[ETCM-1060] rewrite ommers validation to avoid using getBlockByNumber

src/main/scala/io/iohk/ethereum/consensus/pow/validators/OmmersValidator.scala

@@ -30,11 +30,17 @@ trait OmmersValidator {
   )(implicit blockchainConfig: BlockchainConfig): Either[OmmersError, OmmersValid] = {
 
     val getBlockHeaderByHash: ByteString => Option[BlockHeader] = blockchainReader.getBlockHeaderByHash
-    val bestBranch = blockchainReader.getBestBranch()
     val getNBlocksBack: (ByteString, Int) => List[Block] =
-      (_, n) =>
-        ((blockNumber - n) until blockNumber).toList
-          .flatMap(nb => blockchainReader.getBlockByNumber(bestBranch, nb))
+      (tailBlockHash, n) =>
+        Iterator
+          .iterate(blockchainReader.getBlockByHash(tailBlockHash))(
+            _.filter(_.number > 0) // avoid trying to fetch parent of genesis
+              .flatMap(block => blockchainReader.getBlockByHash(block.header.parentHash))
+          )
+          .collect { case Some(block) => block }
+          .take(n)
+          .toList
+          .reverse
 
     validate(parentHash, blockNumber, ommers, getBlockHeaderByHash, getNBlocksBack)
   }

src/main/scala/io/iohk/ethereum/ledger/BlockValidation.scala

@@ -39,15 +39,18 @@ class BlockValidation(
           // The in memory blocks aren't connected to the db ones, we don't have n blocks to return so we return none
           Nil
 
-        case Some(block) =>
+        case Some(highestBlockInStorage) =>
           // We already have |block +: queuedBlocks|
           val remaining = n - queuedBlocks.length - 1
-
-          val numbers = (block.header.number - remaining) until block.header.number
-          val bestBranch = blockchainReader.getBestBranch()
-          val blocks =
-            (numbers.toList.flatMap(nb => blockchainReader.getBlockByNumber(bestBranch, nb)) :+ block) ::: queuedBlocks
-          blocks
+          val remainingBlocks = Iterator
+            .iterate(blockchainReader.getBlockByHash(highestBlockInStorage.header.parentHash))(
+              _.filter(_.number > 0) // avoid trying to fetch parent of genesis
+                .flatMap(p => blockchainReader.getBlockByHash(p.header.parentHash))
+            )
+            .take(remaining)
+            .collect { case Some(block) => block }
+            .toList
+          (remainingBlocks :+ highestBlockInStorage) ::: queuedBlocks
       }
     }
   }