coder · spikecurtis · Jul 27, 2022 · Jul 25, 2022 · Jul 27, 2022 · Jul 27, 2022
diff --git a/agent/agent.go b/agent/agent.go
@@ -43,6 +43,11 @@ const (
 	ProtocolReconnectingPTY = "reconnecting-pty"
 	ProtocolSSH             = "ssh"
 	ProtocolDial            = "dial"
+
+	// MagicSessionErrorCode indicates that something went wrong with the session, rather than the
+	// command just returning a nonzero exit code, and is chosen as an arbitrary, high number
+	// unlikely to shadow other exit codes, which are typically 1, 2, 3, etc.
+	MagicSessionErrorCode = 229
 )
 
 type Options struct {
@@ -273,9 +278,17 @@ func (a *agent) init(ctx context.Context) {
 		},
 		Handler: func(session ssh.Session) {
 			err := a.handleSSHSession(session)
+			var exitError *exec.ExitError
+			if xerrors.As(err, &exitError) {
+				a.logger.Debug(ctx, "ssh session returned", slog.Error(exitError))
+				_ = session.Exit(exitError.ExitCode())
+				return
+			}
 			if err != nil {
 				a.logger.Warn(ctx, "ssh session failed", slog.Error(err))
-				_ = session.Exit(1)
+				// This exit code is designed to be unlikely to be confused for a legit exit code
+				// from the process.
+				_ = session.Exit(MagicSessionErrorCode)
 				return
 			}
 		},
@@ -403,7 +416,7 @@ func (a *agent) createCommand(ctx context.Context, rawCommand string, env []stri
 	return cmd, nil
 }
 
-func (a *agent) handleSSHSession(session ssh.Session) error {
+func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
 	cmd, err := a.createCommand(session.Context(), session.RawCommand(), session.Environ())
 	if err != nil {
 		return err
@@ -426,14 +439,24 @@ func (a *agent) handleSSHSession(session ssh.Session) error {
 		if err != nil {
 			return xerrors.Errorf("start command: %w", err)
 		}
+		defer func() {
+			closeErr := ptty.Close()
+			if closeErr != nil {
+				a.logger.Warn(context.Background(), "failed to close tty",
+					slog.Error(closeErr))
+				if retErr == nil {
+					retErr = closeErr
+				}
+			}
+		}()
 		err = ptty.Resize(uint16(sshPty.Window.Height), uint16(sshPty.Window.Width))
 		if err != nil {
 			return xerrors.Errorf("resize ptty: %w", err)
 		}
 		go func() {
 			for win := range windowSize {
-				err = ptty.Resize(uint16(win.Height), uint16(win.Width))
-				if err != nil {
+				resizeErr := ptty.Resize(uint16(win.Height), uint16(win.Width))
+				if resizeErr != nil {
 					a.logger.Warn(context.Background(), "failed to resize tty", slog.Error(err))
 				}
 			}
@@ -444,9 +467,15 @@ func (a *agent) handleSSHSession(session ssh.Session) error {
 		go func() {
 			_, _ = io.Copy(session, ptty.Output())
 		}()
-		_, _ = process.Wait()
-		_ = ptty.Close()
-		return nil
+		err = process.Wait()
+		var exitErr *exec.ExitError
+		// ExitErrors just mean the command we run returned a non-zero exit code, which is normal
+		// and not something to be concerned about.  But, if it's something else, we should log it.
+		if err != nil && !xerrors.As(err, &exitErr) {
+			a.logger.Warn(context.Background(), "wait error",
+				slog.Error(err))
+		}
+		return err
 	}
 
 	cmd.Stdout = session
@@ -549,7 +578,7 @@ func (a *agent) handleReconnectingPTY(ctx context.Context, rawID string, conn ne
 		go func() {
 			// If the process dies randomly, we should
 			// close the pty.
-			_, _ = process.Wait()
+			_ = process.Wait()
 			rpty.Close()
 		}()
 		go func() {

diff --git a/agent/agent_test.go b/agent/agent_test.go
@@ -16,6 +16,8 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/xerrors"
+
 	scp "github.com/bramvdbogaerde/go-scp"
 	"github.com/google/uuid"
 	"github.com/pion/udp"
@@ -69,7 +71,7 @@ func TestAgent(t *testing.T) {
 		require.True(t, strings.HasSuffix(strings.TrimSpace(string(output)), "gitssh --"))
 	})
 
-	t.Run("SessionTTY", func(t *testing.T) {
+	t.Run("SessionTTYShell", func(t *testing.T) {
 		t.Parallel()
 		if runtime.GOOS == "windows" {
 			// This might be our implementation, or ConPTY itself.
@@ -103,6 +105,29 @@ func TestAgent(t *testing.T) {
 		require.NoError(t, err)
 	})
 
+	t.Run("SessionTTYExitCode", func(t *testing.T) {
+		t.Parallel()
+		session := setupSSHSession(t, agent.Metadata{})
+		command := "areallynotrealcommand"
+		err := session.RequestPty("xterm", 128, 128, ssh.TerminalModes{})
+		require.NoError(t, err)
+		ptty := ptytest.New(t)
+		require.NoError(t, err)
+		session.Stdout = ptty.Output()
+		session.Stderr = ptty.Output()
+		session.Stdin = ptty.Input()
+		err = session.Start(command)
+		require.NoError(t, err)
+		err = session.Wait()
+		exitErr := &ssh.ExitError{}
+		require.True(t, xerrors.As(err, &exitErr))
+		if runtime.GOOS == "windows" {
+			assert.Equal(t, 1, exitErr.ExitStatus())
+		} else {
+			assert.Equal(t, 127, exitErr.ExitStatus())
+		}
+	})
+
 	t.Run("LocalForwarding", func(t *testing.T) {
 		t.Parallel()
 		random, err := net.Listen("tcp", "127.0.0.1:0")

diff --git a/pty/pty.go b/pty/pty.go
@@ -29,6 +29,16 @@ type PTY interface {
 	Resize(height uint16, width uint16) error
 }
 
+// Process represents a process running in a PTY
+type Process interface {
+
+	// Wait for the command to complete.  Returned error is as for exec.Cmd.Wait()
+	Wait() error
+
+	// Kill the command process.  Returned error is as for os.Process.Kill()
+	Kill() error
+}
+
 // WithFlags represents a PTY whose flags can be inspected, in particular
 // to determine whether local echo is enabled.
 type WithFlags interface {

diff --git a/pty/pty_other.go b/pty/pty_other.go
@@ -5,6 +5,8 @@ package pty
 
 import (
 	"os"
+	"os/exec"
+	"runtime"
 	"sync"
 
 	"github.com/creack/pty"
@@ -27,6 +29,15 @@ type otherPty struct {
 	pty, tty *os.File
 }
 
+type otherProcess struct {
+	pty *os.File
+	cmd *exec.Cmd
+
+	// cmdDone protects access to cmdErr: anything reading cmdErr should read from cmdDone first.
+	cmdDone chan any
+	cmdErr  error
+}
+
 func (p *otherPty) Input() ReadWriter {
 	return ReadWriter{
 		Reader: p.tty,
@@ -66,3 +77,21 @@ func (p *otherPty) Close() error {
 	}
 	return nil
 }
+
+func (p *otherProcess) Wait() error {
+	<-p.cmdDone
+	return p.cmdErr
+}
+
+func (p *otherProcess) Kill() error {
+	return p.cmd.Process.Kill()
+}
+
+func (p *otherProcess) waitInternal() {
+	// The GC can garbage collect the TTY FD before the command
+	// has finished running. See:
+	// https://github.com/creack/pty/issues/127#issuecomment-932764012
+	p.cmdErr = p.cmd.Wait()
+	runtime.KeepAlive(p.pty)
+	close(p.cmdDone)
+}
diff --git a/pty/pty_windows.go b/pty/pty_windows.go
@@ -5,6 +5,7 @@ package pty
 
 import (
 	"os"
+	"os/exec"
 	"sync"
 	"unsafe"
 
@@ -66,6 +67,13 @@ type ptyWindows struct {
 	closed     bool
 }
 
+type windowsProcess struct {
+	// cmdDone protects access to cmdErr: anything reading cmdErr should read from cmdDone first.
+	cmdDone chan any
+	cmdErr  error
+	proc    *os.Process
+}
+
 func (p *ptyWindows) Output() ReadWriter {
 	return ReadWriter{
 		Reader: p.outputRead,
@@ -111,3 +119,25 @@ func (p *ptyWindows) Close() error {
 
 	return nil
 }
+
+func (p *windowsProcess) waitInternal() {
+	defer close(p.cmdDone)
+	state, err := p.proc.Wait()
+	if err != nil {
+		p.cmdErr = err
+		return
+	}
+	if !state.Success() {
+		p.cmdErr = &exec.ExitError{ProcessState: state}
+		return
+	}
+}
+
+func (p *windowsProcess) Wait() error {
+	<-p.cmdDone
+	return p.cmdErr
+}
+
+func (p *windowsProcess) Kill() error {
+	return p.proc.Kill()
+}
diff --git a/pty/ptytest/ptytest.go b/pty/ptytest/ptytest.go
@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"context"
 	"io"
-	"os"
 	"os/exec"
 	"runtime"
 	"strings"
@@ -27,7 +26,7 @@ func New(t *testing.T) *PTY {
 	return create(t, ptty, "cmd")
 }
 
-func Start(t *testing.T, cmd *exec.Cmd) (*PTY, *os.Process) {
+func Start(t *testing.T, cmd *exec.Cmd) (*PTY, pty.Process) {
 	ptty, ps, err := pty.Start(cmd)
 	require.NoError(t, err)
 	return create(t, ptty, cmd.Args[0]), ps

diff --git a/pty/start.go b/pty/start.go
@@ -1,10 +1,11 @@
 package pty
 
 import (
-	"os"
 	"os/exec"
 )
 
-func Start(cmd *exec.Cmd) (PTY, *os.Process, error) {
+// Start the command in a TTY.  The calling code must not use cmd after passing it to the PTY, and
+// instead rely on the returned Process to manage the command/process.
+func Start(cmd *exec.Cmd) (PTY, Process, error) {
 	return startPty(cmd)
 }
diff --git a/pty/start_other.go b/pty/start_other.go
@@ -4,7 +4,6 @@
 package pty
 
 import (
-	"os"
 	"os/exec"
 	"runtime"
 	"strings"
@@ -14,7 +13,7 @@ import (
 	"golang.org/x/xerrors"
 )
 
-func startPty(cmd *exec.Cmd) (PTY, *os.Process, error) {
+func startPty(cmd *exec.Cmd) (PTY, Process, error) {
 	ptty, tty, err := pty.Open()
 	if err != nil {
 		return nil, nil, xerrors.Errorf("open: %w", err)
@@ -37,16 +36,15 @@ func startPty(cmd *exec.Cmd) (PTY, *os.Process, error) {
 		}
 		return nil, nil, xerrors.Errorf("start: %w", err)
 	}
-	go func() {
-		// The GC can garbage collect the TTY FD before the command
-		// has finished running. See:
-		// https://github.com/creack/pty/issues/127#issuecomment-932764012
-		_ = cmd.Wait()
-		runtime.KeepAlive(ptty)
-	}()
 	oPty := &otherPty{
 		pty: ptty,
 		tty: tty,
 	}
-	return oPty, cmd.Process, nil
+	oProcess := &otherProcess{
+		pty:     ptty,
+		cmd:     cmd,
+		cmdDone: make(chan any),
+	}
+	go oProcess.waitInternal()
+	return oPty, oProcess, nil
 }
diff --git a/pty/start_other_test.go b/pty/start_other_test.go
@@ -7,6 +7,10 @@ import (
 	"os/exec"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/xerrors"
+
 	"go.uber.org/goleak"
 
 	"github.com/coder/coder/pty/ptytest"
@@ -20,7 +24,20 @@ func TestStart(t *testing.T) {
 	t.Parallel()
 	t.Run("Echo", func(t *testing.T) {
 		t.Parallel()
-		pty, _ := ptytest.Start(t, exec.Command("echo", "test"))
+		pty, ps := ptytest.Start(t, exec.Command("echo", "test"))
 		pty.ExpectMatch("test")
+		err := ps.Wait()
+		require.NoError(t, err)
+	})
+
+	t.Run("Kill", func(t *testing.T) {
+		t.Parallel()
+		_, ps := ptytest.Start(t, exec.Command("sleep", "30"))
+		err := ps.Kill()
+		assert.NoError(t, err)
+		err = ps.Wait()
+		var exitErr *exec.ExitError
+		require.True(t, xerrors.As(err, &exitErr))
+		assert.NotEqual(t, 0, exitErr.ExitCode())
 	})
 }
diff --git a/pty/start_windows.go b/pty/start_windows.go
@@ -16,7 +16,7 @@ import (
 
 // Allocates a PTY and starts the specified command attached to it.
 // See: https://docs.microsoft.com/en-us/windows/console/creating-a-pseudoconsole-session#creating-the-hosted-process
-func startPty(cmd *exec.Cmd) (PTY, *os.Process, error) {
+func startPty(cmd *exec.Cmd) (PTY, Process, error) {
 	fullPath, err := exec.LookPath(cmd.Path)
 	if err != nil {
 		return nil, nil, err
@@ -83,7 +83,12 @@ func startPty(cmd *exec.Cmd) (PTY, *os.Process, error) {
 	if err != nil {
 		return nil, nil, xerrors.Errorf("find process %d: %w", processInfo.ProcessId, err)
 	}
-	return pty, process, nil
+	wp := &windowsProcess{
+		cmdDone: make(chan any),
+		proc:    process,
+	}
+	go wp.waitInternal()
+	return pty, wp, nil
 }
 
 // Taken from: https://github.com/microsoft/hcsshim/blob/7fbdca16f91de8792371ba22b7305bf4ca84170a/internal/exec/exec.go#L476