[PAN-2325] Fix IndexOutOfBoundsException in DetermineCommonAncestorTask

ethereum/core/src/main/java/tech/pegasys/pantheon/ethereum/chain/Blockchain.java

@@ -63,6 +63,19 @@ default Block getChainHeadBlock() {
     return new Block(header, body);
   }
 
+  default Block getGenesisBlock() {
+    final Hash genesisHash =
+        getBlockHashByNumber(BlockHeader.GENESIS_BLOCK_NUMBER)
+            .orElseThrow(() -> new IllegalStateException("Missing genesis block."));
+    final BlockHeader header =
+        getBlockHeader(genesisHash)
+            .orElseThrow(() -> new IllegalStateException("Missing genesis block."));
+    final BlockBody body =
+        getBlockBody(genesisHash)
+            .orElseThrow(() -> new IllegalStateException("Missing genesis block."));
+    return new Block(header, body);
+  }
+
   /**
    * Checks whether the block corresponding to the given hash is on the canonical chain.
    *

ethereum/core/src/test-support/java/tech/pegasys/pantheon/ethereum/core/BlockDataGenerator.java

@@ -137,6 +137,19 @@ public List<Block> blockSequence(final int count) {
     return blockSequence(count, worldState, Collections.emptyList(), Collections.emptyList());
   }
 
+  public List<Block> blockSequence(final Block previousBlock, final int count) {
+    final WorldStateArchive worldState = createInMemoryWorldStateArchive();
+    Hash parentHash = previousBlock.getHeader().getHash();
+    long blockNumber = previousBlock.getHeader().getNumber() + 1;
+    return blockSequence(
+        count,
+        blockNumber,
+        parentHash,
+        worldState,
+        Collections.emptyList(),
+        Collections.emptyList());
+  }
+
   public List<Block> blockSequence(
       final int count,
       final WorldStateArchive worldStateArchive,

ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/SynchronizerConfiguration.java

@@ -220,7 +220,7 @@ public static class Builder {
     private Range<Long> blockPropagationRange = Range.closed(-10L, 30L);
     private long downloaderChangeTargetThresholdByHeight = 20L;
     private UInt256 downloaderChangeTargetThresholdByTd = UInt256.of(1_000_000_000L);
-    private int downloaderHeaderRequestSize = 10;
+    private int downloaderHeaderRequestSize = 200;
     private int downloaderCheckpointTimeoutsPermitted = 5;
     private int downloaderChainSegmentTimeoutsPermitted = 5;
     private int downloaderChainSegmentSize = 200;

ethereum/eth/src/main/java/tech/pegasys/pantheon/ethereum/eth/sync/tasks/DetermineCommonAncestorTask.java

@@ -31,11 +31,17 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
-public class DetermineCommonAncestorTask<C> extends AbstractEthTask<BlockHeader> {
+/**
+ * Finds the common ancestor with the given peer. It is assumed that the peer will at least share
+ * the same genesis block with this node. Running this task against a peer with a non-matching
+ * genesis block will result in undefined behavior: the task may complete exceptionally or in some
+ * cases this node's genesis block will be returned.
+ */
+public class DetermineCommonAncestorTask extends AbstractEthTask<BlockHeader> {
   private static final Logger LOG = LogManager.getLogger();
   private final EthContext ethContext;
-  private final ProtocolSchedule<C> protocolSchedule;
-  private final ProtocolContext<C> protocolContext;
+  private final ProtocolSchedule<?> protocolSchedule;
+  private final ProtocolContext<?> protocolContext;
   private final EthPeer peer;
   private final int headerRequestSize;
   private final MetricsSystem metricsSystem;
@@ -46,8 +52,8 @@ public class DetermineCommonAncestorTask<C> extends AbstractEthTask<BlockHeader>
   private boolean initialQuery = true;
 
   private DetermineCommonAncestorTask(
-      final ProtocolSchedule<C> protocolSchedule,
-      final ProtocolContext<C> protocolContext,
+      final ProtocolSchedule<?> protocolSchedule,
+      final ProtocolContext<?> protocolContext,
       final EthContext ethContext,
       final EthPeer peer,
       final int headerRequestSize,
@@ -66,14 +72,14 @@ private DetermineCommonAncestorTask(
         protocolContext.getBlockchain().getBlockHeader(BlockHeader.GENESIS_BLOCK_NUMBER).get();
   }
 
-  public static <C> DetermineCommonAncestorTask<C> create(
-      final ProtocolSchedule<C> protocolSchedule,
-      final ProtocolContext<C> protocolContext,
+  public static DetermineCommonAncestorTask create(
+      final ProtocolSchedule<?> protocolSchedule,
+      final ProtocolContext<?> protocolContext,
       final EthContext ethContext,
       final EthPeer peer,
       final int headerRequestSize,
       final MetricsSystem metricsSystem) {
-    return new DetermineCommonAncestorTask<>(
+    return new DetermineCommonAncestorTask(
         protocolSchedule, protocolContext, ethContext, peer, headerRequestSize, metricsSystem);
   }
 
@@ -144,6 +150,10 @@ private CompletableFuture<Void> processHeaders(
       final AbstractPeerTask.PeerTaskResult<List<BlockHeader>> headersResult) {
     initialQuery = false;
     final List<BlockHeader> headers = headersResult.getResult();
+    if (headers.isEmpty()) {
+      // Nothing to do
+      return CompletableFuture.completedFuture(null);
+    }
 
     final OptionalInt maybeAncestorNumber =
         BlockchainUtil.findHighestKnownBlockIndex(protocolContext.getBlockchain(), headers, false);

ethereum/eth/src/test/java/tech/pegasys/pantheon/ethereum/eth/manager/RespondingEthPeer.java

@@ -32,6 +32,7 @@
 import tech.pegasys.pantheon.ethereum.p2p.api.MessageData;
 import tech.pegasys.pantheon.ethereum.p2p.wire.Capability;
 import tech.pegasys.pantheon.ethereum.p2p.wire.DefaultMessage;
+import tech.pegasys.pantheon.ethereum.p2p.wire.messages.DisconnectMessage.DisconnectReason;
 import tech.pegasys.pantheon.ethereum.worldstate.WorldStateArchive;
 import tech.pegasys.pantheon.util.bytes.BytesValue;
 import tech.pegasys.pantheon.util.uint.UInt256;
@@ -82,6 +83,16 @@ public static void respondOnce(final Responder responder, final RespondingEthPee
     respondOnce(responder, Arrays.asList(peers));
   }
 
+  public boolean disconnect(final DisconnectReason reason) {
+    if (ethPeer.isDisconnected()) {
+      return false;
+    }
+
+    ethPeer.disconnect(reason);
+    ethProtocolManager.handleDisconnect(getPeerConnection(), reason, true);
+    return true;
+  }
+
   public MockPeerConnection getPeerConnection() {
     return peerConnection;
   }