[PIE-1810] Add read-only blockchain factory method

ethereum/core/src/main/java/tech/pegasys/pantheon/ethereum/ProtocolContext.java

@@ -14,7 +14,7 @@
 
 import tech.pegasys.pantheon.ethereum.chain.Blockchain;
 import tech.pegasys.pantheon.ethereum.chain.BlockchainStorage;
-import tech.pegasys.pantheon.ethereum.chain.DefaultMutableBlockchain;
+import tech.pegasys.pantheon.ethereum.chain.DefaultBlockchain;
 import tech.pegasys.pantheon.ethereum.chain.GenesisState;
 import tech.pegasys.pantheon.ethereum.chain.MutableBlockchain;
 import tech.pegasys.pantheon.ethereum.mainnet.ProtocolSchedule;
@@ -60,7 +60,7 @@ public static <T> ProtocolContext<T> init(
         storageProvider.createWorldStatePreimageStorage();
 
     final MutableBlockchain blockchain =
-        new DefaultMutableBlockchain(genesisState.getBlock(), blockchainStorage, metricsSystem);
+        DefaultBlockchain.createMutable(genesisState.getBlock(), blockchainStorage, metricsSystem);
 
     final WorldStateArchive worldStateArchive =
         new WorldStateArchive(worldStateStorage, preimageStorage);

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

@@ -42,7 +42,7 @@
 
 import com.google.common.annotations.VisibleForTesting;
 
-public class DefaultMutableBlockchain implements MutableBlockchain {
+public class DefaultBlockchain implements MutableBlockchain {
 
   protected final BlockchainStorage blockchainStorage;
 
@@ -53,13 +53,16 @@ public class DefaultMutableBlockchain implements MutableBlockchain {
   private volatile int chainHeadTransactionCount;
   private volatile int chainHeadOmmerCount;
 
-  public DefaultMutableBlockchain(
-      final Block genesisBlock,
+  private DefaultBlockchain(
+      final Optional<Block> genesisBlock,
       final BlockchainStorage blockchainStorage,
       final MetricsSystem metricsSystem) {
     checkNotNull(genesisBlock);
+    checkNotNull(blockchainStorage);
+    checkNotNull(metricsSystem);
+
     this.blockchainStorage = blockchainStorage;
-    this.setGenesis(genesisBlock);
+    genesisBlock.ifPresent(this::setGenesis);
 
     final Hash chainHead = blockchainStorage.getChainHead().get();
     chainHeader = blockchainStorage.getBlockHeader(chainHead).get();
@@ -112,6 +115,40 @@ public DefaultMutableBlockchain(
         () -> chainHeadOmmerCount);
   }
 
+  public static MutableBlockchain createMutable(
+      final Block genesisBlock,
+      final BlockchainStorage blockchainStorage,
+      final MetricsSystem metricsSystem) {
+    checkNotNull(genesisBlock);
+    return new DefaultBlockchain(Optional.of(genesisBlock), blockchainStorage, metricsSystem);
+  }
+
+  public static Blockchain create(
+      final BlockchainStorage blockchainStorage, final MetricsSystem metricsSystem) {
+    checkArgument(
+        validateStorageNonEmpty(blockchainStorage), "Cannot create Blockchain from empty storage");
+    return new DefaultBlockchain(Optional.empty(), blockchainStorage, metricsSystem);
+  }
+
+  private static boolean validateStorageNonEmpty(final BlockchainStorage blockchainStorage) {
+    // Run a few basic checks to make sure data looks available and consistent
+    final Optional<Hash> maybeHead = blockchainStorage.getChainHead();
+    if (maybeHead.isEmpty()) {
+      return false;
+    }
+    final Optional<Hash> genesisHash =
+        blockchainStorage.getBlockHash(BlockHeader.GENESIS_BLOCK_NUMBER);
+    if (genesisHash.isEmpty()) {
+      return false;
+    }
+    final Optional<UInt256> td = blockchainStorage.getTotalDifficulty(maybeHead.get());
+    if (td.isEmpty()) {
+      return false;
+    }
+
+    return true;
+  }
+
   @Override
   public ChainHead getChainHead() {
     return new ChainHead(chainHeader.getHash(), totalDifficulty, chainHeader.getNumber());
@@ -359,6 +396,7 @@ private BlockAddedEvent handleChainReorg(
         removedTransactions);
   }
 
+  @Override
   public boolean rewindToBlock(final long blockNumber) {
     final Optional<Hash> blockHash = blockchainStorage.getBlockHash(blockNumber);
     if (blockHash.isEmpty()) {
@@ -413,7 +451,7 @@ Set<Hash> getForks() {
     return new HashSet<>(blockchainStorage.getForkHeads());
   }
 
-  protected void setGenesis(final Block genesisBlock) {
+  private void setGenesis(final Block genesisBlock) {
     checkArgument(
         genesisBlock.getHeader().getNumber() == BlockHeader.GENESIS_BLOCK_NUMBER,
         "Invalid genesis block.");

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

@@ -30,4 +30,13 @@ public interface MutableBlockchain extends Blockchain {
    * @param receipts The list of receipts associated with this block's transactions.
    */
   void appendBlock(Block block, List<TransactionReceipt> receipts);
+
+  /**
+   * Rolls back the canonical chainhead to the specified block number.
+   *
+   * @param blockNumber The block number to roll back to.
+   * @return {@code true} on success, {@code false} if the canonical chain height is less than
+   *     {@code blockNumber}
+   */
+  boolean rewindToBlock(final long blockNumber);
 }

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

@@ -17,7 +17,7 @@
 import tech.pegasys.pantheon.config.GenesisConfigFile;
 import tech.pegasys.pantheon.config.StubGenesisConfigOptions;
 import tech.pegasys.pantheon.ethereum.ProtocolContext;
-import tech.pegasys.pantheon.ethereum.chain.DefaultMutableBlockchain;
+import tech.pegasys.pantheon.ethereum.chain.DefaultBlockchain;
 import tech.pegasys.pantheon.ethereum.chain.GenesisState;
 import tech.pegasys.pantheon.ethereum.chain.MutableBlockchain;
 import tech.pegasys.pantheon.ethereum.mainnet.MainnetBlockHeaderFunctions;
@@ -49,7 +49,7 @@ private ExecutionContextTestFixture(
     this.genesis = genesisState.getBlock();
     this.keyValueStorage = keyValueStorage;
     this.blockchain =
-        new DefaultMutableBlockchain(
+        DefaultBlockchain.createMutable(
             genesis,
             new KeyValueStoragePrefixedKeyBlockchainStorage(
                 keyValueStorage, new MainnetBlockHeaderFunctions()),

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

@@ -13,7 +13,7 @@
 package tech.pegasys.pantheon.ethereum.core;
 
 import tech.pegasys.pantheon.ethereum.chain.BlockchainStorage;
-import tech.pegasys.pantheon.ethereum.chain.DefaultMutableBlockchain;
+import tech.pegasys.pantheon.ethereum.chain.DefaultBlockchain;
 import tech.pegasys.pantheon.ethereum.chain.MutableBlockchain;
 import tech.pegasys.pantheon.ethereum.mainnet.MainnetBlockHeaderFunctions;
 import tech.pegasys.pantheon.ethereum.mainnet.ProtocolSchedule;
@@ -43,7 +43,7 @@ public static MutableBlockchain createInMemoryBlockchain(final Block genesisBloc
   public static MutableBlockchain createInMemoryBlockchain(
       final Block genesisBlock, final BlockHeaderFunctions blockHeaderFunctions) {
     final InMemoryKeyValueStorage keyValueStorage = new InMemoryKeyValueStorage();
-    return new DefaultMutableBlockchain(
+    return DefaultBlockchain.createMutable(
         genesisBlock,
         new KeyValueStoragePrefixedKeyBlockchainStorage(keyValueStorage, blockHeaderFunctions),
         new NoOpMetricsSystem());