tailscale: Add tailssh server

protocol/tailscale/tailssh/waiter_unix.go

@@ -0,0 +1,62 @@
+//go:build unix
+
+package tailssh
+
+import (
+	"os"
+	"syscall"
+)
+
+type ProcessWaiter struct {
+	process *os.Process
+	state   *os.ProcessState
+	waitErr error
+	done    chan struct{}
+}
+
+func NewProcessWaiter(process *os.Process) *ProcessWaiter {
+	pw := &ProcessWaiter{
+		process: process,
+		done:    make(chan struct{}),
+	}
+	go func() {
+		pw.state, pw.waitErr = pw.process.Wait()
+		close(pw.done)
+	}()
+	return pw
+}
+
+func (pw *ProcessWaiter) Wait() (uint32, error) {
+	<-pw.done
+	if pw.waitErr != nil {
+		return 0, pw.waitErr
+	}
+	status, loaded := pw.state.Sys().(syscall.WaitStatus)
+	if !loaded {
+		if pw.state.Success() {
+			return 0, nil
+		}
+		return 1, nil
+	}
+	if status.Signaled() {
+		return uint32(128 + status.Signal()), nil
+	}
+	return uint32(status.ExitStatus()), nil
+}
+
+func (pw *ProcessWaiter) Exited() bool {
+	select {
+	case <-pw.done:
+		return true
+	default:
+		return false
+	}
+}
+
+func (pw *ProcessWaiter) Signal(sig int) error {
+	return pw.process.Signal(syscall.Signal(sig))
+}
+
+func (pw *ProcessWaiter) Pid() int {
+	return pw.process.Pid
+}