Address #4290. (#4333)

beacon_chain/validator_client/duties_service.nim

@@ -11,6 +11,7 @@ import common, api, block_service
 
 const
   ServiceName = "duties_service"
+  SUBSCRIPTION_LOOKAHEAD_EPOCHS* = 4'u64
 
 logScope: service = ServiceName
 
@@ -439,16 +440,41 @@ proc pollForSyncCommitteeDuties* (vc: ValidatorClientRef) {.async.} =
     let
       currentSlot = sres.get()
       currentEpoch = currentSlot.epoch()
-      nextEpoch = currentEpoch + 1'u64
 
     if vc.attachedValidators[].count() != 0:
-      var counts: array[2, tuple[epoch: Epoch, count: int]]
-      counts[0] =
-        (currentEpoch, await vc.pollForSyncCommitteeDuties(currentEpoch))
-      counts[1] =
-        (nextEpoch, await vc.pollForSyncCommitteeDuties(nextEpoch))
+      let
+        dutyPeriods =
+          block:
+            var res: seq[tuple[epoch: Epoch, period: SyncCommitteePeriod]]
+            let
+              currentPeriod = currentSlot.sync_committee_period()
+              lookaheadSlot = currentSlot +
+                              SUBSCRIPTION_LOOKAHEAD_EPOCHS * SLOTS_PER_EPOCH
+              lookaheadPeriod = lookaheadSlot.sync_committee_period()
+            res.add(
+              (epoch: currentSlot.epoch(),
+               period: currentPeriod)
+            )
+            if lookAheadPeriod > currentPeriod:
+              res.add(
+                (epoch: lookaheadPeriod.start_epoch(),
+                 period: lookAheadPeriod)
+              )
+            res
 
-      if (counts[0].count == 0) and (counts[1].count == 0):
+        (counts, total) =
+          block:
+            var res: seq[tuple[epoch: Epoch, period: SyncCommitteePeriod,
+                               count: int]]
+            var total = 0
+            if len(dutyPeriods) > 0:
+              for (epoch, period) in dutyPeriods:
+                let count = await vc.pollForSyncCommitteeDuties(epoch)
+                res.add((epoch: epoch, period: period, count: count))
+                total += count
+            (res, total)
+
+      if total == 0:
         debug "No new sync committee member's duties received",
               slot = currentSlot
 
@@ -457,6 +483,7 @@ proc pollForSyncCommitteeDuties* (vc: ValidatorClientRef) {.async.} =
           var res: seq[RestSyncCommitteeSubscription]
           for item in counts:
             if item.count > 0:
+              let untilEpoch = start_epoch(item.period + 1'u64)
               let subscriptionsInfo =
                 vc.syncMembersSubscriptionInfoForEpoch(item.epoch)
               for subInfo in subscriptionsInfo:
@@ -464,12 +491,11 @@ proc pollForSyncCommitteeDuties* (vc: ValidatorClientRef) {.async.} =
                   validator_index: subInfo.validator_index,
                   sync_committee_indices:
                     subInfo.validator_sync_committee_indices,
-                  until_epoch:
-                    (currentEpoch + EPOCHS_PER_SYNC_COMMITTEE_PERIOD -
-                      currentEpoch.since_sync_committee_period_start()).Epoch
+                  until_epoch: untilEpoch
                 )
                 res.add(sub)
           res
+
       if len(subscriptions) > 0:
         let res = await vc.prepareSyncCommitteeSubnets(subscriptions)
         if res != 0: