (err error) {
+	ptr, l, err := to.sockaddr()
+	if err != nil {
+		return err
+	}
+	return sendto(fd, p, flags, ptr, l)
+}
+
 func SetsockoptTimeval(fd Handle, level, opt int, tv *Timeval) (err error) { return syscall.EWINDOWS }
 
 // The Linger struct is wrong but we only noticed after Go 1.