From 6f68c1a46e268a6e812da1c6cacaf46c53e6f146 Mon Sep 17 00:00:00 2001
From: Etan Kissling <etan@status.im>
Date: Fri, 16 Jun 2023 08:33:13 +0200
Subject: [PATCH] query sync duties for correct slot (#5083)

VC currently misses sync committee duties for first slot of most epochs
because the 1 slot offset is not taken into account. Duties for the next
slot must be used during any given current slot. We use the correct slot
for processing the duty, but do not use the correct slot for fetching.
---
 .../validator_client/duties_service.nim       | 23 ++++++++++---------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/beacon_chain/validator_client/duties_service.nim b/beacon_chain/validator_client/duties_service.nim
index 3ee98d050..86fe35070 100644
--- a/beacon_chain/validator_client/duties_service.nim
+++ b/beacon_chain/validator_client/duties_service.nim
@@ -409,7 +409,9 @@ proc pollForSyncCommitteeDuties*(service: DutiesServiceRef) {.async.} =
   let vc = service.client
   let
     currentSlot = vc.getCurrentSlot().get(Slot(0))
-    currentEpoch = currentSlot.epoch()
+    # https://github.com/ethereum/consensus-specs/blob/v1.4.0-alpha.3/specs/altair/validator.md#sync-committee
+    dutySlot = currentSlot + 1
+    dutyEpoch = dutySlot.epoch()
 
   if vc.attachedValidators[].count() != 0:
     let
@@ -417,15 +419,14 @@ proc pollForSyncCommitteeDuties*(service: DutiesServiceRef) {.async.} =
         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()
+            dutyPeriod = dutySlot.sync_committee_period()
+            lookaheadEpoch = dutyEpoch + SUBSCRIPTION_LOOKAHEAD_EPOCHS
+            lookaheadPeriod = lookaheadEpoch.sync_committee_period()
           res.add(
-            (epoch: currentSlot.epoch(),
-             period: currentPeriod)
+            (epoch: dutyEpoch,
+             period: dutyPeriod)
           )
-          if lookaheadPeriod > currentPeriod:
+          if lookaheadPeriod > dutyPeriod:
             res.add(
               (epoch: lookaheadPeriod.start_epoch(),
                period: lookaheadPeriod)
@@ -446,7 +447,7 @@ proc pollForSyncCommitteeDuties*(service: DutiesServiceRef) {.async.} =
 
     if total == 0:
       debug "No new sync committee member's duties received",
-            slot = currentSlot
+            slot = dutySlot
 
     let subscriptions =
       block:
@@ -470,10 +471,10 @@ proc pollForSyncCommitteeDuties*(service: DutiesServiceRef) {.async.} =
       let res = await vc.prepareSyncCommitteeSubnets(subscriptions)
       if res == 0:
         warn "Failed to subscribe validators to sync committee subnets",
-             slot = currentSlot, epoch = currentEpoch,
+             slot = dutySlot, epoch = dutyEpoch,
              subscriptions_count = len(subscriptions)
 
-  service.pruneSyncCommitteeDuties(currentSlot)
+  service.pruneSyncCommitteeDuties(dutySlot)
 
 proc pruneBeaconProposers(service: DutiesServiceRef, epoch: Epoch) =
   let vc = service.client