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A Codex RPC can deadlock the reader it waits on

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This commit is contained in:
Ian Gulliver
2026-10-16 14:21:23 -07:00
parent 6ee2421d97
commit 66ff641bbd
5 changed files with 109 additions and 39 deletions
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internal/codex/session.go
+90 -32
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@@ -90,11 +90,11 @@ type rpcResult struct {
type Session struct {
cmd *exec.Cmd
stdin io.WriteCloser
stdin *os.File
events chan Event
done chan struct{}
writeMu sync.Mutex
writeLock chan struct{}
recordMu sync.Mutex
transcript io.Writer
@@ -160,18 +160,23 @@ func spawn(opts Options) (*Session, error) {
cmd.Stderr = os.Stderr
cmd.Env = buildEnv(opts)
stdin, err := cmd.StdinPipe()
stdinR, stdin, err := os.Pipe()
if err != nil {
return nil, err
}
cmd.Stdin = stdinR
stdout, err := cmd.StdoutPipe()
if err != nil {
stdinR.Close()
stdin.Close()
return nil, err
}
err = cmd.Start()
stdinR.Close()
if err != nil {
stdin.Close()
return nil, fmt.Errorf("start codex: %w", err)
}
@@ -180,10 +185,11 @@ func spawn(opts Options) (*Session, error) {
return s, nil
}
func newSession(opts Options, stdin io.WriteCloser, stdout io.Reader) *Session {
func newSession(opts Options, stdin *os.File, stdout io.Reader) *Session {
s := &Session{
stdin: stdin,
events: make(chan Event, 256),
writeLock: make(chan struct{}, 1),
done: make(chan struct{}),
transcript: opts.Transcript,
pending: map[int64]chan rpcResult{},
@@ -421,47 +427,81 @@ func (s *Session) Interrupt(ctx context.Context) error {
return s.Call(ctx, MethodTurnInterrupt, params, nil)
}
func (s *Session) Steer(ctx context.Context, text string) error {
func (s *Session) Steer(text string) (*Reply, error) {
s.stateMu.Lock()
params := TurnSteerParams{ThreadID: s.threadID, ExpectedTurnID: s.turnID, Input: []UserInput{{Type: UserInputTypeText, Text: text}}}
s.stateMu.Unlock()
if params.ExpectedTurnID == "" {
return errors.New("no turn in progress")
return nil, errors.New("no turn in progress")
}
return s.Call(ctx, MethodTurnSteer, params, nil)
return s.request(context.Background(), MethodTurnSteer, params)
}
func (s *Session) Compact(ctx context.Context) error {
return s.Call(ctx, MethodThreadCompactStart, ThreadCompactStartParams{ThreadID: s.ID()}, nil)
}
const rpcTimeout = time.Minute
type Reply struct {
s *Session
id int64
ch chan rpcResult
deadline time.Time
}
func (s *Session) Call(ctx context.Context, method string, params any, result any) error {
id := s.nextID.Add(1)
ch := make(chan rpcResult, 1)
r, err := s.request(ctx, method, params)
if err != nil {
return err
}
return r.Wait(ctx, result)
}
s.pendingMu.Lock()
s.pending[id] = ch
s.pendingMu.Unlock()
defer func() {
s.pendingMu.Lock()
delete(s.pending, id)
s.pendingMu.Unlock()
}()
func rpcDeadline(ctx context.Context) time.Time {
deadline := time.Now().Add(rpcTimeout)
d, ok := ctx.Deadline()
if ok && d.Before(deadline) {
return d
}
return deadline
}
func (s *Session) request(ctx context.Context, method string, params any) (*Reply, error) {
raw, err := json.Marshal(params)
if err != nil {
return err
return nil, err
}
err = s.write(message{ID: json.RawMessage(strconv.FormatInt(id, 10)), Method: method, Params: raw})
r := &Reply{s: s, id: s.nextID.Add(1), ch: make(chan rpcResult, 1), deadline: rpcDeadline(ctx)}
s.pendingMu.Lock()
s.pending[r.id] = r.ch
s.pendingMu.Unlock()
err = s.write(message{ID: json.RawMessage(strconv.FormatInt(r.id, 10)), Method: method, Params: raw}, r.deadline)
if err != nil {
return err
r.forget()
return nil, err
}
return r, nil
}
func (r *Reply) forget() {
r.s.pendingMu.Lock()
delete(r.s.pending, r.id)
r.s.pendingMu.Unlock()
}
func (r *Reply) Wait(ctx context.Context, result any) error {
defer r.forget()
ctx, cancel := context.WithDeadline(ctx, r.deadline)
defer cancel()
select {
case res := <-ch:
case res := <-r.ch:
if res.err != nil {
return res.err
}
@@ -469,7 +509,7 @@ func (s *Session) Call(ctx context.Context, method string, params any, result an
return nil
}
return json.Unmarshal(res.result, result)
case <-s.done:
case <-r.s.done:
return errors.New("codex exited")
case <-ctx.Done():
return ctx.Err()
@@ -485,13 +525,13 @@ func (s *Session) notify(method string, params any) error {
}
m.Params = raw
}
return s.write(m)
return s.write(m, time.Now().Add(rpcTimeout))
}
func (s *Session) Close() error {
s.writeMu.Lock()
s.writeLock <- struct{}{}
s.stdin.Close()
s.writeMu.Unlock()
<-s.writeLock
select {
case <-s.done:
@@ -509,18 +549,36 @@ func (s *Session) Kill() {
s.cmd.Wait()
}
func (s *Session) write(m message) error {
func (s *Session) write(m message, deadline time.Time) error {
b, err := json.Marshal(m)
if err != nil {
return err
}
s.writeMu.Lock()
defer s.writeMu.Unlock()
wait := time.NewTimer(time.Until(deadline))
defer wait.Stop()
select {
case s.writeLock <- struct{}{}:
case <-wait.C:
return os.ErrDeadlineExceeded
}
defer func() { <-s.writeLock }()
if !time.Now().Before(deadline) {
return os.ErrDeadlineExceeded
}
s.record("send", b)
_, err = s.stdin.Write(append(b, '\n'))
err = s.stdin.SetWriteDeadline(deadline)
if err != nil {
return err
}
n, err := s.stdin.Write(append(b, '\n'))
if n > 0 && errors.Is(err, os.ErrDeadlineExceeded) {
slog.Error("codex stopped reading its stdin mid-line; killing it", "pid", s.cmd.Process.Pid, "written", n, "len", len(b)+1)
s.cmd.Process.Kill()
}
return err
}
@@ -646,7 +704,7 @@ func (s *Session) handleServerRequest(m message) {
result, err := s.answerServerRequest(m)
if err != nil {
slog.Error("codex server request failed", "method", m.Method, "err", err)
s.write(message{ID: m.ID, Error: &RPCError{Code: -32601, Message: err.Error()}})
s.write(message{ID: m.ID, Error: &RPCError{Code: -32601, Message: err.Error()}}, time.Now().Add(rpcTimeout))
return
}
@@ -655,7 +713,7 @@ func (s *Session) handleServerRequest(m message) {
slog.Error("encode codex server response", "method", m.Method, "err", err)
return
}
s.write(message{ID: m.ID, Result: raw})
s.write(message{ID: m.ID, Result: raw}, time.Now().Add(rpcTimeout))
}
func (s *Session) answerServerRequest(m message) (any, error) {