integrate light client into beacon node (#3557)

Adds a `LightClient` instance to the beacon node as preparation to
accelerate syncing in the future (optimistic sync).

- `--light-client-enable` turns on the feature
- `--light-client-trusted-block-root` configures block to start from

If no block root is configured, light client tracks DAG `finalizedHead`.

beacon_chain/beacon_node.nim

@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2018-2021 Status Research & Development GmbH
+# Copyright (c) 2018-2022 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).
@@ -14,7 +14,7 @@ import
   chronos, json_rpc/servers/httpserver, presto,
 
   # Local modules
-  "."/[beacon_clock, beacon_chain_db, conf],
+  "."/[beacon_clock, beacon_chain_db, conf, light_client],
   ./gossip_processing/[eth2_processor, block_processor, consensus_manager],
   ./networking/eth2_network,
   ./eth1/eth1_monitor,
@@ -27,9 +27,10 @@ import
   ./rpc/state_ttl_cache
 
 export
-  osproc, chronos, httpserver, presto, action_tracker, beacon_clock,
-  beacon_chain_db, conf, attestation_pool, sync_committee_msg_pool,
-  validator_pool, eth2_network, eth1_monitor, request_manager, sync_manager,
+  osproc, chronos, httpserver, presto, action_tracker,
+  beacon_clock, beacon_chain_db, conf, light_client,
+  attestation_pool, sync_committee_msg_pool, validator_pool,
+  eth2_network, eth1_monitor, request_manager, sync_manager,
   eth2_processor, blockchain_dag, block_quarantine, base, exit_pool,
   validator_monitor, consensus_manager
 
@@ -44,6 +45,7 @@ type
     db*: BeaconChainDB
     config*: BeaconNodeConf
     attachedValidators*: ref ValidatorPool
+    lightClient*: LightClient
     dag*: ChainDAGRef
     quarantine*: ref Quarantine
     attestationPool*: ref AttestationPool

beacon_chain/beacon_node_light_client.nim

@@ -0,0 +1,103 @@
+# 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
+  chronicles,
+  ./beacon_node
+
+logScope: topics = "beacnde"
+
+proc initLightClient*(
+    node: BeaconNode,
+    rng: ref BrHmacDrbgContext,
+    cfg: RuntimeConfig,
+    forkDigests: ref ForkDigests,
+    getBeaconTime: GetBeaconTimeFn,
+    genesis_validators_root: Eth2Digest) =
+  template config(): auto = node.config
+
+  # Creating a light client is not dependent on `lightClientEnable`
+  # because the light client module also handles gossip subscriptions
+  # for broadcasting light client data as a server.
+
+  let lightClient = createLightClient(
+    node.network, rng, config, cfg,
+    forkDigests, getBeaconTime, genesis_validators_root)
+
+  if config.lightClientEnable.get:
+    lightClient.trustedBlockRoot = config.lightClientTrustedBlockRoot
+
+  elif config.lightClientTrustedBlockRoot.isSome:
+    warn "Ignoring `lightClientTrustedBlockRoot`, light client not enabled",
+      lightClientEnable = config.lightClientEnable.get,
+      lightClientTrustedBlockRoot = config.lightClientTrustedBlockRoot
+
+  node.lightClient = lightClient
+
+proc startLightClient*(node: BeaconNode) =
+  if not node.config.lightClientEnable.get:
+    return
+
+  node.lightClient.start()
+
+proc installLightClientMessageValidators*(node: BeaconNode) =
+  let eth2Processor =
+    if node.config.serveLightClientData.get:
+      # Process gossip using both full node and light client
+      node.processor
+    elif node.config.lightClientEnable.get:
+      # Only process gossip using light client
+      nil
+    else:
+      # Light client topics will never be subscribed to, no validators needed
+      return
+
+  node.lightClient.installMessageValidators(eth2Processor)
+
+proc updateLightClientGossipStatus*(
+    node: BeaconNode, slot: Slot, dagIsBehind: bool) =
+  let isBehind =
+    if node.config.serveLightClientData.get:
+      # Forward DAG's readiness to handle light client gossip
+      dagIsBehind
+    else:
+      # Full node is not interested in gossip
+      true
+
+  node.lightClient.updateGossipStatus(slot, some isBehind)
+
+proc updateLightClientFromDag*(node: BeaconNode) =
+  if not node.config.lightClientEnable.get:
+    return
+  if node.config.lightClientTrustedBlockRoot.isSome:
+    return
+
+  let
+    dagHead = node.dag.finalizedHead
+    dagPeriod = dagHead.slot.sync_committee_period
+  if dagHead.slot < node.dag.cfg.ALTAIR_FORK_EPOCH.start_slot:
+    return
+
+  let lcHeader = node.lightClient.finalizedHeader
+  if lcHeader.isSome:
+    if dagPeriod <= lcHeader.get.slot.sync_committee_period:
+      return
+
+  let
+    bdata = node.dag.getForkedBlock(dagHead.blck.bid).valueOr:
+      return
+    header = bdata.toBeaconBlockHeader
+    current_sync_committee = block:
+      var tmpState = assignClone(node.dag.headState)
+      node.dag.currentSyncCommitteeForPeriod(tmpState[], dagPeriod).valueOr:
+        return
+  node.lightClient.resetToFinalizedHeader(header, current_sync_committee)

beacon_chain/conf.nim

@@ -267,6 +267,16 @@ type
         desc: "Weak subjectivity checkpoint in the format block_root:epoch_number"
         name: "weak-subjectivity-checkpoint" }: Option[Checkpoint]
 
+      lightClientEnable* {.
+        hidden
+        desc: "BETA: Accelerate sync using light client."
+        name: "light-client-enable" .}: Option[bool]
+
+      lightClientTrustedBlockRoot* {.
+        hidden
+        desc: "BETA: Recent trusted finalized block root to initialize light client from."
+        name: "light-client-trusted-block-root" }: Option[Eth2Digest]
+
       finalizedCheckpointState* {.
         desc: "SSZ file specifying a recent finalized state"
         name: "finalized-checkpoint-state" }: Option[InputFile]
@@ -906,6 +916,13 @@ proc createDumpDirs*(config: BeaconNodeConf) =
       warn "Could not create dump directory",
         path = config.dumpDirOutgoing, err = ioErrorMsg(res.error)
 
+func parseCmdArg*(T: type Eth2Digest, input: string): T
+                 {.raises: [ValueError, Defect].} =
+  Eth2Digest.fromHex(input)
+
+func completeCmdArg*(T: type Eth2Digest, input: string): seq[string] =
+  return @[]
+
 func parseCmdArg*(T: type GraffitiBytes, input: string): T
                  {.raises: [ValueError, Defect].} =
   GraffitiBytes.init(input)

beacon_chain/conf_light_client.nim

@@ -122,10 +122,3 @@ type LightClientConf* = object
     desc: "The wall-time epoch at which to exit the program. (for testing purposes)"
     defaultValue: 0
     name: "stop-at-epoch" }: uint64
-
-func parseCmdArg*(T: type Eth2Digest, input: string): T
-                 {.raises: [ValueError, Defect].} =
-  Eth2Digest.fromHex(input)
-
-func completeCmdArg*(T: type Eth2Digest, input: string): seq[string] =
-  return @[]

beacon_chain/consensus_object_pools/blockchain_dag.nim

@@ -520,6 +520,26 @@ proc getForkedBlock*(
     # In case we didn't have a summary - should be rare, but ..
     dag.db.getForkedBlock(root)
 
+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 = max(dag.tail.slot, dag.cfg.ALTAIR_FORK_EPOCH.start_slot)
+  if period < earliestSlot.sync_committee_period:
+    return err()
+  let
+    periodStartSlot = period.start_slot
+    syncCommitteeSlot = max(periodStartSlot, earliestSlot)
+    bsi = ? dag.getBlockIdAtSlot(syncCommitteeSlot)
+  dag.withUpdatedState(tmpState, bsi) do:
+    withState(state):
+      when stateFork >= BeaconStateFork.Altair:
+        ok state.data.current_sync_committee
+      else: err()
+  do: err()
+
 proc updateBeaconMetrics(
     state: ForkedHashedBeaconState, bid: BlockId, cache: var StateCache) =
   # https://github.com/ethereum/eth2.0-metrics/blob/master/metrics.md#additional-metrics

beacon_chain/consensus_object_pools/blockchain_dag_light_client.nim

@@ -113,24 +113,17 @@ proc getExistingForkedBlock*(
     doAssert verifyFinalization notin dag.updateFlags
   bdata
 
-proc currentSyncCommitteeForPeriod(
+proc existingCurrentSyncCommitteeForPeriod(
     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()
+  ## Wrapper around `currentSyncCommitteeForPeriod` for states known to exist.
+  let syncCommittee = dag.currentSyncCommitteeForPeriod(tmpState, period)
+  if syncCommittee.isErr:
+    error "Current sync committee failed to load unexpectedly",
+      period, tail = dag.tail.slot
+    doAssert verifyFinalization notin dag.updateFlags
+  syncCommittee
 
 template syncCommitteeRoot(
     state: HashedBeaconStateWithSyncCommittee): Eth2Digest =
@@ -795,7 +788,7 @@ proc getLightClientBootstrap*(
       bootstrap.header =
         blck.toBeaconBlockHeader
       bootstrap.current_sync_committee =
-        ? dag.currentSyncCommitteeForPeriod(tmpState[], period)
+        ? dag.existingCurrentSyncCommitteeForPeriod(tmpState[], period)
       bootstrap.current_sync_committee_branch =
         cachedBootstrap.current_sync_committee_branch
       return ok bootstrap

beacon_chain/gossip_processing/eth2_processor.nim

@@ -29,6 +29,8 @@ export
   light_client_pool, sync_committee_msg_pool, validator_pool, beacon_clock,
   gossip_validation, block_processor, batch_validation, block_quarantine
 
+logScope: topics = "gossip_eth2"
+
 # Metrics for tracking attestation and beacon block loss
 declareCounter beacon_attestations_received,
   "Number of valid unaggregated attestations processed by this node"
@@ -62,14 +64,6 @@ declareCounter beacon_sync_committee_contributions_received,
   "Number of valid sync committee contributions processed by this node"
 declareCounter beacon_sync_committee_contributions_dropped,
   "Number of invalid sync committee contributions dropped by this node", labels = ["reason"]
-declareCounter beacon_light_client_finality_updates_received,
-  "Number of valid LC finality updates processed by this node"
-declareCounter beacon_light_client_finality_updates_dropped,
-  "Number of invalid LC finality updates dropped by this node", labels = ["reason"]
-declareCounter beacon_light_client_optimistic_updates_received,
-  "Number of valid LC optimistic updates processed by this node"
-declareCounter beacon_light_client_optimistic_updates_dropped,
-  "Number of invalid LC optimistic updates dropped by this node", labels = ["reason"]
 
 const delayBuckets = [2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, Inf]
 
@@ -553,45 +547,19 @@ proc lightClientFinalityUpdateValidator*(
     self: var Eth2Processor, src: MsgSource,
     finality_update: altair.LightClientFinalityUpdate
 ): Result[void, ValidationError] =
-  logScope:
-    finality_update
-
-  debug "LC finality update received"
-
   let
     wallTime = self.getCurrentBeaconTime()
     v = validateLightClientFinalityUpdate(
       self.lightClientPool[], self.dag, finality_update, wallTime)
-  if v.isOk():
-    trace "LC finality update validated"
-
-    beacon_light_client_finality_updates_received.inc()
-  else:
-    debug "Dropping LC finality update", error = v.error
-    beacon_light_client_finality_updates_dropped.inc(1, [$v.error[0]])
-
   v
 
 # https://github.com/ethereum/consensus-specs/blob/vFuture/specs/altair/sync-protocol.md#light_client_optimistic_update
 proc lightClientOptimisticUpdateValidator*(
     self: var Eth2Processor, src: MsgSource,
     optimistic_update: altair.LightClientOptimisticUpdate
 ): Result[void, ValidationError] =
-  logScope:
-    optimistic_update
-
-  debug "LC optimistic update received"
-
   let
     wallTime = self.getCurrentBeaconTime()
     v = validateLightClientOptimisticUpdate(
       self.lightClientPool[], self.dag, optimistic_update, wallTime)
-  if v.isOk():
-    trace "LC optimistic update validated"
-
-    beacon_light_client_optimistic_updates_received.inc()
-  else:
-    debug "Dropping LC optimistic update", error = v.error
-    beacon_light_client_optimistic_updates_dropped.inc(1, [$v.error[0]])
-
   v