stream: Return a single event from a subscription.Next

Handle batch events as a single event

agent/consul/state/store_integration_test.go

@@ -5,10 +5,11 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/require"
+
 	"github.com/hashicorp/consul/acl"
 	"github.com/hashicorp/consul/agent/consul/stream"
 	"github.com/hashicorp/consul/agent/structs"
-	"github.com/stretchr/testify/require"
 )
 
 func TestStore_IntegrationWithEventPublisher_ACLTokenUpdate(t *testing.T) {
@@ -294,8 +295,8 @@ func TestStore_IntegrationWithEventPublisher_ACLRoleUpdate(t *testing.T) {
 }
 
 type nextResult struct {
-	Events []stream.Event
+	Event stream.Event
-	Err    error
+	Err   error
 }
 
 func testRunSub(sub *stream.Subscription) <-chan nextResult {
@@ -304,8 +305,8 @@ func testRunSub(sub *stream.Subscription) <-chan nextResult {
 		for {
 			es, err := sub.Next(context.TODO())
 			eventCh <- nextResult{
-				Events: es,
+				Event: es,
-				Err:    err,
+				Err:   err,
 			}
 			if err != nil {
 				return
@@ -320,8 +321,8 @@ func assertNoEvent(t *testing.T, eventCh <-chan nextResult) {
 	select {
 	case next := <-eventCh:
 		require.NoError(t, next.Err)
-		require.Len(t, next.Events, 1)
+		require.Len(t, next.Event, 1)
-		t.Fatalf("got unwanted event: %#v", next.Events[0].Payload)
+		t.Fatalf("got unwanted event: %#v", next.Event.Payload)
 	case <-time.After(100 * time.Millisecond):
 	}
 }
@@ -331,8 +332,7 @@ func assertEvent(t *testing.T, eventCh <-chan nextResult) *stream.Event {
 	select {
 	case next := <-eventCh:
 		require.NoError(t, next.Err)
-		require.Len(t, next.Events, 1)
+		return &next.Event
-		return &next.Events[0]
 	case <-time.After(100 * time.Millisecond):
 		t.Fatalf("no event after 100ms")
 	}
@@ -362,7 +362,7 @@ func assertReset(t *testing.T, eventCh <-chan nextResult, allowEOS bool) {
 		select {
 		case next := <-eventCh:
 			if allowEOS {
-				if next.Err == nil && len(next.Events) == 1 && next.Events[0].IsEndOfSnapshot() {
+				if next.Err == nil && next.Event.IsEndOfSnapshot() {
 					continue
 				}
 			}

agent/consul/stream/event.go

@@ -19,6 +19,51 @@ type Event struct {
 	Payload interface{}
 }
 
+// Len returns the number of events contained within this event. If the Payload
+// is a []Event, the length of that slice is returned. Otherwise 1 is returned.
+func (e Event) Len() int {
+	if batch, ok := e.Payload.([]Event); ok {
+		return len(batch)
+	}
+	return 1
+}
+
+// Filter returns an Event filtered to only those Events where f returns true.
+// If the second return value is false, every Event was removed by the filter.
+func (e Event) Filter(f func(Event) bool) (Event, bool) {
+	batch, ok := e.Payload.([]Event)
+	if !ok {
+		return e, f(e)
+	}
+
+	// To avoid extra allocations, iterate over the list of events first and
+	// get a count of the total desired size. This trades off some extra cpu
+	// time in the worse case (when not all items match the filter), for
+	// fewer memory allocations.
+	var size int
+	for idx := range batch {
+		if f(batch[idx]) {
+			size++
+		}
+	}
+	if len(batch) == size || size == 0 {
+		return e, size != 0
+	}
+
+	filtered := make([]Event, 0, size)
+	for idx := range batch {
+		event := batch[idx]
+		if f(event) {
+			filtered = append(filtered, event)
+		}
+	}
+	if len(filtered) == 0 {
+		return e, false
+	}
+	e.Payload = filtered
+	return e, true
+}
+
 // IsEndOfSnapshot returns true if this is a framing event that indicates the
 // snapshot has completed. Subsequent events from Subscription.Next will be
 // streamed as they occur.

agent/consul/stream/event_publisher_test.go

@@ -32,13 +32,11 @@ func TestEventPublisher_SubscribeWithIndex0(t *testing.T) {
 	require.NoError(t, err)
 	eventCh := runSubscription(ctx, sub)
 
-	next := getNextEvents(t, eventCh)
+	next := getNextEvent(t, eventCh)
-	expected := []Event{testSnapshotEvent}
+	require.Equal(t, testSnapshotEvent, next)
-	require.Equal(t, expected, next)
 
-	next = getNextEvents(t, eventCh)
+	next = getNextEvent(t, eventCh)
-	require.Len(t, next, 1)
+	require.True(t, next.IsEndOfSnapshot())
-	require.True(t, next[0].IsEndOfSnapshot())
 
 	assertNoResult(t, eventCh)
 
@@ -50,8 +48,8 @@ func TestEventPublisher_SubscribeWithIndex0(t *testing.T) {
 	publisher.Publish(events)
 
 	// Subscriber should see the published event
-	next = getNextEvents(t, eventCh)
+	next = getNextEvent(t, eventCh)
-	expected = []Event{{Payload: "the-published-event-payload", Key: "sub-key", Topic: testTopic}}
+	expected := Event{Payload: "the-published-event-payload", Key: "sub-key", Topic: testTopic}
 	require.Equal(t, expected, next)
 }
 
@@ -80,8 +78,8 @@ func runSubscription(ctx context.Context, sub *Subscription) <-chan eventOrErr {
 		for {
 			es, err := sub.Next(ctx)
 			eventCh <- eventOrErr{
-				Events: es,
+				Event: es,
-				Err:    err,
+				Err:   err,
 			}
 			if err != nil {
 				return
@@ -92,19 +90,19 @@ func runSubscription(ctx context.Context, sub *Subscription) <-chan eventOrErr {
 }
 
 type eventOrErr struct {
-	Events []Event
+	Event Event
-	Err    error
+	Err   error
 }
 
-func getNextEvents(t *testing.T, eventCh <-chan eventOrErr) []Event {
+func getNextEvent(t *testing.T, eventCh <-chan eventOrErr) Event {
 	t.Helper()
 	select {
 	case next := <-eventCh:
 		require.NoError(t, next.Err)
-		return next.Events
+		return next.Event
 	case <-time.After(100 * time.Millisecond):
 		t.Fatalf("timeout waiting for event from subscription")
-		return nil
+		return Event{}
 	}
 }
 
@@ -113,8 +111,7 @@ func assertNoResult(t *testing.T, eventCh <-chan eventOrErr) {
 	select {
 	case next := <-eventCh:
 		require.NoError(t, next.Err)
-		require.Len(t, next.Events, 1)
+		t.Fatalf("received unexpected event: %#v", next.Event.Payload)
-		t.Fatalf("received unexpected event: %#v", next.Events[0].Payload)
 	case <-time.After(25 * time.Millisecond):
 	}
 }
@@ -152,11 +149,11 @@ func TestEventPublisher_ShutdownClosesSubscriptions(t *testing.T) {
 
 func consumeSub(ctx context.Context, sub *Subscription) error {
 	for {
-		events, err := sub.Next(ctx)
+		event, err := sub.Next(ctx)
 		switch {
 		case err != nil:
 			return err
-		case len(events) == 1 && events[0].IsEndOfSnapshot():
+		case event.IsEndOfSnapshot():
 			continue
 		}
 	}
@@ -183,28 +180,25 @@ func TestEventPublisher_SubscribeWithIndex0_FromCache(t *testing.T) {
 	require.NoError(t, err)
 
 	eventCh := runSubscription(ctx, sub)
-	next := getNextEvents(t, eventCh)
+	next := getNextEvent(t, eventCh)
-	expected := []Event{testSnapshotEvent}
+	require.Equal(t, testSnapshotEvent, next)
-	require.Equal(t, expected, next)
 
-	next = getNextEvents(t, eventCh)
+	next = getNextEvent(t, eventCh)
-	require.Len(t, next, 1)
+	require.True(t, next.IsEndOfSnapshot())
-	require.True(t, next[0].IsEndOfSnapshot())
 
 	// Now subscriber should block waiting for updates
 	assertNoResult(t, eventCh)
 
-	events := []Event{{
+	expected := Event{
 		Topic:   testTopic,
 		Key:     "sub-key",
 		Payload: "the-published-event-payload",
 		Index:   3,
-	}}
+	}
-	publisher.Publish(events)
+	publisher.Publish([]Event{expected})
 
 	// Subscriber should see the published event
-	next = getNextEvents(t, eventCh)
+	next = getNextEvent(t, eventCh)
-	expected = []Event{events[0]}
 	require.Equal(t, expected, next)
 }
 
@@ -228,14 +222,12 @@ func TestEventPublisher_SubscribeWithIndexNotZero_CanResume(t *testing.T) {
 
 		eventCh := runSubscription(ctx, sub)
 
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		expected := []Event{testSnapshotEvent}
+		require.Equal(t, testSnapshotEvent, next)
-		require.Equal(t, expected, next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Len(t, next, 1)
+		require.True(t, next.IsEndOfSnapshot())
-		require.True(t, next[0].IsEndOfSnapshot())
+		require.Equal(t, uint64(1), next.Index)
-		require.Equal(t, uint64(1), next[0].Index)
 	})
 
 	runStep(t, "resume the subscription", func(t *testing.T) {
@@ -255,8 +247,8 @@ func TestEventPublisher_SubscribeWithIndexNotZero_CanResume(t *testing.T) {
 		}
 		publisher.publishEvent([]Event{expected})
 
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		require.Equal(t, []Event{expected}, next)
+		require.Equal(t, expected, next)
 	})
 }
 
@@ -280,14 +272,12 @@ func TestEventPublisher_SubscribeWithIndexNotZero_NewSnapshot(t *testing.T) {
 
 		eventCh := runSubscription(ctx, sub)
 
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		expected := []Event{testSnapshotEvent}
+		require.Equal(t, testSnapshotEvent, next)
-		require.Equal(t, expected, next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Len(t, next, 1)
+		require.True(t, next.IsEndOfSnapshot())
-		require.True(t, next[0].IsEndOfSnapshot())
+		require.Equal(t, uint64(1), next.Index)
-		require.Equal(t, uint64(1), next[0].Index)
 	})
 
 	nextEvent := Event{
@@ -308,14 +298,14 @@ func TestEventPublisher_SubscribeWithIndexNotZero_NewSnapshot(t *testing.T) {
 		require.NoError(t, err)
 
 		eventCh := runSubscription(ctx, sub)
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		require.True(t, next[0].IsNewSnapshotToFollow(), next)
+		require.True(t, next.IsNewSnapshotToFollow(), next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Equal(t, testSnapshotEvent, next[0])
+		require.Equal(t, testSnapshotEvent, next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.True(t, next[0].IsEndOfSnapshot())
+		require.True(t, next.IsEndOfSnapshot())
 	})
 }
 
@@ -339,14 +329,12 @@ func TestEventPublisher_SubscribeWithIndexNotZero_NewSnapshotFromCache(t *testin
 
 		eventCh := runSubscription(ctx, sub)
 
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		expected := []Event{testSnapshotEvent}
+		require.Equal(t, testSnapshotEvent, next)
-		require.Equal(t, expected, next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Len(t, next, 1)
+		require.True(t, next.IsEndOfSnapshot())
-		require.True(t, next[0].IsEndOfSnapshot())
+		require.Equal(t, uint64(1), next.Index)
-		require.Equal(t, uint64(1), next[0].Index)
 	})
 
 	nextEvent := Event{
@@ -371,17 +359,17 @@ func TestEventPublisher_SubscribeWithIndexNotZero_NewSnapshotFromCache(t *testin
 		require.NoError(t, err)
 
 		eventCh := runSubscription(ctx, sub)
-		next := getNextEvents(t, eventCh)
+		next := getNextEvent(t, eventCh)
-		require.True(t, next[0].IsNewSnapshotToFollow(), next)
+		require.True(t, next.IsNewSnapshotToFollow(), next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Equal(t, testSnapshotEvent, next[0])
+		require.Equal(t, testSnapshotEvent, next)
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.True(t, next[0].IsEndOfSnapshot())
+		require.True(t, next.IsEndOfSnapshot())
 
-		next = getNextEvents(t, eventCh)
+		next = getNextEvent(t, eventCh)
-		require.Equal(t, nextEvent, next[0])
+		require.Equal(t, nextEvent, next)
 	})
 }
 

agent/consul/stream/subscription.go

@@ -65,59 +65,56 @@ func newSubscription(req SubscribeRequest, item *bufferItem, unsub func()) *Subs
 	}
 }
 
-// Next returns the next set of events to deliver. It must only be called from a
+// 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) {
+func (s *Subscription) Next(ctx context.Context) (Event, error) {
 	if atomic.LoadUint32(&s.state) == subscriptionStateClosed {
-		return nil, ErrSubscriptionClosed
+		return Event{}, ErrSubscriptionClosed
 	}
 
 	for {
 		next, err := s.currentItem.Next(ctx, s.forceClosed)
 		switch {
 		case err != nil && atomic.LoadUint32(&s.state) == subscriptionStateClosed:
-			return nil, ErrSubscriptionClosed
+			return Event{}, ErrSubscriptionClosed
 		case err != nil:
-			return nil, err
+			return Event{}, err
 		}
 		s.currentItem = next
-
+		if len(next.Events) == 0 {
-		events := filter(s.req.Key, next.Events)
-		if len(events) == 0 {
 			continue
 		}
-		return events, nil
+		event, ok := filterByKey(s.req, next.Events)
+		if !ok {
+			continue
+		}
+		return event, nil
 	}
 }
 
-// filter events to only those that match the key exactly.
+func newEventFromBatch(req SubscribeRequest, events []Event) Event {
-func filter(key string, events []Event) []Event {
+	first := events[0]
-	if key == "" || len(events) == 0 {
+	if len(events) == 1 {
-		return events
+		return first
+	}
+	return Event{
+		Topic:   req.Topic,
+		Key:     req.Key,
+		Index:   first.Index,
+		Payload: events,
+	}
+}
+
+func filterByKey(req SubscribeRequest, events []Event) (Event, bool) {
+	event := newEventFromBatch(req, events)
+	if req.Key == "" {
+		return event, true
 	}
 
-	var count int
+	fn := func(e Event) bool {
-	for _, e := range events {
+		return req.Key == e.Key
-		if key == e.Key {
-			count++
-		}
 	}
-
+	return event.Filter(fn)
-	// Only allocate a new slice if some events need to be filtered out
-	switch count {
-	case 0:
-		return nil
-	case len(events):
-		return events
-	}
-
-	result := make([]Event, 0, count)
-	for _, e := range events {
-		if key == e.Key {
-			result = append(result, e)
-		}
-	}
-	return result
 }
 
 // Close the subscription. Subscribers will receive an error when they call Next,

agent/consul/stream/subscription_test.go

@@ -36,8 +36,7 @@ func TestSubscription(t *testing.T) {
 	require.NoError(t, err)
 	require.True(t, elapsed < 200*time.Millisecond,
 		"Event should have been delivered immediately, took %s", elapsed)
-	require.Len(t, got, 1)
+	require.Equal(t, index, got.Index)
-	require.Equal(t, index, got[0].Index)
 
 	// Schedule an event publish in a while
 	index++
@@ -54,8 +53,7 @@ func TestSubscription(t *testing.T) {
 		"Event should have been delivered after blocking 200ms, took %s", elapsed)
 	require.True(t, elapsed < 2*time.Second,
 		"Event should have been delivered after short time, took %s", elapsed)
-	require.Len(t, got, 1)
+	require.Equal(t, index, got.Index)
-	require.Equal(t, index, got[0].Index)
 
 	// Event with wrong key should not be delivered. Deliver a good message right
 	// so we don't have to block test thread forever or cancel func yet.
@@ -70,9 +68,8 @@ func TestSubscription(t *testing.T) {
 	require.NoError(t, err)
 	require.True(t, elapsed < 200*time.Millisecond,
 		"Event should have been delivered immediately, took %s", elapsed)
-	require.Len(t, got, 1)
+	require.Equal(t, index, got.Index)
-	require.Equal(t, index, got[0].Index)
+	require.Equal(t, "test", got.Key)
-	require.Equal(t, "test", got[0].Key)
 
 	// Cancelling the subscription context should unblock Next
 	start = time.Now()
@@ -91,9 +88,7 @@ func TestSubscription(t *testing.T) {
 
 func TestSubscription_Close(t *testing.T) {
 	eb := newEventBuffer()
-
 	index := uint64(100)
-
 	startHead := eb.Head()
 
 	// Start with an event in the buffer
@@ -115,8 +110,7 @@ func TestSubscription_Close(t *testing.T) {
 	require.NoError(t, err)
 	require.True(t, elapsed < 200*time.Millisecond,
 		"Event should have been delivered immediately, took %s", elapsed)
-	require.Len(t, got, 1)
+	require.Equal(t, index, got.Index)
-	require.Equal(t, index, got[0].Index)
 
 	// Schedule a Close simulating the server deciding this subscroption
 	// needs to reset (e.g. on ACL perm change).
@@ -149,46 +143,55 @@ func publishTestEvent(index uint64, b *eventBuffer, key string) {
 
 func TestFilter_NoKey(t *testing.T) {
 	events := make([]Event, 0, 5)
-	events = append(events, Event{Key: "One"}, Event{Key: "Two"})
+	events = append(events, Event{Key: "One", Index: 102}, Event{Key: "Two"})
 
-	actual := filter("", events)
+	req := SubscribeRequest{Topic: testTopic}
-	require.Equal(t, events, actual)
+	actual, ok := filterByKey(req, events)
+	require.True(t, ok)
+	require.Equal(t, Event{Topic: testTopic, Index: 102, Payload: events}, actual)
 
 	// test that a new array was not allocated
-	require.Equal(t, cap(actual), 5)
+	require.Equal(t, cap(actual.Payload.([]Event)), 5)
 }
 
 func TestFilter_WithKey_AllEventsMatch(t *testing.T) {
 	events := make([]Event, 0, 5)
-	events = append(events, Event{Key: "Same"}, Event{Key: "Same"})
+	events = append(events, Event{Key: "Same", Index: 103}, Event{Key: "Same"})
 
-	actual := filter("Same", events)
+	req := SubscribeRequest{Topic: testTopic, Key: "Same"}
-	require.Equal(t, events, actual)
+	actual, ok := filterByKey(req, events)
+	require.True(t, ok)
+	expected := Event{Topic: testTopic, Index: 103, Key: "Same", Payload: events}
+	require.Equal(t, expected, actual)
 
 	// test that a new array was not allocated
-	require.Equal(t, cap(actual), 5)
+	require.Equal(t, 5, cap(actual.Payload.([]Event)))
 }
 
 func TestFilter_WithKey_SomeEventsMatch(t *testing.T) {
 	events := make([]Event, 0, 5)
-	events = append(events, Event{Key: "Same"}, Event{Key: "Other"}, Event{Key: "Same"})
+	events = append(events, Event{Key: "Same", Index: 104}, Event{Key: "Other"}, Event{Key: "Same"})
 
-	actual := filter("Same", events)
+	req := SubscribeRequest{Topic: testTopic, Key: "Same"}
-	expected := []Event{{Key: "Same"}, {Key: "Same"}}
+	actual, ok := filterByKey(req, events)
+	require.True(t, ok)
+	expected := Event{
+		Topic:   testTopic,
+		Index:   104,
+		Key:     "Same",
+		Payload: []Event{{Key: "Same", Index: 104}, {Key: "Same"}},
+	}
 	require.Equal(t, expected, actual)
 
 	// test that a new array was allocated with the correct size
-	require.Equal(t, cap(actual), 2)
+	require.Equal(t, cap(actual.Payload.([]Event)), 2)
 }
 
 func TestFilter_WithKey_NoEventsMatch(t *testing.T) {
 	events := make([]Event, 0, 5)
 	events = append(events, Event{Key: "Same"}, Event{Key: "Same"})
 
-	actual := filter("Other", events)
+	req := SubscribeRequest{Topic: testTopic, Key: "Other"}
-	var expected []Event
+	_, ok := filterByKey(req, events)
-	require.Equal(t, expected, actual)
+	require.False(t, ok)
-
-	// test that no array was allocated
-	require.Equal(t, cap(actual), 0)
 }

agent/rpc/subscribe/logger.go

@@ -52,21 +52,17 @@ type eventLogger struct {
 	count        uint64
 }
 
-func (l *eventLogger) Trace(e []stream.Event) {
+func (l *eventLogger) Trace(e stream.Event) {
-	if len(e) == 0 {
-		return
-	}
-
-	first := e[0]
 	switch {
-	case first.IsEndOfSnapshot():
+	case e.IsEndOfSnapshot():
 		l.snapshotDone = true
-		l.logger.Trace("snapshot complete", "index", first.Index, "sent", l.count)
+		l.logger.Trace("snapshot complete", "index", e.Index, "sent", l.count)
-	case first.IsNewSnapshotToFollow():
+	case e.IsNewSnapshotToFollow():
+		l.logger.Trace("starting new snapshot", "sent", l.count)
 		return
 	case l.snapshotDone:
-		l.logger.Trace("sending events", "index", first.Index, "sent", l.count, "batch_size", len(e))
+		l.logger.Trace("sending events", "index", e.Index, "sent", l.count, "batch_size", e.Len())
 	}
 
-	l.count += uint64(len(e))
+	l.count += uint64(e.Len())
 }

agent/rpc/subscribe/subscribe.go

@@ -67,7 +67,7 @@ func (h *Server) Subscribe(req *pbsubscribe.SubscribeRequest, serverStream pbsub
 
 	elog := &eventLogger{logger: logger}
 	for {
-		events, err := sub.Next(ctx)
+		event, err := sub.Next(ctx)
 		switch {
 		case errors.Is(err, stream.ErrSubscriptionClosed):
 			logger.Trace("subscription reset by server")
@@ -76,13 +76,14 @@ func (h *Server) Subscribe(req *pbsubscribe.SubscribeRequest, serverStream pbsub
 			return err
 		}
 
-		events = filterStreamEvents(authz, events)
+		var ok bool
-		if len(events) == 0 {
+		event, ok = filterByAuth(authz, event)
+		if !ok {
 			continue
 		}
 
-		elog.Trace(events)
+		elog.Trace(event)
-		e := newEventFromStreamEvents(req, events)
+		e := newEventFromStreamEvent(req, event)
 		if err := serverStream.Send(e); err != nil {
 			return err
 		}
@@ -126,68 +127,44 @@ func forwardToDC(
 	}
 }
 
-// filterStreamEvents to only those allowed by the acl token.
+// filterByAuth to only those Events allowed by the acl token.
-func filterStreamEvents(authz acl.Authorizer, events []stream.Event) []stream.Event {
+func filterByAuth(authz acl.Authorizer, event stream.Event) (stream.Event, bool) {
 	// authz will be nil when ACLs are disabled
-	if authz == nil || len(events) == 0 {
+	if authz == nil {
-		return events
+		return event, true
 	}
-
+	fn := func(e stream.Event) bool {
-	// Fast path for the common case of only 1 event since we can avoid slice
+		return enforceACL(authz, e) == acl.Allow
-	// allocation in the hot path of every single update event delivered in vast
-	// majority of cases with this. Note that this is called _per event/item_ when
-	// sending snapshots which is a lot worse than being called once on regular
-	// result.
-	if len(events) == 1 {
-		if enforceACL(authz, events[0]) == acl.Allow {
-			return events
-		}
-		return nil
 	}
-
+	return event.Filter(fn)
-	var filtered []stream.Event
-	for idx := range events {
-		event := events[idx]
-		if enforceACL(authz, event) == acl.Allow {
-			filtered = append(filtered, event)
-		}
-	}
-	return filtered
 }
 
-func newEventFromStreamEvents(req *pbsubscribe.SubscribeRequest, events []stream.Event) *pbsubscribe.Event {
+func newEventFromStreamEvent(req *pbsubscribe.SubscribeRequest, event stream.Event) *pbsubscribe.Event {
 	e := &pbsubscribe.Event{
 		Topic: req.Topic,
 		Key:   req.Key,
-		Index: events[0].Index,
+		Index: event.Index,
 	}
-
+	switch {
-	if len(events) == 1 {
+	case event.IsEndOfSnapshot():
-		event := events[0]
+		e.Payload = &pbsubscribe.Event_EndOfSnapshot{EndOfSnapshot: true}
-		// TODO: refactor so these are only checked once, instead of 3 times.
+		return e
-		switch {
+	case event.IsNewSnapshotToFollow():
-		case event.IsEndOfSnapshot():
+		e.Payload = &pbsubscribe.Event_NewSnapshotToFollow{NewSnapshotToFollow: true}
-			e.Payload = &pbsubscribe.Event_EndOfSnapshot{EndOfSnapshot: true}
-			return e
-		case event.IsNewSnapshotToFollow():
-			e.Payload = &pbsubscribe.Event_NewSnapshotToFollow{NewSnapshotToFollow: true}
-			return e
-		}
-
-		setPayload(e, event.Payload)
 		return e
 	}
-
+	setPayload(e, event.Payload)
-	e.Payload = &pbsubscribe.Event_EventBatch{
-		EventBatch: &pbsubscribe.EventBatch{
-			Events: batchEventsFromEventSlice(events),
-		},
-	}
 	return e
 }
 
 func setPayload(e *pbsubscribe.Event, payload interface{}) {
 	switch p := payload.(type) {
+	case []stream.Event:
+		e.Payload = &pbsubscribe.Event_EventBatch{
+			EventBatch: &pbsubscribe.EventBatch{
+				Events: batchEventsFromEventSlice(p),
+			},
+		}
 	case state.EventPayloadCheckServiceNode:
 		e.Payload = &pbsubscribe.Event_ServiceHealth{
 			ServiceHealth: &pbsubscribe.ServiceHealthUpdate{