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chore: update X11 forward session usage when there is a connection #18567

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Merged
merged 1 commit into from
Jun 27, 2025
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chore: update X11 forward session usage when there is a connection #18567

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5 changes: 5 additions & 0 deletions agent/agentssh/x11.go
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,11 @@ func (x *x11Forwarder) listenForConnections(
x.logger.Warn(ctx, "failed to accept X11 connection", slog.Error(err))
return
}

// Update session usage time since a new X11 connection was forwarded.
x.mu.Lock()
session.usedAt = time.Now()
x.mu.Unlock()
if x11.SingleConnection {
x.logger.Debug(ctx, "single connection requested, closing X11 listener")
x.closeAndRemoveSession(session)
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56 changes: 48 additions & 8 deletions agent/agentssh/x11_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -232,8 +232,31 @@ func TestServer_X11_EvictionLRU(t *testing.T) {
})
}

// Create one more session which should evict the first (LRU) session and
// therefore reuse the very first display/port.
// Connect X11 forwarding to the first session. This is used to test that
// connecting counts as a use of the display.
x11Chans := c.HandleChannelOpen("x11")
payload := "hello world"
go func() {
conn, err := inproc.Dial(ctx, testutil.NewAddr("tcp", fmt.Sprintf("localhost:%d", agentssh.X11StartPort+agentssh.X11DefaultDisplayOffset)))
assert.NoError(t, err)
_, err = conn.Write([]byte(payload))
assert.NoError(t, err)
_ = conn.Close()
}()

x11 := testutil.RequireReceive(ctx, t, x11Chans)
ch, reqs, err := x11.Accept()
require.NoError(t, err)
go gossh.DiscardRequests(reqs)
got := make([]byte, len(payload))
_, err = ch.Read(got)
require.NoError(t, err)
assert.Equal(t, payload, string(got))
_ = ch.Close()

// Create one more session which should evict a session and reuse the display.
// The first session was used to connect X11 forwarding, so it should not be evicted.
// Therefore, the second session should be evicted and its display reused.
extraSess, err := c.NewSession()
require.NoError(t, err)

Expand Down Expand Up @@ -271,17 +294,34 @@ func TestServer_X11_EvictionLRU(t *testing.T) {
require.NoError(t, sc.Err())
}

// The display number should have wrapped around to the starting value.
assert.Equal(t, agentssh.X11DefaultDisplayOffset, newDisplayNumber, "expected display number to be reused after eviction")
// The display number reused should correspond to the SECOND session (display offset 12)
expectedDisplay := agentssh.X11DefaultDisplayOffset + 2 // +1 was blocked port
assert.Equal(t, expectedDisplay, newDisplayNumber, "second session should have been evicted and its display reused")

// validate that the first session was torn down.
_, err = sessions[0].stdin.Write([]byte("echo DISPLAY=$DISPLAY\n"))
// First session should still be alive: send cmd and read output.
msgFirst := "still-alive"
_, err = sessions[0].stdin.Write([]byte("echo " + msgFirst + "\n"))
require.NoError(t, err)
for sessions[0].scanner.Scan() {
line := strings.TrimSpace(sessions[0].scanner.Text())
if strings.Contains(line, msgFirst) {
break
}
}
require.NoError(t, sessions[0].scanner.Err())

// Second session should now be closed.
_, err = sessions[1].stdin.Write([]byte("echo dead\n"))
require.ErrorIs(t, err, io.EOF)
err = sessions[0].sess.Wait()
err = sessions[1].sess.Wait()
require.Error(t, err)

// Cleanup.
for _, sh := range sessions[1:] {
for i, sh := range sessions {
if i == 1 {
// already closed
continue
}
err = sh.stdin.Close()
require.NoError(t, err)
err = sh.sess.Wait()
Expand Down
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