[PAN-2949] Add rewind to block functionality

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

@@ -44,7 +44,7 @@
 
 public class DefaultMutableBlockchain implements MutableBlockchain {
 
-  private final BlockchainStorage blockchainStorage;
+  protected final BlockchainStorage blockchainStorage;
 
   private final Subscribers<BlockAddedObserver> blockAddedObservers = Subscribers.create();
 
@@ -211,10 +211,7 @@ private BlockAddedEvent appendBlockHelper(
 
     updater.commit();
     if (blockAddedEvent.isNewCanonicalHead()) {
-      chainHeader = block.getHeader();
-      totalDifficulty = td;
-      chainHeadTransactionCount = block.getBody().getTransactions().size();
-      chainHeadOmmerCount = block.getBody().getOmmers().size();
+      updateCacheForNewCanonicalHead(block, td);
     }
 
     return blockAddedEvent;
@@ -362,6 +359,39 @@ private BlockAddedEvent handleChainReorg(
         removedTransactions);
   }
 
+  public boolean rewindToBlock(final long blockNumber) {
+    final Optional<Hash> blockHash = blockchainStorage.getBlockHash(blockNumber);
+    if (blockHash.isEmpty()) {
+      return false;
+    }
+
+    final BlockchainStorage.Updater updater = blockchainStorage.updater();
+    try {
+      final Optional<BlockHeader> oldBlockHeader =
+          blockchainStorage.getBlockHeader(blockHash.get());
+      final Optional<BlockBody> oldBlockBody = blockchainStorage.getBlockBody(blockHash.get());
+      final Block block = new Block(oldBlockHeader.get(), oldBlockBody.get());
+
+      handleChainReorg(updater, block);
+      updater.commit();
+
+      updateCacheForNewCanonicalHead(block, calculateTotalDifficulty(block));
+      return true;
+    } catch (final NoSuchElementException e) {
+      // Any Optional.get() calls in this block should be present, missing data means data
+      // corruption or a bug.
+      updater.rollback();
+      throw new IllegalStateException("Blockchain is missing data that should be present.", e);
+    }
+  }
+
+  void updateCacheForNewCanonicalHead(final Block block, final UInt256 uInt256) {
+    chainHeader = block.getHeader();
+    totalDifficulty = uInt256;
+    chainHeadTransactionCount = block.getBody().getTransactions().size();
+    chainHeadOmmerCount = block.getBody().getOmmers().size();
+  }
+
   private static void indexTransactionForBlock(
       final BlockchainStorage.Updater updater, final Hash hash, final List<Transaction> txs) {
     for (int i = 0; i < txs.size(); i++) {

ethereum/core/src/test/java/tech/pegasys/pantheon/ethereum/chain/DefaultMutableBlockchainTest.java

@@ -455,6 +455,44 @@ public void reorgWithOverlappingTransactions() {
     }
   }
 
+  @Test
+  public void rewindChain() {
+    final BlockDataGenerator gen = new BlockDataGenerator(2);
+
+    // Setup an initial blockchain
+    final int originalChainLength = 4;
+    final List<Block> chain = gen.blockSequence(originalChainLength);
+    final List<List<TransactionReceipt>> blockReceipts =
+        chain.stream().map(gen::receipts).collect(Collectors.toList());
+    final KeyValueStorage kvStore = new InMemoryKeyValueStorage();
+    final DefaultMutableBlockchain blockchain = createBlockchain(kvStore, chain.get(0));
+    for (int i = 1; i < chain.size(); i++) {
+      blockchain.appendBlock(chain.get(i), blockReceipts.get(i));
+    }
+    final Block originalHead = blockchain.getChainHeadBlock();
+    final Block targetHead = blockchain.getBlockByHash(originalHead.getHeader().getParentHash());
+
+    // rewind it by 1 block
+    blockchain.rewindToBlock(targetHead.getHeader().getNumber());
+
+    // Check chain has the expected blocks
+    for (int i = 0; i < chain.size() - 1; i++) {
+      assertBlockDataIsStored(blockchain, chain.get(i), blockReceipts.get(i));
+    }
+    assertBlockIsHead(blockchain, targetHead);
+
+    // Check transactions were not indexed
+    for (final Transaction tx : originalHead.getBody().getTransactions()) {
+      assertThat(blockchain.getTransactionByHash(tx.hash())).isNotPresent();
+    }
+
+    // Check that blockNumber index for previous chain head has been removed
+    assertThat(blockchain.getBlockHashByNumber(originalHead.getHeader().getNumber()))
+        .isNotPresent();
+    // Old chain head should not be tracked.
+    assertThat(blockchain.blockIsOnCanonicalChain(originalHead.getHash())).isFalse();
+  }
+
   @Test
   public void appendBlockForFork() {
     final BlockDataGenerator gen = new BlockDataGenerator(2);
@@ -614,10 +652,7 @@ public void blockAddedObserver_invokedSingle() {
     final List<TransactionReceipt> receipts = gen.receipts(newBlock);
 
     final AtomicBoolean observerInvoked = new AtomicBoolean(false);
-    blockchain.observeBlockAdded(
-        (block, chain) -> {
-          observerInvoked.set(true);
-        });
+    blockchain.observeBlockAdded((block, chain) -> observerInvoked.set(true));
 
     blockchain.appendBlock(newBlock, receipts);
 
@@ -638,22 +673,13 @@ public void blockAddedObserver_invokedMultiple() {
     final List<TransactionReceipt> receipts = gen.receipts(newBlock);
 
     final AtomicBoolean observer1Invoked = new AtomicBoolean(false);
-    blockchain.observeBlockAdded(
-        (block, chain) -> {
-          observer1Invoked.set(true);
-        });
+    blockchain.observeBlockAdded((block, chain) -> observer1Invoked.set(true));
 
     final AtomicBoolean observer2Invoked = new AtomicBoolean(false);
-    blockchain.observeBlockAdded(
-        (block, chain) -> {
-          observer2Invoked.set(true);
-        });
+    blockchain.observeBlockAdded((block, chain) -> observer2Invoked.set(true));
 
     final AtomicBoolean observer3Invoked = new AtomicBoolean(false);
-    blockchain.observeBlockAdded(
-        (block, chain) -> {
-          observer3Invoked.set(true);
-        });
+    blockchain.observeBlockAdded((block, chain) -> observer3Invoked.set(true));
 
     blockchain.appendBlock(newBlock, receipts);