nimbus-eth2/beacon_chain/attestation_pool.nim

539 lines
21 KiB
Nim

# 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
deques, sequtils, tables, options,
chronicles, stew/[bitseqs, byteutils], json_serialization/std/sets,
./spec/[beaconstate, datatypes, crypto, digest, helpers, validator],
./extras, ./ssz, ./block_pool, ./beacon_node_types
logScope: topics = "attpool"
func init*(T: type AttestationPool, blockPool: BlockPool): T =
# TODO blockPool is only used when resolving orphaned attestations - it should
# probably be removed as a dependency of AttestationPool (or some other
# smart refactoring)
T(
slots: initDeque[SlotData](),
blockPool: blockPool,
unresolved: initTable[Eth2Digest, UnresolvedAttestation](),
latestAttestations: initTable[ValidatorPubKey, BlockRef]()
)
proc combine*(tgt: var Attestation, src: Attestation, flags: UpdateFlags) =
## Combine the signature and participation bitfield, with the assumption that
## the same data is being signed - if the signatures overlap, they are not
## combined.
doAssert tgt.data == src.data
# In a BLS aggregate signature, one needs to count how many times a
# particular public key has been added - since we use a single bit per key, we
# can only it once, thus we can never combine signatures that overlap already!
if not tgt.aggregation_bits.overlaps(src.aggregation_bits):
tgt.aggregation_bits.combine(src.aggregation_bits)
if skipBlsValidation notin flags:
tgt.signature.aggregate(src.signature)
else:
trace "Ignoring overlapping attestations"
# TODO remove/merge with p2p-interface validation
proc validate(
state: BeaconState, attestation: Attestation): bool =
# TODO what constitutes a valid attestation when it's about to be added to
# the pool? we're interested in attestations that will become viable
# for inclusion in blocks in the future and on any fork, so we need to
# consider that validations might happen using the state of a different
# fork.
# Some things are always invalid (like out-of-bounds issues etc), but
# others are more subtle - how do we validate the signature for example?
# It might be valid on one fork but not another. One thing that helps
# is that committees are stable per epoch and that it should be OK to
# include an attestation in a block even if the corresponding validator
# was slashed in the same epoch - there's no penalty for doing this and
# the vote counting logic will take care of any ill effects (TODO verify)
let data = attestation.data
# TODO re-enable check
#if not (data.crosslink.shard < SHARD_COUNT):
# notice "Attestation shard too high",
# attestation_shard = data.crosslink.shard
# return
# Without this check, we can't get a slot number for the attestation as
# certain helpers will assert
# TODO this could probably be avoided by being smart about the specific state
# used to validate the attestation: most likely if we pick the state of
# the beacon block being voted for and a slot in the target epoch
# of the attestation, we'll be safe!
# TODO the above state selection logic should probably live here in the
# attestation pool
if not (data.target.epoch == get_previous_epoch(state) or
data.target.epoch == get_current_epoch(state)):
notice "Target epoch not current or previous epoch"
return
true
proc slotIndex(
pool: var AttestationPool, state: BeaconState, attestationSlot: Slot): int =
## Grow and garbage collect pool, returning the deque index of the slot
# We keep a sliding window of attestations, roughly from the last finalized
# epoch to now, because these are the attestations that may affect the voting
# outcome. Some of these attestations will already have been added to blocks,
# while others are fresh off the network.
# TODO only the latest vote of each validator counts. Can we use that somehow?
logScope: pcs = "atp_slot_maintenance"
doAssert attestationSlot >= pool.startingSlot,
"""
We should have checked in validate that attestation is newer than
finalized_slot and we never prune things before that, per below condition!
""" &
", attestationSlot: " & $shortLog(attestationSlot) &
", startingSlot: " & $shortLog(pool.startingSlot)
if pool.slots.len == 0:
# Because the first attestations may arrive in any order, we'll make sure
# to start counting at the last finalized epoch start slot - anything
# earlier than that is thrown out by the above check
info "First attestation!",
attestationSlot = $shortLog(attestationSlot),
cat = "init"
pool.startingSlot =
state.finalized_checkpoint.epoch.compute_start_slot_at_epoch()
if pool.startingSlot + pool.slots.len.uint64 <= attestationSlot:
trace "Growing attestation pool",
attestationSlot = $shortLog(attestationSlot),
startingSlot = $shortLog(pool.startingSlot),
cat = "caching"
# Make sure there's a pool entry for every slot, even when there's a gap
while pool.startingSlot + pool.slots.len.uint64 <= attestationSlot:
pool.slots.addLast(SlotData())
if pool.startingSlot <
state.finalized_checkpoint.epoch.compute_start_slot_at_epoch():
debug "Pruning attestation pool",
startingSlot = $shortLog(pool.startingSlot),
finalizedSlot = $shortLog(
state.finalized_checkpoint
.epoch.compute_start_slot_at_epoch()),
cat = "pruning"
# TODO there should be a better way to remove a whole epoch of stuff..
while pool.startingSlot <
state.finalized_checkpoint.epoch.compute_start_slot_at_epoch():
pool.slots.popFirst()
pool.startingSlot += 1
int(attestationSlot - pool.startingSlot)
func updateLatestVotes(
pool: var AttestationPool, state: BeaconState, attestationSlot: Slot,
participants: seq[ValidatorIndex], blck: BlockRef) =
for validator in participants:
let
pubKey = state.validators[validator].pubkey
current = pool.latestAttestations.getOrDefault(pubKey)
if current.isNil or current.slot < attestationSlot:
pool.latestAttestations[pubKey] = blck
func get_attesting_indices_seq(state: BeaconState,
attestation_data: AttestationData,
bits: CommitteeValidatorsBits): seq[ValidatorIndex] =
var cache = get_empty_per_epoch_cache()
toSeq(items(get_attesting_indices(
state, attestation_data, bits, cache)))
func addUnresolved(pool: var AttestationPool, attestation: Attestation) =
pool.unresolved[attestation.data.beacon_block_root] =
UnresolvedAttestation(
attestation: attestation,
)
proc addResolved(pool: var AttestationPool, blck: BlockRef, attestation: Attestation) =
doAssert blck.root == attestation.data.beacon_block_root
# TODO Which state should we use to validate the attestation? It seems
# reasonable to involve the head being voted for as well as the intended
# slot of the attestation - double-check this with spec
# A basic check is that the attestation is at least as new as the block being
# voted for..
if blck.slot > attestation.data.slot:
notice "Invalid attestation (too new!)",
attestation = shortLog(attestation),
blockSlot = shortLog(blck.slot)
return
updateStateData(
pool.blockPool, pool.blockPool.tmpState,
BlockSlot(blck: blck, slot: attestation.data.slot))
template state(): BeaconState = pool.blockPool.tmpState.data.data
if not validate(state, attestation):
notice "Invalid attestation",
attestation = shortLog(attestation),
current_epoch = get_current_epoch(state),
cat = "filtering"
return
# TODO inefficient data structures..
let
attestationSlot = attestation.data.slot
idx = pool.slotIndex(state, attestationSlot)
slotData = addr pool.slots[idx]
validation = Validation(
aggregation_bits: attestation.aggregation_bits,
aggregate_signature: attestation.signature)
participants = get_attesting_indices_seq(
state, attestation.data, validation.aggregation_bits)
var found = false
for a in slotData.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
# TODO what if the new attestation is useful for creating bigger
# sets by virtue of not overlapping with some other attestation
# and therefore being useful after all?
trace "Ignoring subset attestation",
existingParticipants = get_attesting_indices_seq(
state, a.data, v.aggregation_bits),
newParticipants = participants,
cat = "filtering"
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",
existingParticipants = a.validations.filterIt(
it.aggregation_bits.isSubsetOf(validation.aggregation_bits)
).mapIt(get_attesting_indices_seq(
state, a.data, it.aggregation_bits)),
newParticipants = participants,
cat = "pruning"
a.validations.keepItIf(
not it.aggregation_bits.isSubsetOf(validation.aggregation_bits))
a.validations.add(validation)
pool.updateLatestVotes(state, attestationSlot, participants, a.blck)
info "Attestation resolved",
attestation = shortLog(attestation),
validations = a.validations.len(),
current_epoch = get_current_epoch(state),
blockSlot = shortLog(blck.slot),
cat = "filtering"
found = true
break
if not found:
slotData.attestations.add(AttestationEntry(
data: attestation.data,
blck: blck,
validations: @[validation]
))
pool.updateLatestVotes(state, attestationSlot, participants, blck)
info "Attestation resolved",
attestation = shortLog(attestation),
current_epoch = get_current_epoch(state),
validations = 1,
blockSlot = shortLog(blck.slot),
cat = "filtering"
proc add*(pool: var AttestationPool, attestation: Attestation) =
logScope: pcs = "atp_add_attestation"
let blck = pool.blockPool.getOrResolve(attestation.data.beacon_block_root)
if blck.isNil:
pool.addUnresolved(attestation)
return
pool.addResolved(blck, attestation)
proc getAttestationsForSlot(pool: AttestationPool, newBlockSlot: Slot):
Option[SlotData] =
if newBlockSlot < (GENESIS_SLOT + MIN_ATTESTATION_INCLUSION_DELAY):
debug "Too early for attestations",
newBlockSlot = shortLog(newBlockSlot),
cat = "query"
return none(SlotData)
if pool.slots.len == 0: # startingSlot not set yet!
info "No attestations found (pool empty)",
newBlockSlot = shortLog(newBlockSlot),
cat = "query"
return none(SlotData)
let
# TODO in theory we could include attestations from other slots also, but
# we're currently not tracking which attestations have already been included
# in blocks on the fork we're aiming for.. this is a conservative approach
# that's guaranteed to not include any duplicates, because it's the first
# time the attestations are up for inclusion!
attestationSlot = newBlockSlot - MIN_ATTESTATION_INCLUSION_DELAY
if attestationSlot < pool.startingSlot or
attestationSlot >= pool.startingSlot + pool.slots.len.uint64:
info "No attestations matching the slot range",
attestationSlot = shortLog(attestationSlot),
startingSlot = shortLog(pool.startingSlot),
endingSlot = shortLog(pool.startingSlot + pool.slots.len.uint64),
cat = "query"
return none(SlotData)
let slotDequeIdx = int(attestationSlot - pool.startingSlot)
some(pool.slots[slotDequeIdx])
proc getAttestationsForBlock*(pool: AttestationPool,
state: BeaconState): seq[Attestation] =
## Retrieve attestations that may be added to a new block at the slot of the
## given state
logScope: pcs = "retrieve_attestation"
# TODO this shouldn't really need state -- it's to recheck/validate, but that
# should be refactored
let
newBlockSlot = state.slot
maybeSlotData = getAttestationsForSlot(pool, newBlockSlot)
if maybeSlotData.isNone:
# Logging done in getAttestationsForSlot(...)
return
let slotData = maybeSlotData.get
var cache = get_empty_per_epoch_cache()
for a in slotData.attestations:
var
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/validator.md#construct-attestation
attestation = Attestation(
aggregation_bits: a.validations[0].aggregation_bits,
data: a.data,
signature: a.validations[0].aggregate_signature
)
if not validate(state, attestation):
warn "Attestation no longer validates...",
cat = "query"
continue
# TODO what's going on here is that when producing a block, we need to
# include only such attestations that will not cause block validation
# to fail. How this interacts with voting and the acceptance of
# attestations into the pool in general is an open question that needs
# revisiting - for example, when attestations are added, against which
# state should they be validated, if at all?
# TODO we're checking signatures here every time which is very slow - this
# is needed because validate does nothing for now and we don't want
# to include a broken attestation
if not check_attestation(state, attestation, {}, cache):
continue
for v in a.validations[1..^1]:
# TODO We need to select a set of attestations that maximise profit by
# adding the largest combined attestation set that we can find - this
# unfortunately looks an awful lot like
# https://en.wikipedia.org/wiki/Set_packing - here we just iterate
# and naively add as much as possible in one go, by we could also
# add the same attestation data twice, as long as there's at least
# one new attestation in there
if not attestation.aggregation_bits.overlaps(v.aggregation_bits):
attestation.aggregation_bits.combine(v.aggregation_bits)
attestation.signature.aggregate(v.aggregate_signature)
result.add(attestation)
if result.len >= MAX_ATTESTATIONS:
return
proc resolve*(pool: var AttestationPool) =
logScope: pcs = "atp_resolve"
var
done: seq[Eth2Digest]
resolved: seq[tuple[blck: BlockRef, attestation: Attestation]]
for k, v in pool.unresolved.mpairs():
if (let blck = pool.blockPool.getRef(k); not blck.isNil()):
resolved.add((blck, v.attestation))
done.add(k)
elif v.tries > 8:
done.add(k)
else:
inc v.tries
for k in done:
pool.unresolved.del(k)
for a in resolved:
pool.addResolved(a.blck, a.attestation)
func latestAttestation*(
pool: AttestationPool, pubKey: ValidatorPubKey): BlockRef =
pool.latestAttestations.getOrDefault(pubKey)
# https://github.com/ethereum/eth2.0-specs/blob/v0.8.4/specs/core/0_fork-choice.md
# The structure of this code differs from the spec since we use a different
# strategy for storing states and justification points - it should nonetheless
# be close in terms of functionality.
func lmdGhost*(
pool: AttestationPool, start_state: BeaconState,
start_block: BlockRef): BlockRef =
# TODO: a Fenwick Tree datastructure to keep track of cumulated votes
# in O(log N) complexity
# https://en.wikipedia.org/wiki/Fenwick_tree
# Nim implementation for cumulative frequencies at
# https://github.com/numforge/laser/blob/990e59fffe50779cdef33aa0b8f22da19e1eb328/benchmarks/random_sampling/fenwicktree.nim
let
active_validator_indices =
get_active_validator_indices(
start_state, compute_epoch_at_slot(start_state.slot))
var latest_messages: seq[tuple[validator: ValidatorIndex, blck: BlockRef]]
for i in active_validator_indices:
let pubKey = start_state.validators[i].pubkey
if (let vote = pool.latestAttestation(pubKey); not vote.isNil):
latest_messages.add((i, vote))
# TODO: update to 0.10.1: https://github.com/ethereum/eth2.0-specs/pull/1589/files#diff-9fc3792aa94456eb29506fa77f77b918R143
template get_latest_attesting_balance(blck: BlockRef): uint64 =
var res: uint64
for validator_index, target in latest_messages.items():
if get_ancestor(target, blck.slot) == blck:
res += start_state.validators[validator_index].effective_balance
res
var head = start_block
while true:
if head.children.len() == 0:
return head
if head.children.len() == 1:
head = head.children[0]
else:
var
winner = head.children[0]
winCount = get_latest_attesting_balance(winner)
for i in 1..<head.children.len:
let
candidate = head.children[i]
candCount = get_latest_attesting_balance(candidate)
if (candCount > winCount) or
((candCount == winCount and candidate.root.data < winner.root.data)):
winner = candidate
winCount = candCount
head = winner
proc selectHead*(pool: AttestationPool): BlockRef =
let
justifiedHead = pool.blockPool.latestJustifiedBlock()
let newHead =
lmdGhost(pool, pool.blockPool.justifiedState.data.data, justifiedHead.blck)
newHead
# https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/p2p-interface.md#attestation-subnets
proc isValidAttestation*(
pool: AttestationPool, attestation: Attestation, current_slot: Slot,
topicCommitteeIndex: uint64, flags: UpdateFlags): bool =
# The attestation's committee index (attestation.data.index) is for the
# correct subnet.
if attestation.data.index != topicCommitteeIndex:
debug "isValidAttestation: attestation's committee index not for the correct subnet",
topicCommitteeIndex = topicCommitteeIndex,
attestation_data_index = attestation.data.index
return false
if not (attestation.data.slot + ATTESTATION_PROPAGATION_SLOT_RANGE >=
current_slot and current_slot >= attestation.data.slot):
debug "isValidAttestation: attestation.data.slot not within ATTESTATION_PROPAGATION_SLOT_RANGE"
return false
# The attestation is unaggregated -- that is, it has exactly one
# participating validator (len([bit for bit in attestation.aggregation_bits
# if bit == 0b1]) == 1).
# TODO a cleverer algorithm, along the lines of countOnes() in nim-stew
# But that belongs in nim-stew, since it'd break abstraction layers, to
# use details of its representation from nim-beacon-chain.
var onesCount = 0
for aggregation_bit in attestation.aggregation_bits:
if not aggregation_bit:
continue
onesCount += 1
if onesCount > 1:
debug "isValidAttestation: attestation has too many aggregation bits",
aggregation_bits = attestation.aggregation_bits
return false
if onesCount != 1:
debug "isValidAttestation: attestation has too few aggregation bits"
return false
# The attestation is the first valid attestation received for the
# participating validator for the slot, attestation.data.slot.
let maybeSlotData = getAttestationsForSlot(pool, attestation.data.slot)
if maybeSlotData.isSome:
for attestationEntry in maybeSlotData.get.attestations:
if attestation.data != attestationEntry.data:
continue
# Attestations might be aggregated eagerly or lazily; allow for both.
for validation in attestationEntry.validations:
if attestation.aggregation_bits.isSubsetOf(validation.aggregation_bits):
debug "isValidAttestation: attestation already exists at slot",
attestation_data_slot = attestation.data.slot,
attestation_aggregation_bits = attestation.aggregation_bits,
attestation_pool_validation = validation.aggregation_bits
return false
# The block being voted for (attestation.data.beacon_block_root) passes
# validation.
# We rely on the block pool to have been validated, so check for the
# existence of the block in the pool.
# TODO: consider a "slush pool" of attestations whose blocks have not yet
# propagated - i.e. imagine that attestations are smaller than blocks and
# therefore propagate faster, thus reordering their arrival in some nodes
if pool.blockPool.get(attestation.data.beacon_block_root).isNone():
debug "isValidAttestation: block doesn't exist in block pool",
attestation_data_beacon_block_root = attestation.data.beacon_block_root
return false
# The signature of attestation is valid.
# TODO need to know above which validator anyway, and this is too general
# as it supports aggregated attestations (which this can't be)
var cache = get_empty_per_epoch_cache()
if not is_valid_indexed_attestation(
pool.blockPool.headState.data.data,
get_indexed_attestation(
pool.blockPool.headState.data.data, attestation, cache), {}):
debug "isValidAttestation: signature verification failed"
return false
true