[NC-1616] Added iBFT NewChainHeadHeader event and related blockchain observer (#59)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

consensus/ibft/src/main/java/tech/pegasys/pantheon/consensus/ibft/IbftChainObserver.java

@@ -0,0 +1,31 @@
+package tech.pegasys.pantheon.consensus.ibft;
+
+import tech.pegasys.pantheon.consensus.ibft.ibftevent.NewChainHead;
+import tech.pegasys.pantheon.ethereum.chain.BlockAddedEvent;
+import tech.pegasys.pantheon.ethereum.chain.BlockAddedObserver;
+import tech.pegasys.pantheon.ethereum.chain.Blockchain;
+
+/**
+ * Blockchain observer that adds {@link NewChainHead} events to the event queue when a new block is
+ * added to the chain head
+ */
+public class IbftChainObserver implements BlockAddedObserver {
+  private final IbftEventQueue queue;
+
+  public IbftChainObserver(final IbftEventQueue queue) {
+    this.queue = queue;
+  }
+
+  @Override
+  public void onBlockAdded(final BlockAddedEvent event, final Blockchain blockchain) {
+    switch (event.getEventType()) {
+      case HEAD_ADVANCED:
+        queue.add(new NewChainHead(event.getBlock().getHeader()));
+        break;
+
+      default:
+        throw new IllegalStateException(
+            String.format("Unexpected BlockAddedEvent received: %s", event.getEventType()));
+    }
+  }
+}

consensus/ibft/src/main/java/tech/pegasys/pantheon/consensus/ibft/IbftEvents.java

@@ -9,6 +9,7 @@ public class IbftEvents {
   }
 
   public enum Type {
-    ROUND_EXPIRY
+    ROUND_EXPIRY,
+    NEW_CHAIN_HEAD_HEADER
   }
 }

consensus/ibft/src/main/java/tech/pegasys/pantheon/consensus/ibft/ibftevent/NewChainHead.java

@@ -0,0 +1,56 @@
+package tech.pegasys.pantheon.consensus.ibft.ibftevent;
+
+import tech.pegasys.pantheon.consensus.ibft.IbftEvent;
+import tech.pegasys.pantheon.consensus.ibft.IbftEvents.Type;
+import tech.pegasys.pantheon.ethereum.core.BlockHeader;
+
+import java.util.Objects;
+
+import com.google.common.base.MoreObjects;
+
+/** Event indicating that new chain head has been received */
+public final class NewChainHead implements IbftEvent {
+  private final BlockHeader newChainHeadHeader;
+
+  /**
+   * Constructor for a NewChainHead event
+   *
+   * @param newChainHeadHeader The header of the current blockchain head
+   */
+  public NewChainHead(final BlockHeader newChainHeadHeader) {
+    this.newChainHeadHeader = newChainHeadHeader;
+  }
+
+  @Override
+  public Type getType() {
+    return Type.NEW_CHAIN_HEAD_HEADER;
+  }
+
+  @Override
+  public String toString() {
+    return MoreObjects.toStringHelper(this)
+        .add("New Chain Head Header", newChainHeadHeader)
+        .toString();
+  }
+
+  @Override
+  public boolean equals(final Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    final NewChainHead that = (NewChainHead) o;
+    return Objects.equals(newChainHeadHeader, that.newChainHeadHeader);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(newChainHeadHeader);
+  }
+
+  public BlockHeader getNewChainHeadHeader() {
+    return newChainHeadHeader;
+  }
+}

consensus/ibft/src/test/java/tech/pegasys/pantheon/consensus/ibft/IbftChainObserverTest.java

@@ -0,0 +1,78 @@
+package tech.pegasys.pantheon.consensus.ibft;
+
+import static java.util.Collections.emptyList;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import tech.pegasys.pantheon.consensus.ibft.ibftevent.NewChainHead;
+import tech.pegasys.pantheon.ethereum.chain.BlockAddedEvent;
+import tech.pegasys.pantheon.ethereum.chain.Blockchain;
+import tech.pegasys.pantheon.ethereum.core.Address;
+import tech.pegasys.pantheon.ethereum.core.Block;
+import tech.pegasys.pantheon.ethereum.core.BlockBody;
+import tech.pegasys.pantheon.ethereum.core.BlockHeader;
+import tech.pegasys.pantheon.ethereum.core.BlockHeaderTestFixture;
+import tech.pegasys.pantheon.ethereum.core.Hash;
+
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+
+public class IbftChainObserverTest {
+  @Test
+  public void newChainHeadHeaderEventIsAddedToTheQueue() {
+    final Blockchain mockBlockchain = mock(Blockchain.class);
+    final IbftEventQueue mockQueue = mock(IbftEventQueue.class);
+    final BlockAddedEvent mockBlockAddedEvent = mock(BlockAddedEvent.class);
+
+    final IbftChainObserver ibftChainObserver = new IbftChainObserver(mockQueue);
+
+    final BlockHeader header =
+        new BlockHeaderTestFixture()
+            .number(1234)
+            .coinbase(Address.ECREC)
+            .parentHash(Hash.EMPTY_LIST_HASH)
+            .buildHeader();
+
+    final Block block = new Block(header, new BlockBody(emptyList(), emptyList()));
+
+    when(mockBlockAddedEvent.getEventType()).thenReturn(BlockAddedEvent.EventType.HEAD_ADVANCED);
+    when(mockBlockAddedEvent.getBlock()).thenReturn(block);
+
+    ibftChainObserver.onBlockAdded(mockBlockAddedEvent, mockBlockchain);
+
+    ArgumentCaptor<IbftEvent> ibftEventArgumentCaptor = ArgumentCaptor.forClass(IbftEvent.class);
+    verify(mockQueue).add(ibftEventArgumentCaptor.capture());
+
+    assertThat(ibftEventArgumentCaptor.getValue() instanceof NewChainHead).isTrue();
+    assertThat(((NewChainHead) ibftEventArgumentCaptor.getValue()).getNewChainHeadHeader())
+        .isEqualTo(header);
+  }
+
+  @Test(expected = IllegalStateException.class)
+  public void exceptionIsThrownWhenEventTypeIsFork() {
+    final Blockchain mockBlockchain = mock(Blockchain.class);
+    final IbftEventQueue mockQueue = mock(IbftEventQueue.class);
+    final BlockAddedEvent mockBlockAddedEvent = mock(BlockAddedEvent.class);
+
+    when(mockBlockAddedEvent.getEventType()).thenReturn(BlockAddedEvent.EventType.FORK);
+
+    final IbftChainObserver ibftChainObserver = new IbftChainObserver(mockQueue);
+
+    ibftChainObserver.onBlockAdded(mockBlockAddedEvent, mockBlockchain);
+  }
+
+  @Test(expected = IllegalStateException.class)
+  public void exceptionIsThrownWhenEventTypeIsChainReorg() {
+    final Blockchain mockBlockchain = mock(Blockchain.class);
+    final IbftEventQueue mockQueue = mock(IbftEventQueue.class);
+    final BlockAddedEvent mockBlockAddedEvent = mock(BlockAddedEvent.class);
+
+    when(mockBlockAddedEvent.getEventType()).thenReturn(BlockAddedEvent.EventType.CHAIN_REORG);
+
+    final IbftChainObserver ibftChainObserver = new IbftChainObserver(mockQueue);
+
+    ibftChainObserver.onBlockAdded(mockBlockAddedEvent, mockBlockchain);
+  }
+}

pantheon/src/main/java/tech/pegasys/pantheon/controller/IbftPantheonController.java

@@ -5,6 +5,7 @@ import static org.apache.logging.log4j.LogManager.getLogger;
 import tech.pegasys.pantheon.consensus.common.EpochManager;
 import tech.pegasys.pantheon.consensus.common.VoteProposer;
 import tech.pegasys.pantheon.consensus.common.VoteTally;
+import tech.pegasys.pantheon.consensus.ibft.IbftChainObserver;
 import tech.pegasys.pantheon.consensus.ibft.IbftContext;
 import tech.pegasys.pantheon.consensus.ibft.IbftEventQueue;
 import tech.pegasys.pantheon.consensus.ibft.IbftProcessor;
@@ -145,6 +146,8 @@ public class IbftPantheonController implements PantheonController<IbftContext, I
 
     final IbftEventQueue ibftEventQueue = new IbftEventQueue();
 
+    blockchain.observeBlockAdded(new IbftChainObserver(ibftEventQueue));
+
     final IbftStateMachine ibftStateMachine = new IbftStateMachine();
     final IbftProcessor ibftProcessor =
         new IbftProcessor(