reduce LC optsync latency (#4002)

The optimistic sync spec was updated since the LC based optsync module
was introduced. It is no longer necessary to wait for the justified
checkpoint to have execution enabled; instead, any block is okay to be
optimistically imported to the EL client, as long as its parent block
has execution enabled. Complex syncing logic has been removed, and the
LC optsync module will now follow gossip directly, reducing the latency
when using this module. Note that because this is now based on gossip
instead of using sync manager / request manager, that individual blocks
may be missed. However, EL clients should recover from this by fetching
missing blocks themselves.

AllTests-mainnet.md

@@ -56,17 +56,6 @@ OK: 6/6 Fail: 0/6 Skip: 0/6
 + basics                                                                                     OK
 ```
 OK: 1/1 Fail: 0/1 Skip: 0/1
-## Block clearance (light client) [Preset: mainnet]
-```diff
-+ Delayed finality update                                                                    OK
-+ Error conditions                                                                           OK
-+ Incremental sync                                                                           OK
-+ Initial sync                                                                               OK
-+ Low slot numbers                                                                           OK
-+ Reorg                                                                                      OK
-+ Reverse incremental sync                                                                   OK
-```
-OK: 7/7 Fail: 0/7 Skip: 0/7
 ## Block pool altair processing [Preset: mainnet]
 ```diff
 + Invalid signatures [Preset: mainnet]                                                       OK
@@ -596,4 +585,4 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 OK: 9/9 Fail: 0/9 Skip: 0/9
 
 ---TOTAL---
-OK: 333/338 Fail: 0/338 Skip: 5/338
+OK: 326/331 Fail: 0/331 Skip: 5/331

beacon_chain/beacon_node.nim

@@ -15,15 +15,15 @@ import
 
   # Local modules
   "."/[beacon_clock, beacon_chain_db, conf, light_client],
-  ./gossip_processing/[eth2_processor, block_processor],
+  ./gossip_processing/[eth2_processor, block_processor, optimistic_processor],
   ./networking/eth2_network,
   ./eth1/eth1_monitor,
   ./consensus_object_pools/[
     blockchain_dag, block_quarantine, consensus_manager, exit_pool,
     attestation_pool, sync_committee_msg_pool],
   ./spec/datatypes/[base, altair],
   ./spec/eth2_apis/dynamic_fee_recipients,
-  ./sync/[optimistic_sync_light_client, sync_manager, request_manager],
+  ./sync/[sync_manager, request_manager],
   ./validators/[
     action_tracker, message_router, validator_monitor, validator_pool,
     keystore_management],
@@ -33,9 +33,9 @@ export
   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, optimistic_sync_light_client,
-  request_manager, sync_manager, eth2_processor, blockchain_dag,
-  block_quarantine, base, exit_pool,  message_router, validator_monitor,
+  eth2_network, eth1_monitor, request_manager, sync_manager,
+  eth2_processor, optimistic_processor, blockchain_dag, block_quarantine,
+  base, exit_pool,  message_router, validator_monitor,
   consensus_manager, dynamic_fee_recipients
 
 type
@@ -58,7 +58,7 @@ type
     db*: BeaconChainDB
     config*: BeaconNodeConf
     attachedValidators*: ref ValidatorPool
-    lcOptSync*: LCOptimisticSync
+    optimisticProcessor*: OptimisticProcessor
     lightClient*: LightClient
     dag*: ChainDAGRef
     quarantine*: ref Quarantine
@@ -83,6 +83,7 @@ type
     consensusManager*: ref ConsensusManager
     attachedValidatorBalanceTotal*: uint64
     gossipState*: GossipState
+    blocksGossipState*: GossipState
     beaconClock*: BeaconClock
     restKeysCache*: Table[ValidatorPubKey, ValidatorIndex]
     validatorMonitor*: ref ValidatorMonitor

beacon_chain/beacon_node_light_client.nim

@@ -16,6 +16,24 @@ import
 
 logScope: topics = "beacnde"
 
+func shouldSyncOptimistically*(node: BeaconNode, wallSlot: Slot): bool =
+  # Check whether light client is used for syncing
+  let optimisticHeader = node.lightClient.optimisticHeader.valueOr:
+    return false
+
+  # Check whether light client is sufficiently ahead of DAG
+  const minProgress = 8 * SLOTS_PER_EPOCH  # Set arbitrarily
+  let dagSlot = getStateField(node.dag.headState, slot)
+  if dagSlot + minProgress > optimisticHeader.slot:
+    return false
+
+  # Check whether light client has synced sufficiently close to wall slot
+  const maxAge = 2 * SLOTS_PER_EPOCH
+  if optimisticHeader.slot < max(wallSlot, maxAge.Slot) - maxAge:
+    return false
+
+  true
+
 proc initLightClient*(
     node: BeaconNode,
     rng: ref HmacDrbgContext,
@@ -30,52 +48,28 @@ proc initLightClient*(
   # for broadcasting light client data as a server.
 
   let
-    optimisticProcessor = proc(signedBlock: ForkedMsgTrustedSignedBeaconBlock):
+    optimisticHandler = proc(signedBlock: ForkedMsgTrustedSignedBeaconBlock):
         Future[void] {.async.} =
       debug "New LC optimistic block",
         opt = signedBlock.toBlockId(),
         dag = node.dag.head.bid,
         wallSlot = node.currentSlot
       return
-    optSync = initLCOptimisticSync(
-      node.network, getBeaconTime, optimisticProcessor,
-      config.safeSlotsToImportOptimistically)
+    optimisticProcessor = initOptimisticProcessor(
+      getBeaconTime, optimisticHandler)
 
     lightClient = createLightClient(
       node.network, rng, config, cfg, forkDigests, getBeaconTime,
       genesis_validators_root, LightClientFinalizationMode.Strict)
 
   if config.lightClientEnable:
-    proc shouldSyncOptimistically(slot: Slot): bool =
-      const
-        # Minimum number of slots to be ahead of DAG to use optimistic sync
-        minProgress = 8 * SLOTS_PER_EPOCH
-        # Maximum age of light client optimistic header to use optimistic sync
-        maxAge = 2 * SLOTS_PER_EPOCH
-
-      if slot < getStateField(node.dag.headState, slot) + minProgress:
-        false
-      elif getBeaconTime().slotOrZero > slot + maxAge:
-        false
-      else:
-        true
-
-    proc onFinalizedHeader(lightClient: LightClient) =
-      let optimisticHeader = lightClient.optimisticHeader.valueOr:
-        return
-      if not shouldSyncOptimistically(optimisticHeader.slot):
-        return
-      let finalizedHeader = lightClient.finalizedHeader.valueOr:
-        return
-      optSync.setOptimisticHeader(optimisticHeader)
-      optSync.setFinalizedHeader(finalizedHeader)
+    proc onFinalizedHeader(
+        lightClient: LightClient, finalizedHeader: BeaconBlockHeader) =
+      optimisticProcessor.setFinalizedHeader(finalizedHeader)
 
-    proc onOptimisticHeader(lightClient: LightClient) =
-      let optimisticHeader = lightClient.optimisticHeader.valueOr:
-        return
-      if not shouldSyncOptimistically(optimisticHeader.slot):
-        return
-      optSync.setOptimisticHeader(optimisticHeader)
+    proc onOptimisticHeader(
+        lightClient: LightClient, optimisticHeader: BeaconBlockHeader) =
+      optimisticProcessor.setOptimisticHeader(optimisticHeader)
 
     lightClient.onFinalizedHeader = onFinalizedHeader
     lightClient.onOptimisticHeader = onOptimisticHeader
@@ -86,14 +80,13 @@ proc initLightClient*(
       lightClientEnable = config.lightClientEnable,
       lightClientTrustedBlockRoot = config.lightClientTrustedBlockRoot
 
-  node.lcOptSync = optSync
+  node.optimisticProcessor = optimisticProcessor
   node.lightClient = lightClient
 
 proc startLightClient*(node: BeaconNode) =
   if not node.config.lightClientEnable:
     return
 
-  node.lcOptSync.start()
   node.lightClient.start()
 
 proc installLightClientMessageValidators*(node: BeaconNode) =

beacon_chain/conf_light_client.nim

@@ -133,12 +133,6 @@ type LightClientConf* = object
     desc: "A file containing the hex-encoded 256 bit secret key to be used for verifying/generating JWT tokens"
     name: "jwt-secret" .}: Option[string]
 
-  safeSlotsToImportOptimistically* {.
-    hidden
-    desc: "Modify SAFE_SLOTS_TO_IMPORT_OPTIMISTICALLY"
-    defaultValue: 128
-    name: "safe-slots-to-import-optimistically" .}: uint16
-
   # Testing
   stopAtEpoch* {.
     hidden