Fix compatibility

Author: wwqgtxx

errors_go120.go

@@ -0,0 +1,7 @@
+//go:build !go1.21
+
+package tfo
+
+import "errors"
+
+var ErrUnsupported = errors.New("unsupported operation")

errors_go121.go

@@ -0,0 +1,7 @@
+//go:build go1.21
+
+package tfo
+
+import "errors"
+
+var ErrUnsupported = errors.ErrUnsupported

go.mod

@@ -1,5 +1,5 @@
 module github.com/metacubex/tfo-go
 
-go 1.22.0
+go 1.20.0
 
 require golang.org/x/sys v0.17.0

mptcp_go120.go

@@ -0,0 +1,13 @@
+//go:build !go1.21
+
+package tfo
+
+import "net"
+
+func multipathTCP(d net.Dialer) bool {
+	return false
+}
+
+func setMultipathTCP(d net.Dialer, use bool) {
+	return
+}

mptcp_go121.go

@@ -0,0 +1,13 @@
+//go:build go1.21
+
+package tfo
+
+import "net"
+
+func multipathTCP(d net.Dialer) bool {
+	return d.MultipathTCP()
+}
+
+func setMultipathTCP(d net.Dialer, use bool) {
+	d.SetMultipathTCP(use)
+}

tfo.go

@@ -32,7 +32,7 @@ func (PlatformUnsupportedError) Error() string {
 }
 
 func (PlatformUnsupportedError) Is(target error) bool {
-	return target == errors.ErrUnsupported
+	return target == ErrUnsupported
 }
 
 var runtimeListenNoTFO atomic.Bool

tfo_bsd+linux.go

@@ -64,7 +64,7 @@ func (d *Dialer) dialSingle(ctx context.Context, network string, laddr, raddr *n
 	}
 
 	if err = setTFODialerFromSocket(uintptr(fd)); err != nil {
-		if !d.Fallback || !errors.Is(err, errors.ErrUnsupported) {
+		if !d.Fallback || !errors.Is(err, ErrUnsupported) {
 			unix.Close(fd)
 			return nil, wrapSyscallError("setsockopt("+setTFODialerFromSocketSockoptName+")", err)
 		}

tfo_bsd+windows.go

@@ -16,7 +16,7 @@ func (d *Dialer) dialTFO(ctx context.Context, network, address string, b []byte)
 
 func dialTCPAddr(network string, laddr, raddr *net.TCPAddr, b []byte) (*net.TCPConn, error) {
 	var d Dialer
-	d.SetMultipathTCP(false) // Align with [net.DialTCP].
+	setMultipathTCP(d.Dialer, false) // Align with [net.DialTCP].
 	c, err := d.dialSingle(context.Background(), network, laddr, raddr, b, nil)
 	if err != nil {
 		return nil, &net.OpError{Op: "dial", Net: network, Source: laddr, Addr: raddr, Err: err}

tfo_darwin.go

@@ -32,7 +32,7 @@ func (lc *ListenConfig) listenTFO(ctx context.Context, network, address string)
 		}
 
 		if err != nil {
-			if !lc.Fallback || !errors.Is(err, errors.ErrUnsupported) {
+			if !lc.Fallback || !errors.Is(err, ErrUnsupported) {
 				return wrapSyscallError("setsockopt(TCP_FASTOPEN_FORCE_ENABLE)", err)
 			}
 			runtimeListenNoTFO.Store(true)
@@ -60,7 +60,7 @@ func (lc *ListenConfig) listenTFO(ctx context.Context, network, address string)
 
 	if err != nil {
 		ln.Close()
-		if !lc.Fallback || !errors.Is(err, errors.ErrUnsupported) {
+		if !lc.Fallback || !errors.Is(err, ErrUnsupported) {
 			return nil, wrapSyscallError("setsockopt(TCP_FASTOPEN)", err)
 		}
 		runtimeListenNoTFO.Store(true)
@@ -72,7 +72,7 @@ func (lc *ListenConfig) listenTFO(ctx context.Context, network, address string)
 const AF_MULTIPATH = 39
 
 func (d *Dialer) socket(domain int) (fd int, err error) {
-	if d.MultipathTCP() {
+	if multipathTCP(d.Dialer) {
 		domain = AF_MULTIPATH
 	}
 	fd, err = unix.Socket(domain, unix.SOCK_STREAM, unix.IPPROTO_TCP)
@@ -89,7 +89,7 @@ func (d *Dialer) socket(domain int) (fd int, err error) {
 }
 
 func (d *Dialer) setIPv6Only(fd int, family int, ipv6only bool) error {
-	if d.MultipathTCP() {
+	if multipathTCP(d.Dialer) {
 		return nil
 	}
 	return setIPv6Only(fd, family, ipv6only)

tfo_linux.go

@@ -63,7 +63,7 @@ func (d *Dialer) dialTFO(ctx context.Context, network, address string, b []byte)
 		}
 
 		if err != nil {
-			if d.Fallback && errors.Is(err, errors.ErrUnsupported) {
+			if d.Fallback && errors.Is(err, ErrUnsupported) {
 				canFallback = true
 			}
 			return wrapSyscallError("setsockopt(TCP_FASTOPEN_CONNECT)", err)