Use SlotTickerWithOffset for StreamIndexedAttestations (#5999)

* Change streamindexed to slot ticker with offset
* Make 2/3rds
* Add test
* Merge branch 'master' of github.com:prysmaticlabs/prysm into ticker-offset
* Add check for offset
* Merge branch 'master' of github.com:prysmaticlabs/prysm into ticker-offset
* Fix test
* Merge refs/heads/master into ticker-offset

beacon-chain/rpc/beacon/attestations.go

@@ -5,7 +5,6 @@ import (
 	"sort"
 	"strconv"
 	"strings"
-	"time"
 
 	ptypes "github.com/gogo/protobuf/types"
 	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
@@ -332,11 +331,11 @@ func (bs *Server) StreamIndexedAttestations(
 // already being done by the attestation pool in the operations service.
 func (bs *Server) collectReceivedAttestations(ctx context.Context) {
 	attsByRoot := make(map[[32]byte][]*ethpb.Attestation)
-	halfASlot := slotutil.DivideSlotBy(2 /* 1/2 slot duration */)
-	ticker := time.NewTicker(halfASlot)
+	twoThirdsASlot := 2 * slotutil.DivideSlotBy(3) /* 2/3 slot duration */
+	ticker := slotutil.GetSlotTickerWithOffset(bs.GenesisTimeFetcher.GenesisTime(), twoThirdsASlot, params.BeaconConfig().SecondsPerSlot)
 	for {
 		select {
-		case <-ticker.C:
+		case _ = <-ticker.C():
 			aggregatedAttsByTarget := make(map[[32]byte][]*ethpb.Attestation)
 			for root, atts := range attsByRoot {
 				// We aggregate the received attestations, we know they all have the same data root.

beacon-chain/rpc/beacon/attestations_test.go

@@ -983,6 +983,9 @@ func TestServer_StreamIndexedAttestations_ContextCanceled(t *testing.T) {
 	server := &Server{
 		Ctx:                 ctx,
 		AttestationNotifier: chainService.OperationNotifier(),
+		GenesisTimeFetcher: &chainMock.ChainService{
+			Genesis: time.Now(),
+		},
 	}
 
 	exitRoutine := make(chan bool)

shared/slotutil/slotticker.go

@@ -51,6 +51,23 @@ func GetSlotTicker(genesisTime time.Time, secondsPerSlot uint64) *SlotTicker {
 	return ticker
 }
 
+// GetSlotTickerWithOffset is a constructor for SlotTicker that allows a offset of time from genesis,
+// entering a offset greater than secondsPerSlot is not allowed.
+func GetSlotTickerWithOffset(genesisTime time.Time, offset time.Duration, secondsPerSlot uint64) *SlotTicker {
+	if genesisTime.Unix() == 0 {
+		panic("zero genesis time")
+	}
+	if offset > time.Duration(secondsPerSlot)*time.Second {
+		panic("invalid ticker offset")
+	}
+	ticker := &SlotTicker{
+		c:    make(chan uint64),
+		done: make(chan struct{}),
+	}
+	ticker.start(genesisTime.Add(offset), secondsPerSlot, roughtime.Since, roughtime.Until, time.After)
+	return ticker
+}
+
 func (s *SlotTicker) start(
 	genesisTime time.Time,
 	secondsPerSlot uint64,

shared/slotutil/slotticker_test.go

@@ -109,3 +109,31 @@ func TestSlotTickerGenesis(t *testing.T) {
 		t.Fatalf("Expected %d, got %d", 1, slot)
 	}
 }
+
+func TestGetSlotTickerWithOffset_OK(t *testing.T) {
+	genesisTime := time.Now()
+	secondsPerSlot := uint64(4)
+	offset := time.Duration(secondsPerSlot/2) * time.Second
+
+	offsetTicker := GetSlotTickerWithOffset(genesisTime, offset, secondsPerSlot)
+	normalTicker := GetSlotTicker(genesisTime, secondsPerSlot)
+
+	firstTicked := 0
+	for {
+		select {
+		case _ = <-offsetTicker.C():
+			if firstTicked != 1 {
+				t.Fatal("Expected other ticker to tick first")
+			}
+			firstTicked = 2
+			return
+		case _ = <-normalTicker.C():
+			if firstTicked != 0 {
+				t.Fatal("Expected normal ticker to tick first")
+			}
+			firstTicked = 1
+			break
+		}
+	}
+
+}