Merge pull request #8975 from hashicorp/dnephin/stream-close-on-unsub

stream: close the subscription on Unsubscribe

agent/consul/state/store_integration_test.go

@@ -64,7 +64,7 @@ func TestStore_IntegrationWithEventPublisher_ACLTokenUpdate(t *testing.T) {
 
 	// Ensure the reset event was sent.
 	err = assertErr(t, eventCh)
-	require.Equal(stream.ErrSubscriptionClosed, err)
+	require.Equal(stream.ErrSubForceClosed, err)
 
 	// Register another subscription.
 	subscription2 := &stream.SubscribeRequest{
@@ -93,7 +93,7 @@ func TestStore_IntegrationWithEventPublisher_ACLTokenUpdate(t *testing.T) {
 
 	// Ensure the reset event was sent.
 	err = assertErr(t, eventCh2)
-	require.Equal(stream.ErrSubscriptionClosed, err)
+	require.Equal(stream.ErrSubForceClosed, err)
 }
 
 func TestStore_IntegrationWithEventPublisher_ACLPolicyUpdate(t *testing.T) {
@@ -162,6 +162,7 @@ func TestStore_IntegrationWithEventPublisher_ACLPolicyUpdate(t *testing.T) {
 	}
 	sub, err = publisher.Subscribe(subscription2)
 	require.NoError(err)
+	defer sub.Unsubscribe()
 
 	eventCh = testRunSub(sub)
 
@@ -180,7 +181,7 @@ func TestStore_IntegrationWithEventPublisher_ACLPolicyUpdate(t *testing.T) {
 
 	// Ensure the reload event was sent.
 	err = assertErr(t, eventCh)
-	require.Equal(stream.ErrSubscriptionClosed, err)
+	require.Equal(stream.ErrSubForceClosed, err)
 
 	// Register another subscription.
 	subscription3 := &stream.SubscribeRequest{
@@ -367,7 +368,7 @@ func assertReset(t *testing.T, eventCh <-chan nextResult, allowEOS bool) {
 				}
 			}
 			require.Error(t, next.Err)
-			require.Equal(t, stream.ErrSubscriptionClosed, next.Err)
+			require.Equal(t, stream.ErrSubForceClosed, next.Err)
 			return
 		case <-time.After(100 * time.Millisecond):
 			t.Fatalf("no err after 100ms")

agent/consul/stream/event_buffer.go

@@ -170,13 +170,13 @@ func newBufferItem(events []Event) *bufferItem {
 
 // Next return the next buffer item in the buffer. It may block until ctx is
 // cancelled or until the next item is published.
-func (i *bufferItem) Next(ctx context.Context, forceClose <-chan struct{}) (*bufferItem, error) {
+func (i *bufferItem) Next(ctx context.Context, closed <-chan struct{}) (*bufferItem, error) {
 	// See if there is already a next value, block if so. Note we don't rely on
 	// state change (chan nil) as that's not threadsafe but detecting close is.
 	select {
 	case <-ctx.Done():
 		return nil, ctx.Err()
-	case <-forceClose:
+	case <-closed:
 		return nil, fmt.Errorf("subscription closed")
 	case <-i.link.ch:
 	}

agent/consul/stream/event_publisher_test.go

@@ -30,6 +30,7 @@ func TestEventPublisher_SubscribeWithIndex0(t *testing.T) {
 
 	sub, err := publisher.Subscribe(req)
 	require.NoError(t, err)
+	defer sub.Unsubscribe()
 	eventCh := runSubscription(ctx, sub)
 
 	next := getNextEvent(t, eventCh)
@@ -141,10 +142,10 @@ func TestEventPublisher_ShutdownClosesSubscriptions(t *testing.T) {
 	cancel() // Shutdown
 
 	err = consumeSub(context.Background(), sub1)
-	require.Equal(t, err, ErrSubscriptionClosed)
+	require.Equal(t, err, ErrSubForceClosed)
 
 	_, err = sub2.Next(context.Background())
-	require.Equal(t, err, ErrSubscriptionClosed)
+	require.Equal(t, err, ErrSubForceClosed)
 }
 
 func consumeSub(ctx context.Context, sub *Subscription) error {
@@ -169,14 +170,15 @@ func TestEventPublisher_SubscribeWithIndex0_FromCache(t *testing.T) {
 
 	publisher := NewEventPublisher(newTestSnapshotHandlers(), time.Second)
 	go publisher.Run(ctx)
-	_, err := publisher.Subscribe(req)
+	sub, err := publisher.Subscribe(req)
 	require.NoError(t, err)
+	sub.Unsubscribe()
 
 	publisher.snapshotHandlers[testTopic] = func(_ SubscribeRequest, _ SnapshotAppender) (uint64, error) {
 		return 0, fmt.Errorf("error should not be seen, cache should have been used")
 	}
 
-	sub, err := publisher.Subscribe(req)
+	sub, err = publisher.Subscribe(req)
 	require.NoError(t, err)
 
 	eventCh := runSubscription(ctx, sub)
@@ -357,6 +359,7 @@ func TestEventPublisher_SubscribeWithIndexNotZero_NewSnapshotFromCache(t *testin
 		newReq.Index = 1
 		sub, err := publisher.Subscribe(&newReq)
 		require.NoError(t, err)
+		defer sub.Unsubscribe()
 
 		eventCh := runSubscription(ctx, sub)
 		next := getNextEvent(t, eventCh)
@@ -379,3 +382,25 @@ func runStep(t *testing.T, name string, fn func(t *testing.T)) {
 		t.FailNow()
 	}
 }
+
+func TestEventPublisher_Unsubscribe_ClosesSubscription(t *testing.T) {
+	req := &SubscribeRequest{
+		Topic: testTopic,
+		Key:   "sub-key",
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+
+	publisher := NewEventPublisher(newTestSnapshotHandlers(), time.Second)
+
+	sub, err := publisher.Subscribe(req)
+	require.NoError(t, err)
+
+	_, err = sub.Next(ctx)
+	require.NoError(t, err)
+
+	sub.Unsubscribe()
+	_, err = sub.Next(ctx)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "subscription was closed by unsubscribe")
+}

agent/consul/stream/subscription.go

@@ -3,28 +3,33 @@ package stream
 import (
 	"context"
 	"errors"
+	"fmt"
 	"sync/atomic"
 )
 
 const (
-	// subscriptionStateOpen is the default state of a subscription. An open
-	// subscription may receive new events.
-	subscriptionStateOpen uint32 = 0
+	// subStateOpen is the default state of a subscription. An open subscription
+	// may return new events.
+	subStateOpen = 0
 
-	// subscriptionStateClosed indicates that the subscription was closed, possibly
-	// as a result of a change to an ACL token, and will not receive new events.
+	// subStateForceClosed indicates the subscription was forced closed by
+	// the EventPublisher, possibly as a result of a change to an ACL token, and
+	// will not return new events.
 	// The subscriber must issue a new Subscribe request.
-	subscriptionStateClosed uint32 = 1
+	subStateForceClosed = 1
+
+	// subStateUnsub indicates the subscription was closed by the caller, and
+	// will not return new events.
+	subStateUnsub = 2
 )
 
-// ErrSubscriptionClosed is a error signalling the subscription has been
+// ErrSubForceClosed is a error signalling the subscription has been
 // closed. The client should Unsubscribe, then re-Subscribe.
-var ErrSubscriptionClosed = errors.New("subscription closed by server, client must reset state and resubscribe")
+var ErrSubForceClosed = errors.New("subscription closed by server, client must reset state and resubscribe")
 
 // Subscription provides events on a Topic. Events may be filtered by Key.
 // Events are returned by Next(), and may start with a Snapshot of events.
 type Subscription struct {
-	// state is accessed atomically 0 means open, 1 means closed with reload
 	state uint32
 
 	// req is the requests that we are responding to
@@ -34,9 +39,9 @@ type Subscription struct {
 	// is mutated by calls to Next.
 	currentItem *bufferItem
 
-	// forceClosed is closed when forceClose is called. It is used by
-	// EventPublisher to cancel Next().
-	forceClosed chan struct{}
+	// closed is a channel which is closed when the subscription is closed. It
+	// is used to exit the blocking select.
+	closed chan struct{}
 
 	// unsub is a function set by EventPublisher that is called to free resources
 	// when the subscription is no longer needed.
@@ -58,7 +63,7 @@ type SubscribeRequest struct {
 // calling Unsubscribe when it is done with the subscription, to free resources.
 func newSubscription(req SubscribeRequest, item *bufferItem, unsub func()) *Subscription {
 	return &Subscription{
-		forceClosed: make(chan struct{}),
+		closed:      make(chan struct{}),
 		req:         req,
 		currentItem: item,
 		unsub:       unsub,
@@ -68,16 +73,16 @@ func newSubscription(req SubscribeRequest, item *bufferItem, unsub func()) *Subs
 // Next returns the next Event to deliver. It must only be called from a
 // single goroutine concurrently as it mutates the Subscription.
 func (s *Subscription) Next(ctx context.Context) (Event, error) {
-	if atomic.LoadUint32(&s.state) == subscriptionStateClosed {
-		return Event{}, ErrSubscriptionClosed
+	for {
+		if err := s.requireStateOpen(); err != nil {
+			return Event{}, err
 		}
 
-	for {
-		next, err := s.currentItem.Next(ctx, s.forceClosed)
-		switch {
-		case err != nil && atomic.LoadUint32(&s.state) == subscriptionStateClosed:
-			return Event{}, ErrSubscriptionClosed
-		case err != nil:
+		next, err := s.currentItem.Next(ctx, s.closed)
+		if err := s.requireStateOpen(); err != nil {
+			return Event{}, err
+		}
+		if err != nil {
 			return Event{}, err
 		}
 		s.currentItem = next
@@ -92,6 +97,17 @@ func (s *Subscription) Next(ctx context.Context) (Event, error) {
 	}
 }
 
+func (s *Subscription) requireStateOpen() error {
+	switch atomic.LoadUint32(&s.state) {
+	case subStateForceClosed:
+		return ErrSubForceClosed
+	case subStateUnsub:
+		return fmt.Errorf("subscription was closed by unsubscribe")
+	default:
+		return nil
+	}
+}
+
 func newEventFromBatch(req SubscribeRequest, events []Event) Event {
 	first := events[0]
 	if len(events) == 1 {
@@ -121,13 +137,15 @@ func filterByKey(req SubscribeRequest, events []Event) (Event, bool) {
 // and will need to perform a new Subscribe request.
 // It is safe to call from any goroutine.
 func (s *Subscription) forceClose() {
-	swapped := atomic.CompareAndSwapUint32(&s.state, subscriptionStateOpen, subscriptionStateClosed)
-	if swapped {
-		close(s.forceClosed)
+	if atomic.CompareAndSwapUint32(&s.state, subStateOpen, subStateForceClosed) {
+		close(s.closed)
 	}
 }
 
 // Unsubscribe the subscription, freeing resources.
 func (s *Subscription) Unsubscribe() {
+	if atomic.CompareAndSwapUint32(&s.state, subStateOpen, subStateUnsub) {
+		close(s.closed)
+	}
 	s.unsub()
 }

agent/consul/stream/subscription_test.go

@@ -122,7 +122,7 @@ func TestSubscription_Close(t *testing.T) {
 	_, err = sub.Next(ctx)
 	elapsed = time.Since(start)
 	require.Error(t, err)
-	require.Equal(t, ErrSubscriptionClosed, err)
+	require.Equal(t, ErrSubForceClosed, err)
 	require.True(t, elapsed > 200*time.Millisecond,
 		"Reload should have happened after blocking 200ms, took %s", elapsed)
 	require.True(t, elapsed < 2*time.Second,

agent/rpc/subscribe/subscribe.go

@@ -69,7 +69,7 @@ func (h *Server) Subscribe(req *pbsubscribe.SubscribeRequest, serverStream pbsub
 	for {
 		event, err := sub.Next(ctx)
 		switch {
-		case errors.Is(err, stream.ErrSubscriptionClosed):
+		case errors.Is(err, stream.ErrSubForceClosed):
 			logger.Trace("subscription reset by server")
 			return status.Error(codes.Aborted, err.Error())
 		case err != nil: