Correct implementation of the /validator/duties/sync/{epoch} API

According to the spec, this call should return the positions of
the specified validators within the sync committee. The existing
code was instead returning the indices of the sync sub-committees
where the validator is a member.

beacon_chain/rpc/rest_validator_api.nim

@@ -3,7 +3,7 @@
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
 # at your option. This file may not be copied, modified, or distributed except according to those terms.
-import std/[typetraits, strutils, sets, sequtils]
+import std/[typetraits, strutils, sets]
 import stew/[results, base10], chronicles,
        nimcrypto/utils as ncrutils
 import ".."/[beacon_chain_db, beacon_node],
@@ -11,7 +11,7 @@ import ".."/[beacon_chain_db, beacon_node],
        ".."/consensus_object_pools/[blockchain_dag, spec_cache,
                                     attestation_pool, sync_committee_msg_pool],
        ".."/validators/validator_duties,
-       ".."/spec/[forks, network],
+       ".."/spec/[beaconstate, forks, network],
        ".."/spec/datatypes/[phase0, altair],
        "."/rest_utils
 
@@ -190,8 +190,7 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
     let bslot = node.dag.head.atSlot(qepoch.compute_start_slot_at_epoch())
 
     node.withStateForBlockSlot(bslot):
-      let validatorsCount = lenu64(getStateField(stateData.data, validators))
-      let participants =
+      let syncCommittee =
         block:
           let res = syncCommitteeParticipants(stateData().data, qepoch)
           if res.isErr():
@@ -203,52 +202,20 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
                                  "List of sync committee participants is empty")
           kres
 
-      # TODO: We doing this because `participants` are stored as array of
-      # validator keys, so we need to convert it to indices, and if any of
-      # public keys are missing, it means some unexpected error.
-      let participantIndices =
-        block:
-          var res: seq[ValidatorIndex]
-          let optIndices = keysToIndices(node.restKeysCache, stateData().data,
-                                         participants)
-          for item in optIndices:
-            if item.isNone():
-              return RestApiResponse.jsonError(Http500, InternalServerError,
-                                              "Could not get validator indices")
-            res.add(item.get())
-          res
-
-      let validatorsSet =
-        block:
-          var res: Table[ValidatorIndex, int]
-          for listIndex, validatorIndex in indexList.pairs():
-            # We ignore indices which could not fit in current list of
-            # validators.
-            if uint64(validatorIndex) < validatorsCount:
-              res[validatorIndex] = listIndex
-          res
-
-      template isEmpty(duty: RestSyncCommitteeDuty): bool =
-        len(duty.validator_sync_committee_indices) == 0
-
       var duties =
-        block:
+        withState(stateData().data):
           var res = newSeq[RestSyncCommitteeDuty](len(indexList))
-          for committeeIdx in allSyncSubcommittees():
-            for valIndex, arrIndex in syncSubcommitteePairs(participantIndices,
-                                                            committeeIdx):
-              let listIndex = validatorsSet.getOrDefault(valIndex, -1)
-              if listIndex >= 0:
-                if res[listIndex].isEmpty():
-                  let key =
-                    getStateField(stateData().data, validators)[valIndex].pubkey
-                  res[listIndex] = RestSyncCommitteeDuty(
-                    validator_index: valIndex,
-                    pubkey: key
-                  )
-                res[listIndex].validator_sync_committee_indices.add(
-                  committeeIdx)
-          res.keepItIf(not(isEmpty(it)))
+          for resIdx, validatorIdx in indexList:
+            if not validatorIdx.isValidInState(state.data):
+              return RestApiResponse.jsonError(Http400, "Invalid index: " & $validatorIdx)
+
+            res[resIdx].pubkey = state.data.validators[validatorIdx].pubkey
+            res[resIdx].validator_index = validatorIdx
+
+            for idx, pubkey in syncCommittee:
+              if pubkey == res[resIdx].pubkey:
+                res[resIdx].validator_sync_committee_indices.add(
+                  ValidatorIndexInSyncCommittee idx)
           res
 
       return RestApiResponse.jsonResponse(duties)

beacon_chain/spec/beaconstate.nim

@@ -19,6 +19,9 @@ import
 
 export extras, forks, validator
 
+type
+  SomeBeaconState* = phase0.BeaconState | altair.BeaconState | merge.BeaconState
+
 # https://github.com/ethereum/consensus-specs/blob/v1.1.5/specs/phase0/beacon-chain.md#increase_balance
 func increase_balance*(balance: var Gwei, delta: Gwei) =
   balance += delta
@@ -860,3 +863,7 @@ func upgrade_to_merge*(cfg: RuntimeConfig, pre: altair.BeaconState):
     # Execution-layer
     latest_execution_payload_header: ExecutionPayloadHeader()
   )
+
+template isValidInState*(idx: ValidatorIndex, state: SomeBeaconState): bool =
+  idx.int < state.validators.len
+

beacon_chain/spec/datatypes/altair.nim

@@ -432,6 +432,7 @@ type
   SomeBeaconBlockBody* = BeaconBlockBody | SigVerifiedBeaconBlockBody | TrustedBeaconBlockBody
 
   SyncSubcommitteeIndex* = distinct uint8
+  ValidatorIndexInSyncCommittee* = distinct uint16
 
 chronicles.formatIt BeaconBlock: it.shortLog
 chronicles.formatIt SyncSubcommitteeIndex: uint8(it)
@@ -440,7 +441,12 @@ template asInt*(x: SyncSubcommitteeIndex): int = int(x)
 template asUInt8*(x: SyncSubcommitteeIndex): uint8 = uint8(x)
 template asUInt64*(x: SyncSubcommitteeIndex): uint64 = uint64(x)
 
-template `[]`*(a: auto; i: SyncSubcommitteeIndex): auto = a[i.asInt]
+template `[]`*(a: auto; i: SyncSubcommitteeIndex): auto =
+  a[i.asInt]
+
+template `[]`*(arr: array[SYNC_COMMITTEE_SIZE, any] | seq;
+               idx: ValidatorIndexInSyncCommittee): auto =
+  arr[int idx]
 
 template `==`*(x, y: SyncSubcommitteeIndex): bool =
   distinctBase(x) == distinctBase(y)

beacon_chain/spec/eth2_apis/eth2_rest_serialization.nim

@@ -412,12 +412,12 @@ proc readValue*(reader: var JsonReader[RestJson], value: var Epoch) {.
     reader.raiseUnexpectedValue($res.error())
 
 ## ValidatorIndex
-proc writeValue*(writer: var JsonWriter[RestJson], value: ValidatorIndex) {.
-     raises: [IOError, Defect].} =
+proc writeValue*(writer: var JsonWriter[RestJson], value: ValidatorIndex)
+                {.raises: [IOError, Defect].} =
   writeValue(writer, Base10.toString(uint64(value)))
 
-proc readValue*(reader: var JsonReader[RestJson], value: var ValidatorIndex) {.
-     raises: [IOError, SerializationError, Defect].} =
+proc readValue*(reader: var JsonReader[RestJson], value: var ValidatorIndex)
+               {.raises: [IOError, SerializationError, Defect].} =
   let svalue = reader.readValue(string)
   let res = Base10.decode(uint64, svalue)
   if res.isOk():
@@ -430,6 +430,24 @@ proc readValue*(reader: var JsonReader[RestJson], value: var ValidatorIndex) {.
   else:
     reader.raiseUnexpectedValue($res.error())
 
+proc writeValue*(writer: var JsonWriter[RestJson], value: ValidatorIndexInSyncCommittee)
+                {.raises: [IOError, Defect].} =
+  writeValue(writer, Base10.toString(distinctBase(value)))
+
+proc readValue*(reader: var JsonReader[RestJson], value: var ValidatorIndexInSyncCommittee)
+               {.raises: [IOError, SerializationError, Defect].} =
+  let svalue = reader.readValue(string)
+  let res = Base10.decode(uint64, svalue)
+  if res.isOk():
+    let v = res.get()
+    if v < SYNC_COMMITTEE_SIZE:
+      value = ValidatorIndexInSyncCommittee(v)
+    else:
+      reader.raiseUnexpectedValue(
+        "Validator index is bigger then SYNC_COMMITTEE_SIZE")
+  else:
+    reader.raiseUnexpectedValue($res.error())
+
 ## RestValidatorIndex
 proc writeValue*(writer: var JsonWriter[RestJson],
                  value: RestValidatorIndex) {.

beacon_chain/spec/eth2_apis/rest_types.nim

@@ -105,7 +105,7 @@ type
   RestSyncCommitteeDuty* = object
     pubkey*: ValidatorPubKey
     validator_index*: ValidatorIndex
-    validator_sync_committee_indices*: seq[SyncSubcommitteeIndex]
+    validator_sync_committee_indices*: seq[ValidatorIndexInSyncCommittee]
 
   RestSyncCommitteeMessage* = object
     slot*: Slot