tailscale: Add tailssh server

protocol/tailscale/tailssh/shell_unix.go

@@ -0,0 +1,88 @@
+//go:build unix && !ios
+
+package tailssh
+
+import (
+	"os"
+	"syscall"
+)
+
+type Shell struct {
+	master *os.File
+	waiter *ProcessWaiter
+	isPty  bool
+}
+
+func OpenPtyShell(shell string, args, env []string, dir string, uid, gid int, groups []int, rows, cols uint16) (*Shell, error) {
+	master, process, err := StartPtyProcess(shell, args, env, dir, uid, gid, groups, rows, cols)
+	if err != nil {
+		return nil, err
+	}
+	return &Shell{
+		master: master,
+		waiter: NewProcessWaiter(process),
+		isPty:  true,
+	}, nil
+}
+
+func OpenSocketpairShell(shell string, args, env []string, dir string, uid, gid int, groups []int) (*Shell, error) {
+	master, process, err := StartSocketpairProcess(shell, args, env, dir, uid, gid, groups)
+	if err != nil {
+		return nil, err
+	}
+	return &Shell{
+		master: master,
+		waiter: NewProcessWaiter(process),
+	}, nil
+}
+
+func (s *Shell) MasterFD() int {
+	return int(s.master.Fd())
+}
+
+func (s *Shell) IsPty() bool {
+	return s.isPty
+}
+
+func (s *Shell) Read(p []byte) (int, error) {
+	return s.master.Read(p)
+}
+
+func (s *Shell) Write(p []byte) (int, error) {
+	return s.master.Write(p)
+}
+
+func (s *Shell) Resize(rows, cols uint16) error {
+	if !s.isPty {
+		return nil
+	}
+	return SetWinsize(int(s.master.Fd()), rows, cols)
+}
+
+func (s *Shell) Signal(sig int) error {
+	return s.waiter.Signal(sig)
+}
+
+func (s *Shell) CloseWrite() error {
+	if s.isPty {
+		// A pty has no half-close; stdin EOF is delivered via the line discipline.
+		return nil
+	}
+	// The socketpair is a single SOCK_STREAM used for both directions; shutting
+	// down the write side delivers EOF to the child without killing it.
+	return syscall.Shutdown(int(s.master.Fd()), syscall.SHUT_WR)
+}
+
+func (s *Shell) Wait() (uint32, error) {
+	return s.waiter.Wait()
+}
+
+func (s *Shell) Close() error {
+	// Skip the kill once the child has been reaped: its PID may already have been
+	// reused, and Kill(-pid) would then signal an unrelated process group.
+	if !s.waiter.Exited() {
+		syscall.Kill(-s.waiter.Pid(), syscall.SIGKILL)
+	}
+	s.master.Close()
+	return nil
+}