update compute_subnet_for_attestation() to use https://github.com/ethereum/eth2.0-specs/pull/1876 signature, which isn't in v0.12.1, which works with lookahead (#1346)

beacon_chain/attestation_aggregation.nim

@@ -171,7 +171,9 @@ proc isValidAttestation*(
       epochInfo = blck.getEpochInfo(state)
       requiredSubnetIndex =
         compute_subnet_for_attestation(
-          epochInfo.shuffled_active_validator_indices.len.uint64, attestation)
+          get_committee_count_at_slot(
+            epochInfo.shuffled_active_validator_indices.len.uint64),
+          attestation.data.slot, attestation.data.index.CommitteeIndex)
 
     if requiredSubnetIndex != topicCommitteeIndex:
       debug "isValidAttestation: attestation's committee index not for the correct subnet",

beacon_chain/spec/network.nim

@@ -58,26 +58,27 @@ func getAggregateAndProofsTopic*(forkDigest: ForkDigest): string =
     raiseAssert e.msg
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#broadcast-attestation
+# https://github.com/ethereum/eth2.0-specs/pull/1876
 func compute_subnet_for_attestation*(
-    num_active_validators: uint64, attestation: Attestation): uint64 =
+    committees_per_slot: uint64, slot: Slot, committee_index: CommitteeIndex):
+    uint64 =
   # Compute the correct subnet for an attestation for Phase 0.
   # Note, this mimics expected Phase 1 behavior where attestations will be
   # mapped to their shard subnet.
-  #
-  # The spec version has params (state: BeaconState, attestation: Attestation),
-  # but it's only to call get_committee_count_at_slot(), which needs only epoch
-  # and the number of active validators.
   let
-    slots_since_epoch_start = attestation.data.slot mod SLOTS_PER_EPOCH
+    slots_since_epoch_start = slot mod SLOTS_PER_EPOCH
     committees_since_epoch_start =
-      get_committee_count_at_slot(num_active_validators) * slots_since_epoch_start
+      committees_per_slot * slots_since_epoch_start
 
-  (committees_since_epoch_start + attestation.data.index) mod ATTESTATION_SUBNET_COUNT
+  (committees_since_epoch_start + committee_index.uint64) mod
+    ATTESTATION_SUBNET_COUNT
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#broadcast-attestation
 func getAttestationTopic*(forkDigest: ForkDigest, subnetIndex: uint64):
     string =
   # This is for subscribing or broadcasting manually to a known index.
+  doAssert subnetIndex < ATTESTATION_SUBNET_COUNT
+
   try:
     &"/eth2/{$forkDigest}/beacon_attestation_{subnetIndex}/ssz"
   except ValueError as e:
@@ -86,4 +87,6 @@ func getAttestationTopic*(forkDigest: ForkDigest, subnetIndex: uint64):
 func getAttestationTopic*(forkDigest: ForkDigest, attestation: Attestation, num_active_validators: uint64): string =
   getAttestationTopic(
     forkDigest,
-    compute_subnet_for_attestation(num_active_validators, attestation))
+    compute_subnet_for_attestation(
+      get_committee_count_at_slot(num_active_validators),
+      attestation.data.slot, attestation.data.index.CommitteeIndex))

beacon_chain/spec/validator.nim

@@ -10,7 +10,7 @@
 
 import
   algorithm, options, sequtils, math, tables, sets,
-  ./datatypes, ./digest, ./helpers
+  ./datatypes, ./digest, ./helpers, ./network
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_shuffled_index
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/beacon-chain.md#compute_committee
@@ -274,17 +274,14 @@ func get_beacon_proposer_index*(state: BeaconState, cache: var StateCache):
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#validator-assignments
 func get_committee_assignment*(
     state: BeaconState, epoch: Epoch,
-    validator_indices: HashSet[ValidatorIndex]):
-    Option[tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot]] {.used.} =
+    validator_index: ValidatorIndex):
+    Option[tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot]] =
   # Return the committee assignment in the ``epoch`` for ``validator_index``.
   # ``assignment`` returned is a tuple of the following form:
   #     * ``assignment[0]`` is the list of validators in the committee
   #     * ``assignment[1]`` is the index to which the committee is assigned
   #     * ``assignment[2]`` is the slot at which the committee is assigned
   # Return None if no assignment.
-  #
-  # Slightly adapted from spec version to support multiple validator indices,
-  # since each beacon_node supports many validators.
   let next_epoch = get_current_epoch(state) + 1
   doAssert epoch <= next_epoch
 
@@ -295,10 +292,32 @@ func get_committee_assignment*(
     for index in 0 ..< get_committee_count_at_slot(state, slot):
       let idx = index.CommitteeIndex
       let committee = get_beacon_committee(state, slot, idx, cache)
-      if not disjoint(validator_indices, toHashSet(committee)):
+      if validator_index in committee:
         return some((committee, idx, slot))
   none(tuple[a: seq[ValidatorIndex], b: CommitteeIndex, c: Slot])
 
+func get_committee_assignments*(
+    state: BeaconState, epoch: Epoch,
+    validator_indices: HashSet[ValidatorIndex]):
+    seq[tuple[subnetIndex: uint64, slot: Slot]] =
+  let next_epoch = get_current_epoch(state) + 1
+  doAssert epoch <= next_epoch
+
+  var cache = StateCache()
+  let start_slot = compute_start_slot_at_epoch(epoch)
+
+  # get_committee_count_at_slot is constant throughout an epoch
+  let committee_count_at_slot = get_committee_count_at_slot(state, start_slot)
+
+  for slot in start_slot ..< start_slot + SLOTS_PER_EPOCH:
+    for index in 0 ..< committee_count_at_slot:
+      let idx = index.CommitteeIndex
+      if not disjoint(validator_indices,
+          get_beacon_committee(state, slot, idx, cache).toHashSet):
+        result.add(
+          (compute_subnet_for_attestation(committee_count_at_slot, slot, idx),
+            slot))
+
 # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#validator-assignments
 func is_proposer(
     state: BeaconState, validator_index: ValidatorIndex): bool {.used.} =

beacon_chain/validator_api.nim

@@ -7,7 +7,7 @@
 
 import
   # Standard library
-  tables, strutils, parseutils, sequtils, sets,
+  tables, strutils, parseutils, sequtils,
 
   # Nimble packages
   stew/[byteutils, objects],
@@ -356,8 +356,7 @@ proc installValidatorApiHandlers*(rpcServer: RpcServer, node: BeaconNode) =
         let idx = state.validators.asSeq.findIt(it.pubKey == pubkey)
         if idx == -1:
           continue
-        let ca = state.get_committee_assignment(
-          epoch, toHashSet([idx.ValidatorIndex]))
+        let ca = state.get_committee_assignment(epoch, idx.ValidatorIndex)
         if ca.isSome:
           result.add((public_key: pubkey,
                       committee_index: ca.get.b,

beacon_chain/validator_duties.nim

@@ -425,7 +425,7 @@ proc broadcastAggregatedAttestations(
 
 proc handleValidatorDuties*(
     node: BeaconNode, lastSlot, slot: Slot) {.async.} =
-  ## Perform validator duties - create blocks, vote and aggreagte existing votes
+  ## Perform validator duties - create blocks, vote and aggregate existing votes
   var head = node.updateHead()
   if node.attachedValidators.count == 0:
     # Nothing to do because we have no validator attached

ncli/ncli_db.nim

@@ -4,8 +4,7 @@
   ../beacon_chain/[beacon_chain_db, block_pool, extras],
   ../beacon_chain/spec/[crypto, datatypes, digest, helpers,
                         state_transition, validator, presets],
-  ../beacon_chain/sszdump, ../beacon_chain/ssz/merkleization,
-  ../research/simutils,
+  ../beacon_chain/sszdump, ../research/simutils,
   eth/db/[kvstore, kvstore_sqlite3]
 
 type Timers = enum

research/state_sim.nim

@@ -151,7 +151,7 @@ cli do(slots = SLOTS_PER_EPOCH * 6,
 
     flushFile(stdout)
 
-    if (state[].data.slot) mod SLOTS_PER_EPOCH == 0:
+    if (state[].data.slot).isEpoch:
       echo &" slot: {shortLog(state[].data.slot)} ",
         &"epoch: {shortLog(state[].data.slot.compute_epoch_at_slot)}"
 

tests/spec_epoch_processing/justification_finalization_helpers.nim

@@ -22,7 +22,7 @@ proc addMockAttestations*(
        sufficient_support = false
   ) =
   # We must be at the end of the epoch
-  doAssert (state.slot + 1) mod SLOTS_PER_EPOCH == 0
+  doAssert (state.slot + 1).isEpoch
 
   # Alias the attestations container
   var attestations: ptr seq[PendingAttestation]