# beacon_chain # Copyright (c) 2022 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].} # This implements the pre-release proposal of the libp2p based light client sync # protocol. See https://github.com/ethereum/consensus-specs/pull/2802 import # Standard library std/[algorithm, sequtils], # Status libraries stew/[bitops2, objects], chronos, # Beacon chain internals ../spec/datatypes/[phase0, altair, bellatrix], "."/[block_pools_types, blockchain_dag] logScope: topics = "chaindag" type HashedBeaconStateWithSyncCommittee = bellatrix.HashedBeaconState | altair.HashedBeaconState TrustedSignedBeaconBlockWithSyncAggregate = bellatrix.TrustedSignedBeaconBlock | altair.TrustedSignedBeaconBlock template nextEpochBoundarySlot(slot: Slot): Slot = ## Compute the first possible epoch boundary state slot of a `Checkpoint` ## referring to a block at given slot. (slot + (SLOTS_PER_EPOCH - 1)).epoch.start_slot func computeEarliestLightClientSlot*(dag: ChainDAGRef): Slot = ## Compute the earliest slot for which light client data is retained. let minSupportedSlot = max( dag.cfg.ALTAIR_FORK_EPOCH.start_slot, dag.lightClientCache.importTailSlot) currentSlot = getStateField(dag.headState, slot) if currentSlot < minSupportedSlot: return minSupportedSlot let MIN_EPOCHS_FOR_BLOCK_REQUESTS = dag.cfg.MIN_VALIDATOR_WITHDRAWABILITY_DELAY + dag.cfg.CHURN_LIMIT_QUOTIENT div 2 MIN_SLOTS_FOR_BLOCK_REQUESTS = MIN_EPOCHS_FOR_BLOCK_REQUESTS * SLOTS_PER_EPOCH if currentSlot - minSupportedSlot < MIN_SLOTS_FOR_BLOCK_REQUESTS: return minSupportedSlot let earliestSlot = currentSlot - MIN_SLOTS_FOR_BLOCK_REQUESTS max(earliestSlot.sync_committee_period.start_slot, minSupportedSlot) proc updateExistingState( dag: ChainDAGRef, state: var ForkedHashedBeaconState, bsi: BlockSlotId, save: bool, cache: var StateCache): bool = ## Wrapper around `updateState` for states expected to exist. let ok = dag.updateState(state, bsi, save, cache) if not ok: error "State failed to load unexpectedly", bsi, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags ok template withUpdatedExistingState( dag: ChainDAGRef, state: var ForkedHashedBeaconState, bsiParam: BlockSlotId, okBody: untyped, failureBody: untyped): untyped = ## Wrapper around `withUpdatedState` for states expected to exist. block: let bsi = bsiParam dag.withUpdatedState(state, bsiParam) do: okBody do: error "State failed to load unexpectedly", bsi, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags failureBody proc getExistingBlockIdAtSlot(dag: ChainDAGRef, slot: Slot): Opt[BlockSlotId] = ## Wrapper around `getBlockIdAtSlot` for blocks expected to exist. let bsi = dag.getBlockIdAtSlot(slot) if bsi.isErr: error "Block failed to load unexpectedly", slot, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags bsi proc existingParent*(dag: ChainDAGRef, bid: BlockId): Opt[BlockId] = ## Wrapper around `parent` for parents known to exist. let parent = dag.parent(bid) if parent.isErr: error "Parent failed to load unexpectedly", bid, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags parent proc getExistingForkedBlock(dag: ChainDAGRef, root: Eth2Digest): Opt[ForkedTrustedSignedBeaconBlock] = ## Wrapper around `getForkedBlock` for blocks expected to exist. let bdata = dag.getForkedBlock(root) if bdata.isErr: error "Block failed to load unexpectedly", root, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags bdata proc getExistingForkedBlock*( dag: ChainDAGRef, bid: BlockId): Opt[ForkedTrustedSignedBeaconBlock] = ## Wrapper around `getForkedBlock` for blocks expected to exist. let bdata = dag.getForkedBlock(bid) if bdata.isErr: error "Block failed to load unexpectedly", bid, tail = dag.tail.slot doAssert verifyFinalization notin dag.updateFlags bdata proc currentSyncCommitteeForPeriod( dag: ChainDAGRef, tmpState: var ForkedHashedBeaconState, period: SyncCommitteePeriod): Opt[SyncCommittee] = ## Fetch a `SyncCommittee` for a given sync committee period. ## For non-finalized periods, follow the chain as selected by fork choice. let earliestSlot = dag.computeEarliestLightClientSlot doAssert period >= earliestSlot.sync_committee_period let periodStartSlot = period.start_slot syncCommitteeSlot = max(periodStartSlot, earliestSlot) bsi = ? dag.getExistingBlockIdAtSlot(syncCommitteeSlot) dag.withUpdatedExistingState(tmpState, bsi) do: withState(state): when stateFork >= BeaconStateFork.Altair: ok state.data.current_sync_committee else: raiseAssert "Unreachable" do: err() template syncCommitteeRoot( state: HashedBeaconStateWithSyncCommittee): Eth2Digest = ## Compute a root to uniquely identify `current_sync_committee` and ## `next_sync_committee`. withEth2Hash: h.update state.data.current_sync_committee.hash_tree_root().data h.update state.data.next_sync_committee.hash_tree_root().data proc syncCommitteeRootForPeriod( dag: ChainDAGRef, tmpState: var ForkedHashedBeaconState, period: SyncCommitteePeriod): Opt[Eth2Digest] = ## Compute a root to uniquely identify `current_sync_committee` and ## `next_sync_committee` for a given sync committee period. ## For non-finalized periods, follow the chain as selected by fork choice. let earliestSlot = dag.computeEarliestLightClientSlot doAssert period >= earliestSlot.sync_committee_period let periodStartSlot = period.start_slot syncCommitteeSlot = max(periodStartSlot, earliestSlot) bsi = ? dag.getExistingBlockIdAtSlot(syncCommitteeSlot) dag.withUpdatedExistingState(tmpState, bsi) do: withState(state): when stateFork >= BeaconStateFork.Altair: ok state.syncCommitteeRoot else: raiseAssert "Unreachable" do: err() proc getLightClientData( dag: ChainDAGRef, bid: BlockId): CachedLightClientData = ## Fetch cached light client data about a given block. ## Data must be cached (`cacheLightClientData`) before calling this function. try: dag.lightClientCache.data[bid] except KeyError: raiseAssert "Unreachable" proc cacheLightClientData*( dag: ChainDAGRef, state: HashedBeaconStateWithSyncCommittee, blck: TrustedSignedBeaconBlockWithSyncAggregate) = ## Cache data for a given block and its post-state to speed up creating future ## `LightClientUpdate` and `LightClientBootstrap` instances that refer to this ## block and state. var current_sync_committee_branch {.noinit.}: array[log2trunc(altair.CURRENT_SYNC_COMMITTEE_INDEX), Eth2Digest] state.data.build_proof( altair.CURRENT_SYNC_COMMITTEE_INDEX, current_sync_committee_branch) var next_sync_committee_branch {.noinit.}: array[log2trunc(altair.NEXT_SYNC_COMMITTEE_INDEX), Eth2Digest] state.data.build_proof( altair.NEXT_SYNC_COMMITTEE_INDEX, next_sync_committee_branch) var finality_branch {.noinit.}: array[log2trunc(altair.FINALIZED_ROOT_INDEX), Eth2Digest] state.data.build_proof( altair.FINALIZED_ROOT_INDEX, finality_branch) let bid = BlockId(root: blck.root, slot: blck.message.slot) earliest_slot = dag.computeEarliestLightClientSlot finalized_slot = state.data.finalized_checkpoint.epoch.start_slot finalized_bsi = if finalized_slot >= earliest_slot: dag.getExistingBlockIdAtSlot(finalized_slot).valueOr: default(BlockSlotId) # Ignored in `createLightClientUpdates` else: default(BlockSlotId) # Ignored in `createLightClientUpdates` if dag.lightClientCache.data.hasKeyOrPut( bid, CachedLightClientData( current_sync_committee_branch: current_sync_committee_branch, next_sync_committee_branch: next_sync_committee_branch, finalized_bid: finalized_bsi.bid, finality_branch: finality_branch)): doAssert false, "Redundant `cacheLightClientData` call" proc deleteLightClientData*(dag: ChainDAGRef, bid: BlockId) = ## Delete cached light client data for a given block. This needs to be called ## when a block becomes unreachable due to finalization of a different fork. if dag.importLightClientData == ImportLightClientData.None: return dag.lightClientCache.data.del bid template lazy_header(name: untyped): untyped {.dirty.} = ## `createLightClientUpdates` helper to lazily load a known block header. var `name ptr`: ptr[BeaconBlockHeader] template `assign name`(target: var BeaconBlockHeader, bid: BlockId): untyped = if `name ptr` != nil: target = `name ptr`[] else: let bdata = dag.getExistingForkedBlock(bid).valueOr: return target = toBeaconBlockHeader(bdata) `name ptr` = addr target template lazy_data(name: untyped): untyped {.dirty.} = ## `createLightClientUpdates` helper to lazily load cached light client state. var `name` {.noinit.}: CachedLightClientData `name`.finalized_bid.slot = FAR_FUTURE_SLOT template `load name`(bid: BlockId): untyped = if `name`.finalized_bid.slot == FAR_FUTURE_SLOT: `name` = dag.getLightClientData(bid) proc createLightClientUpdates( dag: ChainDAGRef, state: HashedBeaconStateWithSyncCommittee, blck: TrustedSignedBeaconBlockWithSyncAggregate, parent_bid: BlockId) = ## Create `LightClientUpdate` and `OptimisticLightClientUpdate` instances for ## a given block and its post-state, and keep track of best / latest ones. ## Data about the parent block's post-state and its `finalized_checkpoint`'s ## block's post-state needs to be cached (`cacheLightClientData`) before ## calling this function. # Verify sync committee has sufficient participants template sync_aggregate(): auto = blck.message.body.sync_aggregate template sync_committee_bits(): auto = sync_aggregate.sync_committee_bits let num_active_participants = countOnes(sync_committee_bits).uint64 if num_active_participants < MIN_SYNC_COMMITTEE_PARTICIPANTS: return # Verify attested block (parent) is recent enough and that state is available let earliest_slot = dag.computeEarliestLightClientSlot attested_slot = parent_bid.slot if attested_slot < earliest_slot: return # Verify signature does not skip a sync committee period let signature_slot = blck.message.slot signature_period = signature_slot.sync_committee_period attested_period = attested_slot.sync_committee_period if signature_period > attested_period + 1: return # Update to new `OptimisticLightClientUpdate` if it attests to a later slot lazy_header(attested_header) template optimistic_update(): auto = dag.lightClientCache.optimisticUpdate if attested_slot > optimistic_update.attested_header.slot: optimistic_update.attested_header .assign_attested_header(parent_bid) optimistic_update.sync_aggregate = isomorphicCast[SyncAggregate](sync_aggregate) optimistic_update.fork_version = state.data.fork.current_version optimistic_update.is_signed_by_next_sync_committee = signature_period == attested_period + 1 if dag.onOptimisticLightClientUpdate != nil: dag.onOptimisticLightClientUpdate(optimistic_update) # Update to new latest `LightClientUpdate` if it attests to a later slot lazy_data(attested_data) lazy_data(finalized_data) lazy_header(finalized_header) template latest_update(): auto = dag.lightClientCache.latestUpdate if attested_slot > latest_update.attested_header.slot: latest_update.attested_header .assign_attested_header(parent_bid) latest_update.sync_aggregate = isomorphicCast[SyncAggregate](sync_aggregate) latest_update.fork_version = state.data.fork.current_version load_attested_data(parent_bid) let finalized_slot = attested_data.finalized_bid.slot if finalized_slot + UPDATE_TIMEOUT < attested_slot or finalized_slot < earliest_slot or attested_data.finalized_bid.root.isZero: latest_update.finalized_header = BeaconBlockHeader() latest_update.finality_branch.fill(Eth2Digest()) if signature_period == attested_period + 1: latest_update.next_sync_committee = SyncCommittee() latest_update.next_sync_committee_branch.fill(Eth2Digest()) else: latest_update.next_sync_committee = state.data.next_sync_committee latest_update.next_sync_committee_branch = attested_data.next_sync_committee_branch else: latest_update.finalized_header .assign_finalized_header(attested_data.finalized_bid) latest_update.finality_branch = attested_data.finality_branch if signature_period == finalized_slot.sync_committee_period + 1: latest_update.next_sync_committee = SyncCommittee() latest_update.next_sync_committee_branch.fill(Eth2Digest()) else: load_finalized_data(attested_data.finalized_bid) latest_update.next_sync_committee = state.data.next_sync_committee latest_update.next_sync_committee_branch = finalized_data.next_sync_committee_branch # Update best `LightClientUpdate` for current period if it improved if signature_period == attested_period: let isNextSyncCommitteeFinalized = signature_period.start_slot <= dag.finalizedHead.slot var best_update = if isNextSyncCommitteeFinalized: dag.lightClientCache.bestUpdates.getOrDefault(signature_period) else: let key = (signature_period, state.syncCommitteeRoot) dag.lightClientCache.pendingBestUpdates.getOrDefault(key) type Verdict = enum unknown new_update_is_worse new_update_is_better var verdict = unknown # If no best update has been recorded, new update is better template best_sync_aggregate(): auto = best_update.sync_aggregate let best_num_active_participants = countOnes(best_sync_aggregate.sync_committee_bits).uint64 if best_num_active_participants < MIN_SYNC_COMMITTEE_PARTICIPANTS: verdict = new_update_is_better else: # If finality changes, the finalized update is better template finalized_period_at_signature(): auto = state.data.finalized_checkpoint.epoch.sync_committee_period template best_attested_slot(): auto = best_update.attested_header.slot if best_update.finality_branch.isZeroMemory: if (attested_slot > dag.finalizedHead.slot or attested_slot > best_attested_slot) and signature_period == finalized_period_at_signature: load_attested_data(parent_bid) let finalized_slot = attested_data.finalized_bid.slot if signature_period == finalized_slot.sync_committee_period and finalized_slot >= earliest_slot: verdict = new_update_is_better elif attested_slot > dag.finalizedHead.slot or attested_slot < best_attested_slot: if signature_period == finalized_period_at_signature: load_attested_data(parent_bid) let finalized_slot = attested_data.finalized_bid.slot if signature_period != finalized_slot.sync_committee_period or finalized_slot < earliest_slot: verdict = new_update_is_worse else: verdict = new_update_is_worse if verdict == unknown: # If participation changes, higher participation is better if num_active_participants < best_num_active_participants: verdict = new_update_is_worse elif num_active_participants > best_num_active_participants: verdict = new_update_is_better else: # Older updates are better if attested_slot >= best_attested_slot: verdict = new_update_is_worse else: verdict = new_update_is_better if verdict == new_update_is_better: best_update.attested_header .assign_attested_header(parent_bid) best_update.sync_aggregate = isomorphicCast[SyncAggregate](sync_aggregate) best_update.fork_version = state.data.fork.current_version load_attested_data(parent_bid) let finalized_slot = attested_data.finalized_bid.slot if signature_period != finalized_slot.sync_committee_period or finalized_slot < earliest_slot: best_update.finalized_header = BeaconBlockHeader() best_update.finality_branch.fill(Eth2Digest()) best_update.next_sync_committee = state.data.next_sync_committee best_update.next_sync_committee_branch = attested_data.next_sync_committee_branch else: best_update.finalized_header .assign_finalized_header(attested_data.finalized_bid) best_update.finality_branch = attested_data.finality_branch load_finalized_data(attested_data.finalized_bid) best_update.next_sync_committee = state.data.next_sync_committee best_update.next_sync_committee_branch = finalized_data.next_sync_committee_branch if isNextSyncCommitteeFinalized: dag.lightClientCache.bestUpdates[signature_period] = best_update debug "Best update for period improved", period = signature_period, update = best_update else: let key = (signature_period, state.syncCommitteeRoot) dag.lightClientCache.pendingBestUpdates[key] = best_update debug "Best update for period improved", period = key, update = best_update proc processNewBlockForLightClient*( dag: ChainDAGRef, state: ForkedHashedBeaconState, signedBlock: ForkyTrustedSignedBeaconBlock, parentBid: BlockId) = ## Update light client data with information from a new block. if dag.importLightClientData == ImportLightClientData.None: return if signedBlock.message.slot < dag.computeEarliestLightClientSlot: return when signedBlock is bellatrix.TrustedSignedBeaconBlock: dag.cacheLightClientData(state.bellatrixData, signedBlock) dag.createLightClientUpdates(state.bellatrixData, signedBlock, parentBid) elif signedBlock is altair.TrustedSignedBeaconBlock: dag.cacheLightClientData(state.altairData, signedBlock) dag.createLightClientUpdates(state.altairData, signedBlock, parentBid) elif signedBlock is phase0.TrustedSignedBeaconBlock: raiseAssert "Unreachable" # These cannot occur after `earliestSlot` else: {.error: "Unreachable".} proc processHeadChangeForLightClient*(dag: ChainDAGRef) = ## Update light client data to account for a new head block. ## Note that `dag.finalizedHead` is not yet updated when this is called. if dag.importLightClientData == ImportLightClientData.None: return if dag.head.slot < dag.computeEarliestLightClientSlot: return let headPeriod = dag.head.slot.sync_committee_period if headPeriod.start_slot > dag.finalizedHead.slot: let finalizedPeriod = dag.finalizedHead.slot.sync_committee_period if headPeriod > finalizedPeriod + 1: var tmpState = assignClone(dag.headState) for period in finalizedPeriod + 1 ..< headPeriod: let syncCommitteeRoot = dag.syncCommitteeRootForPeriod(tmpState[], period).valueOr: continue key = (period, syncCommitteeRoot) dag.lightClientCache.bestUpdates[period] = dag.lightClientCache.pendingBestUpdates.getOrDefault(key) withState(dag.headState): when stateFork >= BeaconStateFork.Altair: let key = (headPeriod, state.syncCommitteeRoot) dag.lightClientCache.bestUpdates[headPeriod] = dag.lightClientCache.pendingBestUpdates.getOrDefault(key) else: raiseAssert "Unreachable" proc processFinalizationForLightClient*(dag: ChainDAGRef) = ## Prune cached data that is no longer useful for creating future ## `LightClientUpdate` and `LightClientBootstrap` instances. ## This needs to be called whenever `finalized_checkpoint` changes. if dag.importLightClientData == ImportLightClientData.None: return let earliestSlot = dag.computeEarliestLightClientSlot finalizedSlot = dag.finalizedHead.slot if finalizedSlot < earliestSlot: return # Keep track of latest four finalized checkpoints let lastIndex = dag.lightClientCache.lastCheckpointIndex lastCheckpoint = addr dag.lightClientCache.latestCheckpoints[lastIndex] if dag.finalizedHead.slot.epoch != lastCheckpoint.epoch or dag.finalizedHead.blck.root != lastCheckpoint.root: let nextIndex = (lastIndex + 1) mod dag.lightClientCache.latestCheckpoints.len nextCheckpoint = addr dag.lightClientCache.latestCheckpoints[nextIndex] nextCheckpoint[].epoch = dag.finalizedHead.slot.epoch nextCheckpoint[].root = dag.finalizedHead.blck.root dag.lightClientCache.lastCheckpointIndex = nextIndex # Cache `LightClientBootstrap` for newly finalized epoch boundary blocks. # Epoch boundary blocks are the block for the initial slot of an epoch, # or the most recent block if no block was proposed at that slot let lowSlot = max(lastCheckpoint[].epoch.start_slot, earliestSlot) var boundarySlot = dag.finalizedHead.slot while boundarySlot >= lowSlot: let bsi = dag.getExistingBlockIdAtSlot(boundarySlot).valueOr: break bid = bsi.bid if bid.slot >= lowSlot: dag.lightClientCache.bootstrap[bid.slot] = CachedLightClientBootstrap( current_sync_committee_branch: dag.getLightClientData(bid).current_sync_committee_branch) boundarySlot = bid.slot.nextEpochBoundarySlot if boundarySlot < SLOTS_PER_EPOCH: break boundarySlot -= SLOTS_PER_EPOCH # Prune light client data that is no longer relevant, # i.e., can no longer be referred to by future updates, or is too old var bidsToDelete: seq[BlockId] for bid, data in dag.lightClientCache.data: if bid.slot >= earliestSlot: if bid.slot >= finalizedSlot: continue if dag.lightClientCache.latestCheckpoints.anyIt(bid.root == it.root): continue bidsToDelete.add bid for bid in bidsToDelete: dag.lightClientCache.data.del bid # Prune bootstrap data that is no longer relevant var slotsToDelete: seq[Slot] for slot in dag.lightClientCache.bootstrap.keys: if slot < earliestSlot: slotsToDelete.add slot for slot in slotsToDelete: dag.lightClientCache.bootstrap.del slot # Prune best `LightClientUpdate` that are no longer relevant let earliestPeriod = earliestSlot.sync_committee_period var periodsToDelete: seq[SyncCommitteePeriod] for period in dag.lightClientCache.bestUpdates.keys: if period < earliestPeriod: periodsToDelete.add period for period in periodsToDelete: dag.lightClientCache.bestUpdates.del period # Prune best `LightClientUpdate` referring to non-finalized sync committees # that are no longer relevant, i.e., orphaned or too old let finalizedPeriod = finalizedSlot.sync_committee_period var keysToDelete: seq[(SyncCommitteePeriod, Eth2Digest)] for (period, committeeRoot) in dag.lightClientCache.pendingBestUpdates.keys: if period <= finalizedPeriod: keysToDelete.add (period, committeeRoot) for key in keysToDelete: dag.lightClientCache.pendingBestUpdates.del key proc initBestLightClientUpdateForPeriod( dag: ChainDAGRef, period: SyncCommitteePeriod) = ## Compute and cache the `LightClientUpdate` with the most sync committee ## signatures (i.e., participation) for a given sync committee period. let periodStartSlot = period.start_slot if periodStartSlot > dag.finalizedHead.slot: return let earliestSlot = dag.computeEarliestLightClientSlot periodEndSlot = periodStartSlot + SLOTS_PER_SYNC_COMMITTEE_PERIOD - 1 if periodEndSlot < earliestSlot: return if dag.lightClientCache.bestUpdates.hasKey(period): return let startTick = Moment.now() debug "Computing best update for period", period proc logBestUpdate(endTick = Moment.now()) = # Using a helper function reduces code size as the `defer` beneath is # replicated on every `return`, and the log statement allocates another # copy of the arguments on the stack for each instantiation (~1 MB stack!) debug "Best update for period computed", period, update = dag.lightClientCache.bestUpdates.getOrDefault(period), computeDur = endTick - startTick defer: logBestUpdate() proc maxParticipantsBlock( dag: ChainDAGRef, highBid: BlockId, lowSlot: Slot): Option[BlockId] = ## Determine the earliest block with most sync committee signatures among ## ancestors of `highBid` with at least `lowSlot` as parent block slot. ## Return `none` if no block with `MIN_SYNC_COMMITTEE_PARTICIPANTS` exists. var maxParticipants = 0 maxBid: Option[BlockId] bid = highBid while true: let parentBid = dag.parent(bid).valueOr: break if parentBid.slot < lowSlot: break let bdata = dag.getExistingForkedBlock(bid).valueOr: break numParticipants = withBlck(bdata): when stateFork >= BeaconStateFork.Altair: countOnes(blck.message.body.sync_aggregate.sync_committee_bits) else: raiseAssert "Unreachable" if numParticipants >= maxParticipants: maxParticipants = numParticipants maxBid = some bid bid = parentBid if maxParticipants < MIN_SYNC_COMMITTEE_PARTICIPANTS: maxBid.reset() maxBid # Determine the block in the period with highest sync committee participation let lowSlot = max(periodStartSlot, earliestSlot) highSlot = min(periodEndSlot, dag.finalizedHead.blck.slot) highBsi = dag.getExistingBlockIdAtSlot(highSlot).valueOr: return highBid = highBsi.bid bestNonFinalizedBid = dag.maxParticipantsBlock(highBid, lowSlot) if bestNonFinalizedBid.isNone: dag.lightClientCache.bestUpdates[period] = default(altair.LightClientUpdate) return # The block with highest participation may refer to a `finalized_checkpoint` # in a different sync committee period. If that is the case, search for a # later block with a `finalized_checkpoint` within the given sync committee # period, despite it having a lower sync committee participation var tmpState = assignClone(dag.headState) bestFinalizedBid = bestNonFinalizedBid finalizedBid {.noinit.}: BlockId bestFinalizedHasCheckpointInPeriod = false while bestFinalizedBid.isSome: defer: if not bestFinalizedHasCheckpointInPeriod: let newLowSlot = bestFinalizedBid.get.slot + 1 bestFinalizedBid = dag.maxParticipantsBlock(highBid, newLowSlot) let attestedBid = dag.existingParent(bestFinalizedBid.get).valueOr: continue finalizedEpoch = block: dag.withUpdatedExistingState(tmpState[], attestedBid.atSlot) do: withState(state): when stateFork >= BeaconStateFork.Altair: state.data.finalized_checkpoint.epoch else: raiseAssert "Unreachable" do: continue finalizedSlot = finalizedEpoch.start_slot if finalizedSlot >= lowSlot: let finalizedBsi = dag.getExistingBlockIdAtSlot(finalizedSlot).valueOr: continue finalizedBid = finalizedBsi.bid if finalizedBid.slot >= lowSlot: bestFinalizedHasCheckpointInPeriod = true break # If a finalized block has been found within the sync commitee period, # create a `LightClientUpdate` for that one. Otherwise, create a non-finalized # `LightClientUpdate` var update {.noinit.}: LightClientUpdate if bestFinalizedBid.isSome: # Fill data from attested block let attestedBid = dag.existingParent(bestFinalizedBid.get).valueOr: return dag.withUpdatedExistingState(tmpState[], attestedBid.atSlot) do: let bdata = dag.getExistingForkedBlock(bid).valueOr: return withStateAndBlck(state, bdata): when stateFork >= BeaconStateFork.Altair: update.attested_header = blck.toBeaconBlockHeader state.data.build_proof( altair.FINALIZED_ROOT_INDEX, update.finality_branch) else: raiseAssert "Unreachable" do: return # Fill data from signature block let bdata = dag.getExistingForkedBlock(bestFinalizedBid.get).valueOr: return withBlck(bdata): when stateFork >= BeaconStateFork.Altair: update.sync_aggregate = isomorphicCast[SyncAggregate](blck.message.body.sync_aggregate) else: raiseAssert "Unreachable" update.fork_version = dag.cfg.forkAtEpoch(bestFinalizedBid.get.slot.epoch).current_version # Fill data from finalized block dag.withUpdatedExistingState(tmpState[], finalizedBid.atSlot) do: let bdata = dag.getExistingForkedBlock(bid).valueOr: return withStateAndBlck(state, bdata): when stateFork >= BeaconStateFork.Altair: update.next_sync_committee = state.data.next_sync_committee state.data.build_proof( altair.NEXT_SYNC_COMMITTEE_INDEX, update.next_sync_committee_branch) update.finalized_header = blck.toBeaconBlockHeader else: raiseAssert "Unreachable" do: return else: # Fill data from attested block let attestedBid = dag.existingParent(bestNonFinalizedBid.get).valueOr: return dag.withUpdatedExistingState(tmpState[], attestedBid.atSlot) do: let bdata = dag.getExistingForkedBlock(bid).valueOr: return withStateAndBlck(state, bdata): when stateFork >= BeaconStateFork.Altair: update.attested_header = blck.toBeaconBlockHeader update.next_sync_committee = state.data.next_sync_committee state.data.build_proof( altair.NEXT_SYNC_COMMITTEE_INDEX, update.next_sync_committee_branch) update.finalized_header = BeaconBlockHeader() update.finality_branch.fill(Eth2Digest()) else: raiseAssert "Unreachable" do: raiseAssert "Unreachable" # Fill data from signature block let bdata = dag.getExistingForkedBlock(bestNonFinalizedBid.get).valueOr: return withBlck(bdata): when stateFork >= BeaconStateFork.Altair: update.sync_aggregate = isomorphicCast[SyncAggregate](blck.message.body.sync_aggregate) else: raiseAssert "Unreachable" update.fork_version = dag.cfg.forkAtEpoch(bestNonFinalizedBid.get.slot.epoch).current_version dag.lightClientCache.bestUpdates[period] = update proc initLightClientBootstrapForPeriod( dag: ChainDAGRef, period: SyncCommitteePeriod) = ## Compute and cache `LightClientBootstrap` data for all epoch boundary blocks ## within a given sync committee period. let periodStartSlot = period.start_slot if periodStartSlot > dag.finalizedHead.slot: return let earliestSlot = dag.computeEarliestLightClientSlot periodEndSlot = periodStartSlot + SLOTS_PER_SYNC_COMMITTEE_PERIOD - 1 if periodEndSlot < earliestSlot: return let startTick = Moment.now() debug "Caching bootstrap data for period", period defer: let endTick = Moment.now() debug "Bootstrap data for period cached", period, cacheDur = endTick - startTick let lowSlot = max(periodStartSlot, earliestSlot) highSlot = min(periodEndSlot, dag.finalizedHead.blck.slot) lowBoundarySlot = lowSlot.nextEpochBoundarySlot highBoundarySlot = highSlot.nextEpochBoundarySlot var tmpState = assignClone(dag.headState) tmpCache: StateCache nextBoundarySlot = lowBoundarySlot while nextBoundarySlot <= highBoundarySlot: defer: nextBoundarySlot += SLOTS_PER_EPOCH let bsi = dag.getExistingBlockIdAtSlot(nextBoundarySlot).valueOr: continue bid = bsi.bid boundarySlot = bid.slot.nextEpochBoundarySlot if boundarySlot == nextBoundarySlot and bid.slot >= lowSlot and bid.slot <= highSlot and not dag.lightClientCache.bootstrap.hasKey(bid.slot): var cachedBootstrap {.noinit.}: CachedLightClientBootstrap if not dag.updateExistingState( tmpState[], bid.atSlot, save = false, tmpCache): continue withStateVars(tmpState[]): withState(state): when stateFork >= BeaconStateFork.Altair: state.data.build_proof( altair.CURRENT_SYNC_COMMITTEE_INDEX, cachedBootstrap.current_sync_committee_branch) else: raiseAssert "Unreachable" dag.lightClientCache.bootstrap[bid.slot] = cachedBootstrap proc initLightClientCache*(dag: ChainDAGRef) = ## Initialize cached light client data if dag.importLightClientData == ImportLightClientData.None: return dag.lightClientCache.importTailSlot = dag.tail.slot if dag.importLightClientData == ImportLightClientData.OnlyNew: dag.lightClientCache.importTailSlot = dag.head.slot var earliestSlot = dag.computeEarliestLightClientSlot if dag.head.slot < earliestSlot: return let finalizedSlot = dag.finalizedHead.slot finalizedPeriod = finalizedSlot.sync_committee_period dag.initBestLightClientUpdateForPeriod(finalizedPeriod) let lightClientStartTick = Moment.now() debug "Initializing cached light client data" template handleUnexpectedError(buggedBid: BlockId) = # Light client data is expected to be available from `earliestSlot` onward. # If there is an error, adjust `importTailSlot` to avoid failed lookups of # cached light client data. For new blocks / states, the caches can always # be updated incrementally, because those blocks / states are passed in # directly. It is only historical blocks (or sync committees) that depend # on a potentially corrupted database. doAssert buggedBid.slot > dag.lightClientCache.importTailSlot dag.lightClientCache.importTailSlot = buggedBid.slot + 1 earliestSlot = dag.computeEarliestLightClientSlot # Build lists of block to process. # As it is slow to load states in descending order, # first build a todo list, then process them in ascending order let lowSlot = max(finalizedSlot, earliestSlot) var blocksBetween = newSeqOfCap[BlockId](dag.head.slot - lowSlot + 1) bid = dag.head.bid while bid.slot > lowSlot: blocksBetween.add bid bid = dag.existingParent(bid).valueOr: handleUnexpectedError(bid) break if bid.slot >= earliestSlot: # Add the finalized head itself (`== lowSlot`, or the last block before it) blocksBetween.add bid # Process blocks (reuses `dag.headState`, but restores it to the current head) var tmpState = assignClone(dag.headState) tmpCache, cache: StateCache oldCheckpoint: Checkpoint cpIndex = 0 for i in countdown(blocksBetween.high, blocksBetween.low): bid = blocksBetween[i] if not dag.updateExistingState( dag.headState, bid.atSlot, save = false, cache): handleUnexpectedError(bid) continue withStateVars(dag.headState): let bdata = dag.getExistingForkedBlock(bid).valueOr: handleUnexpectedError(bid) continue withStateAndBlck(state, bdata): when stateFork >= BeaconStateFork.Altair: # Cache data for `LightClientUpdate` of descendant blocks dag.cacheLightClientData(state, blck) # Cache data for the block's `finalized_checkpoint`. # The `finalized_checkpoint` may refer to: # 1. `finalizedHead.blck -> finalized_checkpoint` # This may happen when there were skipped slots. # 2. `finalizedHead -> finalized_checkpoint` # 3. One epoch boundary that got justified then finalized # between `finalizedHead -> finalized_checkpoint` # and `finalizedHead` # 4. `finalizedHead` let checkpoint = state.data.finalized_checkpoint if checkpoint != oldCheckpoint: oldCheckpoint = checkpoint doAssert cpIndex < dag.lightClientCache.latestCheckpoints.len dag.lightClientCache.latestCheckpoints[cpIndex] = checkpoint dag.lightClientCache.lastCheckpointIndex = cpIndex inc cpIndex # Save new checkpoint block using `tmpState` (avoid replay after it) # Note that light client finality proofs refer to checkpoint blocks # at their original slot, without advancing to an epoch boundary. # This is because light clients are unable to advance slots. if checkpoint.root != dag.finalizedHead.blck.root: let cpSlot = checkpoint.epoch.start_slot if cpSlot >= earliestSlot: let cpBsi = dag.getExistingBlockIdAtSlot(cpSlot).valueOr: handleUnexpectedError(bid) continue cpBid = cpBsi.bid if cpBid.slot >= earliestSlot: assert cpBid.root == checkpoint.root if not dag.updateExistingState( tmpState[], cpBid.atSlot, save = false, tmpCache): handleUnexpectedError(bid) continue withStateVars(tmpState[]): let bdata = dag.getExistingForkedBlock(cpBid).valueOr: handleUnexpectedError(bid) continue withStateAndBlck(state, bdata): when stateFork >= BeaconStateFork.Altair: dag.cacheLightClientData(state, blck) else: raiseAssert "Unreachable" # Create `LightClientUpdate` for non-finalized blocks. if bid.slot > finalizedSlot: let parentBid = dag.existingParent(bid).valueOr: handleUnexpectedError(bid) continue dag.createLightClientUpdates(state, blck, parentBid) else: raiseAssert "Unreachable" let lightClientEndTick = Moment.now() debug "Initialized cached light client data", initDur = lightClientEndTick - lightClientStartTick # Import historic data if dag.importLightClientData == ImportLightClientData.Full: let earliestPeriod = earliestSlot.sync_committee_period for period in earliestPeriod ..< finalizedPeriod: dag.initBestLightClientUpdateForPeriod(period) dag.initLightClientBootstrapForPeriod(period) dag.initLightClientBootstrapForPeriod(finalizedPeriod) proc getBestLightClientUpdateForPeriod*( dag: ChainDAGRef, period: SyncCommitteePeriod): Option[altair.LightClientUpdate] = if not dag.serveLightClientData: return none(altair.LightClientUpdate) if dag.importLightClientData == ImportLightClientData.OnDemand: dag.initBestLightClientUpdateForPeriod(period) result = some(dag.lightClientCache.bestUpdates.getOrDefault(period)) let numParticipants = countOnes(result.get.sync_aggregate.sync_committee_bits) if numParticipants < MIN_SYNC_COMMITTEE_PARTICIPANTS: result = none(altair.LightClientUpdate) proc getLatestLightClientUpdate*( dag: ChainDAGRef): Option[altair.LightClientUpdate] = if not dag.serveLightClientData: return none(altair.LightClientUpdate) result = some(dag.lightClientCache.latestUpdate) let numParticipants = countOnes(result.get.sync_aggregate.sync_committee_bits) if numParticipants < MIN_SYNC_COMMITTEE_PARTICIPANTS: result = none(altair.LightClientUpdate) proc getOptimisticLightClientUpdate*( dag: ChainDAGRef): Option[OptimisticLightClientUpdate] = if not dag.serveLightClientData: return none(OptimisticLightClientUpdate) result = some(dag.lightClientCache.optimisticUpdate) let numParticipants = countOnes(result.get.sync_aggregate.sync_committee_bits) if numParticipants < MIN_SYNC_COMMITTEE_PARTICIPANTS: result = none(OptimisticLightClientUpdate) proc getLightClientBootstrap*( dag: ChainDAGRef, blockRoot: Eth2Digest): Opt[altair.LightClientBootstrap] = if not dag.serveLightClientData: return err() let bdata = dag.getForkedBlock(blockRoot).valueOr: debug "Bootstrap unavailable: Block not found", blockRoot return err() withBlck(bdata): let slot = blck.message.slot when stateFork >= BeaconStateFork.Altair: let earliestSlot = dag.computeEarliestLightClientSlot if slot < earliestSlot: debug "Bootstrap unavailable: Block too old", slot return err() if slot > dag.finalizedHead.blck.slot: debug "Bootstrap unavailable: Not finalized", blockRoot return err() var cachedBootstrap = dag.lightClientCache.bootstrap.getOrDefault(slot) if cachedBootstrap.current_sync_committee_branch.isZeroMemory: if dag.importLightClientData == ImportLightClientData.OnDemand: let bsi = ? dag.getExistingBlockIdAtSlot(slot) var tmpState = assignClone(dag.headState) dag.withUpdatedExistingState(tmpState[], bsi) do: withState(state): when stateFork >= BeaconStateFork.Altair: state.data.build_proof( altair.CURRENT_SYNC_COMMITTEE_INDEX, cachedBootstrap.current_sync_committee_branch) else: raiseAssert "Unreachable" do: return err() dag.lightClientCache.bootstrap[slot] = cachedBootstrap else: debug "Bootstrap unavailable: Data not cached", slot return err() let period = slot.sync_committee_period var tmpState = assignClone(dag.headState) var bootstrap {.noinit.}: altair.LightClientBootstrap bootstrap.header = blck.toBeaconBlockHeader bootstrap.current_sync_committee = ? dag.currentSyncCommitteeForPeriod(tmpState[], period) bootstrap.current_sync_committee_branch = cachedBootstrap.current_sync_committee_branch return ok bootstrap else: debug "Bootstrap unavailable: Block before Altair", slot return err()