api: add skip_randao_verification for produceBlockV2 (#3837)

beacon_chain/extras.nim

@@ -27,6 +27,9 @@ type
     ## Skip verification of BLS signatures in block processing.
     ## Predominantly intended for use in testing, e.g. to allow extra coverage.
     ## Also useful to avoid unnecessary work when replaying known, good blocks.
+    skipRandaoVerification ##\
+    ## Skip verification of the proposer's randao reveal in block processing, but do ensure
+    ## that they set the randao reveal to the point at infinity.
     skipStateRootValidation ##\
     ## Skip verification of block state root.
     strictVerification ##\

beacon_chain/rpc/rest_constants.nim

@@ -90,6 +90,8 @@ const
     "Missing `randao_reveal` value"
   InvalidRandaoRevealValue* =
     "Invalid randao reveal value"
+  InvalidSkipRandaoVerificationValue* =
+    "Invalid skip_randao_verification value"
   InvalidGraffitiBytesValue* =
     "Invalid graffiti bytes value"
   InvalidEpochValueError* =

beacon_chain/rpc/rest_validator_api.nim

@@ -369,7 +369,7 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
   # https://ethereum.github.io/beacon-APIs/#/Validator/produceBlockV2
   router.api(MethodGet, "/eth/v2/validator/blocks/{slot}") do (
     slot: Slot, randao_reveal: Option[ValidatorSig],
-    graffiti: Option[GraffitiBytes]) -> RestApiResponse:
+    graffiti: Option[GraffitiBytes], skip_randao_verification: Option[string]) -> RestApiResponse:
     let message =
       block:
         let qslot = block:
@@ -387,6 +387,15 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
             return RestApiResponse.jsonError(Http400, InvalidSlotValueError,
                                              "Slot cannot be in the future")
           res
+        let qskip_randao_verification =
+          if skip_randao_verification.isNone():
+            false
+          else:
+            let res = skip_randao_verification.get()
+            if res.isErr() or res.get() != "":
+              return RestApiResponse.jsonError(Http400,
+                                               InvalidSkipRandaoVerificationValue)
+            true
         let qrandao =
           if randao_reveal.isNone():
             return RestApiResponse.jsonError(Http400, MissingRandaoRevealValue)
@@ -418,7 +427,7 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
         if proposer.isNone():
           return RestApiResponse.jsonError(Http400, ProposerNotFoundError)
         let res = await makeBeaconBlockForHeadAndSlot(
-          node, qrandao, proposer.get(), qgraffiti, qhead, qslot)
+          node, qrandao, proposer.get(), qgraffiti, qhead, qslot, qskip_randao_verification)
         if res.isErr():
           return RestApiResponse.jsonError(Http400, res.error())
         res.get()

beacon_chain/spec/state_transition_block.nim

@@ -88,7 +88,10 @@ proc process_randao(
   let
     epoch = state.get_current_epoch()
 
-  if skipBlsValidation notin flags:
+  if skipRandaoVerification in flags:
+    if body.randao_reveal.toRaw != ValidatorSig.infinity.toRaw:
+      return err("process_randao: expected point-at-infinity for skipRandaoVerification")
+  elif skipBlsValidation notin flags:
     let proposer_pubkey = state.validators.item(proposer_index.get).pubkey
 
     if not verify_epoch_signature(

beacon_chain/validators/validator_duties.nim

@@ -446,6 +446,7 @@ proc makeBeaconBlockForHeadAndSlot*(
     node: BeaconNode, randao_reveal: ValidatorSig,
     validator_index: ValidatorIndex, graffiti: GraffitiBytes, head: BlockRef,
     slot: Slot,
+    skip_randao_verification_bool: bool = false,
     execution_payload: Opt[ExecutionPayload] = Opt.none(ExecutionPayload),
     transactions_root: Opt[Eth2Digest] = Opt.none(Eth2Digest),
     execution_payload_root: Opt[Eth2Digest] = Opt.none(Eth2Digest)):
@@ -521,6 +522,7 @@ proc makeBeaconBlockForHeadAndSlot*(
       effectiveExecutionPayload,
       noRollback, # Temporary state - no need for rollback
       cache,
+      verificationFlags = if skip_randao_verification_bool: {skipRandaoVerification} else: {},
       transactions_root =
         if transactions_root.isSome:
           Opt.some transactions_root.get