VC: Obtain randao signature before slot proposal. (#5490)

* Randao calculation caching for VC implementation.

* Add time monitoring for randao signatures process.

* Add delay calculation.

* Address review comments.

* Address review comments.

beacon_chain/validator_client/block_service.nim

@@ -32,6 +32,9 @@ type
     blockRoot*: Eth2Digest
     data*: ForkedBlindedBeaconBlock
 
+proc proposeBlock(vc: ValidatorClientRef, slot: Slot,
+                  proposerKey: ValidatorPubKey) {.async.}
+
 proc produceBlock(
        vc: ValidatorClientRef,
        currentSlot, slot: Slot,
@@ -86,7 +89,6 @@ proc produceBlock(
                                         data: ForkedBeaconBlock.init(blck),
                                         blobsOpt: Opt.some(blobs)))
 
-
 proc produceBlindedBlock(
        vc: ValidatorClientRef,
        currentSlot, slot: Slot,
@@ -125,6 +127,58 @@ proc lazyWait[T](fut: Future[T]) {.async.} =
   except CatchableError:
     discard
 
+proc prepareRandao(vc: ValidatorClientRef, slot: Slot,
+                   proposerKey: ValidatorPubKey) {.async.} =
+  if slot == GENESIS_SLOT:
+    return
+
+  let
+    destSlot = slot - 1'u64
+    destOffset = TimeDiff(nanoseconds: NANOSECONDS_PER_SLOT.int64 div 2)
+    deadline = destSlot.start_beacon_time() + destOffset
+    epoch = slot.epoch()
+    # We going to wait to T - (T / 4 * 2), where T is proposer's
+    # duty slot.
+    currentSlot = (await vc.checkedWaitForSlot(destSlot, destOffset,
+                   false)).valueOr:
+      debug "Unable to perform RANDAO signature preparation because of " &
+            "system time failure"
+      return
+    validator =
+      vc.getValidatorForDuties(proposerKey, slot, true).valueOr: return
+
+  if currentSlot <= destSlot:
+    # We do not need result, because we want it to be cached.
+    let
+      start = Moment.now()
+      genesisRoot = vc.beaconGenesis.genesis_validators_root
+      fork = vc.forkAtEpoch(epoch)
+      rsig = await validator.getEpochSignature(fork, genesisRoot, epoch)
+      timeElapsed = Moment.now() - start
+    if rsig.isErr():
+      debug "Unable to prepare RANDAO signature", epoch = epoch,
+            validator = shortLog(validator), elapsed_time = timeElapsed,
+            current_slot = currentSlot, destination_slot = destSlot,
+            delay = vc.getDelay(deadline)
+    else:
+      debug "RANDAO signature has been prepared", epoch = epoch,
+            validator = shortLog(validator), elapsed_time = timeElapsed,
+            current_slot = currentSlot, destination_slot = destSlot,
+            delay = vc.getDelay(deadline)
+  else:
+    debug "RANDAO signature preparation timed out", epoch = epoch,
+          validator = shortLog(validator),
+          current_slot = currentSlot, destination_slot = destSlot,
+          delay = vc.getDelay(deadline)
+
+proc spawnProposalTask(vc: ValidatorClientRef,
+                       duty: RestProposerDuty): ProposerTask =
+  ProposerTask(
+    randaoFut: prepareRandao(vc, duty.slot, duty.pubkey),
+    proposeFut: proposeBlock(vc, duty.slot, duty.pubkey),
+    duty: duty
+  )
+
 proc publishBlock(vc: ValidatorClientRef, currentSlot, slot: Slot,
                   validator: AttachedValidator) {.async.} =
   let
@@ -146,21 +200,22 @@ proc publishBlock(vc: ValidatorClientRef, currentSlot, slot: Slot,
   debug "Publishing block", delay = vc.getDelay(slot.block_deadline()),
                             genesis_root = genesisRoot,
                             graffiti = graffiti, fork = fork
-  let randaoReveal =
-    try:
-      let res = await validator.getEpochSignature(fork, genesisRoot, slot.epoch)
-      if res.isErr():
-        warn "Unable to generate randao reveal using remote signer",
-             reason = res.error()
+
+  let
+    randaoReveal =
+      try:
+        (await validator.getEpochSignature(fork, genesisRoot,
+                                           slot.epoch())).valueOr:
+          warn "Unable to generate RANDAO reveal using remote signer",
+               reason = error
+          return
+      except CancelledError as exc:
+        debug "RANDAO reveal production has been interrupted"
+        raise exc
+      except CatchableError as exc:
+        error "An unexpected error occurred while receiving RANDAO data",
+              error_name = exc.name, error_msg = exc.msg
         return
-      res.get()
-    except CancelledError as exc:
-      debug "Randao reveal production has been interrupted"
-      raise exc
-    except CatchableError as exc:
-      error "An unexpected error occurred while receiving randao data",
-            error_name = exc.name, error_msg = exc.msg
-      return
 
   var beaconBlocks =
     block:
@@ -408,11 +463,6 @@ proc proposeBlock(vc: ValidatorClientRef, slot: Slot,
     error "Unexpected error encountered while proposing block",
           slot = slot, validator = shortLog(validator)
 
-proc spawnProposalTask(vc: ValidatorClientRef,
-                       duty: RestProposerDuty): ProposerTask =
-  let future = proposeBlock(vc, duty.slot, duty.pubkey)
-  ProposerTask(future: future, duty: duty)
-
 proc contains(data: openArray[RestProposerDuty], task: ProposerTask): bool =
   for item in data:
     if (item.pubkey == task.duty.pubkey) and (item.slot == task.duty.slot):
@@ -462,13 +512,14 @@ proc addOrReplaceProposers*(vc: ValidatorClientRef, epoch: Epoch,
           for task in epochDuties.duties:
             if task notin duties:
               # Task is no more relevant, so cancel it.
-              debug "Cancelling running proposal duty task",
+              debug "Cancelling running proposal duty tasks",
                     slot = task.duty.slot,
                     validator = shortLog(task.duty.pubkey)
-              task.future.cancelSoon()
+              task.proposeFut.cancelSoon()
+              task.randaoFut.cancelSoon()
             else:
               # If task is already running for proper slot, we keep it alive.
-              debug "Keep running previous proposal duty task",
+              debug "Keep running previous proposal duty tasks",
                     slot = task.duty.slot,
                     validator = shortLog(task.duty.pubkey)
               res.add(task)
@@ -783,8 +834,10 @@ proc mainLoop(service: BlockServiceRef) {.async.} =
   var res: seq[FutureBase]
   for epoch, data in vc.proposers.pairs():
     for duty in data.duties.items():
-      if not(duty.future.finished()):
-        res.add(duty.future.cancelAndWait())
+      if not(duty.proposeFut.finished()):
+        res.add(duty.proposeFut.cancelAndWait())
+      if not(duty.randaoFut.finished()):
+        res.add(duty.randaoFut.cancelAndWait())
   await noCancel allFutures(res)
 
 proc init*(t: typedesc[BlockServiceRef],

beacon_chain/validator_client/common.nim

@@ -95,7 +95,8 @@ type
 
   ProposerTask* = object
     duty*: RestProposerDuty
-    future*: Future[void]
+    proposeFut*: Future[void]
+    randaoFut*: Future[void]
 
   ProposedData* = object
     epoch*: Epoch

beacon_chain/validators/validator_pool.nim

@@ -66,6 +66,10 @@ type
     # if the validator will be aggregating (in the near future)
     slotSignature*: Opt[tuple[slot: Slot, signature: ValidatorSig]]
 
+    # Cache the latest epoch signature - the epoch signature is used for block
+    # proposing.
+    epochSignature*: Opt[tuple[epoch: Epoch, signature: ValidatorSig]]
+
     # For the external payload builder; each epoch, the external payload
     # builder should be informed of current validators
     externalBuilderRegistration*: Opt[SignedValidatorRegistrationV1]
@@ -746,7 +750,10 @@ proc getContributionAndProofSignature*(v: AttachedValidator, fork: Fork,
 proc getEpochSignature*(v: AttachedValidator, fork: Fork,
                         genesis_validators_root: Eth2Digest, epoch: Epoch
                        ): Future[SignatureResult] {.async.} =
-  return
+  if v.epochSignature.isSome and v.epochSignature.get.epoch == epoch:
+    return SignatureResult.ok(v.epochSignature.get.signature)
+
+  let signature =
     case v.kind
     of ValidatorKind.Local:
       SignatureResult.ok(get_epoch_signature(
@@ -757,6 +764,12 @@ proc getEpochSignature*(v: AttachedValidator, fork: Fork,
         fork, genesis_validators_root, epoch)
       await v.signData(request)
 
+  if signature.isErr:
+    return signature
+
+  v.epochSignature = Opt.some((epoch, signature.get))
+  signature
+
 # https://github.com/ethereum/consensus-specs/blob/v1.4.0-beta.1/specs/phase0/validator.md#aggregation-selection
 proc getSlotSignature*(v: AttachedValidator, fork: Fork,
                        genesis_validators_root: Eth2Digest, slot: Slot