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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
deques, sequtils, tables, options,
# Status libraries
chronicles, stew/[byteutils], json_serialization/std/sets,
# Internal
./spec/[beaconstate, datatypes, crypto, digest, helpers],
./extras, ./block_pool, ./block_pools/candidate_chains, ./beacon_node_types,
./fork_choice/fork_choice
logScope: topics = "attpool"
proc init*(T: type AttestationPool, blockPool: BlockPool): T =
## Initialize an AttestationPool from the blockPool `headState`
## The `finalized_root` works around the finalized_checkpoint of the genesis block
## holding a zero_root.
# TODO blockPool is only used when resolving orphaned attestations - it should
# probably be removed as a dependency of AttestationPool (or some other
# smart refactoring)
# TODO: Return Value Optimization
# TODO: In tests, on blockpool.init the finalized root
# from the `headState` and `justifiedState` is zero
var forkChoice = initForkChoice(
finalized_block_slot = default(Slot), # This is unnecessary for fork choice but may help external components for example logging/debugging
finalized_block_state_root = default(Eth2Digest), # This is unnecessary for fork choice but may help external components for example logging/debugging
justified_epoch = blockPool.headState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = blockPool.headState.data.data.finalized_checkpoint.epoch,
# We should use the checkpoint, but at genesis the headState finalized checkpoint is 0x0000...0000
# finalized_root = blockPool.headState.data.data.finalized_checkpoint.root
finalized_root = blockPool.finalizedHead.blck.root
).get()
# Load all blocks since finalized head - TODO a proper test
for blck in blockPool.dag.topoSortedSinceLastFinalization():
if blck.root == blockPool.finalizedHead.blck.root:
continue
# BlockRef
# should ideally contain the justified_epoch and finalized_epoch
# so that we can pass them directly to `process_block` without having to
# redo "updateStateData"
#
# In any case, `updateStateData` should shortcut
# to `getStateDataCached`
updateStateData(
blockPool,
blockPool.tmpState,
BlockSlot(blck: blck, slot: blck.slot)
)
debug "Preloading fork choice with block",
block_root = shortlog(blck.root),
parent_root = shortlog(blck.parent.root),
justified_epoch = $blockPool.tmpState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = $blockPool.tmpState.data.data.finalized_checkpoint.epoch,
slot = $blck.slot
let status = forkChoice.process_block(
block_root = blck.root,
parent_root = blck.parent.root,
justified_epoch = blockPool.tmpState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = blockPool.tmpState.data.data.finalized_checkpoint.epoch,
# Unused in fork choice - i.e. for logging or caching extra metadata
slot = blck.slot,
state_root = default(Eth2Digest)
)
doAssert status.isOk(), "Error in preloading the fork choice: " & $status.error
info "Fork choice initialized",
justified_epoch = $blockPool.headState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = $blockPool.headState.data.data.finalized_checkpoint.epoch,
finalized_root = shortlog(blockPool.finalizedHead.blck.root)
T(
mapSlotsToAttestations: initDeque[AttestationsSeen](),
blockPool: blockPool,
unresolved: initTable[Eth2Digest, UnresolvedAttestation](),
forkChoice_v2: forkChoice
)
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.
# TODO: Exported only for testing, all usage are internals
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"
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 addResolved 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.mapSlotsToAttestations.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)
pool.startingSlot =
state.finalized_checkpoint.epoch.compute_start_slot_at_epoch()
if pool.startingSlot + pool.mapSlotsToAttestations.len.uint64 <= attestationSlot:
trace "Growing attestation pool",
attestationSlot = shortLog(attestationSlot),
startingSlot = shortLog(pool.startingSlot)
# Make sure there's a pool entry for every slot, even when there's a gap
while pool.startingSlot + pool.mapSlotsToAttestations.len.uint64 <= attestationSlot:
pool.mapSlotsToAttestations.addLast(AttestationsSeen())
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())
# 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.mapSlotsToAttestations.popFirst()
pool.startingSlot += 1
int(attestationSlot - pool.startingSlot)
func updateLatestVotes(
pool: var AttestationPool, state: BeaconState, attestationSlot: Slot,
participants: seq[ValidatorIndex], blck: BlockRef) =
# ForkChoice v2
let target_epoch = compute_epoch_at_slot(attestationSlot)
for validator in participants:
# ForkChoice v1
let
pubKey = state.validators[validator].pubkey
current = pool.latestAttestations.getOrDefault(pubKey)
if current.isNil or current.slot < attestationSlot:
pool.latestAttestations[pubKey] = blck
# # ForkChoice v2
# pool.forkChoice_v2.process_attestation(validator, blck.root, target_epoch)
func get_attesting_indices_seq(state: BeaconState,
attestation_data: AttestationData,
bits: CommitteeValidatorsBits,
cache: var StateCache): seq[ValidatorIndex] =
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
# TODO: How fast is state rewind?
# Can this be a DOS vector.
# TODO: filter valid attestation as much as possible before state rewind
# TODO: the below check does not respect the inclusion delay
# we should use isValidAttestationSlot instead
if blck.slot > attestation.data.slot:
notice "Invalid attestation (too new!)",
attestation = shortLog(attestation),
blockSlot = shortLog(blck.slot)
return
if attestation.data.slot < pool.startingSlot:
# It can happen that attestations in blocks for example are included even
# though they no longer are relevant for finalization - let's clear
# these out
debug "Old attestation",
attestation = shortLog(attestation),
startingSlot = pool.startingSlot
return
# if not isValidAttestationSlot(attestation.data.slot, blck.slot):
# # Logging in isValidAttestationSlot
# return
# Get a temporary state at the (block, slot) targeted by the attestation
updateStateData(
pool.blockPool, pool.blockPool.tmpState,
BlockSlot(blck: blck, slot: attestation.data.slot))
template state(): BeaconState = pool.blockPool.tmpState.data.data
# Check that the attestation is indeed valid
# TODO: we might want to split checks that depend
# on the state and those that don't to cheaply
# discard invalid attestations before rewinding state.
if not isValidAttestationTargetEpoch(state, attestation.data):
notice "Invalid attestation",
attestation = shortLog(attestation),
current_epoch = get_current_epoch(state)
return
# TODO inefficient data structures..
var cache = getEpochCache(blck, state)
let
attestationSlot = attestation.data.slot
idx = pool.slotIndex(state, attestationSlot)
attestationsSeen = addr pool.mapSlotsToAttestations[idx]
validation = Validation(
aggregation_bits: attestation.aggregation_bits,
aggregate_signature: attestation.signature)
participants = get_attesting_indices_seq(
state, attestation.data, validation.aggregation_bits, cache)
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
# 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",
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.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)
found = true
break
if not found:
attestationsSeen.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)
proc addAttestation*(pool: var AttestationPool, attestation: Attestation) =
## Add a verified attestation to the fork choice context
logScope: pcs = "atp_add_attestation"
# Fetch the target block or notify the block pool that it's needed
let blck = pool.blockPool.getOrResolve(attestation.data.beacon_block_root)
# If the block exist, add it to the fork choice context
# Otherwise delay until it resolves
if blck.isNil:
pool.addUnresolved(attestation)
return
pool.addResolved(blck, attestation)
proc addForkChoice_v2*(pool: var AttestationPool, blck: BlockRef) =
## Add a verified block to the fork choice context
## The current justifiedState of the block pool is used as reference
# TODO: add(BlockPool, blockRoot: Eth2Digest, SignedBeaconBlock): BlockRef
# should ideally return the justified_epoch and finalized_epoch
# so that we can pass them directly to this proc without having to
# redo "updateStateData"
#
# In any case, `updateStateData` should shortcut
# to `getStateDataCached`
var state: Result[void, string]
# A stack of block to add in case recovery is needed
var blockStack: seq[BlockSlot]
var current = BlockSlot(blck: blck, slot: blck.slot)
while true: # The while loop should not be needed but it seems a block addition
# scenario is unaccounted for
updateStateData(
pool.blockPool,
pool.blockPool.tmpState,
current
)
let blockData = pool.blockPool.get(current.blck)
state = pool.forkChoice_v2.process_block(
slot = current.blck.slot,
block_root = current.blck.root,
parent_root = if not current.blck.parent.isNil: current.blck.parent.root else: default(Eth2Digest),
state_root = default(Eth2Digest), # This is unnecessary for fork choice but may help external components
justified_epoch = pool.blockPool.tmpState.data.data.current_justified_checkpoint.epoch,
finalized_epoch = pool.blockPool.tmpState.data.data.finalized_checkpoint.epoch,
)
# This should not happen and might lead to unresponsive networking while processing occurs
if state.isErr:
# TODO investigate, potential sources:
# - Pruning
# - Quarantine adding multiple blocks at once
# - Own block proposal
error "Desync between fork_choice and blockpool services, trying to recover.",
msg = state.error,
blck = shortlog(current.blck),
parent = shortlog(current.blck.parent),
finalizedHead = shortLog(pool.blockPool.finalizedHead),
justifiedHead = shortLog(pool.blockPool.head.justified),
head = shortLog(pool.blockPool.head.blck)
blockStack.add(current)
current = BlockSlot(blck: blck.parent, slot: blck.parent.slot)
elif blockStack.len == 0:
break
else:
info "Re-added missing or pruned block to fork choice",
msg = state.error,
blck = shortlog(current.blck),
parent = shortlog(current.blck.parent),
finalizedHead = shortLog(pool.blockPool.finalizedHead),
justifiedHead = shortLog(pool.blockPool.head.justified),
head = shortLog(pool.blockPool.head.blck)
current = blockStack.pop()
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)
if pool.mapSlotsToAttestations.len == 0: # startingSlot not set yet!
info "No attestations found (pool empty)",
newBlockSlot = shortLog(newBlockSlot)
return none(AttestationsSeen)
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.mapSlotsToAttestations.len.uint64:
info "No attestations matching the slot range",
attestationSlot = shortLog(attestationSlot),
startingSlot = shortLog(pool.startingSlot),
endingSlot = shortLog(pool.startingSlot + pool.mapSlotsToAttestations.len.uint64)
return none(AttestationsSeen)
let slotDequeIdx = int(attestationSlot - pool.startingSlot)
some(pool.mapSlotsToAttestations[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
var attestations: seq[AttestationEntry]
# This isn't maximally efficient -- iterators or other approaches would
# avoid lots of memory allocations -- but this provides a more flexible
# base upon which to experiment with, and isn't yet profiling hot-path,
# while avoiding penalizing slow attesting too much (as, in the spec it
# is supposed to be available two epochs back; it's not meant as). This
# isn't a good solution, either -- see the set-packing comment below as
# one issue. It also creates problems with lots of repeat attestations,
# as a bunch of synchronized beacon_nodes do almost the opposite of the
# intended thing -- sure, _blocks_ have to be popular (via attestation)
# but _attestations_ shouldn't have to be so frequently repeated, as an
# artifact of this state-free, identical-across-clones choice basis. In
# addResolved, too, the new attestations get added to the end, while in
# these functions, it's reading from the beginning, et cetera. This all
# needs a single unified strategy.
const LOOKBACK_WINDOW = 3
for i in max(1, newBlockSlot.int64 - LOOKBACK_WINDOW) .. newBlockSlot.int64:
let maybeSlotData = getAttestationsForSlot(pool, i.Slot)
if maybeSlotData.isSome:
insert(attestations, maybeSlotData.get.attestations)
if attestations.len == 0:
return
var cache = StateCache()
for a in attestations:
var
# https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#construct-attestation
attestation = Attestation(
aggregation_bits: a.validations[0].aggregation_bits,
data: a.data,
signature: a.validations[0].aggregate_signature
)
# 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 and we don't want
# to include a broken attestation
if not check_attestation(state, attestation, {}, cache):
warn "Attestation no longer validates...",
attestation = shortLog(attestation)
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.int:
debug "getAttestationsForBlock: returning early after hitting MAX_ATTESTATIONS",
attestationSlot = newBlockSlot - 1
return
proc resolve*(pool: var AttestationPool) =
## Check attestations in our unresolved deque
## if they can be integrated to the fork choice
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)
# Fork choice v1
# ---------------------------------------------------------------
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_v1(pool: AttestationPool): BlockRef =
let
justifiedHead = pool.blockPool.latestJustifiedBlock()
let newHead =
lmdGhost(pool, pool.blockPool.justifiedState.data.data, justifiedHead.blck)
newHead
# Fork choice v2
# ---------------------------------------------------------------
func getAttesterBalances(state: StateData): seq[Gwei] {.noInit.}=
## Get the balances from a state
result.newSeq(state.data.data.validators.len) # zero-init
let epoch = state.data.data.slot.compute_epoch_at_slot()
for i in 0 ..< result.len:
# All non-active validators have a 0 balance
template validator: Validator = state.data.data.validators[i]
if validator.is_active_validator(epoch):
result[i] = validator.effective_balance
proc selectHead_v2(pool: var AttestationPool): BlockRef =
let attesterBalances = pool.blockPool.justifiedState.getAttesterBalances()
let newHead = pool.forkChoice_v2.find_head(
justified_epoch = pool.blockPool.justifiedState.data.data.slot.compute_epoch_at_slot(),
justified_root = pool.blockPool.head.justified.blck.root,
finalized_epoch = pool.blockPool.headState.data.data.finalized_checkpoint.epoch,
justified_state_balances = attesterBalances
).get()
pool.blockPool.getRef(newHead)
proc pruneBefore*(pool: var AttestationPool, finalizedhead: BlockSlot) =
pool.forkChoice_v2.maybe_prune(finalizedHead.blck.root).get()
# Dual-Headed Fork choice
# ---------------------------------------------------------------
proc selectHead*(pool: var AttestationPool): BlockRef =
let head_v1 = pool.selectHead_v1()
# let head_v2 = pool.selectHead_v2()
#
# if head_v1 != head_v2:
# error "Fork choice engines in disagreement, using block from v1.",
# v1_block = shortlog(head_v1),
# v2_block = shortlog(head_v2)
return head_v1
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