internal/syscall/windows: implement SupportUnixSocket by enumerating protocols

windows.SupportUnixSocket is currently implemented using a Windows
version check. This approach is not reliable, see #27943 and #28061.
Also, it uses the undocumented RtlGetNtVersionNumbers API, which
we should try to avoid.

This PR implements SupportUnixSocket by enumerating the available
protocols and checking for AF_UNIX support.

Cq-Include-Trybots: luci.golang.try:gotip-windows-arm64
Change-Id: I76cd635067309f09571ad0eac4a5699450a2709a
Reviewed-on: https://go-review.googlesource.com/c/go/+/570075
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/internal/syscall/windows/syscall_windows.go

@@ -201,7 +201,9 @@ const (
 	WSA_FLAG_OVERLAPPED        = 0x01
 	WSA_FLAG_NO_HANDLE_INHERIT = 0x80
 
-	WSAEMSGSIZE syscall.Errno = 10040
+	WSAEINVAL       syscall.Errno = 10022
+	WSAEMSGSIZE     syscall.Errno = 10040
+	WSAEAFNOSUPPORT syscall.Errno = 10047
 
 	MSG_PEEK   = 0x2
 	MSG_TRUNC  = 0x0100

src/internal/syscall/windows/version_windows.go

@@ -6,7 +6,8 @@ package windows
 
 import (
 	"sync"
-	_ "unsafe" // for linkname
+	"syscall"
+	"unsafe"
 )
 
 // version retrieves the major, minor, and build version numbers
@@ -42,6 +43,21 @@ var SupportTCPInitialRTONoSYNRetransmissions = sync.OnceValue(func() bool {
 // Unix Domain Sockets.
 // The minimal requirement is Windows 10.0.17063.
 var SupportUnixSocket = sync.OnceValue(func() bool {
-	major, _, build := version()
-	return major >= 10 && build >= 17063
+	var size uint32
+	// First call to get the required buffer size in bytes.
+	// Ignore the error, it will always fail.
+	_, _ = syscall.WSAEnumProtocols(nil, nil, &size)
+	n := int32(size) / int32(unsafe.Sizeof(syscall.WSAProtocolInfo{}))
+	// Second call to get the actual protocols.
+	buf := make([]syscall.WSAProtocolInfo, n)
+	n, err := syscall.WSAEnumProtocols(nil, &buf[0], &size)
+	if err != nil {
+		return false
+	}
+	for i := int32(0); i < n; i++ {
+		if buf[i].AddressFamily == syscall.AF_UNIX {
+			return true
+		}
+	}
+	return false
 })

src/internal/syscall/windows/version_windows_test.go

@@ -0,0 +1,31 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package windows_test
+
+import (
+	"errors"
+	"internal/syscall/windows"
+	"syscall"
+	"testing"
+)
+
+func TestSupportUnixSocket(t *testing.T) {
+	var d syscall.WSAData
+	if err := syscall.WSAStartup(uint32(0x202), &d); err != nil {
+		t.Fatal(err)
+	}
+	defer syscall.WSACleanup()
+
+	// Test that SupportUnixSocket returns true if WSASocket succeeds with AF_UNIX.
+	got := windows.SupportUnixSocket()
+	s, err := windows.WSASocket(syscall.AF_UNIX, syscall.SOCK_STREAM, 0, nil, 0, windows.WSA_FLAG_NO_HANDLE_INHERIT)
+	if err == nil {
+		syscall.Closesocket(s)
+	}
+	want := !errors.Is(err, windows.WSAEAFNOSUPPORT) && !errors.Is(err, windows.WSAEINVAL)
+	if want != got {
+		t.Errorf("SupportUnixSocket = %v; want %v", got, want)
+	}
+}

src/net/unixsock_windows_test.go

@@ -10,26 +10,13 @@ import (
 	"internal/syscall/windows"
 	"os"
 	"reflect"
-	"runtime"
 	"testing"
 )
 
-func skipIfUnixSocketNotSupported(t *testing.T) {
-	// TODO: the windows.SupportUnixSocket check should be enough, investigate why 386 and arm
-	// can't run these tests on newer Windows.
-	switch runtime.GOARCH {
-	case "386":
-		t.Skip("not supported on windows/386, see golang.org/issue/27943")
-	case "arm":
-		t.Skip("not supported on windows/arm, see golang.org/issue/28061")
-	}
+func TestUnixConnLocalWindows(t *testing.T) {
 	if !windows.SupportUnixSocket() {
 		t.Skip("unix test")
 	}
-}
-
-func TestUnixConnLocalWindows(t *testing.T) {
-	skipIfUnixSocketNotSupported(t)
 	handler := func(ls *localServer, ln Listener) {}
 	for _, laddr := range []string{"", testUnixAddr(t)} {
 		laddr := laddr
@@ -83,7 +70,10 @@ func TestUnixConnLocalWindows(t *testing.T) {
 }
 
 func TestModeSocket(t *testing.T) {
-	skipIfUnixSocketNotSupported(t)
+	if !windows.SupportUnixSocket() {
+		t.Skip("unix test")
+	}
+
 	addr := testUnixAddr(t)
 
 	l, err := Listen("unix", addr)