ETCM-845: Make get best block fallback to the best saved to storage (#999)

Fallback to stored best block

Author: AnastasiiaL

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

@@ -289,10 +289,11 @@ class BlockchainImpl(
   override def getLatestCheckpointBlockNumber(): BigInt =
     bestKnownBlockAndLatestCheckpoint.get().latestCheckpointNumber
 
+  //returns the best known block if it's available in the storage, otherwise the best stored block
   override def getBestBlock(): Option[Block] = {
     val bestBlockNumber = getBestBlockNumber()
     log.debug("Trying to get best block with number {}", bestBlockNumber)
-    getBlockByNumber(bestBlockNumber)
+    getBlockByNumber(bestBlockNumber) orElse getBlockByNumber(appStateStorage.getBestBlockNumber())
   }
 
   override def getAccount(address: Address, blockNumber: BigInt): Option[Account] =

src/main/scala/io/iohk/ethereum/jsonrpc/EthProofService.scala

@@ -10,8 +10,7 @@ import io.iohk.ethereum.jsonrpc.ProofService.{
   GetProofResponse,
   ProofAccount,
   StorageProof,
-  StorageProofKey,
-  StorageValueProof
+  StorageProofKey
 }
 import io.iohk.ethereum.mpt.{MptNode, MptTraversals}
 import monix.eval.Task
@@ -201,16 +200,20 @@ class EthProofService(blockchain: Blockchain, blockGenerator: BlockGenerator, et
     ByteString(MptTraversals.encodeNode(node))
 
   private def resolveBlock(blockParam: BlockParam): Either[JsonRpcError, ResolvedBlock] = {
-    def getBlock(number: BigInt): Either[JsonRpcError, Block] = {
+    def getBlock(number: BigInt): Either[JsonRpcError, Block] =
       blockchain
         .getBlockByNumber(number)
         .toRight(JsonRpcError.InvalidParams(s"Block $number not found"))
-    }
+
+    def getLatestBlock(): Either[JsonRpcError, Block] =
+      blockchain
+        .getBestBlock()
+        .toRight(JsonRpcError.InvalidParams("Latest block not found"))
 
     blockParam match {
       case BlockParam.WithNumber(blockNumber) => getBlock(blockNumber).map(ResolvedBlock(_, pendingState = None))
       case BlockParam.Earliest => getBlock(0).map(ResolvedBlock(_, pendingState = None))
-      case BlockParam.Latest => getBlock(blockchain.getBestBlockNumber()).map(ResolvedBlock(_, pendingState = None))
+      case BlockParam.Latest => getLatestBlock().map(ResolvedBlock(_, pendingState = None))
       case BlockParam.Pending =>
         blockGenerator.getPendingBlockAndState
           .map(pb => ResolvedBlock(pb.pendingBlock.block, pendingState = Some(pb.worldState)))

src/main/scala/io/iohk/ethereum/jsonrpc/ResolveBlock.scala

@@ -22,7 +22,7 @@ trait ResolveBlock {
     blockParam match {
       case BlockParam.WithNumber(blockNumber) => getBlock(blockNumber).map(ResolvedBlock(_, pendingState = None))
       case BlockParam.Earliest => getBlock(0).map(ResolvedBlock(_, pendingState = None))
-      case BlockParam.Latest => getBlock(blockchain.getBestBlockNumber()).map(ResolvedBlock(_, pendingState = None))
+      case BlockParam.Latest => getLatestBlock().map(ResolvedBlock(_, pendingState = None))
       case BlockParam.Pending =>
         ledger.consensus.blockGenerator.getPendingBlockAndState
           .map(pb => ResolvedBlock(pb.pendingBlock.block, pendingState = Some(pb.worldState)))
@@ -34,7 +34,11 @@ trait ResolveBlock {
   private def getBlock(number: BigInt): Either[JsonRpcError, Block] = {
     blockchain
       .getBlockByNumber(number)
-      .map(Right.apply)
-      .getOrElse(Left(JsonRpcError.InvalidParams(s"Block $number not found")))
+      .toRight(JsonRpcError.InvalidParams(s"Block $number not found"))
   }
+
+  private def getLatestBlock(): Either[JsonRpcError, Block] =
+    blockchain
+      .getBestBlock()
+      .toRight(JsonRpcError.InvalidParams("Latest block not found"))
 }

src/test/scala/io/iohk/ethereum/ledger/BlockImportSpec.scala

@@ -146,7 +146,7 @@ class BlockImportSpec extends AnyFlatSpec with Matchers with ScalaFutures {
     blockQueue.isQueued(oldBlock3.header.hash) shouldBe true
   }
 
-  it should "fail to get bestblock after reorganisation of the longer chain to a shorter one if desync state happened between cache and db" in new EphemBlockchain {
+  it should "get best stored block after reorganisation of the longer chain to a shorter one if desync state happened between cache and db" in new EphemBlockchain {
     val block1: Block = getBlock(bestNum - 2)
     // new chain is shorter but has a higher weight
     val newBlock2: Block = getBlock(bestNum - 1, difficulty = 101, parent = block1.header.hash)
@@ -192,7 +192,7 @@ class BlockImportSpec extends AnyFlatSpec with Matchers with ScalaFutures {
     // dying before updating the storage but after updating the cache, inconsistency is created
     blockchain.saveBestKnownBlocks(oldBlock4.number)
 
-    blockchain.getBestBlock() shouldBe None
+    blockchain.getBestBlock() shouldBe Some(ancestorForValidation)
   }
 
   it should "handle error when trying to reorganise chain" in new EphemBlockchain {