allow beacon_node to verify finalization when appropriate, and enable by default for make eth2_network_simulation

beacon_chain/beacon_node.nim

@@ -645,6 +645,21 @@ proc handleProposal(node: BeaconNode, head: BlockRef, slot: Slot):
 
   return head
 
+proc verifyFinalization(node: BeaconNode, slot: Slot) =
+  # Epoch must be >= 4 to check finalization
+  const SETTLING_TIME_OFFSET = 1'u64
+  let epoch = slot.compute_epoch_at_slot()
+
+  # Don't static-assert this -- if this isn't called, don't require it
+  doAssert SLOTS_PER_EPOCH > SETTLING_TIME_OFFSET
+
+  # Intentionally, loudly assert. Point is to fail visibly and unignorably
+  # during testing.
+  if epoch >= 4 and slot mod SLOTS_PER_EPOCH > SETTLING_TIME_OFFSET:
+    let finalizedEpoch =
+      node.blockPool.finalizedHead.blck.slot.compute_epoch_at_slot()
+    doAssert finalizedEpoch + 2 == epoch
+
 proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, async.} =
   ## Called at the beginning of a slot - usually every slot, but sometimes might
   ## skip a few in case we're running late.
@@ -672,6 +687,17 @@ proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, asyn
     finalizedSlot = shortLog(node.blockPool.finalizedHead.blck.slot.compute_epoch_at_slot()),
     cat = "scheduling"
 
+  # Check before any re-scheduling of onSlotStart()
+  if node.config.checkEpochs > 0'u64 and
+      scheduledSlot.compute_epoch_at_slot() >= node.config.checkEpochs:
+    info "Stopping at pre-chosen epoch",
+      chosenEpoch = node.config.checkEpochs,
+      epoch = scheduledSlot.compute_epoch_at_slot(),
+      slot = scheduledSlot
+
+    # Brute-force, but ensure it's reliably enough to run in CI.
+    quit(0)
+
   if not wallSlot.afterGenesis or (wallSlot.slot < lastSlot):
     let
       slot =
@@ -700,6 +726,9 @@ proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, asyn
 
   beacon_slot.set slot.int64
 
+  if node.config.verifyFinalization:
+    verifyFinalization(node, scheduledSlot)
+
   if slot > lastSlot + SLOTS_PER_EPOCH:
     # We've fallen behind more than an epoch - there's nothing clever we can
     # do here really, except skip all the work and try again later.
@@ -784,7 +813,7 @@ proc onSlotStart(node: BeaconNode, lastSlot, scheduledSlot: Slot) {.gcsafe, asyn
     head = await handleProposal(node, head, slot)
 
     # We've been doing lots of work up until now which took time. Normally, we
-    # send out attestations at the slot mid-point, so we go back to the clock
+    # send out attestations at the slot thirds-point, so we go back to the clock
     # to see how much time we need to wait.
     # TODO the beacon clock might jump here also. It's probably easier to complete
     #      the work for the whole slot using a monotonic clock instead, then deal

beacon_chain/conf.nim

@@ -132,6 +132,16 @@ type
               "If you set this to 'auto', a persistent automatically generated ID will be seleceted for each --dataDir folder."
         name: "node-name" }: string
 
+      verifyFinalization* {.
+        defaultValue: false
+        desc: "Specify whether to verify finalization occurs on schedule, for testing."
+        name: "verify-finalization" }: bool
+
+      checkEpochs* {.
+        defaultValue: 0
+        desc: "A positive checkEpochs selects how many epochs to run."
+        name: "check-epochs" }: uint64
+
       metricsServer* {.
         defaultValue: false
         desc: "Enable the metrics server."

tests/simulation/run_node.sh

@@ -63,6 +63,7 @@ cd "$DATA_DIR" && $NODE_BIN \
   --state-snapshot=$SNAPSHOT_FILE \
   $DEPOSIT_WEB3_URL_ARG \
   --deposit-contract=$DEPOSIT_CONTRACT_ADDRESS \
+  --verify-finalization=on \
   --metrics-server=on \
   --metrics-server-address="127.0.0.1" \
   --metrics-server-port="$(( $BASE_METRICS_PORT + $NODE_ID ))" \