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replace forkpty() with posix_openpt() + posix_spawn() (T-96)

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`forkpty` calls `fork()` underneath. `fork()` in a multithreaded
process is unsafe: only the calling thread survives in the child,
but libc locks held by other threads remain "locked forever." With
the multi-threaded Dart VM as parent, ~5% of spawns deadlocked in
the child before `execve` (forensic probe: child stuck in S state
with comm=`DartWorker`, master fd never sees POLLIN).

`posix_spawn` uses `vfork` on glibc/musl/macOS, keeping the parent
suspended until execve completes — no Dart code runs in the child.
Pty pair built via the POSIX-standard `posix_openpt` / `grantpt` /
`unlockpt` / `ptsname` sequence. Probed: zero hangs in 300
sequential spawns vs ~5% before.

Behavior change: missing executable / missing workingDirectory now
surface as a `PtyException` thrown by `NativePty.start` rather than
a diagnostic written from the child to the slave PTY. Cleaner error
path for callers.

Side benefit: drops the `libutil.so.1` dynamic-library dependency.
PTY now resolves entirely against libc via `DynamicLibrary.process()`.

Splits the library-level `@Tags(['forkpty'])` on session_test.dart
into a per-test tag, so the now-runnable-under-flutter-test cases
contribute to coverage. `dart_test.yaml` declares the tag so the
exclude-tags filters honor it. Drops the `retry: 2` workaround from
the formerly-flaky registry test.

D-5 amended. Trims session-introduced CHANGELOG entries that were
over-verbose for the Keep-a-Changelog format.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
jpmschweitzer
2026-05-17 20:21:41 +02:00
co-authored by Claude Opus 4.7
parent ab2e5e618b
commit 8074bf4201
10 changed files with 291 additions and 225 deletions
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test/pty/session_test.dart
+43 -52
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@@ -1,19 +1,21 @@
/// NativePty smoke tests.
///
/// Exercises forkpty() end-to-end: spawn → child output through the
/// Exercises posix_spawn() end-to-end: spawn → child output through the
/// reader isolate. Linux + macOS only; skipped elsewhere.
///
/// Tagged `forkpty` — must run via `dart test`, not `flutter test`.
/// forkpty() forks the Flutter engine's multi-threaded process; the
/// child exec's fine but the master fd never produces readable output
/// inside the flutter test runner.
@Tags(['forkpty'])
/// Per-test `tags: ['forkpty']` marks the tests that need `dart test`
/// rather than the flutter test runner — currently just the
/// write/read-back bidirectional test (writes to the master fd never
/// reach the child under the flutter test runner; reads work fine).
/// Everything else runs under `flutter test` and contributes to
/// coverage.
library;
import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:clide/src/pty/errors.dart';
import 'package:clide/src/pty/native_pty.dart';
import 'package:test/test.dart';
@@ -48,7 +50,7 @@ void main() {
expect(buf.toString(), contains('hello-pty'));
});
test('write sends keystrokes to child', () async {
test('write sends keystrokes to child', tags: ['forkpty'], () async {
final s = NativePty.start(
executable: '/bin/sh',
arguments: [],
@@ -122,55 +124,44 @@ void main() {
expect(buf.toString(), contains('path-resolution-ok'));
});
test('non-existent workingDirectory produces the chdir-failed diagnostic', () async {
// chdir() fails in the child → writes diagnostic + _exit(1).
final s = NativePty.start(
executable: '/bin/sh',
arguments: ['-c', 'echo should-not-run'],
columns: 80,
rows: 24,
workingDirectory: '/tmp/clide-no-such-dir-${DateTime.now().microsecondsSinceEpoch}',
environment: {
...Platform.environment,
'TERM': 'xterm-256color',
},
test('non-existent workingDirectory surfaces a PtyException at spawn time', () {
// posix_spawn returns ENOENT (errno 2) when the file_actions chdir
// step finds the directory missing — propagates as a thrown
// PtyException, not a child-side diagnostic on the pty.
expect(
() => NativePty.start(
executable: '/bin/sh',
arguments: ['-c', 'echo should-not-run'],
columns: 80,
rows: 24,
workingDirectory: '/tmp/clide-no-such-dir-${DateTime.now().microsecondsSinceEpoch}',
environment: {
...Platform.environment,
'TERM': 'xterm-256color',
},
),
throwsA(isA<PtyException>().having((e) => e.errno, 'errno', 2)),
);
addTearDown(s.close);
final buf = StringBuffer();
final done = Completer<void>();
s.output.listen(
(b) => buf.write(utf8.decode(b, allowMalformed: true)),
onDone: () {
if (!done.isCompleted) done.complete();
},
);
await done.future.timeout(const Duration(seconds: 5), onTimeout: () {});
expect(buf.toString(), contains('chdir failed'));
});
test('non-existent executable produces the exec-failed diagnostic', () async {
final s = NativePty.start(
executable: '/tmp/clide-no-such-binary-${DateTime.now().microsecondsSinceEpoch}',
arguments: const [],
columns: 80,
rows: 24,
workingDirectory: '/',
environment: {
...Platform.environment,
'TERM': 'xterm-256color',
},
test('non-existent executable surfaces a PtyException at spawn time', () {
// posix_spawn surfaces exec-time errors as a non-zero return on
// glibc (which uses vfork — the child is suspended until execve
// either succeeds or fails). ENOENT (errno 2) for missing binary.
expect(
() => NativePty.start(
executable: '/tmp/clide-no-such-binary-${DateTime.now().microsecondsSinceEpoch}',
arguments: const [],
columns: 80,
rows: 24,
workingDirectory: '/',
environment: {
...Platform.environment,
'TERM': 'xterm-256color',
},
),
throwsA(isA<PtyException>().having((e) => e.errno, 'errno', 2)),
);
addTearDown(s.close);
final buf = StringBuffer();
final done = Completer<void>();
s.output.listen(
(b) => buf.write(utf8.decode(b, allowMalformed: true)),
onDone: () {
if (!done.isCompleted) done.complete();
},
);
await done.future.timeout(const Duration(seconds: 5), onTimeout: () {});
expect(buf.toString(), contains('exec failed'));
});
test('resize on a live PTY does not throw', () async {