create BlockchainBranch class with getBlockByNumber and getHashByBlockNumber functions

Author: Aurélien Richez

src/main/scala/io/iohk/ethereum/domain/BlockchainReader.scala

@@ -8,6 +8,8 @@ import io.iohk.ethereum.db.storage.BlockHeadersStorage
 import io.iohk.ethereum.db.storage.BlockNumberMappingStorage
 import io.iohk.ethereum.db.storage.ReceiptStorage
 import io.iohk.ethereum.db.storage.StateStorage
+import io.iohk.ethereum.domain.branch.BestBlockchainBranch
+import io.iohk.ethereum.domain.branch.BlockchainBranch
 import io.iohk.ethereum.mpt.MptNode
 import io.iohk.ethereum.utils.Logger
 
@@ -86,6 +88,13 @@ class BlockchainReader(
     */
   def getReceiptsByHash(blockhash: ByteString): Option[Seq[Receipt]] = receiptStorage.get(blockhash)
 
+  def getBestBranch(): BlockchainBranch =
+    new BestBlockchainBranch(
+      getBestBlock().map(_.header).getOrElse(genesisHeader),
+      blockNumberMappingStorage,
+      this
+    )
+
   def getBestBlockNumber(): BigInt = {
     val bestSavedBlockNumber = appStateStorage.getBestBlockNumber()
     val bestKnownBlockNumber = blockchainMetadata.bestKnownBlockAndLatestCheckpoint.get().bestBlockNumber

src/main/scala/io/iohk/ethereum/domain/branch/BestBlockchainBranch.scala

@@ -0,0 +1,37 @@
+package io.iohk.ethereum.domain.branch
+import akka.util.ByteString
+
+import io.iohk.ethereum.db.storage.BlockNumberMappingStorage
+import io.iohk.ethereum.domain.Block
+import io.iohk.ethereum.domain.BlockHeader
+import io.iohk.ethereum.domain.BlockchainReader
+
+/** A Branch instance which only works for the best canonical branch. As this branch
+  * currently has specific indexes (particularly regarding accessing blocks by number),
+  * it will uses thoses to provide better performance.
+  */
+class BestBlockchainBranch(
+    tipBlockHeader: BlockHeader,
+    bestChainBlockNumberMappingStorage: BlockNumberMappingStorage,
+    blockchainReader: BlockchainReader
+) extends BlockchainBranch {
+
+  /* The following assumptions are made in this class :
+   *  - the whole branch exist in storage
+   *  - The various metadata and index are consistent
+   *
+   * If those assumptions are found to be false, then the application is in an inconsistent
+   * state and the class will throw.
+   * */
+
+  override def getBlockByNumber(number: BigInt): Option[Block] =
+    if (tipBlockHeader.number <= number && number > 0) {
+      for {
+        hash <- blockchainReader.getHashByBlockNumber(number)
+        block <- blockchainReader.getBlockByHash(hash)
+      } yield block
+    } else None
+
+  override def getHashByBlockNumber(number: BigInt): Option[ByteString] =
+    bestChainBlockNumberMappingStorage.get(number)
+}

src/main/scala/io/iohk/ethereum/domain/branch/BlockchainBranch.scala

@@ -0,0 +1,16 @@
+package io.iohk.ethereum.domain.branch
+
+import akka.util.ByteString
+
+import io.iohk.ethereum.domain.Block
+
+// TODO choose a name : ChainInstance, BlockchainBranch, Branch, Blockchain ?
+trait BlockchainBranch {
+
+  /** Returns a block inside this branch based on its number */
+  def getBlockByNumber(number: BigInt): Option[Block]
+
+  /** Returns a block hash for the block at the given height if any */
+  def getHashByBlockNumber(number: BigInt): Option[ByteString]
+
+}