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x/crypto/ssh: handle missing exit status more gracefully.

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According to RFC 4254 section 6.10, SSH server implementations may
omit the exit-status and exit-signal messages.  If this happens, we
now return &ExitMissingError{}, so clients can handle this case
specifically.

This came up in the discussion of issue #16194.

Change-Id: Iae5e916b18aa5bd8e95618e9fcfcab8b19e147d9
Reviewed-on: https://go-review.googlesource.com/24727
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Han-Wen Nienhuys
2016-07-06 18:05:22 +00:00
parent 077efaa604
commit d81fdb778b
2 changed files with 24 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ssh/session.go
+22 -7
View File
@@ -282,9 +282,10 @@ func (s *Session) Start(cmd string) error {
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the command fails to run or doesn't complete successfully, the
// error is of type *ExitError. Other error types may be
// returned for I/O problems.
// If the remote server does not send an exit status, an error of type
// *ExitMissingError is returned. If the command completes
// unsuccessfully or is interrupted by a signal, the error is of type
// *ExitError. Other error types may be returned for I/O problems.
func (s *Session) Run(cmd string) error {
err := s.Start(cmd)
if err != nil {
@@ -371,9 +372,10 @@ func (s *Session) start() error {
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the command fails to run or doesn't complete successfully, the
// error is of type *ExitError. Other error types may be
// returned for I/O problems.
// If the remote server does not send an exit status, an error of type
// *ExitMissingError is returned. If the command completes
// unsuccessfully or is interrupted by a signal, the error is of type
// *ExitError. Other error types may be returned for I/O problems.
func (s *Session) Wait() error {
if !s.started {
return errors.New("ssh: session not started")
@@ -431,16 +433,29 @@ func (s *Session) wait(reqs <-chan *Request) error {
if wm.status == -1 {
// exit-status was never sent from server
if wm.signal == "" {
return errors.New("wait: remote command exited without exit status or exit signal")
// signal was not sent either. RFC 4254
// section 6.10 recommends against this
// behavior, but it is allowed, so we let
// clients handle it.
return &ExitMissingError{}
}
wm.status = 128
if _, ok := signals[Signal(wm.signal)]; ok {
wm.status += signals[Signal(wm.signal)]
}
}
return &ExitError{wm}
}
// ExitMissingError is returned if a session is torn down cleanly, but
// the server sends no confirmation of the exit status.
type ExitMissingError struct{}
func (e *ExitMissingError) Error() string {
return "wait: remote command exited without exit status or exit signal"
}
func (s *Session) stdin() {
if s.stdinpipe {
return
ssh/session_test.go
+2 -6
View File
@@ -297,7 +297,6 @@ func TestUnknownExitSignal(t *testing.T) {
}
}
// Test WaitMsg is not returned if the channel closes abruptly.
func TestExitWithoutStatusOrSignal(t *testing.T) {
conn := dial(exitWithoutSignalOrStatus, t)
defer conn.Close()
@@ -313,11 +312,8 @@ func TestExitWithoutStatusOrSignal(t *testing.T) {
if err == nil {
t.Fatalf("expected command to fail but it didn't")
}
_, ok := err.(*ExitError)
if ok {
// you can't actually test for errors.errorString
// because it's not exported.
t.Fatalf("expected *errorString but got %T", err)
if _, ok := err.(*ExitMissingError); !ok {
t.Fatalf("got %T want *ExitMissingError", err)
}
}