Fix engine_forkchoiceUpdated bug (#2274)

* fCU Ignore update to old head

* Only enable terminal PoW block conditions for fCUV1

* Typo fix: TDD -> TTD

* Add link to Shanghai fCUV2 specification

* Add link to Paris fCUV1 specification

nimbus/beacon/api_handler/api_forkchoice.nim

@@ -102,38 +102,45 @@ proc forkchoiceUpdated*(ben: BeaconEngineRef,
 
  # Block is known locally, just sanity check that the beacon client does not
  # attempt to push us back to before the merge.
- let blockNumber = header.blockNumber.truncate(uint64)
- if header.difficulty > 0.u256 or blockNumber == 0'u64:
- var
- td, ptd: DifficultyInt
- ttd = com.ttd.get(high(common.BlockNumber))
-
- if not db.getTd(blockHash, td) or (blockNumber > 0'u64 and not db.getTd(header.parentHash, ptd)):
- error "TDs unavailable for TTD check",
- number = blockNumber,
- hash = blockHash.short,
- td = td,
- parent = header.parentHash.short,
- ptd = ptd
- return simpleFCU(PayloadExecutionStatus.invalid, "TDs unavailable for TDD check")
-
- if td < ttd or (blockNumber > 0'u64 and ptd > ttd):
- notice "Refusing beacon update to pre-merge",
- number = blockNumber,
- hash = blockHash.short,
- diff = header.difficulty,
- ptd = ptd,
- ttd = ttd
-
- return invalidFCU("Refusing beacon update to pre-merge")
+ #
+ # Disable terminal PoW block conditions validation for fCUV2 and later.
+ # https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.4/src/engine/shanghai.md#specification-1
+ if apiVersion == Version.V1:
+ let blockNumber = header.blockNumber.truncate(uint64)
+ if header.difficulty > 0.u256 or blockNumber == 0'u64:
+ var
+ td, ptd: DifficultyInt
+ ttd = com.ttd.get(high(common.BlockNumber))
+
+ if not db.getTd(blockHash, td) or (blockNumber > 0'u64 and not db.getTd(header.parentHash, ptd)):
+ error "TDs unavailable for TTD check",
+ number = blockNumber,
+ hash = blockHash.short,
+ td = td,
+ parent = header.parentHash.short,
+ ptd = ptd
+ return simpleFCU(PayloadExecutionStatus.invalid, "TDs unavailable for TTD check")
+
+ if td < ttd or (blockNumber > 0'u64 and ptd > ttd):
+ notice "Refusing beacon update to pre-merge",
+ number = blockNumber,
+ hash = blockHash.short,
+ diff = header.difficulty,
+ ptd = ptd,
+ ttd = ttd
+
+ return invalidFCU("Refusing beacon update to pre-merge")
 
  # If the head block is already in our canonical chain, the beacon client is
  # probably resyncing. Ignore the update.
+ # See point 2 of fCUV1 specification
+ # https://github.com/ethereum/execution-apis/blob/v1.0.0-beta.4/src/engine/paris.md#specification-1
  var canonHash: common.Hash256
  if db.getBlockHash(header.blockNumber, canonHash) and canonHash == blockHash:
- # TODO should this be possible?
- # If we allow these types of reorgs, we will do lots and lots of reorgs during sync
- notice "Reorg to previous block", blockHash
+ notice "Ignoring beacon update to old head",
+ blockHash=blockHash.short,
+ blockNumber=header.blockNumber
+ return validFCU(none(PayloadID), blockHash)
 
  chain.setCanonical(header).isOkOr:
  return invalidFCU(error, com, header)