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nimbus-eth2/beacon_chain/gossip_processing/light_client_processor.nim

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# beacon_chain
# Copyright (c) 2022-2023 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: [].}
import
chronos, metrics,
../spec/light_client_sync,
../consensus_object_pools/block_pools_types,
".."/[beacon_clock, sszdump],
"."/[eth2_processor, gossip_validation]
export sszdump, eth2_processor, gossip_validation
logScope: topics = "gossip_lc"
# Light Client Processor
# ------------------------------------------------------------------------------
# The light client processor handles received light client objects
declareHistogram light_client_store_object_duration_seconds,
"storeObject() duration", buckets = [0.25, 0.5, 1, 2, 4, 8, Inf]
type
Nothing = object
GetTrustedBlockRootCallback* =
proc(): Option[Eth2Digest] {.gcsafe, raises: [].}
VoidCallback* =
proc() {.gcsafe, raises: [].}
ValueObserver[V] =
proc(v: V) {.gcsafe, raises: [].}
BootstrapObserver* =
ValueObserver[ForkedLightClientBootstrap]
UpdateObserver* =
ValueObserver[ForkedLightClientUpdate]
FinalityUpdateObserver* =
ValueObserver[ForkedLightClientFinalityUpdate]
OptimisticUpdateObserver* =
ValueObserver[ForkedLightClientOptimisticUpdate]
LightClientFinalizationMode* {.pure.} = enum
Strict
## Only finalize light client data that:
## - has been signed by a supermajority (2/3) of the sync committee
## - has a valid finality proof
##
## Optimizes for security, but may become stuck if there is any of:
## - non-finality for an entire sync committee period
## - low sync committee participation for an entire sync committee period
## Such periods need to be covered by an out-of-band syncing mechanism.
##
## Note that a compromised supermajority of the sync committee is able to
## sign arbitrary light client data, even after being slashed. The light
## client cannot validate the slashing status of sync committee members.
## Likewise, voluntarily exited validators may sign bad light client data
## for the sync committee periods in which they used to be selected.
Optimistic
## Attempt to finalize light client data not satisfying strict conditions
## if there is no progress for an extended period of time and if there are
## repeated messages indicating that it is the best available data on the
## network for the affected time period.
##
## Optimizes for availability of recent data, but may end up on incorrect
## forks if run in a hostile network environment (no honest peers), or if
## the low sync committee participation is being exploited by bad actors.
LightClientProcessor* = object
## This manages the processing of received light client objects
##
## from:
## - Gossip:
## - `LightClientFinalityUpdate`
## - `LightClientOptimisticUpdate`
## - `LightClientManager`:
## - `GetLightClientBootstrap`
## - `LightClientUpdatesByRange`
## - `GetLightClientFinalityUpdate`
## - `GetLightClientOptimisticUpdate`
##
## are then verified and added to:
## - `LightClientStore`
# Config
# ----------------------------------------------------------------
dumpEnabled: bool
dumpDirInvalid: string
dumpDirIncoming: string
strictVerification: bool
# Consumer
# ----------------------------------------------------------------
store: ref ForkedLightClientStore
getBeaconTime: GetBeaconTimeFn
getTrustedBlockRoot: GetTrustedBlockRootCallback
onStoreInitialized, onFinalizedHeader, onOptimisticHeader: VoidCallback
bootstrapObserver: BootstrapObserver
updateObserver: UpdateObserver
finalityUpdateObserver: FinalityUpdateObserver
optimisticUpdateObserver: OptimisticUpdateObserver
cfg: RuntimeConfig
genesis_validators_root: Eth2Digest
case finalizationMode: LightClientFinalizationMode
of LightClientFinalizationMode.Strict:
discard
of LightClientFinalizationMode.Optimistic:
lastProgressTick: BeaconTime # Moment when last update made progress
lastDuplicateTick: BeaconTime # Moment when last duplicate update received
numDupsSinceProgress: int # Number of duplicates since last progress
latestFinalityUpdate: ForkedLightClientOptimisticUpdate
const
# These constants have been chosen empirically and are not backed by spec
duplicateRateLimit = chronos.seconds(5) # Rate limit for counting duplicates
duplicateCountDelay = chronos.minutes(15) # Delay to start counting duplicates
minForceUpdateDelay = chronos.minutes(30) # Minimum delay until forced-update
minForceUpdateDuplicates = 100 # Minimum duplicates until forced-update
# Initialization
# ------------------------------------------------------------------------------
proc new*(
T: type LightClientProcessor,
dumpEnabled: bool,
dumpDirInvalid, dumpDirIncoming: string,
cfg: RuntimeConfig,
genesis_validators_root: Eth2Digest,
finalizationMode: LightClientFinalizationMode,
store: ref ForkedLightClientStore,
getBeaconTime: GetBeaconTimeFn,
getTrustedBlockRoot: GetTrustedBlockRootCallback,
onStoreInitialized: VoidCallback = nil,
onFinalizedHeader: VoidCallback = nil,
onOptimisticHeader: VoidCallback = nil,
bootstrapObserver: BootstrapObserver = nil,
updateObserver: UpdateObserver = nil,
finalityUpdateObserver: FinalityUpdateObserver = nil,
optimisticUpdateObserver: OptimisticUpdateObserver = nil,
strictVerification = false
): ref LightClientProcessor =
(ref LightClientProcessor)(
dumpEnabled: dumpEnabled,
dumpDirInvalid: dumpDirInvalid,
dumpDirIncoming: dumpDirIncoming,
strictVerification: strictVerification,
store: store,
getBeaconTime: getBeaconTime,
getTrustedBlockRoot: getTrustedBlockRoot,
onStoreInitialized: onStoreInitialized,
onFinalizedHeader: onFinalizedHeader,
onOptimisticHeader: onOptimisticHeader,
bootstrapObserver: bootstrapObserver,
updateObserver: updateObserver,
finalityUpdateObserver: finalityUpdateObserver,
optimisticUpdateObserver: optimisticUpdateObserver,
cfg: cfg,
genesis_validators_root: genesis_validators_root,
finalizationMode: finalizationMode)
# Storage
# ------------------------------------------------------------------------------
proc dumpInvalidObject(
self: LightClientProcessor,
obj: SomeForkyLightClientObject) =
if self.dumpEnabled:
dump(self.dumpDirInvalid, obj)
proc dumpObject[T](
self: LightClientProcessor,
obj: SomeForkyLightClientObject,
res: Result[T, VerifierError]) =
if self.dumpEnabled and res.isErr:
case res.error
of VerifierError.Invalid:
self.dumpInvalidObject(obj)
of VerifierError.MissingParent:
dump(self.dumpDirIncoming, obj)
else:
discard
proc tryForceUpdate(
self: var LightClientProcessor,
wallTime: BeaconTime) =
## Try to force-update to the next sync committee period.
let wallSlot = wallTime.slotOrZero()
doAssert self.finalizationMode == LightClientFinalizationMode.Optimistic
withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
case forkyStore.process_light_client_store_force_update(wallSlot)
of NoUpdate:
discard
of DidUpdateWithoutSupermajority:
warn "Light client force-updated without supermajority",
finalizedSlot = forkyStore.finalized_header.beacon.slot,
optimisticSlot = forkyStore.optimistic_header.beacon.slot
of DidUpdateWithoutFinality:
warn "Light client force-updated without finality proof",
finalizedSlot = forkyStore.finalized_header.beacon.slot,
optimisticSlot = forkyStore.optimistic_header.beacon.slot
proc processObject(
self: var LightClientProcessor,
obj: SomeForkedLightClientObject,
wallTime: BeaconTime): Result[void, VerifierError] =
let
wallSlot = wallTime.slotOrZero()
res = withForkyObject(obj):
when lcDataFork > LightClientDataFork.None:
when forkyObject is ForkyLightClientBootstrap:
if self.store[].kind > LightClientDataFork.None:
err(VerifierError.Duplicate)
else:
let trustedBlockRoot = self.getTrustedBlockRoot()
if trustedBlockRoot.isNone:
err(VerifierError.MissingParent)
else:
let initRes = initialize_light_client_store(
trustedBlockRoot.get, forkyObject, self.cfg)
if initRes.isErr:
err(initRes.error)
else:
self.store[] = ForkedLightClientStore.init(initRes.get)
ok()
elif forkyObject is SomeForkyLightClientUpdate:
if self.store[].kind == LightClientDataFork.None:
err(VerifierError.MissingParent)
else:
if lcDataFork > self.store[].kind:
info "Upgrading light client",
oldFork = self.store[].kind, newFork = lcDataFork
self.store[].migrateToDataFork(lcDataFork)
withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
let upgradedObject = obj.migratingToDataFork(lcDataFork)
process_light_client_update(
forkyStore, upgradedObject.forky(lcDataFork), wallSlot,
self.cfg, self.genesis_validators_root)
else: raiseAssert "Unreachable"
else:
err(VerifierError.Invalid)
withForkyObject(obj):
when lcDataFork > LightClientDataFork.None:
self.dumpObject(forkyObject, res)
if res.isErr:
when obj is ForkedLightClientUpdate:
if self.finalizationMode == LightClientFinalizationMode.Optimistic and
obj.kind <= self.store[].kind:
withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
if forkyStore.best_valid_update.isSome:
# `best_valid_update` is set when supermajority / finality proof
# is unavailable. In that case, we will wait for a better update.
# If none is made available within reasonable time, light client
# is force-updated with best known data to ensure sync progress.
case res.error
of VerifierError.Duplicate:
if wallTime >= self.lastDuplicateTick + duplicateRateLimit:
if self.numDupsSinceProgress < minForceUpdateDuplicates:
let upgradedObj = obj.migratingToDataFork(lcDataFork)
if upgradedObj.forky(lcDataFork).matches(
forkyStore.best_valid_update.get):
self.lastDuplicateTick = wallTime
inc self.numDupsSinceProgress
if self.numDupsSinceProgress >= minForceUpdateDuplicates and
wallTime >= self.lastProgressTick + minForceUpdateDelay:
self.tryForceUpdate(wallTime)
self.lastProgressTick = wallTime
self.lastDuplicateTick = wallTime + duplicateCountDelay
self.numDupsSinceProgress = 0
else: discard
return res
when obj is ForkedLightClientBootstrap | ForkedLightClientUpdate:
if self.finalizationMode == LightClientFinalizationMode.Optimistic:
self.lastProgressTick = wallTime
self.lastDuplicateTick = wallTime + duplicateCountDelay
self.numDupsSinceProgress = 0
res
template withReportedProgress(
obj: SomeForkedLightClientObject | Nothing, body: untyped): bool =
block:
let
oldIsInitialized = self.store[].kind > LightClientDataFork.None
oldNextCommitteeKnown = withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
forkyStore.is_next_sync_committee_known
else:
false
var
oldFinalized = withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
ForkedLightClientHeader.init(forkyStore.finalized_header)
else:
default(ForkedLightClientHeader)
oldOptimistic = withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
ForkedLightClientHeader.init(forkyStore.optimistic_header)
else:
default(ForkedLightClientHeader)
body
var
didProgress = false
didSignificantProgress = false
let newIsInitialized = self.store[].kind > LightClientDataFork.None
if newIsInitialized > oldIsInitialized:
didProgress = true
didSignificantProgress = true
if self.onStoreInitialized != nil:
self.onStoreInitialized()
self.onStoreInitialized = nil
withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
if oldOptimistic.kind <= lcDataFork:
oldOptimistic.migrateToDataFork(lcDataFork)
if forkyStore.optimistic_header != oldOptimistic.forky(lcDataFork):
didProgress = true
when obj isnot SomeForkedLightClientUpdateWithFinality:
didSignificantProgress = true
if self.onOptimisticHeader != nil:
self.onOptimisticHeader()
if oldFinalized.kind <= lcDataFork:
oldFinalized.migrateToDataFork(lcDataFork)
if forkyStore.finalized_header != oldFinalized.forky(lcDataFork):
didProgress = true
didSignificantProgress = true
if self.onFinalizedHeader != nil:
self.onFinalizedHeader()
if forkyStore.is_next_sync_committee_known != oldNextCommitteeKnown:
didProgress = true
if didProgress:
when obj is Nothing:
discard
elif obj is ForkedLightClientBootstrap:
if self.bootstrapObserver != nil:
self.bootstrapObserver(obj)
elif obj is ForkedLightClientUpdate:
if self.updateObserver != nil:
self.updateObserver(obj)
elif obj is ForkedLightClientFinalityUpdate:
if self.finalityUpdateObserver != nil:
self.finalityUpdateObserver(obj)
elif obj is ForkedLightClientOptimisticUpdate:
if self.optimisticUpdateObserver != nil:
self.optimisticUpdateObserver(obj)
else: raiseAssert "Unreachable"
didSignificantProgress
template withReportedProgress(body: untyped): bool =
withReportedProgress(Nothing(), body)
proc storeObject*(
self: var LightClientProcessor,
src: MsgSource, wallTime: BeaconTime,
obj: SomeForkedLightClientObject): Result[bool, VerifierError] =
## storeObject is the main entry point for unvalidated light client objects -
## all untrusted objects pass through here. When storing an object, we will
## update the `LightClientStore` accordingly
let
startTick = Moment.now()
didSignificantProgress =
withReportedProgress(obj):
? self.processObject(obj, wallTime)
let
storeObjectTick = Moment.now()
storeObjectDur = storeObjectTick - startTick
light_client_store_object_duration_seconds.observe(
storeObjectDur.toFloatSeconds())
let objSlot = withForkyObject(obj):
when lcDataFork > LightClientDataFork.None:
when forkyObject is ForkyLightClientBootstrap:
forkyObject.header.beacon.slot
elif forkyObject is SomeForkyLightClientUpdateWithFinality:
forkyObject.finalized_header.beacon.slot
else:
forkyObject.attested_header.beacon.slot
else:
GENESIS_SLOT
withForkyStore(self.store[]):
when lcDataFork > LightClientDataFork.None:
debug "LC object processed",
finalizedSlot = forkyStore.finalized_header.beacon.slot,
optimisticSlot = forkyStore.optimistic_header.beacon.slot,
kind = typeof(obj).name,
objectSlot = objSlot,
storeObjectDur
ok didSignificantProgress
proc resetToFinalizedHeader*(
self: var LightClientProcessor,
header: ForkedLightClientHeader,
current_sync_committee: SyncCommittee) =
discard withReportedProgress:
withForkyHeader(header):
when lcDataFork > LightClientDataFork.None:
self.store[] = ForkedLightClientStore.init(lcDataFork.LightClientStore(
finalized_header: forkyHeader,
current_sync_committee: current_sync_committee,
optimistic_header: forkyHeader))
template forkyStore: untyped = self.store[].forky(lcDataFork)
debug "LC reset to finalized header",
finalizedSlot = forkyStore.finalized_header.beacon.slot,
optimisticSlot = forkyStore.optimistic_header.beacon.slot
else:
self.store[].reset()
debug "LC reset"
# Enqueue
# ------------------------------------------------------------------------------
proc addObject*(
self: var LightClientProcessor,
src: MsgSource,
obj: SomeForkedLightClientObject,
resfut: Future[Result[void, VerifierError]] = nil) =
## Enqueue a Gossip-validated light client object for verification
# Backpressure:
# Only one object is validated at any time -
# Light client objects are always "fast" to process
# Producers:
# - Gossip:
# - `LightClientFinalityUpdate`
# - `LightClientOptimisticUpdate`
# - `LightClientManager`:
# - `GetLightClientBootstrap`
# - `LightClientUpdatesByRange`
# - `GetLightClientFinalityUpdate`
# - `GetLightClientOptimisticUpdate`
let
wallTime = self.getBeaconTime()
(afterGenesis, wallSlot) = wallTime.toSlot()
if not afterGenesis:
error "Processing LC object before genesis, clock turned back?"
quit 1
let res = self.storeObject(src, wallTime, obj)
if resfut != nil:
if res.isOk:
resfut.complete(Result[void, VerifierError].ok())
else:
resfut.complete(Result[void, VerifierError].err(res.error))
# Message validators
# ------------------------------------------------------------------------------
func toValidationError(
self: var LightClientProcessor,
r: Result[bool, VerifierError],
wallTime: BeaconTime,
obj: SomeForkedLightClientObject): Result[void, ValidationError] =
if r.isOk:
let didSignificantProgress = r.get
if didSignificantProgress:
let
signature_slot = withForkyObject(obj):
when lcDataFork > LightClientDataFork.None:
forkyObject.signature_slot
else:
GENESIS_SLOT
currentTime = wallTime + MAXIMUM_GOSSIP_CLOCK_DISPARITY
forwardTime = signature_slot.light_client_finality_update_time
if currentTime < forwardTime:
# [IGNORE] The `finality_update` is received after the block
# at `signature_slot` was given enough time to propagate through
# the network.
# [IGNORE] The `optimistic_update` is received after the block
# at `signature_slot` was given enough time to propagate through
# the network.
return errIgnore(typeof(obj).name & ": received too early")
ok()
else:
when obj is ForkedLightClientOptimisticUpdate:
# [IGNORE] The `optimistic_update` either matches corresponding fields
# of the most recently forwarded `LightClientFinalityUpdate` (if any),
# or it advances the `optimistic_header` of the local `LightClientStore`
if obj.matches(self.latestFinalityUpdate):
return ok()
# [IGNORE] The `finality_update` advances the `finalized_header` of the
# local `LightClientStore`.
errIgnore(typeof(obj).name & ": no significant progress")
else:
case r.error
of VerifierError.Invalid:
# [REJECT] The `finality_update` is valid.
# [REJECT] The `optimistic_update` is valid.
errReject($r.error)
of VerifierError.MissingParent,
VerifierError.UnviableFork,
VerifierError.Duplicate:
# [IGNORE] The `finalized_header.beacon.slot` is greater than that of
# all previously forwarded `finality_update`s
# [IGNORE] The `attested_header.beacon.slot` is greater than that of all
# previously forwarded `optimistic_update`s
errIgnore($r.error)
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-beta.4/specs/altair/light-client/sync-protocol.md#process_light_client_finality_update
proc processLightClientFinalityUpdate*(
self: var LightClientProcessor, src: MsgSource,
finality_update: ForkedLightClientFinalityUpdate
): Result[void, ValidationError] =
let
wallTime = self.getBeaconTime()
r = self.storeObject(src, wallTime, finality_update)
v = self.toValidationError(r, wallTime, finality_update)
if v.isErr:
return checkedResult(v.error, self.strictVerification)
self.latestFinalityUpdate = finality_update.toOptimistic
v
# https://github.com/ethereum/consensus-specs/blob/v1.4.0-beta.4/specs/altair/light-client/sync-protocol.md#process_light_client_finality_update
proc processLightClientOptimisticUpdate*(
self: var LightClientProcessor, src: MsgSource,
optimistic_update: ForkedLightClientOptimisticUpdate
): Result[void, ValidationError] =
let
wallTime = self.getBeaconTime()
r = self.storeObject(src, wallTime, optimistic_update)
v = self.toValidationError(r, wallTime, optimistic_update)
if v.isErr:
return checkedResult(v.error, self.strictVerification)
let
latestFinalitySlot = withForkyOptimisticUpdate(self.latestFinalityUpdate):
when lcDataFork > LightClientDataFork.None:
forkyOptimisticUpdate.attested_header.beacon.slot
else:
GENESIS_SLOT
attestedSlot = withForkyOptimisticUpdate(optimistic_update):
when lcDataFork > LightClientDataFork.None:
forkyOptimisticUpdate.attested_header.beacon.slot
else:
GENESIS_SLOT
if attestedSlot >= latestFinalitySlot:
self.latestFinalityUpdate.reset() # Only forward once
v
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