Add -ssh: an opt-in built-in SSH server (public keys only, sessions only)

sshd/run_unix.go

@@ -0,0 +1,87 @@
+//go:build !windows
+
+package sshd
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+
+	"github.com/creack/pty"
+	"golang.org/x/crypto/ssh"
+)
+
+const (
+	ptySupported = true
+	runSupported = true
+)
+
+// run starts the user's shell (or, for exec, runs cmd through it) and returns its exit code.
+// With a pty request it gets a terminal, otherwise plain pipes.
+func run(ch ssh.Channel, cmd string, p *ptyReq, win <-chan [2]uint32) int {
+	shell := os.Getenv("SHELL")
+	if shell == "" {
+		shell = "/bin/sh"
+	}
+	var c *exec.Cmd
+	if cmd == "" {
+		c = exec.Command(shell, "-l")
+	} else {
+		c = exec.Command(shell, "-c", cmd)
+	}
+	c.Env = os.Environ()
+	if p != nil {
+		term := p.term
+		if term == "" {
+			term = "xterm"
+		}
+		c.Env = append(c.Env, "TERM="+term)
+		return runPty(ch, c, p, win)
+	}
+	in, err := c.StdinPipe()
+	if err != nil {
+		fmt.Fprintf(ch.Stderr(), "bamboo: %v\r\n", err)
+		return 255
+	}
+	go func() { io.Copy(in, ch); in.Close() }()
+	c.Stdout = ch
+	c.Stderr = ch.Stderr()
+	return exitCode(c.Run(), c)
+}
+
+func runPty(ch ssh.Channel, c *exec.Cmd, p *ptyReq, win <-chan [2]uint32) int {
+	f, err := pty.StartWithSize(c, &pty.Winsize{Cols: uint16(p.cols), Rows: uint16(p.rows)})
+	if err != nil {
+		fmt.Fprintf(ch.Stderr(), "bamboo: %v\r\n", err)
+		return 255
+	}
+	defer f.Close()
+	done := make(chan struct{})
+	defer close(done)
+	go func() {
+		for {
+			select {
+			case w := <-win:
+				pty.Setsize(f, &pty.Winsize{Cols: uint16(w[0]), Rows: uint16(w[1])})
+			case <-done:
+				return
+			}
+		}
+	}()
+	go func() { io.Copy(f, ch) }()
+	io.Copy(ch, f) // ends with an error when the shell exits and the terminal closes
+	return exitCode(c.Wait(), c)
+}
+
+func exitCode(err error, c *exec.Cmd) int {
+	if err == nil {
+		return 0
+	}
+	var ee *exec.ExitError
+	if errors.As(err, &ee) && ee.ExitCode() >= 0 {
+		return ee.ExitCode()
+	}
+	return 255
+}