Updates for finalizing chain!

* set epoch_boundary_root - chain finalizes!
* fix slotStart to offset GENESIS_SLOT
* work around bug that will be fixed by
ethereum/consensus-specs#732
* compile with debug info (there was a GC-related crash in C land)

beacon_chain/beacon_node.nim

@@ -265,31 +265,23 @@ proc makeAttestation(node: BeaconNode,
   var state = node.state.data
   skipSlots(state, node.state.blck.root, slot)
 
-  let
-    justifiedBlockRoot =
-      get_block_root(state, get_epoch_start_slot(state.justified_epoch))
-
-    attestationData = AttestationData(
-      slot: slot,
-      shard: shard,
-      beacon_block_root: node.state.blck.root,
-      epoch_boundary_root: Eth2Digest(), # TODO
-      crosslink_data_root: Eth2Digest(), # TODO
-      latest_crosslink: state.latest_crosslinks[shard],
-      justified_epoch: state.justified_epoch,
-      justified_block_root: justifiedBlockRoot)
+  # If we call makeAttestation too late, we must advance head only to `slot`
+  doAssert state.slot == slot,
+    "Corner case: head advanced beyond sheduled attestation slot"
 
+  let
+    attestationData = makeAttestationData(state, shard, node.state.blck.root)
     validatorSignature = await validator.signAttestation(attestationData)
 
-  var participationBitfield = repeat(0'u8, ceil_div8(committeeLen))
-  bitSet(participationBitfield, indexInCommittee)
+  var aggregationBitfield = repeat(0'u8, ceil_div8(committeeLen))
+  bitSet(aggregationBitfield, indexInCommittee)
 
   var attestation = Attestation(
     data: attestationData,
     aggregate_signature: validatorSignature,
-    aggregation_bitfield: participationBitfield,
+    aggregation_bitfield: aggregationBitfield,
     # Stub in phase0
-    custody_bitfield: newSeq[byte](participationBitfield.len)
+    custody_bitfield: newSeq[byte](aggregationBitfield.len)
   )
 
   # TODO what are we waiting for here? broadcast should never block, and never

beacon_chain/block_pool.nim

@@ -247,6 +247,15 @@ proc add*(
     return true
 
   # This is an unresolved block - put it on the unresolved list for now...
+  # TODO if we receive spam blocks, one heurestic to implement might be to wait
+  #      for a couple of attestations to appear before fetching parents - this
+  #      would help prevent using up network resources for spam - this serves
+  #      two purposes: one is that attestations are likely to appear for the
+  #      block only if it's valid / not spam - the other is that malicious
+  #      validators that are not proposers can sign invalid blocks and send
+  #      them out without penalty - but signing invalid attestations carries
+  #      a risk of being slashed, making attestations a more valuable spam
+  #      filter.
   debug "Unresolved block",
     slot = humaneSlotNum(blck.slot),
     stateRoot = shortLog(blck.state_root),
@@ -322,7 +331,7 @@ proc maybePutState(pool: BlockPool, state: BeaconState) =
   if state.slot mod SLOTS_PER_EPOCH == 0:
     info "Storing state",
       stateSlot = humaneSlotNum(state.slot),
-      stateRoot = hash_tree_root_final(state) # TODO cache?
+      stateRoot = shortLog(hash_tree_root_final(state)) # TODO cache?
     pool.db.putState(state)
 
 proc updateState*(

beacon_chain/spec/beaconstate.nim

@@ -279,14 +279,15 @@ func get_attestation_participants*(state: BeaconState,
   ## ``bitfield``.
   let crosslink_committees = get_crosslink_committees_at_slot(
     state, attestation_data.slot)
-
-  assert anyIt(
+  doAssert anyIt(
     crosslink_committees,
     it[1] == attestation_data.shard)
   let crosslink_committee = mapIt(
     filterIt(crosslink_committees, it.shard == attestation_data.shard),
     it.committee)[0]
 
+  # TODO this and other attestation-based fields need validation so we don't
+  #      crash on a malicious attestation!
   doAssert verify_bitfield(bitfield, len(crosslink_committee))
 
   # Find the participating attesters in the committee
@@ -493,3 +494,31 @@ func prepare_validator_for_withdrawal*(state: var BeaconState, index: ValidatorI
   # Bug in 0.3.0 spec; constant got renamed. Use 0.3.0 name.
   validator.withdrawable_epoch = get_current_epoch(state) +
     MIN_VALIDATOR_WITHDRAWABILITY_DELAY
+
+# https://github.com/ethereum/eth2.0-specs/blob/0.4.0/specs/validator/0_beacon-chain-validator.md#attestations-1
+proc makeAttestationData*(
+    state: BeaconState, shard: uint64,
+    beacon_block_root: Eth2Digest): AttestationData =
+  ## Fine points:
+  ## Head must be the head state during the slot that validator is
+  ## part of committee - notably, it can't be a newer or older state (!)
+
+  # TODO update when https://github.com/ethereum/eth2.0-specs/issues/742
+  let
+    epoch_start_slot = get_epoch_start_slot(slot_to_epoch(state.slot))
+    epoch_boundary_root =
+      if epoch_start_slot == state.slot: beacon_block_root
+      else: get_block_root(state, epoch_start_slot)
+    justified_slot = get_epoch_start_slot(state.justified_epoch)
+    justified_block_root = get_block_root(state, justified_slot)
+
+  AttestationData(
+    slot: state.slot,
+    shard: shard,
+    beacon_block_root: beacon_block_root,
+    epoch_boundary_root: epoch_boundary_root,
+    crosslink_data_root: Eth2Digest(), # Stub in phase0
+    latest_crosslink: state.latest_crosslinks[shard],
+    justified_epoch: state.justified_epoch,
+    justified_block_root: justified_block_root,
+  )

beacon_chain/spec/helpers.nim

@@ -180,7 +180,7 @@ func get_current_epoch_committee_count*(state: BeaconState): uint64 =
 # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_current_epoch
 func get_current_epoch*(state: BeaconState): Epoch =
   # Return the current epoch of the given ``state``.
-  doAssert state.slot >= GENESIS_SLOT, $state.slot 
+  doAssert state.slot >= GENESIS_SLOT, $state.slot
   slot_to_epoch(state.slot)
 
 # https://github.com/ethereum/eth2.0-specs/blob/v0.3.0/specs/core/0_beacon-chain.md#get_randao_mix

beacon_chain/spec/validator.nim

@@ -134,17 +134,20 @@ func get_crosslink_committees_at_slot*(state: BeaconState, slot: Slot,
   ## ``slot`` in the next epoch -- with and without a `registry_change`
 
   let
-    epoch = slot_to_epoch(slot)
+    # TODO: the + 1 here works around a bug, remove when upgrading to
+    #       some more recent version:
+    # https://github.com/ethereum/eth2.0-specs/pull/732
+    epoch = slot_to_epoch(slot + 1)
     current_epoch = get_current_epoch(state)
     previous_epoch = get_previous_epoch(state)
     next_epoch = current_epoch + 1
 
-  assert previous_epoch <= epoch,
+  doAssert previous_epoch <= epoch,
     "Previous epoch: " & $humaneEpochNum(previous_epoch) &
     ", epoch: " & $humaneEpochNum(epoch) &
     ", Next epoch: " & $humaneEpochNum(next_epoch)
 
-  assert epoch <= next_epoch,
+  doAssert epoch <= next_epoch,
     "Previous epoch: " & $humaneEpochNum(previous_epoch) &
     ", epoch: " & $humaneEpochNum(epoch) &
     ", Next epoch: " & $humaneEpochNum(next_epoch)
@@ -170,7 +173,7 @@ func get_crosslink_committees_at_slot*(state: BeaconState, slot: Slot,
         shuffling_start_shard = state.current_shuffling_start_shard
       (committees_per_epoch, seed, shuffling_epoch, shuffling_start_shard)
     else:
-      assert epoch == next_epoch
+      doAssert epoch == next_epoch
 
       let
         current_committees_per_epoch = get_current_epoch_committee_count(state)

beacon_chain/time.nim

@@ -21,7 +21,7 @@ proc getSlotFromTime*(s: BeaconState, t = now()): Slot =
                          int64(SECONDS_PER_SLOT * 1000))
 
 func slotStart*(s: BeaconState, slot: Slot): Timestamp =
-  (s.genesis_time + (slot * SECONDS_PER_SLOT)) * 1000
+  (s.genesis_time + ((slot - GENESIS_SLOT) * SECONDS_PER_SLOT)) * 1000
 
 func slotMiddle*(s: BeaconState, slot: Slot): Timestamp =
   s.slotStart(slot) + SECONDS_PER_SLOT * 500

tests/simulation/start.sh

@@ -37,7 +37,7 @@ if [ ! -f $LAST_VALIDATOR ]; then
 fi
 
 if [[ -z "$SKIP_BUILDS" ]]; then
-  nim c -o:"$BEACON_NODE_BIN" $DEFS --opt:speed beacon_chain/beacon_node
+  nim c -o:"$BEACON_NODE_BIN" $DEFS --opt:speed --debuginfo beacon_chain/beacon_node
 fi
 
 if [ ! -f $SNAPSHOT_FILE ]; then

tests/testutil.nim

@@ -168,17 +168,7 @@ proc makeAttestation*(
       get_crosslink_committees_at_slot(state, state.slot), validator_index)
     validator = state.validator_registry[validator_index]
     sac_index = sac.committee.find(validator_index)
-
-    data = AttestationData(
-      slot: state.slot,
-      shard: sac.shard,
-      beacon_block_root: beacon_block_root,
-      epoch_boundary_root: Eth2Digest(), # TODO
-      latest_crosslink: state.latest_crosslinks[sac.shard],
-      crosslink_data_root: Eth2Digest(), # TODO
-      justified_epoch: state.justified_epoch,
-      justified_block_root: get_block_root(state, get_epoch_start_slot(state.justified_epoch)),
-    )
+    data = makeAttestationData(state, sac.shard, beacon_block_root)
 
   assert sac_index != -1, "find_shard_committe should guarantee this"
 
@@ -187,7 +177,8 @@ proc makeAttestation*(
   bitSet(aggregation_bitfield, sac_index)
 
   let
-    msg = hash_tree_root_final(AttestationDataAndCustodyBit(data: data, custody_bit: false))
+    msg = hash_tree_root_final(
+      AttestationDataAndCustodyBit(data: data, custody_bit: false))
     sig =
       if skipValidation notin flags:
         bls_sign(
@@ -203,7 +194,7 @@ proc makeAttestation*(
     data: data,
     aggregation_bitfield: aggregation_bitfield,
     aggregate_signature: sig,
-    custody_bitfield: repeat(0'u8, ceil_div8(sac.committee.len))
+    custody_bitfield: repeat(0'u8, aggregation_bitfield.len)
   )
 
 proc makeTestDB*(tailState: BeaconState, tailBlock: BeaconBlock): BeaconChainDB =