Cache the replay event in case we get multiple new client connections

go.mod

@@ -43,6 +43,7 @@ require (
 	github.com/stretchr/testify v1.7.0
 	go.opencensus.io v0.23.0
 	golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4 // indirect
+	golang.org/x/sync v0.0.0-20220513210516-0976fa681c29 // indirect
 	golang.org/x/text v0.3.7 // indirect
 	gopkg.in/gcfg.v1 v1.2.3
 	gopkg.in/launchdarkly/go-jsonstream.v1 v1.0.1

go.sum

@@ -541,6 +541,8 @@ golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c h1:5KslGYwFpkhGh+Q16bwMP3cOontH8FOep7tGV86Y7SQ=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220513210516-0976fa681c29 h1:w8s32wxx3sY+OjLlv9qltkLU5yvJzxjjgiHWLjdIcw4=
+golang.org/x/sync v0.0.0-20220513210516-0976fa681c29/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180823144017-11551d06cbcc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

internal/core/streams/stream_provider_server_side.go

@@ -5,6 +5,7 @@ import (
 	"sync"
 
 	"github.com/launchdarkly/ld-relay/v6/config"
+	"golang.org/x/sync/singleflight"
 
 	"github.com/launchdarkly/eventsource"
 	"gopkg.in/launchdarkly/go-sdk-common.v2/ldlog"
@@ -27,6 +28,8 @@ type serverSideEnvStreamProvider struct {
 type serverSideEnvStreamRepository struct {
 	store   EnvStoreQueries
 	loggers ldlog.Loggers
+
+	flightGroup singleflight.Group
 }
 
 func (s *serverSideStreamProvider) Handler(credential config.SDKCredential) http.HandlerFunc {
@@ -92,22 +95,44 @@ func (r *serverSideEnvStreamRepository) Replay(channel, id string) chan eventsou
 	}
 	go func() {
 		defer close(out)
+		event, err := r.getReplayEvent(channel, id)
+		if err != nil {
+			return
+		}
+		out <- event
+	}()
+	return out
+}
+
+// getReplayEvent will return a ServerSidePutEvent with all the data needed for a Replay.
+func (r *serverSideEnvStreamRepository) getReplayEvent(channel, id string) (eventsource.Event, error) {
+	data, err, _ := r.flightGroup.Do("getReplayEvent", func() (interface{}, error) {
 		flags, err := r.store.GetAll(ldstoreimpl.Features())
 
 		if err != nil {
 			r.loggers.Errorf("Error getting all flags: %s\n", err.Error())
-		} else {
-			segments, err := r.store.GetAll(ldstoreimpl.Segments())
-			if err != nil {
-				r.loggers.Errorf("Error getting all segments: %s\n", err.Error())
-			} else {
-				allData := []ldstoretypes.Collection{
-					{Kind: ldstoreimpl.Features(), Items: removeDeleted(flags)},
-					{Kind: ldstoreimpl.Segments(), Items: removeDeleted(segments)},
-				}
-				out <- MakeServerSidePutEvent(allData)
-			}
+			return nil, err
 		}
-	}()
-	return out
+		segments, err := r.store.GetAll(ldstoreimpl.Segments())
+		if err != nil {
+			r.loggers.Errorf("Error getting all segments: %s\n", err.Error())
+			return nil, err
+		}
+
+		allData := []ldstoretypes.Collection{
+			{Kind: ldstoreimpl.Features(), Items: removeDeleted(flags)},
+			{Kind: ldstoreimpl.Segments(), Items: removeDeleted(segments)},
+		}
+
+		event := MakeServerSidePutEvent(allData)
+		return event, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// panic if it's not an eventsource.Event - as this should be impossible
+	event := data.(eventsource.Event)
+	return event, nil
 }

internal/core/streams/stream_provider_server_side_flags.go

@@ -1,10 +1,12 @@
 package streams
 
 import (
+	"fmt"
 	"net/http"
 	"sync"
 
 	"github.com/launchdarkly/ld-relay/v6/config"
+	"golang.org/x/sync/singleflight"
 
 	"github.com/launchdarkly/eventsource"
 	"gopkg.in/launchdarkly/go-sdk-common.v2/ldlog"
@@ -27,6 +29,8 @@ type serverSideFlagsOnlyEnvStreamProvider struct {
 type serverSideFlagsOnlyEnvStreamRepository struct {
 	store   EnvStoreQueries
 	loggers ldlog.Loggers
+
+	flightGroup singleflight.Group
 }
 
 func (s *serverSideFlagsOnlyStreamProvider) Handler(credential config.SDKCredential) http.HandlerFunc {
@@ -91,16 +95,37 @@ func (r *serverSideFlagsOnlyEnvStreamRepository) Replay(channel, id string) chan
 	}
 	go func() {
 		defer close(out)
-		if r.store.IsInitialized() {
-			flags, err := r.store.GetAll(ldstoreimpl.Features())
-
-			if err != nil {
-				r.loggers.Errorf("Error getting all flags: %s\n", err.Error())
-			} else {
-				out <- MakeServerSideFlagsOnlyPutEvent(
-					[]ldstoretypes.Collection{{Kind: ldstoreimpl.Features(), Items: removeDeleted(flags)}})
-			}
+		event, err := r.getReplayEvent(channel, id)
+		if err != nil {
+			return
 		}
+		out <- event
 	}()
 	return out
 }
+
+func (r *serverSideFlagsOnlyEnvStreamRepository) getReplayEvent(channel, id string) (eventsource.Event, error) {
+	data, err, _ := r.flightGroup.Do("getReplayEvent", func() (interface{}, error) {
+		if !r.store.IsInitialized() {
+			return nil, fmt.Errorf("cannot replay events as store is not initialized.")
+		}
+		flags, err := r.store.GetAll(ldstoreimpl.Features())
+
+		if err != nil {
+			r.loggers.Errorf("Error getting all flags: %s\n", err.Error())
+			return nil, err
+		}
+
+		event := MakeServerSideFlagsOnlyPutEvent(
+			[]ldstoretypes.Collection{{Kind: ldstoreimpl.Features(), Items: removeDeleted(flags)}})
+		return event, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// panic if it's not an eventsource.Event - as this should be impossible
+	event := data.(eventsource.Event)
+	return event, nil
+}

internal/core/streams/stream_provider_server_side_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/launchdarkly/eventsource"
 	"github.com/launchdarkly/ld-relay/v6/internal/basictypes"
 	"github.com/launchdarkly/ld-relay/v6/internal/core/sharedtest"
 
@@ -202,4 +203,85 @@ func TestStreamProviderServerSide(t *testing.T) {
 			verifyHandlerHeartbeat(t, sp, esp, validCredential)
 		})
 	})
+
+	t.Run("Replay", func(t *testing.T) {
+		store := makeMockStore(nil, nil)
+		store.latency = 100 * time.Millisecond
+
+		repo := &serverSideEnvStreamRepository{store: store, loggers: ldlog.NewDisabledLoggers()}
+
+		newData := []ldstoretypes.Collection{
+			{Kind: ldstoreimpl.Features(), Items: store.flags},
+			{Kind: ldstoreimpl.Segments(), Items: store.segments},
+		}
+		expected := MakeServerSidePutEvent(newData)
+		expectedData := expected.Data()
+		t.Run("ConsecutiveCalls", func(t *testing.T) {
+			eventChannel := repo.Replay("", "")
+			select {
+			case actual := <-eventChannel:
+				if actual == nil {
+					t.Fatal("Expected an event from Replay")
+				}
+				if expectedData != actual.Data() {
+					t.Errorf("Replay() = %v; wanted %v", actual.Data(), expectedData)
+				}
+			case <-time.After(time.Second):
+				t.Error("expected an event to be returned")
+			}
+			eventChannel = repo.Replay("", "")
+			select {
+			case actual := <-eventChannel:
+				if actual == nil {
+					t.Fatal("Expected an event from Replay")
+				}
+				if expectedData != actual.Data() {
+					t.Errorf("Replay() = %v; wanted %v", actual.Data(), expectedData)
+				}
+			case <-time.After(time.Second):
+				t.Error("expected an event to be returned")
+			}
+
+		})
+		t.Run("ConcurrentCalls", func(t *testing.T) {
+			eventChannel1 := repo.Replay("", "")
+			eventChannel2 := repo.Replay("", "")
+			var event1, event2 eventsource.Event
+			var events int
+
+			for events < 2 {
+				select {
+				case event, ok := <-eventChannel1:
+					if !ok {
+						break
+					}
+					if event == nil {
+						t.Fatal("Expected an event from Replay")
+					}
+					if expectedData != event.Data() {
+						t.Errorf("Replay() = %v; wanted %v", event.Data(), expectedData)
+					}
+					event1 = event
+					events++
+				case event, ok := <-eventChannel2:
+					if !ok {
+						break
+					}
+					if event == nil {
+						t.Fatal("Expected an event from Replay")
+					}
+					if expectedData != event.Data() {
+						t.Errorf("Replay() = %v; wanted %v", event.Data(), expectedData)
+					}
+					event2 = event
+					events++
+				case <-time.After(time.Second):
+					t.Error("expected an event to be returned")
+				}
+			}
+			if event1 != event2 {
+				t.Error("Expected the same exact event to be returned from the flightgroup")
+			}
+		})
+	})
 }

internal/core/streams/stream_testdata_test.go

@@ -2,6 +2,7 @@ package streams
 
 import (
 	"errors"
+	"time"
 
 	"github.com/launchdarkly/ld-relay/v6/config"
 	"github.com/launchdarkly/ld-relay/v6/internal/core/sharedtest"
@@ -49,13 +50,17 @@ type mockStoreQueries struct {
 	fakeSegmentsError error
 	flags             []ldstoretypes.KeyedItemDescriptor
 	segments          []ldstoretypes.KeyedItemDescriptor
+	latency           time.Duration
 }
 
 func (q mockStoreQueries) IsInitialized() bool {
 	return q.initialized
 }
 
 func (q mockStoreQueries) GetAll(kind ldstoretypes.DataKind) ([]ldstoretypes.KeyedItemDescriptor, error) {
+	if q.latency > 0 {
+		time.Sleep(q.latency)
+	}
 	switch kind {
 	case ldstoreimpl.Features():
 		return q.flags, q.fakeFlagsError