☠️ windows: gate dial support behind build tag

For golang/go#67401.

.github/workflows/test_gotip.yml

@@ -27,3 +27,6 @@ jobs:
 
       - name: Test
         run: gotip test -v
+
+      - name: Test with tag tfogo_checklinkname0
+        run: gotip test -v -ldflags '-checklinkname=0' -tags tfogo_checklinkname0

README.md

@@ -9,6 +9,14 @@
 go get github.com/database64128/tfo-go/v2
 ```
 
+### Windows support with Go 1.23 and later
+
+`tfo-go`'s Windows support requires extensive usage of `//go:linkname` to access Go runtime internals, as there's currently no public API for Windows async IO in the standard library. Unfortunately, the Go team has decided to [lock down future uses of linkname](https://github.com/golang/go/issues/67401), starting with Go 1.23. And our bid to get the linknames we need exempted was [partially rejected](https://github.com/golang/go/issues/67401#issuecomment-2126175774). Therefore, we had to make the following changes:
+
+- Windows support is gated behind the build tag `tfogo_checklinkname0` when building with Go 1.23 and later.
+- With Go 1.21 and 1.22, `tfo-go` still provides full Windows support, with or without the build tag.
+- With Go 1.23 and later, when the build tag is not specified, `tfo-go` only supports `listen` with TFO on Windows. To get full TFO support on Windows, the build tag `tfogo_checklinkname0` must be specified along with linker flag `-checklinkname=0` to disable the linkname check.
+
 ## License
 
 [MIT](LICENSE)

netpoll_windows.go → netpoll_windows_checklinkname0.go

@@ -1,3 +1,5 @@
+//go:build windows && (!go1.23 || (go1.23 && tfogo_checklinkname0))
+
 package tfo
 
 import (

netpoll_windows_go123.go → netpoll_windows_go123_checklinkname0.go

@@ -1,4 +1,4 @@
-//go:build windows && go1.23
+//go:build windows && go1.23 && tfogo_checklinkname0
 
 package tfo
 

sockopt_connect_generic.go

@@ -1,4 +1,4 @@
-//go:build freebsd || windows
+//go:build freebsd || (windows && (!go1.23 || (go1.23 && tfogo_checklinkname0)))
 
 package tfo
 

sockopt_connect_stub.go

@@ -0,0 +1,7 @@
+//go:build !darwin && !freebsd && !linux && (!windows || (windows && go1.23 && !tfogo_checklinkname0))
+
+package tfo
+
+func setTFODialer(_ uintptr) error {
+	return ErrPlatformUnsupported
+}

sockopt_listen_generic.go

@@ -6,6 +6,6 @@ func setTFOListener(fd uintptr) error {
 	return setTFO(int(fd), 1)
 }
 
-func setTFOListenerWithBacklog(fd uintptr, backlog int) error {
+func setTFOListenerWithBacklog(fd uintptr, _ int) error {
 	return setTFOListener(fd)
 }

sockopt_listen_stub.go

@@ -0,0 +1,11 @@
+//go:build !darwin && !freebsd && !linux && !windows
+
+package tfo
+
+func setTFOListener(_ uintptr) error {
+	return ErrPlatformUnsupported
+}
+
+func setTFOListenerWithBacklog(_ uintptr, _ int) error {
+	return ErrPlatformUnsupported
+}

tfo.go

@@ -61,7 +61,7 @@ func (lc *ListenConfig) tfoDisabled() bool {
 }
 
 func (lc *ListenConfig) tfoNeedsFallback() bool {
-	return lc.Fallback && (comptimeNoTFO || runtimeListenNoTFO.Load())
+	return lc.Fallback && (comptimeListenNoTFO || runtimeListenNoTFO.Load())
 }
 
 // Listen is like [net.ListenConfig.Listen] but enables TFO whenever possible,
@@ -70,7 +70,7 @@ func (lc *ListenConfig) Listen(ctx context.Context, network, address string) (ne
 	if lc.tfoDisabled() || !networkIsTCP(network) || lc.tfoNeedsFallback() {
 		return lc.ListenConfig.Listen(ctx, network, address)
 	}
-	return lc.listenTFO(ctx, network, address) // tfo_darwin.go, tfo_listen_generic.go, tfo_unsupported.go
+	return lc.listenTFO(ctx, network, address) // tfo_darwin.go, tfo_listen_generic.go, tfo_listen_stub.go
 }
 
 // ListenContext is like [net.ListenContext] but enables TFO whenever possible.
@@ -94,7 +94,7 @@ func ListenTCP(network string, laddr *net.TCPAddr) (*net.TCPListener, error) {
 		address = laddr.String()
 	}
 	var lc ListenConfig
-	ln, err := lc.listenTFO(context.Background(), network, address) // tfo_darwin.go, tfo_listen_generic.go, tfo_unsupported.go
+	ln, err := lc.listenTFO(context.Background(), network, address) // tfo_darwin.go, tfo_listen_generic.go, tfo_listen_stub.go
 	if err != nil {
 		return nil, err
 	}
@@ -172,7 +172,11 @@ func (d *Dialer) DialContext(ctx context.Context, network, address string, b []b
 	if d.DisableTFO || !networkIsTCP(network) {
 		return d.dialAndWrite(ctx, network, address, b)
 	}
-	return d.dialTFO(ctx, network, address, b) // tfo_bsd+windows.go, tfo_linux.go, tfo_unsupported.go
+	tc, err := d.dialTFO(ctx, network, address, b) // tfo_bsd+windows.go, tfo_connect_stub.go, tfo_linux.go
+	if err != nil {
+		return nil, err // return nil [net.Conn] instead of non-nil [net.Conn] with nil [*net.TCPConn] pointer
+	}
+	return tc, nil
 }
 
 // Dial is like [net.Dialer.Dial] but enables TFO whenever possible,
@@ -205,7 +209,7 @@ func DialTCP(network string, laddr, raddr *net.TCPAddr, b []byte) (*net.TCPConn,
 	if raddr == nil {
 		return nil, &net.OpError{Op: "dial", Net: network, Source: opAddr(laddr), Addr: nil, Err: errMissingAddress}
 	}
-	return dialTCPAddr(network, laddr, raddr, b) // tfo_bsd+windows.go, tfo_linux.go, tfo_unsupported.go
+	return dialTCPAddr(network, laddr, raddr, b) // tfo_bsd+windows.go, tfo_connect_stub.go, tfo_linux.go
 }
 
 func networkIsTCP(network string) bool {

tfo_bsd+windows.go

@@ -1,4 +1,4 @@
-//go:build darwin || freebsd || windows
+//go:build darwin || freebsd || (windows && (!go1.23 || (go1.23 && tfogo_checklinkname0)))
 
 package tfo
 

tfo_bsd.go

@@ -7,6 +7,6 @@ func setTFODialerFromSocket(fd uintptr) error {
 }
 
 // doConnectCanFallback returns whether err from [doConnect] indicates lack of TFO support.
-func doConnectCanFallback(err error) bool {
+func doConnectCanFallback(_ error) bool {
 	return false
 }

tfo_supported.go → tfo_connect_generic.go

@@ -1,4 +1,4 @@
-//go:build darwin || freebsd || linux || windows
+//go:build darwin || freebsd || linux || (windows && (!go1.23 || (go1.23 && tfogo_checklinkname0)))
 
 package tfo
 
@@ -11,7 +11,7 @@ import (
 	_ "unsafe"
 )
 
-const comptimeNoTFO = false
+const comptimeDialNoTFO = false
 
 const (
 	defaultTCPKeepAlive  = 15 * time.Second

tfo_connect_stub.go

@@ -0,0 +1,21 @@
+//go:build !darwin && !freebsd && !linux && (!windows || (windows && go1.23 && !tfogo_checklinkname0))
+
+package tfo
+
+import (
+	"context"
+	"net"
+)
+
+const comptimeDialNoTFO = true
+
+func (d *Dialer) dialTFO(ctx context.Context, network, address string, b []byte) (*net.TCPConn, error) {
+	if d.Fallback {
+		return d.dialAndWriteTCPConn(ctx, network, address, b)
+	}
+	return nil, ErrPlatformUnsupported
+}
+
+func dialTCPAddr(_ string, _, _ *net.TCPAddr, _ []byte) (*net.TCPConn, error) {
+	return nil, ErrPlatformUnsupported
+}

tfo_unsupported_test.go → tfo_connect_stub_test.go

@@ -1,4 +1,4 @@
-//go:build !darwin && !freebsd && !linux && !windows
+//go:build !darwin && !freebsd && !linux && (!windows || (windows && go1.23 && !tfogo_checklinkname0))
 
 package tfo
 
@@ -7,24 +7,6 @@ import (
 	"testing"
 )
 
-func TestListenTFO(t *testing.T) {
-	ln, err := Listen("tcp", "")
-	if ln != nil {
-		t.Error("Expected nil listener")
-	}
-	if err != ErrPlatformUnsupported {
-		t.Errorf("Expected ErrPlatformUnsupported, got %v", err)
-	}
-
-	lntcp, err := ListenTCP("tcp", nil)
-	if lntcp != nil {
-		t.Error("Expected nil listener")
-	}
-	if err != ErrPlatformUnsupported {
-		t.Errorf("Expected ErrPlatformUnsupported, got %v", err)
-	}
-}
-
 func TestDialTFO(t *testing.T) {
 	s, err := newDiscardTCPServer(context.Background())
 	if err != nil {

tfo_listen_stub.go

@@ -0,0 +1,14 @@
+//go:build !darwin && !freebsd && !linux && !windows
+
+package tfo
+
+import (
+	"context"
+	"net"
+)
+
+const comptimeListenNoTFO = true
+
+func (*ListenConfig) listenTFO(_ context.Context, _, _ string) (net.Listener, error) {
+	return nil, ErrPlatformUnsupported
+}

tfo_listen_stub_test.go

@@ -0,0 +1,25 @@
+//go:build !darwin && !freebsd && !linux && !windows
+
+package tfo
+
+import (
+	"testing"
+)
+
+func TestListenTFO(t *testing.T) {
+	ln, err := Listen("tcp", "")
+	if ln != nil {
+		t.Error("Expected nil listener")
+	}
+	if err != ErrPlatformUnsupported {
+		t.Errorf("Expected ErrPlatformUnsupported, got %v", err)
+	}
+
+	lntcp, err := ListenTCP("tcp", nil)
+	if lntcp != nil {
+		t.Error("Expected nil listener")
+	}
+	if err != ErrPlatformUnsupported {
+		t.Errorf("Expected ErrPlatformUnsupported, got %v", err)
+	}
+}

tfo_listen_supported.go

@@ -0,0 +1,5 @@
+//go:build darwin || freebsd || linux || windows
+
+package tfo
+
+const comptimeListenNoTFO = false

tfo_supported_test.go

@@ -1,4 +1,4 @@
-//go:build darwin || freebsd || linux || windows
+//go:build darwin || freebsd || linux || (windows && (!go1.23 || (go1.23 && tfogo_checklinkname0)))
 
 package tfo
 

tfo_test.go

@@ -50,12 +50,24 @@ func runtimeFallbackSetDialLinuxSendto(t *testing.T) {
 	}
 }
 
-var listenConfigCases = []struct {
+type listenConfigTestCase struct {
 	name               string
 	listenConfig       ListenConfig
 	mptcp              mptcpStatus
 	setRuntimeFallback runtimeFallbackHelperFunc
-}{
+}
+
+func (c listenConfigTestCase) shouldSkip() bool {
+	return comptimeListenNoTFO && !c.listenConfig.tfoDisabled()
+}
+
+func (c listenConfigTestCase) checkSkip(t *testing.T) {
+	if c.shouldSkip() {
+		t.Skip("not applicable to the current platform")
+	}
+}
+
+var listenConfigCases = []listenConfigTestCase{
 	{"TFO", ListenConfig{}, mptcpUseDefault, runtimeFallbackAsIs},
 	{"TFO+RuntimeNoTFO", ListenConfig{}, mptcpUseDefault, runtimeFallbackSetListenNoTFO},
 	{"TFO+MPTCPEnabled", ListenConfig{}, mptcpEnabled, runtimeFallbackAsIs},
@@ -79,13 +91,35 @@ var listenConfigCases = []struct {
 	{"NoTFO+MPTCPDisabled", ListenConfig{DisableTFO: true}, mptcpDisabled, runtimeFallbackAsIs},
 }
 
-var dialerCases = []struct {
+type dialerTestCase struct {
 	name               string
 	dialer             Dialer
 	mptcp              mptcpStatus
 	setRuntimeFallback runtimeFallbackHelperFunc
 	linuxOnly          bool
-}{
+}
+
+func (c dialerTestCase) shouldSkip() bool {
+	if comptimeDialNoTFO && !c.dialer.DisableTFO {
+		return true
+	}
+	switch runtime.GOOS {
+	case "linux", "android":
+	default:
+		if c.linuxOnly {
+			return true
+		}
+	}
+	return false
+}
+
+func (c dialerTestCase) checkSkip(t *testing.T) {
+	if c.shouldSkip() {
+		t.Skip("not applicable to the current platform")
+	}
+}
+
+var dialerCases = []dialerTestCase{
 	{"TFO", Dialer{}, mptcpUseDefault, runtimeFallbackAsIs, false},
 	{"TFO+RuntimeNoTFO", Dialer{}, mptcpUseDefault, runtimeFallbackSetDialNoTFO, false},
 	{"TFO+RuntimeLinuxSendto", Dialer{}, mptcpUseDefault, runtimeFallbackSetDialLinuxSendto, true},
@@ -160,20 +194,13 @@ func init() {
 	// Generate [cases].
 	cases = make([]testCase, 0, len(listenConfigCases)*len(dialerCases))
 	for _, lc := range listenConfigCases {
-		if comptimeNoTFO && !lc.listenConfig.tfoDisabled() {
+		if lc.shouldSkip() {
 			continue
 		}
 		for _, d := range dialerCases {
-			if comptimeNoTFO && !d.dialer.DisableTFO {
+			if d.shouldSkip() {
 				continue
 			}
-			switch runtime.GOOS {
-			case "linux", "android":
-			default:
-				if d.linuxOnly {
-					continue
-				}
-			}
 			cases = append(cases, testCase{
 				name:                     lc.name + "/" + d.name,
 				listenConfig:             lc.listenConfig,
@@ -193,7 +220,7 @@ type discardTCPServer struct {
 
 // newDiscardTCPServer creates a new [discardTCPServer] that listens on a random port.
 func newDiscardTCPServer(ctx context.Context) (*discardTCPServer, error) {
-	lc := ListenConfig{DisableTFO: comptimeNoTFO}
+	lc := ListenConfig{DisableTFO: comptimeListenNoTFO}
 	ln, err := lc.Listen(ctx, "tcp", "[::1]:")
 	if err != nil {
 		return nil, err
@@ -293,6 +320,7 @@ func TestListenDialUDP(t *testing.T) {
 func TestListenCtrlFn(t *testing.T) {
 	for _, c := range listenConfigCases {
 		t.Run(c.name, func(t *testing.T) {
+			c.checkSkip(t)
 			c.setRuntimeFallback(t)
 			testListenCtrlFn(t, c.listenConfig)
 		})
@@ -312,6 +340,7 @@ func TestDialCtrlFn(t *testing.T) {
 
 	for _, c := range dialerCases {
 		t.Run(c.name, func(t *testing.T) {
+			c.checkSkip(t)
 			c.setRuntimeFallback(t)
 			testDialCtrlFn(t, c.dialer, address)
 			testDialCtrlCtxFn(t, c.dialer, address)