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Commit197bedc

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fix(agent): Close stdin and stdout separately to fix pty output loss
Fixes#6656Closes#6840
1 parent311327c commit197bedc

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5 files changed

+55
-27
lines changed

5 files changed

+55
-27
lines changed

‎agent/agent.go‎

Lines changed: 23 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1131,19 +1131,32 @@ func (a *agent) handleSSHSession(session ssh.Session) (retErr error) {
11311131
// output being lost. To avoid this, we wait for the output copy to
11321132
// start before waiting for the command to exit. This ensures that the
11331133
// output copy goroutine will be scheduled before calling close on the
1134-
// pty.There is still a risk ofdata loss if a command produces a lot
1135-
//of output, see TestAgent_Session_TTY_HugeOutputIsNotLost (skipped).
1134+
// pty.This shouldn't be needed because of`pty.Dup()` below, but it
1135+
//may not be supported on all platforms.
11361136
outputCopyStarted:=make(chanstruct{})
1137-
ptyOutput:=func() io.Reader {
1137+
ptyOutput:=func() io.ReadCloser {
11381138
deferclose(outputCopyStarted)
1139-
returnptty.Output()
1139+
// Try to dup so we can separate stdin and stdout closure.
1140+
// Once the original pty is closed, the dup will return
1141+
// input/output error once the buffered data has been read.
1142+
stdout,err:=ptty.Dup()
1143+
iferr==nil {
1144+
returnstdout
1145+
}
1146+
// If we can't dup, we shouldn't close
1147+
// the fd since it's tied to stdin.
1148+
returnreadNopCloser{ptty.Output()}
11401149
}
11411150
wg.Add(1)
11421151
gofunc() {
11431152
// Ensure data is flushed to session on command exit, if we
11441153
// close the session too soon, we might lose data.
11451154
deferwg.Done()
1146-
_,_=io.Copy(session,ptyOutput())
1155+
1156+
stdout:=ptyOutput()
1157+
deferstdout.Close()
1158+
1159+
_,_=io.Copy(session,stdout)
11471160
}()
11481161
<-outputCopyStarted
11491162

@@ -1372,6 +1385,11 @@ func (a *agent) handleReconnectingPTY(ctx context.Context, logger slog.Logger, m
13721385
}
13731386
}
13741387

1388+
typereadNopCloserstruct{ io.Reader }
1389+
1390+
// Close implements io.Closer.
1391+
func (readNopCloser)Close()error {returnnil }
1392+
13751393
// startReportingConnectionStats runs the connection stats reporting goroutine.
13761394
func (a*agent)startReportingConnectionStats(ctx context.Context) {
13771395
reportStats:=func(networkStatsmap[netlogtype.Connection]netlogtype.Counts) {

‎agent/agent_test.go‎

Lines changed: 8 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -350,15 +350,8 @@ func TestAgent_Session_TTY_Hushlogin(t *testing.T) {
350350

351351
funcTestAgent_Session_TTY_FastCommandHasOutput(t*testing.T) {
352352
t.Parallel()
353-
ifruntime.GOOS=="windows" {
354-
// This might be our implementation, or ConPTY itself.
355-
// It's difficult to find extensive tests for it, so
356-
// it seems like it could be either.
357-
t.Skip("ConPTY appears to be inconsistent on Windows.")
358-
}
359-
360353
// This test is here to prevent regressions where quickly executing
361-
// commands (with TTY) don'tflush their output to the SSH session.
354+
// commands (with TTY) don'tsync their output to the SSH session.
362355
//
363356
// See: https://github.com/coder/coder/issues/6656
364357
ctx,cancel:=context.WithTimeout(context.Background(),testutil.WaitLong)
@@ -404,20 +397,13 @@ func TestAgent_Session_TTY_FastCommandHasOutput(t *testing.T) {
404397

405398
funcTestAgent_Session_TTY_HugeOutputIsNotLost(t*testing.T) {
406399
t.Parallel()
407-
ifruntime.GOOS=="windows" {
408-
// This might be our implementation, or ConPTY itself.
409-
// It's difficult to find extensive tests for it, so
410-
// it seems like it could be either.
411-
t.Skip("ConPTY appears to be inconsistent on Windows.")
412-
}
413-
t.Skip("This test proves we have a bug where parts of large output on a PTY can be lost after the command exits, skipped to avoid test failures.")
414-
415-
// This test is here to prevent prove we have a bug where quickly executing
416-
// commands (with TTY) don't flush their output to the SSH session. This is
417-
// due to the pty being closed before all the output has been copied, but
418-
// protecting against this requires a non-trivial rewrite of the output
419-
// processing (or figuring out a way to put the pty in a mode where this
420-
// does not happen).
400+
401+
// This test is here to prevent regressions where a command (with or
402+
// without) a large amount of output would not be fully copied to the
403+
// SSH session. On unix systems, this was fixed by duplicating the file
404+
// descriptor of the PTY master and using it for copying the output.
405+
//
406+
// See: https://github.com/coder/coder/issues/6656
421407
ctx,cancel:=context.WithTimeout(context.Background(),testutil.WaitLong)
422408
defercancel()
423409
//nolint:dogsled

‎pty/pty.go‎

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,11 @@ type PTY interface {
3131
// The same stream would be used to provide user input: pty.Input().Write(...)
3232
Input()ReadWriter
3333

34+
// Dup returns a new file descriptor for the PTY.
35+
//
36+
// This is useful for closing stdin and stdout separately.
37+
Dup() (*os.File,error)
38+
3439
// Resize sets the size of the PTY.
3540
Resize(heightuint16,widthuint16)error
3641
}

‎pty/pty_other.go‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@ import (
77
"os/exec"
88
"runtime"
99
"sync"
10+
"syscall"
1011

1112
"github.com/creack/pty"
1213
"github.com/u-root/u-root/pkg/termios"
@@ -113,6 +114,20 @@ func (p *otherPty) Resize(height uint16, width uint16) error {
113114
})
114115
}
115116

117+
func (p*otherPty)Dup() (*os.File,error) {
118+
varnewfdint
119+
err:=p.control(p.pty,func(fduintptr)error {
120+
varerrerror
121+
newfd,err=syscall.Dup(int(fd))
122+
returnerr
123+
})
124+
iferr!=nil {
125+
returnnil,err
126+
}
127+
128+
returnos.NewFile(uintptr(newfd),p.pty.Name()),nil
129+
}
130+
116131
func (p*otherPty)Close()error {
117132
p.mutex.Lock()
118133
deferp.mutex.Unlock()

‎pty/pty_windows.go‎

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -123,6 +123,10 @@ func (p *ptyWindows) Resize(height uint16, width uint16) error {
123123
returnnil
124124
}
125125

126+
func (p*ptyWindows)Dup() (*os.File,error) {
127+
returnnil,xerrors.Errorf("not implemented")
128+
}
129+
126130
func (p*ptyWindows)Close()error {
127131
p.closeMutex.Lock()
128132
deferp.closeMutex.Unlock()

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