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fix(agent): Prevent SSH TTYs from losing command output on exit #6777

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Merged
merged 2 commits into from
Mar 24, 2023
Merged

fix(agent): Prevent SSH TTYs from losing command output on exit #6777

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fix(agent): Prevent SSH TTYs from losing command output on exit
mafredri Mar 24, 2023
03a0bb6
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mafredri Mar 24, 2023
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9 changes: 9 additions & 0 deletions agent/agent.go
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Original file line number Diff line number Diff line change
Expand Up @@ -844,6 +844,7 @@ func (a *agent) init(ctx context.Context) {
_ = session.Exit(MagicSessionErrorCode)
return
}
_ = session.Exit(0)
},
HostSigners: []ssh.Signer{randomSigner},
LocalPortForwardingCallback: func(ctx ssh.Context, destinationHost string, destinationPort uint32) bool {
Expand Down Expand Up @@ -1100,7 +1101,9 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
if err != nil {
return xerrors.Errorf("start command: %w", err)
}
var wg sync.WaitGroup
defer func() {
defer wg.Wait()
closeErr := ptty.Close()
if closeErr != nil {
a.logger.Warn(ctx, "failed to close tty", slog.Error(closeErr))
Expand All @@ -1117,10 +1120,16 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
}
}
}()
// We don't add input copy to wait group because
// it won't return until the session is closed.
go func() {
_, _ = io.Copy(ptty.Input(), session)
}()
wg.Add(1)
go func() {
// Ensure data is flushed to session on command exit, if we
// close the session too soon, we might lose data.
defer wg.Done()
_, _ = io.Copy(session, ptty.Output())
}()
err = process.Wait()
Expand Down
51 changes: 51 additions & 0 deletions agent/agent_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -348,6 +348,57 @@ func TestAgent_Session_TTY_Hushlogin(t *testing.T) {
require.NotContains(t, stdout.String(), wantNotMOTD, "should not show motd")
}

func TestAgent_Session_TTY_FastCommandHasOutput(t *testing.T) {
t.Parallel()
if runtime.GOOS == "windows" {
// This might be our implementation, or ConPTY itself.
// It's difficult to find extensive tests for it, so
// it seems like it could be either.
t.Skip("ConPTY appears to be inconsistent on Windows.")
}

// This test is here to prevent regressions where quickly executing
// commands (with TTY) don't flush their output to the SSH session.
//
// See: https://github.com/coder/coder/issues/6656
ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
defer cancel()
//nolint:dogsled
conn, _, _, _, _ := setupAgent(t, agentsdk.Metadata{}, 0)
sshClient, err := conn.SSHClient(ctx)
require.NoError(t, err)
defer sshClient.Close()

ptty := ptytest.New(t)

var stdout bytes.Buffer
// NOTE(mafredri): Increase iterations to increase chance of failure,
// assuming bug is present.
// Using 1000 iterations is basically a guaranteed failure (but let's
// not increase test times needlessly).
Comment on lines +375 to +378
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I really enjoy comments like this. I should do more of these!

for i := 0; i < 5; i++ {
func() {
stdout.Reset()

session, err := sshClient.NewSession()
require.NoError(t, err)
defer session.Close()
err = session.RequestPty("xterm", 128, 128, ssh.TerminalModes{})
require.NoError(t, err)

session.Stdout = &stdout
session.Stderr = ptty.Output()
session.Stdin = ptty.Input()
err = session.Start("echo wazzup")
require.NoError(t, err)

err = session.Wait()
require.NoError(t, err)
require.Contains(t, stdout.String(), "wazzup", "should output greeting")
}()
}
}

//nolint:paralleltest // This test reserves a port.
func TestAgent_TCPLocalForwarding(t *testing.T) {
random, err := net.Listen("tcp", "127.0.0.1:0")
Expand Down