tailscale: Add tailssh server

protocol/tailscale/tailssh/session_platform.go

@@ -0,0 +1,74 @@
+//go:build with_gvisor && !windows
+
+package tailssh
+
+import (
+	"os"
+	"syscall"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing/common"
+)
+
+type platformShellBackend struct {
+	platform adapter.PlatformInterface
+}
+
+func (b *platformShellBackend) OpenSession(request shellRequest) (shellSession, error) {
+	session, err := b.platform.OpenShellSession(request.User, request.Command, request.Env, request.Term, int32(request.Rows), int32(request.Cols))
+	if err != nil {
+		return nil, err
+	}
+	dupFd, err := syscall.Dup(int(session.MasterFD()))
+	if err != nil {
+		session.Close()
+		return nil, err
+	}
+	master := os.NewFile(uintptr(dupFd), "pty-master")
+	return &platformShellSession{
+		session: session,
+		master:  master,
+	}, nil
+}
+
+func (b *platformShellBackend) Close() error {
+	return nil
+}
+
+type platformShellSession struct {
+	session adapter.ShellSession
+	master  *os.File
+}
+
+func (s *platformShellSession) Read(p []byte) (int, error) {
+	return s.master.Read(p)
+}
+
+func (s *platformShellSession) Write(p []byte) (int, error) {
+	return s.master.Write(p)
+}
+
+func (s *platformShellSession) Close() error {
+	return common.Close(s.master, s.session)
+}
+
+func (s *platformShellSession) CloseWrite() error {
+	// The platform owns the master fd lifecycle; rely on Close for teardown.
+	return nil
+}
+
+func (s *platformShellSession) Resize(rows, cols uint16) error {
+	return s.session.Resize(int32(rows), int32(cols))
+}
+
+func (s *platformShellSession) Signal(sig int) error {
+	return s.session.Signal(int32(sig))
+}
+
+func (s *platformShellSession) Wait() (uint32, error) {
+	exitStatus, err := s.session.WaitExit()
+	if err != nil {
+		return 0, err
+	}
+	return uint32(exitStatus), nil
+}