nimbus-eth2/beacon_chain/attestation_pool.nim

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# beacon_chain
# Copyright (c) 2018-2020 Status Research & Development GmbH
# Licensed and distributed under either of
# * 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.
{.push raises: [Defect].}
import
# Standard libraries
std/[deques, sequtils, sets, tables, options],
# Status libraries
chronicles, stew/[byteutils], json_serialization/std/sets as jsonSets,
# Internal
./spec/[beaconstate, datatypes, crypto, digest, helpers],
ssz/merkleization,
./block_pools/[spec_cache, chain_dag, clearance, quarantine],
./beacon_node_types,
./fork_choice/fork_choice
export beacon_node_types, sets
logScope: topics = "attpool"
proc init*(T: type AttestationPool, chainDag: ChainDAGRef, quarantine: QuarantineRef): T =
## Initialize an AttestationPool from the chainDag `headState`
## The `finalized_root` works around the finalized_checkpoint of the genesis block
## holding a zero_root.
let finalizedEpochRef = chainDag.getFinalizedEpochRef()
var forkChoice = ForkChoice.init(
finalizedEpochRef,
chainDag.finalizedHead.blck)
# Feed fork choice with unfinalized history - during startup, block pool only
# keeps track of a single history so we just need to follow it
doAssert chainDag.heads.len == 1, "Init only supports a single history"
var blocks: seq[BlockRef]
var cur = chainDag.head
# When the chain is finalizing, the votes between the head block and the
# finalized checkpoint should be enough for a stable fork choice - when the
# chain is not finalizing, we want to seed it with as many votes as possible
# since the whole history of each branch might be significant. It is however
# a game of diminishing returns, and we have to weigh it against the time
# it takes to replay that many blocks during startup and thus miss _new_
# votes.
const ForkChoiceHorizon = 256
while cur != chainDag.finalizedHead.blck:
blocks.add cur
cur = cur.parent
info "Initializing fork choice", unfinalized_blocks = blocks.len
var epochRef = finalizedEpochRef
for i in 0..<blocks.len:
let
blck = blocks[blocks.len - i - 1]
status =
if i < (blocks.len - ForkChoiceHorizon) and (i mod 1024 != 0):
# Fork choice needs to know about the full block tree up to the
# finalization point, but doesn't really need to have overly accurate
# justification and finalization points until we get close to head -
# nonetheless, we'll make sure to pass a fresh finalization point now
# and then to make sure the fork choice data structure doesn't grow
# too big - getting an EpochRef can be expensive.
forkChoice.backend.process_block(
blck.root, blck.parent.root,
epochRef.current_justified_checkpoint.epoch,
epochRef.finalized_checkpoint.epoch)
else:
epochRef = chainDag.getEpochRef(blck, blck.slot.epoch)
forkChoice.process_block(
chainDag, epochRef, blck, chainDag.get(blck).data.message, blck.slot)
doAssert status.isOk(), "Error in preloading the fork choice: " & $status.error
info "Fork choice initialized",
justified_epoch = chainDag.headState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = chainDag.headState.data.data.finalized_checkpoint.epoch,
finalized_root = shortlog(chainDag.finalizedHead.blck.root)
T(
chainDag: chainDag,
quarantine: quarantine,
forkChoice: forkChoice
)
proc addForkChoiceVotes(
pool: var AttestationPool, slot: Slot, participants: HashSet[ValidatorIndex],
block_root: Eth2Digest, wallSlot: Slot) =
# Add attestation votes to fork choice
if (let v = pool.forkChoice.on_attestation(
pool.chainDag, slot, block_root, participants, wallSlot);
v.isErr):
# This indicates that the fork choice and the chain dag are out of sync -
# this is most likely the result of a bug, but we'll try to keep going -
# hopefully the fork choice will heal itself over time.
error "Couldn't add attestation to fork choice, bug?", err = v.error()
func candidateIdx(pool: AttestationPool, slot: Slot): Option[uint64] =
if slot >= pool.startingSlot and
slot < (pool.startingSlot + pool.candidates.lenu64):
some(slot mod pool.candidates.lenu64)
else:
none(uint64)
proc updateCurrent(pool: var AttestationPool, wallSlot: Slot) =
if wallSlot + 1 < pool.candidates.lenu64:
return
if pool.startingSlot + pool.candidates.lenu64 - 1 > wallSlot:
error "Current slot older than attestation pool view, clock reset?",
poolSlot = pool.startingSlot, wallSlot
return
# As time passes we'll clear out any old attestations as they are no longer
# viable to be included in blocks
let newWallSlot = wallSlot + 1 - pool.candidates.lenu64
for i in pool.startingSlot..newWallSlot:
pool.candidates[i.uint64 mod pool.candidates.lenu64] = AttestationsSeen()
pool.startingSlot = newWallSlot
# now also clear old aggregated attestations
var keysToRemove: seq[Slot] = @[]
for k, v in pool.attestationAggregates.pairs:
if k < pool.startingSlot:
keysToRemove.add k
for k in keysToRemove:
pool.attestationAggregates.del k
func addToAggregates(pool: var AttestationPool, attestation: Attestation) =
# do a lookup for the current slot and get it's associated htrs/attestations
var aggregated_attestation = pool.attestationAggregates.mgetOrPut(
attestation.data.slot, Table[Eth2Digest, Attestation]()).
# do a lookup for the same attestation data htr and get the attestation
mgetOrPut(attestation.data.hash_tree_root, attestation)
# if the aggregation bits differ (we didn't just insert it into the table)
# and only if there is no overlap of the signatures ==> aggregate!
if not aggregated_attestation.aggregation_bits.overlaps(attestation.aggregation_bits):
var agg {.noInit.}: AggregateSignature
agg.init(aggregated_attestation.signature)
aggregated_attestation.aggregation_bits.combine(attestation.aggregation_bits)
agg.aggregate(attestation.signature)
aggregated_attestation.signature = agg.finish()
proc addAttestation*(pool: var AttestationPool,
attestation: Attestation,
participants: HashSet[ValidatorIndex],
wallSlot: Slot) =
## Add an attestation to the pool, assuming it's been validated already.
## Attestations may be either agggregated or not - we're pursuing an eager
## strategy where we'll drop validations we already knew about and combine
## the new attestation with an existing one if possible.
##
## This strategy is not optimal in the sense that it would be possible to find
## a better packing of attestations by delaying the aggregation, but because
## it's possible to include more than one aggregate in a block we can be
## somewhat lazy instead of looking for a perfect packing.
logScope:
attestation = shortLog(attestation)
updateCurrent(pool, wallSlot)
let candidateIdx = pool.candidateIdx(attestation.data.slot)
if candidateIdx.isNone:
debug "Skipping old attestation for block production",
startingSlot = pool.startingSlot
return
pool.addToAggregates(attestation)
let
attestationsSeen = addr pool.candidates[candidateIdx.get]
validation = Validation(
aggregation_bits: attestation.aggregation_bits,
aggregate_signature: attestation.signature)
var found = false
for a in attestationsSeen.attestations.mitems():
if a.data == attestation.data:
for v in a.validations:
if validation.aggregation_bits.isSubsetOf(v.aggregation_bits):
# The validations in the new attestation are a subset of one of the
# attestations that we already have on file - no need to add this
# attestation to the database
trace "Ignoring subset attestation", newParticipants = participants
found = true
break
if not found:
# Attestations in the pool that are a subset of the new attestation
# can now be removed per same logic as above
trace "Removing subset attestations", newParticipants = participants
a.validations.keepItIf(
not it.aggregation_bits.isSubsetOf(validation.aggregation_bits))
a.validations.add(validation)
pool.addForkChoiceVotes(
attestation.data.slot, participants, attestation.data.beacon_block_root,
wallSlot)
debug "Attestation resolved",
2020-01-23 17:48:11 +00:00
attestation = shortLog(attestation),
validations = a.validations.len()
found = true
break
if not found:
attestationsSeen.attestations.add(AttestationEntry(
data: attestation.data,
validations: @[validation],
aggregation_bits: attestation.aggregation_bits
))
pool.addForkChoiceVotes(
attestation.data.slot, participants, attestation.data.beacon_block_root,
wallSlot)
debug "Attestation resolved",
2020-01-23 17:48:11 +00:00
attestation = shortLog(attestation),
validations = 1
proc addForkChoice*(pool: var AttestationPool,
epochRef: EpochRef,
blckRef: BlockRef,
blck: BeaconBlock,
wallSlot: Slot) =
## Add a verified block to the fork choice context
let state = pool.forkChoice.process_block(
pool.chainDag, epochRef, blckRef, blck, wallSlot)
if state.isErr:
# This indicates that the fork choice and the chain dag are out of sync -
# this is most likely the result of a bug, but we'll try to keep going -
# hopefully the fork choice will heal itself over time.
error "Couldn't add block to fork choice, bug?",
blck = shortLog(blck), err = state.error
proc getAttestationsForSlot(pool: AttestationPool, newBlockSlot: Slot):
Option[AttestationsSeen] =
if newBlockSlot < (GENESIS_SLOT + MIN_ATTESTATION_INCLUSION_DELAY):
debug "Too early for attestations", newBlockSlot = shortLog(newBlockSlot)
return none(AttestationsSeen)
let
attestationSlot = newBlockSlot - MIN_ATTESTATION_INCLUSION_DELAY
candidateIdx = pool.candidateIdx(attestationSlot)
if candidateIdx.isNone:
trace "No attestations matching the slot range",
2019-08-15 16:01:55 +00:00
attestationSlot = shortLog(attestationSlot),
startingSlot = shortLog(pool.startingSlot)
return none(AttestationsSeen)
some(pool.candidates[candidateIdx.get()])
iterator attestations*(pool: AttestationPool, slot: Option[Slot],
index: Option[CommitteeIndex]): Attestation =
for seenAttestations in pool.candidates.items():
for entry in seenAttestations.attestations.items():
let slotInclude =
if slot.isSome():
entry.data.slot == slot.get()
else:
true
let committeeInclude =
if index.isSome():
CommitteeIndex(entry.data.index) == index.get()
else:
true
if slotInclude or committeeInclude:
for validation in entry.validations.items():
yield Attestation(
aggregation_bits: validation.aggregation_bits,
data: entry.data,
signature: validation.aggregate_signature
)
func getAttestationDataKey(ad: AttestationData): AttestationDataKey =
# This determines the rest of the AttestationData
(ad.slot, ad.index, ad.source.epoch, ad.target.epoch)
func incorporateCacheAttestation(
pool: var AttestationPool, attestation: PendingAttestation) =
let key = attestation.data.getAttestationDataKey
try:
var validatorBits = pool.attestedValidators[key]
validatorBits.combine(attestation.aggregation_bits)
pool.attestedValidators[key] = validatorBits
except KeyError:
pool.attestedValidators[key] = attestation.aggregation_bits
func populateAttestationCache(pool: var AttestationPool, state: BeaconState) =
pool.attestedValidators.clear()
for pendingAttestation in state.previous_epoch_attestations:
pool.incorporateCacheAttestation(pendingAttestation)
for pendingAttestation in state.current_epoch_attestations:
pool.incorporateCacheAttestation(pendingAttestation)
func updateAttestationsCache(pool: var AttestationPool,
state: BeaconState) =
# There have likely been additional attestations integrated into BeaconState
# since last block production, an epoch change, or even a tree restructuring
# so that there's nothing in common in the BeaconState altogether, since the
# last time requested.
if (
(pool.lastPreviousEpochAttestationsLen == 0 or
(pool.lastPreviousEpochAttestationsLen <= state.previous_epoch_attestations.len and
pool.lastPreviousEpochAttestation ==
state.previous_epoch_attestations[pool.lastPreviousEpochAttestationsLen - 1])) and
(pool.lastCurrentEpochAttestationsLen == 0 or
(pool.lastCurrentEpochAttestationsLen <= state.current_epoch_attestations.len and
pool.lastCurrentEpochAttestation ==
state.current_epoch_attestations[pool.lastCurrentEpochAttestationsLen - 1]))
):
# There are multiple validators attached to this node proposing in the
# same epoch. As such, incorporate that new attestation. Both previous
# and current attestations lists might have been appended to.
for i in pool.lastPreviousEpochAttestationsLen ..<
state.previous_epoch_attestations.len:
pool.incorporateCacheAttestation(state.previous_epoch_attestations[i])
for i in pool.lastCurrentEpochAttestationsLen ..<
state.current_epoch_attestations.len:
pool.incorporateCacheAttestation(state.current_epoch_attestations[i])
else:
# Tree restructuring or other cache flushing event. This must trigger
# sometimes to clear old attestations.
pool.populateAttestationCache(state)
pool.lastPreviousEpochAttestationsLen = state.previous_epoch_attestations.len
pool.lastCurrentEpochAttestationsLen = state.current_epoch_attestations.len
if pool.lastPreviousEpochAttestationsLen > 0:
pool.lastPreviousEpochAttestation =
state.previous_epoch_attestations[pool.lastPreviousEpochAttestationsLen - 1]
if pool.lastCurrentEpochAttestationsLen > 0:
pool.lastCurrentEpochAttestation =
state.current_epoch_attestations[pool.lastCurrentEpochAttestationsLen - 1]
proc getAttestationsForBlock*(pool: var AttestationPool,
state: BeaconState,
cache: var StateCache): seq[Attestation] =
## Retrieve attestations that may be added to a new block at the slot of the
## given state
let newBlockSlot = state.slot
var attestations: seq[AttestationEntry]
pool.updateAttestationsCache(state)
for i in max(1, newBlockSlot.int64 - ATTESTATION_LOOKBACK.int64) ..
newBlockSlot.int64:
let maybeSlotData = getAttestationsForSlot(pool, i.Slot)
if maybeSlotData.isSome:
insert(attestations, maybeSlotData.get.attestations)
if attestations.len == 0:
return
for a in attestations:
var
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#construct-attestation
attestation = Attestation(
aggregation_bits: a.validations[0].aggregation_bits,
data: a.data,
signature: a.validations[0].aggregate_signature
)
agg {.noInit.}: AggregateSignature
agg.init(a.validations[0].aggregate_signature)
# Signature verification here is more of a sanity check - it could
# be optimized away, though for now it's easier to reuse the logic from
# the state transition function to ensure that the new block will not
# fail application.
if (let v = check_attestation(state, attestation, {}, cache); v.isErr):
warn "Attestation no longer validates...",
attestation = shortLog(attestation),
err = v.error
continue
for i in 1..a.validations.high:
if not attestation.aggregation_bits.overlaps(
a.validations[i].aggregation_bits):
attestation.aggregation_bits.combine(a.validations[i].aggregation_bits)
agg.aggregate(a.validations[i].aggregate_signature)
# Since each validator attests exactly once per epoch and its attestation
# has been validated to have been included in the attestation pool, there
# only exists one possible slot/committee combination to check.
try:
if a.aggregation_bits.isSubsetOf(
pool.attestedValidators[a.data.getAttestationDataKey]):
continue
except KeyError:
# No record of inclusion, so go ahead and include attestation.
discard
attestation.signature = agg.finish()
result.add(attestation)
if result.lenu64 >= MAX_ATTESTATIONS:
debug "getAttestationsForBlock: returning early after hitting MAX_ATTESTATIONS",
attestationSlot = newBlockSlot - 1
return
func getAggregatedAttestation*(pool: AttestationPool,
slot: Slot,
ad_htr: Eth2Digest): Option[Attestation] =
try:
if pool.attestationAggregates.contains(slot) and
pool.attestationAggregates[slot].contains(ad_htr):
return some pool.attestationAggregates[slot][ad_htr]
except KeyError:
doAssert(false) # shouldn't be possible because we check with `contains`
none(Attestation)
proc getAggregatedAttestation*(pool: AttestationPool,
slot: Slot,
index: CommitteeIndex): Option[Attestation] =
let attestations = pool.getAttestationsForSlot(
slot + MIN_ATTESTATION_INCLUSION_DELAY)
if attestations.isNone:
return none(Attestation)
for a in attestations.get.attestations:
doAssert a.data.slot == slot
if index.uint64 != a.data.index:
continue
var
# https://github.com/ethereum/eth2.0-specs/blob/v1.0.0/specs/phase0/validator.md#construct-attestation
attestation = Attestation(
aggregation_bits: a.validations[0].aggregation_bits,
data: a.data,
signature: a.validations[0].aggregate_signature
)
agg {.noInit.}: AggregateSignature
agg.init(a.validations[0].aggregate_signature)
for v in a.validations[1..^1]:
if not attestation.aggregation_bits.overlaps(v.aggregation_bits):
attestation.aggregation_bits.combine(v.aggregation_bits)
agg.aggregate(v.aggregate_signature)
attestation.signature = agg.finish()
return some(attestation)
none(Attestation)
proc selectHead*(pool: var AttestationPool, wallSlot: Slot): BlockRef =
## Trigger fork choice and returns the new head block.
## Can return `nil`
let newHead = pool.forkChoice.get_head(pool.chainDag, wallSlot)
if newHead.isErr:
error "Couldn't select head", err = newHead.error
nil
else:
let ret = pool.chainDag.getRef(newHead.get())
if ret.isNil:
# This should normally not happen, but if the chain dag and fork choice
# get out of sync, we'll need to try to download the selected head - in
# the meantime, return nil to indicate that no new head was chosen
warn "Fork choice selected unknown head, trying to sync", root = newHead.get()
pool.quarantine.addMissing(newHead.get())
ret
proc prune*(pool: var AttestationPool) =
if (let v = pool.forkChoice.prune(); v.isErr):
# If pruning fails, it's likely the result of a bug - this shouldn't happen
# but we'll keep running hoping that the fork chocie will recover eventually
error "Couldn't prune fork choice, bug?", err = v.error()