Fix Overflow in Status Check

beacon-chain/sync/BUILD.bazel

@@ -100,6 +100,7 @@ go_test(
         "rpc_ping_test.go",
         "rpc_status_test.go",
         "rpc_test.go",
+        "service_test.go",
         "subscriber_beacon_aggregate_proof_test.go",
         "subscriber_beacon_blocks_test.go",
         "subscriber_committee_index_beacon_attestation_test.go",

beacon-chain/sync/service.go

@@ -160,8 +160,8 @@ func (r *Service) Status() error {
 		}
 		// If our head slot is on a previous epoch and our peers are reporting their head block are
 		// in the most recent epoch, then we might be out of sync.
-		if headEpoch := helpers.SlotToEpoch(r.chain.HeadSlot()); headEpoch < helpers.SlotToEpoch(r.chain.CurrentSlot())-1 &&
-			headEpoch < r.p2p.Peers().CurrentEpoch()-1 {
+		if headEpoch := helpers.SlotToEpoch(r.chain.HeadSlot()); headEpoch+1 < helpers.SlotToEpoch(r.chain.CurrentSlot()) &&
+			headEpoch+1 < r.p2p.Peers().CurrentEpoch() {
 			return errors.New("out of sync")
 		}
 	}

beacon-chain/sync/service_test.go

@@ -0,0 +1,33 @@
+package sync
+
+import (
+	"testing"
+	"time"
+
+	stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
+	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
+	mockChain "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
+	p2ptest "github.com/prysmaticlabs/prysm/beacon-chain/p2p/testing"
+	mockSync "github.com/prysmaticlabs/prysm/beacon-chain/sync/initial-sync/testing"
+)
+
+func TestService_StatusZeroEpoch(t *testing.T) {
+	bState, err := stateTrie.InitializeFromProto(&pb.BeaconState{Slot: 0})
+	if err != nil {
+		t.Fatal(err)
+	}
+	r := &Service{
+		p2p:         p2ptest.NewTestP2P(t),
+		initialSync: new(mockSync.Sync),
+		chain: &mockChain.ChainService{
+			Genesis: time.Now(),
+			State:   bState,
+		},
+	}
+	r.chainStarted = true
+
+	err = r.Status()
+	if err != nil {
+		t.Errorf("Wanted non failing status but got: %v", err)
+	}
+}