only retrieve pubkey once for all validators (partially fixes #4865) (#4895)

## Description

in consensus/state.go, when calulating metrics, retrieve address (ergo, pubkey) once prior to iterating over validatorset to ensure we do not make excessive calls to signer.

Partially closes: #4865

CHANGELOG_PENDING.md

@@ -87,3 +87,4 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
 - [types] [\#4764](https://github.com/tendermint/tendermint/pull/4764) Return an error if voting power overflows in `VerifyCommitTrusting` (@melekes)
 - [privval] [\#4812](https://github.com/tendermint/tendermint/pull/4812) Retry `GetPubKey/SignVote/SignProposal` a few times before returning an error (@melekes)
 - [p2p] [\#4847](https://github.com/tendermint/tendermint/pull/4847) Return masked IP (not the actual IP) in addrbook#groupKey (@melekes)
+- [consensus] [\#4895](https://github.com/tendermint/tendermint/pull/4895) Cache the address of the validator to reduce querying a remote KMS (@joe-bowman)

consensus/state.go

@@ -1552,12 +1552,23 @@ func (cs *State) recordMetrics(height int64, block *types.Block) {
 		var (
 			commitSize = block.LastCommit.Size()
 			valSetLen  = len(cs.LastValidators.Validators)
+			address    types.Address
 		)
 		if commitSize != valSetLen {
 			panic(fmt.Sprintf("commit size (%d) doesn't match valset length (%d) at height %d\n\n%v\n\n%v",
 				commitSize, valSetLen, block.Height, block.LastCommit.Signatures, cs.LastValidators.Validators))
 		}
 
+		if cs.privValidator != nil {
+			pubkey, err := cs.privValidator.GetPubKey()
+			if err != nil {
+				// Metrics won't be updated, but it's not critical.
+				cs.Logger.Error("Error on retrieval of pubkey", "err", err)
+			} else {
+				address = pubkey.Address()
+			}
+		}
+
 		for i, val := range cs.LastValidators.Validators {
 			commitSig := block.LastCommit.Signatures[i]
 			if commitSig.Absent() {
@@ -1565,26 +1576,18 @@ func (cs *State) recordMetrics(height int64, block *types.Block) {
 				missingValidatorsPower += val.VotingPower
 			}
 
-			if cs.privValidator != nil {
-				pubKey, err := cs.privValidator.GetPubKey()
-				if err != nil {
-					// Metrics won't be updated, but it's not critical.
-					cs.Logger.Error("Error on retrival of pubkey", "err", err)
-					continue
+			if bytes.Equal(val.Address, address) {
+				label := []string{
+					"validator_address", val.Address.String(),
 				}
-
-				if bytes.Equal(val.Address, pubKey.Address()) {
-					label := []string{
-						"validator_address", val.Address.String(),
-					}
-					cs.metrics.ValidatorPower.With(label...).Set(float64(val.VotingPower))
-					if commitSig.ForBlock() {
-						cs.metrics.ValidatorLastSignedHeight.With(label...).Set(float64(height))
-					} else {
-						cs.metrics.ValidatorMissedBlocks.With(label...).Add(float64(1))
-					}
+				cs.metrics.ValidatorPower.With(label...).Set(float64(val.VotingPower))
+				if commitSig.ForBlock() {
+					cs.metrics.ValidatorLastSignedHeight.With(label...).Set(float64(height))
+				} else {
+					cs.metrics.ValidatorMissedBlocks.With(label...).Add(float64(1))
 				}
 			}
+
 		}
 	}
 	cs.metrics.MissingValidators.Set(float64(missingValidators))