Make ActiveEth2P2PNetwork aware of seed lookahead period and compute distance (Consensys#8172)

Author: courtneyeh

Diff for: networking/eth2/src/main/java/tech/pegasys/teku/networking/eth2/ActiveEth2P2PNetwork.java

@@ -179,11 +179,21 @@ public void onSyncStateChanged(final boolean isInSync, final boolean isOptimisti
     gossipForkManager.onOptimisticHeadChanged(isOptimistic);
   }
 
-  private boolean isCloseToInSync() {
+  @VisibleForTesting
+  boolean isCloseToInSync() {
+    final Optional<UInt64> currentEpoch = recentChainData.getCurrentEpoch();
+    if (currentEpoch.isEmpty()) {
+      return false;
+    }
+
+    final int maxLookaheadEpochs = spec.getSpecConfig(currentEpoch.get()).getMaxSeedLookahead();
+    final int slotsPerEpoch = spec.slotsPerEpoch(currentEpoch.get());
+    final int maxLookaheadSlots = slotsPerEpoch * maxLookaheadEpochs;
+
     return recentChainData
         .getChainHeadSlotsBehind()
         .orElse(UInt64.MAX_VALUE)
-        .isLessThanOrEqualTo(500);
+        .isLessThanOrEqualTo(maxLookaheadSlots);
   }
 
   private void setTopicScoringParams() {

Diff for: networking/eth2/src/test/java/tech/pegasys/teku/networking/eth2/ActiveEth2P2PNetworkTest.java

@@ -81,6 +81,10 @@ public class ActiveEth2P2PNetworkTest {
   private Fork altairFork;
   private Bytes32 genesisValidatorsRoot;
 
+  private final int maxFollowDistanceSlots =
+      spec.getGenesisSpecConfig().getMaxSeedLookahead()
+          * spec.slotsPerEpoch(storageSystem.combinedChainDataClient().getCurrentEpoch());
+
   @BeforeEach
   public void setup() {
     when(discoveryNetwork.start()).thenReturn(SafeFuture.completedFuture(null));
@@ -255,6 +259,41 @@ void onSyncStateChanged_shouldNotResultInMultipleSubscriptions() {
     verify(eventChannels, times(1)).subscribe(eq(BlockGossipChannel.class), any());
   }
 
+  @Test
+  void isCloseToInSync_shouldCalculateWhenDistanceOutOfRange() {
+    storageSystem.chainUpdater().setCurrentSlot(UInt64.valueOf(maxFollowDistanceSlots + 1));
+    assertThat(network.isCloseToInSync()).isFalse();
+  }
+
+  @Test
+  void isCloseToInSync_shouldCalculateWhenDistanceInRange() {
+    storageSystem.chainUpdater().setCurrentSlot(UInt64.valueOf(maxFollowDistanceSlots));
+    assertThat(network.isCloseToInSync()).isTrue();
+  }
+
+  @Test
+  void isCloseToInSync_shouldReturnFalseWhenEmptyCurrentEpoch() {
+    final StorageSystem storageSystem = InMemoryStorageSystemBuilder.buildDefault();
+    final RecentChainData recentChainData = storageSystem.recentChainData();
+    final ActiveEth2P2PNetwork network =
+        new ActiveEth2P2PNetwork(
+            spec,
+            asyncRunner,
+            discoveryNetwork,
+            peerManager,
+            gossipForkManager,
+            eventChannels,
+            recentChainData,
+            attestationSubnetService,
+            syncCommitteeSubnetService,
+            gossipEncoding,
+            gossipConfigurator,
+            processedAttestationSubscriptionProvider,
+            true);
+
+    assertThat(network.isCloseToInSync()).isFalse();
+  }
+
   @SuppressWarnings("unchecked")
   private ArgumentCaptor<Iterable<Integer>> subnetIdCaptor() {
     return ArgumentCaptor.forClass(Iterable.class);