driver/kubernetes: close exec-stream pipes when the stream ends

driver/kubernetes/execconn/execconn.go

@@ -34,6 +34,12 @@ func ExecConn(ctx context.Context, restClient rest.Interface, restConfig *rest.C
 	if err != nil {
 		return nil, err
 	}
+	return newExecConn(ctx, exec), nil
+}
+
+// newExecConn wires a remotecommand.Executor's stdin/stdout streams up as a net.Conn.
+// It is split from ExecConn to ease testing.
+func newExecConn(ctx context.Context, exec remotecommand.Executor) net.Conn {
 	stdinR, stdinW := io.Pipe()
 	stdoutR, stdoutW := io.Pipe()
 	kc := &kubeConn{
@@ -52,8 +58,11 @@ func ExecConn(ctx context.Context, restClient rest.Interface, restConfig *rest.C
 		if serr != nil && serr != context.Canceled {
 			logrus.Error(serr)
 		}
+		// Ensure the pipes are closed to unblock Read/Write on kubeConn and avoid infinite hangs.
+		stdoutW.CloseWithError(serr)
+		stdinR.CloseWithError(serr)
 	}()
-	return kc, nil
+	return kc
 }
 
 type kubeConn struct {

driver/kubernetes/execconn/execconn_test.go

@@ -0,0 +1,118 @@
+package execconn
+
+import (
+	"context"
+	"errors"
+	"io"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"k8s.io/client-go/tools/remotecommand"
+)
+
+// fakeExecutor is a fake remotecommand.Executor whose StreamWithContext blocks until
+// unblock is closed, then returns err. It stands in for the real SPDY exec stream
+// to a builder pod, so the pipe-closing behavior in newExecConn can be tested
+// without a real Kubernetes API server.
+type fakeExecutor struct {
+	unblock chan struct{}
+	err     error
+}
+
+func (f *fakeExecutor) Stream(_ remotecommand.StreamOptions) error {
+	panic("unimplemented")
+}
+
+func (f *fakeExecutor) StreamWithContext(ctx context.Context, _ remotecommand.StreamOptions) error {
+	select {
+	case <-f.unblock:
+		return f.err
+	case <-ctx.Done():
+		return context.Cause(ctx)
+	}
+}
+
+func TestNewExecConnPropagatesStreamEnd(t *testing.T) {
+	t.Run("stream ends with an error", func(t *testing.T) {
+		streamErr := errors.New("exec stream terminated")
+		fe := &fakeExecutor{
+			unblock: make(chan struct{}),
+			err:     streamErr,
+		}
+
+		conn := newExecConn(context.Background(), fe)
+		close(fe.unblock)
+
+		_, err := conn.Read(make([]byte, 16))
+		require.ErrorIs(t, err, streamErr)
+
+		_, err = conn.Write([]byte("test"))
+		require.ErrorIs(t, err, streamErr)
+	})
+
+	t.Run("stream ends with no error", func(t *testing.T) {
+		fe := &fakeExecutor{unblock: make(chan struct{})}
+
+		conn := newExecConn(context.Background(), fe)
+		close(fe.unblock) // StreamWithContext returns nil
+
+		_, err := conn.Read(make([]byte, 16))
+		require.ErrorIs(t, err, io.EOF)
+
+		_, err = conn.Write([]byte("test"))
+		require.ErrorIs(t, err, io.ErrClosedPipe)
+	})
+
+	t.Run("stream still active: reads stay blocked, not closed early", func(t *testing.T) {
+		fe := &fakeExecutor{unblock: make(chan struct{})}
+		conn := newExecConn(context.Background(), fe)
+		defer close(fe.unblock)
+
+		done := make(chan struct{})
+		go func() {
+			buf := make([]byte, 16)
+			_, _ = conn.Read(buf) //nolint:errcheck
+			close(done)
+		}()
+		select {
+		case <-done:
+			t.Fatal("Read returned before the exec stream ended; it should still be blocked")
+		case <-time.After(200 * time.Millisecond):
+			// expected: still blocked, exactly like a real in-progress build
+		}
+	})
+
+	t.Run("stream still active: writes stay blocked, not closed early", func(t *testing.T) {
+		fe := &fakeExecutor{unblock: make(chan struct{})}
+		conn := newExecConn(context.Background(), fe)
+		defer close(fe.unblock)
+
+		done := make(chan struct{})
+		go func() {
+			_, _ = conn.Write([]byte("test")) //nolint:errcheck
+			close(done)
+		}()
+		select {
+		case <-done:
+			t.Fatal("Write returned before the exec stream ended; it should still be blocked")
+		case <-time.After(200 * time.Millisecond):
+			// expected: still blocked, exactly like a real in-progress build
+		}
+	})
+
+	t.Run("stream cancelled by context", func(t *testing.T) {
+		fe := &fakeExecutor{unblock: make(chan struct{})}
+		ctx, cancel := context.WithCancelCause(context.Background())
+		conn := newExecConn(ctx, fe)
+		defer close(fe.unblock)
+
+		cancel(context.Canceled)
+
+		_, err := conn.Read(make([]byte, 16))
+		require.ErrorIs(t, err, context.Canceled)
+
+		_, err = conn.Write([]byte("test"))
+		require.ErrorIs(t, err, context.Canceled)
+	})
+}