Close piped processes on cancellation

internal/process/process.go

@@ -55,6 +55,8 @@ type PipedProcess struct {
 	stdout   io.ReadCloser
 	parent   context.Context
 	cancel   context.CancelFunc
+	stopIO   func() bool
+	ioDone   <-chan struct{}
 	waitOnce sync.Once
 	waitErr  error
 }
@@ -80,6 +82,9 @@ func (child *PipedProcess) Cancel() {
 func (child *PipedProcess) Wait() error {
 	child.waitOnce.Do(func() {
 		err := child.command.Wait()
+		if !child.stopIO() {
+			<-child.ioDone
+		}
 		child.cancel()
 		if err == nil {
 			return
@@ -121,12 +126,20 @@ func StartPiped(ctx context.Context, invocation Invocation) (*PipedProcess, erro
 		cancel()
 		return nil, fmt.Errorf("start %q: %w", invocation.Args[0], err)
 	}
+	done := make(chan struct{})
+	stopIO := context.AfterFunc(childContext, func() {
+		defer close(done)
+		_ = stdin.Close()
+		_ = stdout.Close()
+	})
 	return &PipedProcess{
 		command: command,
 		stdin:   stdin,
 		stdout:  stdout,
 		parent:  ctx,
 		cancel:  cancel,
+		stopIO:  stopIO,
+		ioDone:  done,
 	}, nil
 }
 

internal/process/process_test.go

@@ -260,6 +260,52 @@ func TestStartPipedCancellationAfterReadinessReapsChild(t *testing.T) {
 	}
 }
 
+func TestStartPipedCancellationInterruptsInheritedOutputDrain(t *testing.T) {
+	ready := filepath.Join(t.TempDir(), "descendant")
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	child, err := StartPiped(ctx, Invocation{
+		Args: []string{helperExecutable(t), "-test.run=TestProcessHelper", "--", "unused", "exit-descendant"},
+		Env:  map[string]string{"RELEASEKIT_PROCESS_HELPER": "1", "RELEASEKIT_DESCENDANT_READY": ready},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_ = child.Stdin().Close()
+	drained := make(chan error, 1)
+	go func() {
+		_, err := io.Copy(io.Discard, child.Stdout())
+		drained <- err
+	}()
+	deadline := time.After(10 * time.Second)
+	var pid int
+	for pid == 0 {
+		if data, err := os.ReadFile(ready); err == nil {
+			pid, _ = strconv.Atoi(string(data))
+		}
+		select {
+		case <-deadline:
+			t.Fatal("descendant did not become ready")
+		default:
+			time.Sleep(10 * time.Millisecond)
+		}
+	}
+	t.Cleanup(func() {
+		if descendant, err := os.FindProcess(pid); err == nil {
+			_ = descendant.Kill()
+		}
+	})
+	cancel()
+	select {
+	case <-drained:
+	case <-time.After(10 * time.Second):
+		t.Fatal("inherited stdout did not close after cancellation")
+	}
+	if err := child.Wait(); err != nil && !errors.Is(err, context.Canceled) {
+		t.Fatalf("wait after cancellation: %v", err)
+	}
+}
+
 func TestStartPipedCancelDoesNotCancelParentContext(t *testing.T) {
 	ctx := context.Background()
 	child, err := StartPiped(ctx, Invocation{