Fix iteration issue. (#5105)

Add elapsed_time to log statement.

beacon_chain/validator_client/common.nim

@@ -1231,3 +1231,7 @@ proc waitForBlock*(
     let dur = Moment.now() - startTime
     debug "Waiting for block cutoff was interrupted", duration = dur
     raise exc
+
+iterator chunks*[T](data: openArray[T], maxCount: Positive): seq[T] =
+  for i in countup(0, len(data) - 1, maxCount):
+    yield @(data.toOpenArray(i, min(i + maxCount, len(data)) - 1))

beacon_chain/validator_client/duties_service.nim

@@ -49,21 +49,11 @@ proc pollForValidatorIndices*(service: DutiesServiceRef) {.async.} =
           res.add(ValidatorIdent.init(validator.pubkey))
       res
 
+  let start = Moment.now()
+
   var validators: seq[RestValidator]
-  var offset = 0
-
-  while offset < len(validatorIdents):
-    let arraySize = min(ClientMaximumValidatorIds, len(validatorIdents))
-
-    let idents =
-      block:
-        var res = newSeq[ValidatorIdent](arraySize)
-        var k = 0
-        for i in offset ..< arraySize:
-          res[k] = validatorIdents[i]
-          inc(k)
-        res
 
+  for idents in chunks(validatorIdents, ClientMaximumValidatorIds):
     let res =
       try:
         await vc.getValidators(idents, ApiStrategyKind.First)
@@ -78,12 +68,9 @@ proc pollForValidatorIndices*(service: DutiesServiceRef) {.async.} =
         error "Unexpected error occurred while getting validator information",
               err_name = exc.name, err_msg = exc.msg
         return
-
     for item in res:
       validators.add(item)
 
-    offset += arraySize
-
   var
     missing: seq[string]
     updated: seq[string]
@@ -104,7 +91,8 @@ proc pollForValidatorIndices*(service: DutiesServiceRef) {.async.} =
     info "Validator indices updated",
       pending = len(validatorIdents) - len(updated),
       missing = len(missing),
-      updated = len(updated)
+      updated = len(updated),
+      elapsed_time = (Moment.now() - start)
     trace "Validator indices update dump", missing_validators = missing,
           updated_validators = updated
     vc.indicesAvailable.fire()