Merge pull request #5794 from ethereum-optimism/felipe/consensus-finalized-safe

feat(proxyd): track consensus for {safe,finalized} blocks and rewrite tags

proxyd/proxyd/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.18.0-alpine3.15 as builder
+FROM golang:1.20.4-alpine3.18 as builder
 
 ARG GITCOMMIT=docker
 ARG GITDATE=docker
@@ -12,7 +12,7 @@ WORKDIR /app
 
 RUN make proxyd
 
-FROM alpine:3.15
+FROM alpine:3.18
 
 COPY ./proxyd/entrypoint.sh /bin/entrypoint.sh
 

proxyd/proxyd/backend.go

@@ -374,7 +374,6 @@ func (b *Backend) ForwardRPC(ctx context.Context, res *RPCRes, id string, method
 func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool) ([]*RPCRes, error) {
 	// we are concerned about network error rates, so we record 1 request independently of how many are in the batch
 	b.networkRequestsSlidingWindow.Incr()
-	RecordBackendNetworkRequestCountSlidingWindow(b, b.networkRequestsSlidingWindow.Count())
 
 	isSingleElementBatch := len(rpcReqs) == 1
 
@@ -391,7 +390,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 	httpReq, err := http.NewRequestWithContext(ctx, "POST", b.rpcURL, bytes.NewReader(body))
 	if err != nil {
 		b.networkErrorsSlidingWindow.Incr()
-		RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+		RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 		return nil, wrapErr(err, "error creating backend request")
 	}
 
@@ -413,7 +412,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 	httpRes, err := b.client.DoLimited(httpReq)
 	if err != nil {
 		b.networkErrorsSlidingWindow.Incr()
-		RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+		RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 		return nil, wrapErr(err, "error in backend request")
 	}
 
@@ -432,7 +431,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 	// Alchemy returns a 400 on bad JSONs, so handle that case
 	if httpRes.StatusCode != 200 && httpRes.StatusCode != 400 {
 		b.networkErrorsSlidingWindow.Incr()
-		RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+		RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 		return nil, fmt.Errorf("response code %d", httpRes.StatusCode)
 	}
 
@@ -440,7 +439,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 	resB, err := io.ReadAll(io.LimitReader(httpRes.Body, b.maxResponseSize))
 	if err != nil {
 		b.networkErrorsSlidingWindow.Incr()
-		RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+		RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 		return nil, wrapErr(err, "error reading response body")
 	}
 
@@ -458,18 +457,18 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 			// Infura may return a single JSON-RPC response if, for example, the batch contains a request for an unsupported method
 			if responseIsNotBatched(resB) {
 				b.networkErrorsSlidingWindow.Incr()
-				RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+				RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 				return nil, ErrBackendUnexpectedJSONRPC
 			}
 			b.networkErrorsSlidingWindow.Incr()
-			RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+			RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 			return nil, ErrBackendBadResponse
 		}
 	}
 
 	if len(rpcReqs) != len(res) {
 		b.networkErrorsSlidingWindow.Incr()
-		RecordBackendNetworkErrorCountSlidingWindow(b, b.networkErrorsSlidingWindow.Count())
+		RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 		return nil, ErrBackendUnexpectedJSONRPC
 	}
 
@@ -483,6 +482,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 	duration := time.Since(start)
 	b.latencySlidingWindow.Add(float64(duration))
 	RecordBackendNetworkLatencyAverageSlidingWindow(b, time.Duration(b.latencySlidingWindow.Avg()))
+	RecordBackendNetworkErrorRateSlidingWindow(b, b.ErrorRate())
 
 	sortBatchRPCResponse(rpcReqs, res)
 	return res, nil
@@ -490,11 +490,7 @@ func (b *Backend) doForward(ctx context.Context, rpcReqs []*RPCReq, isBatch bool
 
 // IsHealthy checks if the backend is able to serve traffic, based on dynamic parameters
 func (b *Backend) IsHealthy() bool {
-	errorRate := float64(0)
+	errorRate := b.ErrorRate()
-	// avoid division-by-zero when the window is empty
-	if b.networkRequestsSlidingWindow.Sum() >= 10 {
-		errorRate = b.networkErrorsSlidingWindow.Sum() / b.networkRequestsSlidingWindow.Sum()
-	}
 	avgLatency := time.Duration(b.latencySlidingWindow.Avg())
 	if errorRate >= b.maxErrorRateThreshold {
 		return false
@@ -505,6 +501,16 @@ func (b *Backend) IsHealthy() bool {
 	return true
 }
 
+// ErrorRate returns the instant error rate of the backend
+func (b *Backend) ErrorRate() (errorRate float64) {
+	// we only really start counting the error rate after a minimum of 10 requests
+	// this is to avoid false positives when the backend is just starting up
+	if b.networkRequestsSlidingWindow.Sum() >= 10 {
+		errorRate = b.networkErrorsSlidingWindow.Sum() / b.networkRequestsSlidingWindow.Sum()
+	}
+	return errorRate
+}
+
 // IsDegraded checks if the backend is serving traffic in a degraded state (i.e. used as a last resource)
 func (b *Backend) IsDegraded() bool {
 	avgLatency := time.Duration(b.latencySlidingWindow.Avg())
@@ -556,7 +562,11 @@ func (bg *BackendGroup) Forward(ctx context.Context, rpcReqs []*RPCReq, isBatch
 		backends = bg.loadBalancedConsensusGroup()
 
 		// We also rewrite block tags to enforce compliance with consensus
-		rctx := RewriteContext{latest: bg.Consensus.GetConsensusBlockNumber()}
+		rctx := RewriteContext{
+			latest:    bg.Consensus.GetLatestBlockNumber(),
+			finalized: bg.Consensus.GetFinalizedBlockNumber(),
+			safe:      bg.Consensus.GetSafeBlockNumber(),
+		}
 
 		for i, req := range rpcReqs {
 			res := RPCRes{JSONRPC: JSONRPCVersion, ID: req.ID}

proxyd/proxyd/consensus_poller.go

@@ -35,7 +35,6 @@ type ConsensusPoller struct {
 	asyncHandler ConsensusAsyncHandler
 
 	minPeerCount       uint64
-
 	banPeriod          time.Duration
 	maxUpdateThreshold time.Duration
 	maxBlockLag        uint64
@@ -46,6 +45,10 @@ type backendState struct {
 
 	latestBlockNumber hexutil.Uint64
 	latestBlockHash   string
+
+	finalizedBlockNumber hexutil.Uint64
+	safeBlockNumber      hexutil.Uint64
+
 	peerCount uint64
 	inSync    bool
 
@@ -54,6 +57,10 @@ type backendState struct {
 	bannedUntil time.Time
 }
 
+func (bs *backendState) IsBanned() bool {
+	return time.Now().Before(bs.bannedUntil)
+}
+
 // GetConsensusGroup returns the backend members that are agreeing in a consensus
 func (cp *ConsensusPoller) GetConsensusGroup() []*Backend {
 	defer cp.consensusGroupMux.Unlock()
@@ -65,9 +72,19 @@ func (cp *ConsensusPoller) GetConsensusGroup() []*Backend {
 	return g
 }
 
-// GetConsensusBlockNumber returns the agreed block number in a consensus
+// GetLatestBlockNumber returns the `latest` agreed block number in a consensus
-func (ct *ConsensusPoller) GetConsensusBlockNumber() hexutil.Uint64 {
+func (ct *ConsensusPoller) GetLatestBlockNumber() hexutil.Uint64 {
-	return ct.tracker.GetConsensusBlockNumber()
+	return ct.tracker.GetLatestBlockNumber()
+}
+
+// GetFinalizedBlockNumber returns the `finalized` agreed block number in a consensus
+func (ct *ConsensusPoller) GetFinalizedBlockNumber() hexutil.Uint64 {
+	return ct.tracker.GetFinalizedBlockNumber()
+}
+
+// GetSafeBlockNumber returns the `safe` agreed block number in a consensus
+func (ct *ConsensusPoller) GetSafeBlockNumber() hexutil.Uint64 {
+	return ct.tracker.GetSafeBlockNumber()
 }
 
 func (cp *ConsensusPoller) Shutdown() {
@@ -163,6 +180,10 @@ func (cp *ConsensusPoller) AddListener(listener OnConsensusBroken) {
 	cp.listeners = append(cp.listeners, listener)
 }
 
+func (cp *ConsensusPoller) ClearListeners() {
+	cp.listeners = []OnConsensusBroken{}
+}
+
 func WithBanPeriod(banPeriod time.Duration) ConsensusOpt {
 	return func(cp *ConsensusPoller) {
 		cp.banPeriod = banPeriod
@@ -202,7 +223,7 @@ func NewConsensusPoller(bg *BackendGroup, opts ...ConsensusOpt) *ConsensusPoller
 
 		banPeriod:          5 * time.Minute,
 		maxUpdateThreshold: 30 * time.Second,
-		maxBlockLag:        50,
+		maxBlockLag:        8, // 8*12 seconds = 96 seconds ~ 1.6 minutes
 		minPeerCount:       3,
 	}
 
@@ -225,22 +246,21 @@ func NewConsensusPoller(bg *BackendGroup, opts ...ConsensusOpt) *ConsensusPoller
 
 // UpdateBackend refreshes the consensus state of a single backend
 func (cp *ConsensusPoller) UpdateBackend(ctx context.Context, be *Backend) {
-	banned := cp.IsBanned(be)
+	bs := cp.getBackendState(be)
-	RecordConsensusBackendBanned(be, banned)
+	RecordConsensusBackendBanned(be, bs.IsBanned())
 
-	if banned {
+	if bs.IsBanned() {
 		log.Debug("skipping backend - banned", "backend", be.Name)
 		return
 	}
 
 	// if backend is not healthy state we'll only resume checking it after ban
 	if !be.IsHealthy() {
-		log.Warn("backend banned - not online or not healthy", "backend", be.Name)
+		log.Warn("backend banned - not healthy", "backend", be.Name)
 		cp.Ban(be)
 		return
 	}
 
-	// if backend it not in sync we'll check again after ban
 	inSync, err := cp.isInSync(ctx, be)
 	RecordConsensusBackendInSync(be, err == nil && inSync)
 	if err != nil {
@@ -258,120 +278,123 @@ func (cp *ConsensusPoller) UpdateBackend(ctx context.Context, be *Backend) {
 
 	latestBlockNumber, latestBlockHash, err := cp.fetchBlock(ctx, be, "latest")
 	if err != nil {
-		log.Warn("error updating backend", "name", be.Name, "err", err)
+		log.Warn("error updating backend - latest block", "name", be.Name, "err", err)
 	}
 
-	changed, updateDelay := cp.setBackendState(be, peerCount, inSync, latestBlockNumber, latestBlockHash)
+	safeBlockNumber, _, err := cp.fetchBlock(ctx, be, "safe")
+	if err != nil {
+		log.Warn("error updating backend - safe block", "name", be.Name, "err", err)
+	}
+
+	finalizedBlockNumber, _, err := cp.fetchBlock(ctx, be, "finalized")
+	if err != nil {
+		log.Warn("error updating backend - finalized block", "name", be.Name, "err", err)
+	}
+
+	oldFinalized := bs.finalizedBlockNumber
+	oldSafe := bs.safeBlockNumber
+
+	updateDelay := time.Since(bs.lastUpdate)
+	RecordConsensusBackendUpdateDelay(be, updateDelay)
+
+	changed := cp.setBackendState(be, peerCount, inSync,
+		latestBlockNumber, latestBlockHash,
+		finalizedBlockNumber, safeBlockNumber)
+
+	RecordBackendLatestBlock(be, latestBlockNumber)
+	RecordBackendSafeBlock(be, safeBlockNumber)
+	RecordBackendFinalizedBlock(be, finalizedBlockNumber)
 
 	if changed {
-		RecordBackendLatestBlock(be, latestBlockNumber)
-		RecordConsensusBackendUpdateDelay(be, updateDelay)
 		log.Debug("backend state updated",
 			"name", be.Name,
 			"peerCount", peerCount,
 			"inSync", inSync,
 			"latestBlockNumber", latestBlockNumber,
 			"latestBlockHash", latestBlockHash,
+			"finalizedBlockNumber", finalizedBlockNumber,
+			"safeBlockNumber", safeBlockNumber,
 			"updateDelay", updateDelay)
 	}
+
+	// sanity check for latest, safe and finalized block tags
+	expectedBlockTags := cp.checkExpectedBlockTags(
+		finalizedBlockNumber, oldFinalized,
+		safeBlockNumber, oldSafe,
+		latestBlockNumber)
+
+	RecordBackendUnexpectedBlockTags(be, !expectedBlockTags)
+
+	if !expectedBlockTags {
+		log.Warn("backend banned - unexpected block tags",
+			"backend", be.Name,
+			"oldFinalized", oldFinalized,
+			"finalizedBlockNumber", finalizedBlockNumber,
+			"oldSafe", oldSafe,
+			"safeBlockNumber", safeBlockNumber,
+			"latestBlockNumber", latestBlockNumber,
+		)
+		cp.Ban(be)
+	}
+}
+
+// checkExpectedBlockTags for unexpected conditions on block tags
+// - finalized block number should never decrease
+// - safe block number should never decrease
+// - finalized block should be <= safe block <= latest block
+func (cp *ConsensusPoller) checkExpectedBlockTags(currentFinalized hexutil.Uint64, oldFinalized hexutil.Uint64,
+	currentSafe hexutil.Uint64, oldSafe hexutil.Uint64,
+	currentLatest hexutil.Uint64) bool {
+	return currentFinalized >= oldFinalized &&
+		currentSafe >= oldSafe &&
+		currentFinalized <= currentSafe &&
+		currentSafe <= currentLatest
 }
 
 // UpdateBackendGroupConsensus resolves the current group consensus based on the state of the backends
 func (cp *ConsensusPoller) UpdateBackendGroupConsensus(ctx context.Context) {
-	var highestBlock hexutil.Uint64
+	// get the latest block number from the tracker
-	var lowestBlock hexutil.Uint64
+	currentConsensusBlockNumber := cp.GetLatestBlockNumber()
-	var lowestBlockHash string
 
-	currentConsensusBlockNumber := cp.GetConsensusBlockNumber()
+	// get the candidates for the consensus group
+	candidates := cp.getConsensusCandidates()
 
-	// find the highest block, in order to use it defining the highest non-lagging ancestor block
+	// update the lowest latest block number and hash
-	for _, be := range cp.backendGroup.Backends {
+	//        the lowest safe block number
-		peerCount, inSync, backendLatestBlockNumber, _, lastUpdate, _ := cp.getBackendState(be)
+	//        the lowest finalized block number
-
+	var lowestLatestBlock hexutil.Uint64
-		if !be.skipPeerCountCheck && peerCount < cp.minPeerCount {
+	var lowestLatestBlockHash string
-			continue
+	var lowestFinalizedBlock hexutil.Uint64
+	var lowestSafeBlock hexutil.Uint64
+	for _, bs := range candidates {
+		if lowestLatestBlock == 0 || bs.latestBlockNumber < lowestLatestBlock {
+			lowestLatestBlock = bs.latestBlockNumber
+			lowestLatestBlockHash = bs.latestBlockHash
 		}
-		if !inSync {
+		if lowestFinalizedBlock == 0 || bs.finalizedBlockNumber < lowestFinalizedBlock {
-			continue
+			lowestFinalizedBlock = bs.finalizedBlockNumber
 		}
-		if lastUpdate.Add(cp.maxUpdateThreshold).Before(time.Now()) {
+		if lowestSafeBlock == 0 || bs.safeBlockNumber < lowestSafeBlock {
-			continue
+			lowestSafeBlock = bs.safeBlockNumber
-		}
-
-		if backendLatestBlockNumber > highestBlock {
-			highestBlock = backendLatestBlockNumber
 		}
 	}
 
-	// find the highest common ancestor block
+	// find the proposed block among the candidates
-	for _, be := range cp.backendGroup.Backends {
+	// the proposed block needs have the same hash in the entire consensus group
-		peerCount, inSync, backendLatestBlockNumber, backendLatestBlockHash, lastUpdate, _ := cp.getBackendState(be)
+	proposedBlock := lowestLatestBlock
-
+	proposedBlockHash := lowestLatestBlockHash
-		if !be.skipPeerCountCheck && peerCount < cp.minPeerCount {
-			continue
-		}
-		if !inSync {
-			continue
-		}
-		if lastUpdate.Add(cp.maxUpdateThreshold).Before(time.Now()) {
-			continue
-		}
-
-		// check if backend is lagging behind the highest block
-		if backendLatestBlockNumber < highestBlock && uint64(highestBlock-backendLatestBlockNumber) > cp.maxBlockLag {
-			continue
-		}
-
-		if lowestBlock == 0 || backendLatestBlockNumber < lowestBlock {
-			lowestBlock = backendLatestBlockNumber
-			lowestBlockHash = backendLatestBlockHash
-		}
-	}
-
-	// no block to propose (i.e. initializing consensus)
-	if lowestBlock == 0 {
-		return
-	}
-
-	proposedBlock := lowestBlock
-	proposedBlockHash := lowestBlockHash
 	hasConsensus := false
+	broken := false
 
-	// check if everybody agrees on the same block hash
+	if lowestLatestBlock > currentConsensusBlockNumber {
-	consensusBackends := make([]*Backend, 0, len(cp.backendGroup.Backends))
+		log.Debug("validating consensus on block", "lowestLatestBlock", lowestLatestBlock)
-	consensusBackendsNames := make([]string, 0, len(cp.backendGroup.Backends))
-	filteredBackendsNames := make([]string, 0, len(cp.backendGroup.Backends))
-
-	if lowestBlock > currentConsensusBlockNumber {
-		log.Debug("validating consensus on block", "lowestBlock", lowestBlock)
 	}
 
-	broken := false
+	// if there is a block to propose, check if it is the same in all backends
+	if proposedBlock > 0 {
 		for !hasConsensus {
 			allAgreed := true
-		consensusBackends = consensusBackends[:0]
+			for be := range candidates {
-		filteredBackendsNames = filteredBackendsNames[:0]
-		for _, be := range cp.backendGroup.Backends {
-			/*
-				a serving node needs to be:
-				- healthy (network)
-				- updated recently
-				- not banned
-				- with minimum peer count
-				- not lagging latest block
-				- in sync
-			*/
-
-			peerCount, inSync, latestBlockNumber, _, lastUpdate, bannedUntil := cp.getBackendState(be)
-			notUpdated := lastUpdate.Add(cp.maxUpdateThreshold).Before(time.Now())
-			isBanned := time.Now().Before(bannedUntil)
-			notEnoughPeers := !be.skipPeerCountCheck && peerCount < cp.minPeerCount
-			lagging := latestBlockNumber < proposedBlock
-			if !be.IsHealthy() || notUpdated || isBanned || notEnoughPeers || lagging || !inSync {
-				filteredBackendsNames = append(filteredBackendsNames, be.Name)
-				continue
-			}
-
 				actualBlockNumber, actualBlockHash, err := cp.fetchBlock(ctx, be, proposedBlock.String())
 				if err != nil {
 					log.Warn("error updating backend", "name", be.Name, "err", err)
@@ -383,14 +406,17 @@ func (cp *ConsensusPoller) UpdateBackendGroupConsensus(ctx context.Context) {
 				blocksDontMatch := (actualBlockNumber != proposedBlock) || (actualBlockHash != proposedBlockHash)
 				if blocksDontMatch {
 					if currentConsensusBlockNumber >= actualBlockNumber {
-					log.Warn("backend broke consensus", "name", be.Name, "blockNum", actualBlockNumber, "proposedBlockNum", proposedBlock, "blockHash", actualBlockHash, "proposedBlockHash", proposedBlockHash)
+						log.Warn("backend broke consensus",
+							"name", be.Name,
+							"actualBlockNumber", actualBlockNumber,
+							"actualBlockHash", actualBlockHash,
+							"proposedBlock", proposedBlock,
+							"proposedBlockHash", proposedBlockHash)
 						broken = true
 					}
 					allAgreed = false
 					break
 				}
-			consensusBackends = append(consensusBackends, be)
-			consensusBackendsNames = append(consensusBackendsNames, be.Name)
 			}
 			if allAgreed {
 				hasConsensus = true
@@ -401,26 +427,54 @@ func (cp *ConsensusPoller) UpdateBackendGroupConsensus(ctx context.Context) {
 				log.Debug("no consensus, now trying", "block:", proposedBlock)
 			}
 		}
+	}
 
 	if broken {
 		// propagate event to other interested parts, such as cache invalidator
 		for _, l := range cp.listeners {
 			l()
 		}
-		log.Info("consensus broken", "currentConsensusBlockNumber", currentConsensusBlockNumber, "proposedBlock", proposedBlock, "proposedBlockHash", proposedBlockHash)
+		log.Info("consensus broken",
+			"currentConsensusBlockNumber", currentConsensusBlockNumber,
+			"proposedBlock", proposedBlock,
+			"proposedBlockHash", proposedBlockHash)
+	}
+
+	// update tracker
+	cp.tracker.SetLatestBlockNumber(proposedBlock)
+	cp.tracker.SetSafeBlockNumber(lowestSafeBlock)
+	cp.tracker.SetFinalizedBlockNumber(lowestFinalizedBlock)
+
+	// update consensus group
+	group := make([]*Backend, 0, len(candidates))
+	consensusBackendsNames := make([]string, 0, len(candidates))
+	filteredBackendsNames := make([]string, 0, len(cp.backendGroup.Backends))
+	for _, be := range cp.backendGroup.Backends {
+		_, exist := candidates[be]
+		if exist {
+			group = append(group, be)
+			consensusBackendsNames = append(consensusBackendsNames, be.Name)
+		} else {
+			filteredBackendsNames = append(filteredBackendsNames, be.Name)
+		}
 	}
 
-	cp.tracker.SetConsensusBlockNumber(proposedBlock)
 	cp.consensusGroupMux.Lock()
-	cp.consensusGroup = consensusBackends
+	cp.consensusGroup = group
 	cp.consensusGroupMux.Unlock()
 
 	RecordGroupConsensusLatestBlock(cp.backendGroup, proposedBlock)
-	RecordGroupConsensusCount(cp.backendGroup, len(consensusBackends))
+	RecordGroupConsensusSafeBlock(cp.backendGroup, lowestSafeBlock)
+	RecordGroupConsensusFinalizedBlock(cp.backendGroup, lowestFinalizedBlock)
+
+	RecordGroupConsensusCount(cp.backendGroup, len(group))
 	RecordGroupConsensusFilteredCount(cp.backendGroup, len(filteredBackendsNames))
 	RecordGroupTotalCount(cp.backendGroup, len(cp.backendGroup.Backends))
 
-	log.Debug("group state", "proposedBlock", proposedBlock, "consensusBackends", strings.Join(consensusBackendsNames, ", "), "filteredBackends", strings.Join(filteredBackendsNames, ", "))
+	log.Debug("group state",
+		"proposedBlock", proposedBlock,
+		"consensusBackends", strings.Join(consensusBackendsNames, ", "),
+		"filteredBackends", strings.Join(filteredBackendsNames, ", "))
 }
 
 // IsBanned checks if a specific backend is banned
@@ -428,7 +482,7 @@ func (cp *ConsensusPoller) IsBanned(be *Backend) bool {
 	bs := cp.backendState[be]
 	defer bs.backendStateMux.Unlock()
 	bs.backendStateMux.Lock()
-	return time.Now().Before(bs.bannedUntil)
+	return bs.IsBanned()
 }
 
 // Ban bans a specific backend
@@ -437,19 +491,29 @@ func (cp *ConsensusPoller) Ban(be *Backend) {
 	defer bs.backendStateMux.Unlock()
 	bs.backendStateMux.Lock()
 	bs.bannedUntil = time.Now().Add(cp.banPeriod)
+
+	// when we ban a node, we give it the chance to start from any block when it is back
+	bs.latestBlockNumber = 0
+	bs.safeBlockNumber = 0
+	bs.finalizedBlockNumber = 0
 }
 
-// Unban remove any bans from the backends
+// Unban removes any bans from the backends
-func (cp *ConsensusPoller) Unban() {
+func (cp *ConsensusPoller) Unban(be *Backend) {
-	for _, be := range cp.backendGroup.Backends {
 	bs := cp.backendState[be]
+	defer bs.backendStateMux.Unlock()
 	bs.backendStateMux.Lock()
 	bs.bannedUntil = time.Now().Add(-10 * time.Hour)
-		bs.backendStateMux.Unlock()
+}
+
+// Reset reset all backend states
+func (cp *ConsensusPoller) Reset() {
+	for _, be := range cp.backendGroup.Backends {
+		cp.backendState[be] = &backendState{}
 	}
 }
 
-// fetchBlock Convenient wrapper to make a request to get a block directly from the backend
+// fetchBlock is a convenient wrapper to make a request to get a block directly from the backend
 func (cp *ConsensusPoller) fetchBlock(ctx context.Context, be *Backend, block string) (blockNumber hexutil.Uint64, blockHash string, err error) {
 	var rpcRes RPCRes
 	err = be.ForwardRPC(ctx, &rpcRes, "67", "eth_getBlockByNumber", block, false)
@@ -467,7 +531,7 @@ func (cp *ConsensusPoller) fetchBlock(ctx context.Context, be *Backend, block st
 	return
 }
 
-// getPeerCount Convenient wrapper to retrieve the current peer count from the backend
+// getPeerCount is a convenient wrapper to retrieve the current peer count from the backend
 func (cp *ConsensusPoller) getPeerCount(ctx context.Context, be *Backend) (count uint64, err error) {
 	var rpcRes RPCRes
 	err = be.ForwardRPC(ctx, &rpcRes, "67", "net_peerCount")
@@ -512,29 +576,97 @@ func (cp *ConsensusPoller) isInSync(ctx context.Context, be *Backend) (result bo
 	return res, nil
 }
 
-func (cp *ConsensusPoller) getBackendState(be *Backend) (peerCount uint64, inSync bool, blockNumber hexutil.Uint64, blockHash string, lastUpdate time.Time, bannedUntil time.Time) {
+// getBackendState creates a copy of backend state so that the caller can use it without locking
+func (cp *ConsensusPoller) getBackendState(be *Backend) *backendState {
 	bs := cp.backendState[be]
 	defer bs.backendStateMux.Unlock()
 	bs.backendStateMux.Lock()
-	peerCount = bs.peerCount
+
-	inSync = bs.inSync
+	return &backendState{
-	blockNumber = bs.latestBlockNumber
+		latestBlockNumber:    bs.latestBlockNumber,
-	blockHash = bs.latestBlockHash
+		latestBlockHash:      bs.latestBlockHash,
-	lastUpdate = bs.lastUpdate
+		safeBlockNumber:      bs.safeBlockNumber,
-	bannedUntil = bs.bannedUntil
+		finalizedBlockNumber: bs.finalizedBlockNumber,
-	return
+		peerCount:            bs.peerCount,
+		inSync:               bs.inSync,
+		lastUpdate:           bs.lastUpdate,
+		bannedUntil:          bs.bannedUntil,
+	}
 }
 
-func (cp *ConsensusPoller) setBackendState(be *Backend, peerCount uint64, inSync bool, blockNumber hexutil.Uint64, blockHash string) (changed bool, updateDelay time.Duration) {
+func (cp *ConsensusPoller) setBackendState(be *Backend, peerCount uint64, inSync bool,
+	latestBlockNumber hexutil.Uint64, latestBlockHash string,
+	finalizedBlockNumber hexutil.Uint64,
+	safeBlockNumber hexutil.Uint64) bool {
 	bs := cp.backendState[be]
 	bs.backendStateMux.Lock()
-	changed = bs.latestBlockHash != blockHash
+	changed := bs.latestBlockHash != latestBlockHash
 	bs.peerCount = peerCount
 	bs.inSync = inSync
-	bs.latestBlockNumber = blockNumber
+	bs.latestBlockNumber = latestBlockNumber
-	bs.latestBlockHash = blockHash
+	bs.latestBlockHash = latestBlockHash
-	updateDelay = time.Since(bs.lastUpdate)
+	bs.finalizedBlockNumber = finalizedBlockNumber
+	bs.safeBlockNumber = safeBlockNumber
 	bs.lastUpdate = time.Now()
 	bs.backendStateMux.Unlock()
-	return
+	return changed
+}
+
+// getConsensusCandidates find out what backends are the candidates to be in the consensus group
+// and create a copy of current their state
+//
+// a candidate is a serving node within the following conditions:
+//   - not banned
+//   - healthy (network latency and error rate)
+//   - with minimum peer count
+//   - in sync
+//   - updated recently
+//   - not lagging latest block
+func (cp *ConsensusPoller) getConsensusCandidates() map[*Backend]*backendState {
+	candidates := make(map[*Backend]*backendState, len(cp.backendGroup.Backends))
+
+	for _, be := range cp.backendGroup.Backends {
+		bs := cp.getBackendState(be)
+		if bs.IsBanned() {
+			continue
+		}
+		if !be.IsHealthy() {
+			continue
+		}
+		if !be.skipPeerCountCheck && bs.peerCount < cp.minPeerCount {
+			continue
+		}
+		if !bs.inSync {
+			continue
+		}
+		if bs.lastUpdate.Add(cp.maxUpdateThreshold).Before(time.Now()) {
+			continue
+		}
+
+		candidates[be] = bs
+	}
+
+	// find the highest block, in order to use it defining the highest non-lagging ancestor block
+	var highestLatestBlock hexutil.Uint64
+	for _, bs := range candidates {
+		if bs.latestBlockNumber > highestLatestBlock {
+			highestLatestBlock = bs.latestBlockNumber
+		}
+	}
+
+	// find the highest common ancestor block
+	lagging := make([]*Backend, 0, len(candidates))
+	for be, bs := range candidates {
+		// check if backend is lagging behind the highest block
+		if bs.latestBlockNumber < highestLatestBlock && uint64(highestLatestBlock-bs.latestBlockNumber) > cp.maxBlockLag {
+			lagging = append(lagging, be)
+		}
+	}
+
+	// remove lagging backends from the candidates
+	for _, be := range lagging {
+		delete(candidates, be)
+	}
+
+	return candidates
 }

proxyd/proxyd/consensus_tracker.go

@@ -13,35 +13,68 @@ import (
 // ConsensusTracker abstracts how we store and retrieve the current consensus
 // allowing it to be stored locally in-memory or in a shared Redis cluster
 type ConsensusTracker interface {
-	GetConsensusBlockNumber() hexutil.Uint64
+	GetLatestBlockNumber() hexutil.Uint64
-	SetConsensusBlockNumber(blockNumber hexutil.Uint64)
+	SetLatestBlockNumber(blockNumber hexutil.Uint64)
+	GetFinalizedBlockNumber() hexutil.Uint64
+	SetFinalizedBlockNumber(blockNumber hexutil.Uint64)
+	GetSafeBlockNumber() hexutil.Uint64
+	SetSafeBlockNumber(blockNumber hexutil.Uint64)
 }
 
 // InMemoryConsensusTracker store and retrieve in memory, async-safe
 type InMemoryConsensusTracker struct {
-	consensusBlockNumber hexutil.Uint64
+	latestBlockNumber    hexutil.Uint64
+	finalizedBlockNumber hexutil.Uint64
+	safeBlockNumber      hexutil.Uint64
 	mutex                sync.Mutex
 }
 
 func NewInMemoryConsensusTracker() ConsensusTracker {
 	return &InMemoryConsensusTracker{
-		consensusBlockNumber: 0,
 		mutex: sync.Mutex{},
 	}
 }
 
-func (ct *InMemoryConsensusTracker) GetConsensusBlockNumber() hexutil.Uint64 {
+func (ct *InMemoryConsensusTracker) GetLatestBlockNumber() hexutil.Uint64 {
 	defer ct.mutex.Unlock()
 	ct.mutex.Lock()
 
-	return ct.consensusBlockNumber
+	return ct.latestBlockNumber
 }
 
-func (ct *InMemoryConsensusTracker) SetConsensusBlockNumber(blockNumber hexutil.Uint64) {
+func (ct *InMemoryConsensusTracker) SetLatestBlockNumber(blockNumber hexutil.Uint64) {
 	defer ct.mutex.Unlock()
 	ct.mutex.Lock()
 
-	ct.consensusBlockNumber = blockNumber
+	ct.latestBlockNumber = blockNumber
+}
+
+func (ct *InMemoryConsensusTracker) GetFinalizedBlockNumber() hexutil.Uint64 {
+	defer ct.mutex.Unlock()
+	ct.mutex.Lock()
+
+	return ct.finalizedBlockNumber
+}
+
+func (ct *InMemoryConsensusTracker) SetFinalizedBlockNumber(blockNumber hexutil.Uint64) {
+	defer ct.mutex.Unlock()
+	ct.mutex.Lock()
+
+	ct.finalizedBlockNumber = blockNumber
+}
+
+func (ct *InMemoryConsensusTracker) GetSafeBlockNumber() hexutil.Uint64 {
+	defer ct.mutex.Unlock()
+	ct.mutex.Lock()
+
+	return ct.safeBlockNumber
+}
+
+func (ct *InMemoryConsensusTracker) SetSafeBlockNumber(blockNumber hexutil.Uint64) {
+	defer ct.mutex.Unlock()
+	ct.mutex.Lock()
+
+	ct.safeBlockNumber = blockNumber
 }
 
 // RedisConsensusTracker uses a Redis `client` to store and retrieve consensus, async-safe
@@ -59,14 +92,29 @@ func NewRedisConsensusTracker(ctx context.Context, r *redis.Client, namespace st
 	}
 }
 
-func (ct *RedisConsensusTracker) key() string {
+func (ct *RedisConsensusTracker) key(tag string) string {
-	return fmt.Sprintf("consensus_latest_block:%s", ct.backendGroup)
+	return fmt.Sprintf("consensus:%s:%s", ct.backendGroup, tag)
 }
 
-func (ct *RedisConsensusTracker) GetConsensusBlockNumber() hexutil.Uint64 {
+func (ct *RedisConsensusTracker) GetLatestBlockNumber() hexutil.Uint64 {
-	return hexutil.Uint64(hexutil.MustDecodeUint64(ct.client.Get(ct.ctx, ct.key()).Val()))
+	return hexutil.Uint64(hexutil.MustDecodeUint64(ct.client.Get(ct.ctx, ct.key("latest")).Val()))
 }
 
-func (ct *RedisConsensusTracker) SetConsensusBlockNumber(blockNumber hexutil.Uint64) {
+func (ct *RedisConsensusTracker) SetLatestBlockNumber(blockNumber hexutil.Uint64) {
-	ct.client.Set(ct.ctx, ct.key(), blockNumber, 0)
+	ct.client.Set(ct.ctx, ct.key("latest"), blockNumber, 0)
+}
+
+func (ct *RedisConsensusTracker) GetFinalizedBlockNumber() hexutil.Uint64 {
+	return hexutil.Uint64(hexutil.MustDecodeUint64(ct.client.Get(ct.ctx, ct.key("finalized")).Val()))
+}
+
+func (ct *RedisConsensusTracker) SetFinalizedBlockNumber(blockNumber hexutil.Uint64) {
+	ct.client.Set(ct.ctx, ct.key("finalized"), blockNumber, 0)
+}
+func (ct *RedisConsensusTracker) GetSafeBlockNumber() hexutil.Uint64 {
+	return hexutil.Uint64(hexutil.MustDecodeUint64(ct.client.Get(ct.ctx, ct.key("safe")).Val()))
+}
+
+func (ct *RedisConsensusTracker) SetSafeBlockNumber(blockNumber hexutil.Uint64) {
+	ct.client.Set(ct.ctx, ct.key("safe"), blockNumber, 0)
 }

proxyd/proxyd/example.config.toml

@@ -93,8 +93,8 @@ backends = ["infura"]
 # consensus_ban_period = "1m"
 # Maximum delay for update the backend, default 30s
 # consensus_max_update_threshold = "20s"
-# Maximum block lag, default 50
+# Maximum block lag, default 8
-# consensus_max_block_lag = 10
+# consensus_max_block_lag = 16
 # Minimum peer count, default 3
 # consensus_min_peer_count = 4
 

proxyd/proxyd/integration_tests/testdata/consensus.toml

@@ -18,7 +18,7 @@ consensus_aware = true
 consensus_handler = "noop" # allow more control over the consensus poller for tests
 consensus_ban_period = "1m"
 consensus_max_update_threshold = "2m"
-consensus_max_block_lag = 50
+consensus_max_block_lag = 8
 consensus_min_peer_count = 4
 
 [rpc_method_mappings]

proxyd/proxyd/integration_tests/testdata/consensus_responses.yml

@@ -26,40 +26,161 @@
       "jsonrpc": "2.0",
       "id": 67,
       "result": {
-        "hash": "hash1",
+        "hash": "hash_0x101",
-        "number": "0x1"
+        "number": "0x101"
       }
     }
 - method: eth_getBlockByNumber
-  block: 0x1
+  block: 0x101
   response: >
     {
       "jsonrpc": "2.0",
       "id": 67,
       "result": {
-        "hash": "hash1",
+        "hash": "hash_0x101",
-        "number": "0x1"
+        "number": "0x101"
       }
     }
 - method: eth_getBlockByNumber
-  block: 0x2
+  block: 0x102
   response: >
     {
       "jsonrpc": "2.0",
       "id": 67,
       "result": {
-        "hash": "hash2",
+        "hash": "hash_0x102",
-        "number": "0x2"
+        "number": "0x102"
       }
     }
 - method: eth_getBlockByNumber
-  block: 0x3
+  block: 0x103
   response: >
     {
       "jsonrpc": "2.0",
       "id": 67,
       "result": {
-        "hash": "hash3",
+        "hash": "hash_0x103",
-        "number": "0x3"
+        "number": "0x103"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x10a
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x10a",
+        "number": "0x10a"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x132
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x132",
+        "number": "0x132"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x133
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x133",
+        "number": "0x133"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x134
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x134",
+        "number": "0x134"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x200
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x200",
+        "number": "0x200"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0x91
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0x91",
+        "number": "0x91"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: safe
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0xe1",
+        "number": "0xe1"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0xe1
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0xe1",
+        "number": "0xe1"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: finalized
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0xc1",
+        "number": "0xc1"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0xc1
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0xc1",
+        "number": "0xc1"
+      }
+    }
+- method: eth_getBlockByNumber
+  block: 0xd1
+  response: >
+    {
+      "jsonrpc": "2.0",
+      "id": 67,
+      "result": {
+        "hash": "hash_0xd1",
+        "number": "0xd1"
       }
     }

proxyd/proxyd/metrics.go

@@ -246,6 +246,22 @@ var (
 		"backend_group_name",
 	})
 
+	consensusSafeBlock = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: MetricsNamespace,
+		Name:      "group_consensus_safe_block",
+		Help:      "Consensus safe block",
+	}, []string{
+		"backend_group_name",
+	})
+
+	consensusFinalizedBlock = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: MetricsNamespace,
+		Name:      "group_consensus_finalized_block",
+		Help:      "Consensus finalized block",
+	}, []string{
+		"backend_group_name",
+	})
+
 	backendLatestBlockBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: MetricsNamespace,
 		Name:      "backend_latest_block",
@@ -254,6 +270,30 @@ var (
 		"backend_name",
 	})
 
+	backendSafeBlockBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: MetricsNamespace,
+		Name:      "backend_safe_block",
+		Help:      "Current safe block observed per backend",
+	}, []string{
+		"backend_name",
+	})
+
+	backendFinalizedBlockBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: MetricsNamespace,
+		Name:      "backend_finalized_block",
+		Help:      "Current finalized block observed per backend",
+	}, []string{
+		"backend_name",
+	})
+
+	backendUnexpectedBlockTagsBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: MetricsNamespace,
+		Name:      "backend_unexpected_block_tags",
+		Help:      "Bool gauge for unexpected block tags",
+	}, []string{
+		"backend_name",
+	})
+
 	consensusGroupCount = promauto.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: MetricsNamespace,
 		Name:      "group_consensus_count",
@@ -318,18 +358,10 @@ var (
 		"backend_name",
 	})
 
-	networkErrorCountBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
+	networkErrorRateBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: MetricsNamespace,
-		Name:      "backend_net_error_count",
+		Name:      "backend_error_rate",
-		Help:      "Network error count per backend",
+		Help:      "Request error rate per backend",
-	}, []string{
-		"backend_name",
-	})
-
-	requestCountBackend = promauto.NewGaugeVec(prometheus.GaugeOpts{
-		Namespace: MetricsNamespace,
-		Name:      "backend_request_count",
-		Help:      "Request count per backend",
 	}, []string{
 		"backend_name",
 	})
@@ -402,6 +434,14 @@ func RecordGroupConsensusLatestBlock(group *BackendGroup, blockNumber hexutil.Ui
 	consensusLatestBlock.WithLabelValues(group.Name).Set(float64(blockNumber))
 }
 
+func RecordGroupConsensusSafeBlock(group *BackendGroup, blockNumber hexutil.Uint64) {
+	consensusSafeBlock.WithLabelValues(group.Name).Set(float64(blockNumber))
+}
+
+func RecordGroupConsensusFinalizedBlock(group *BackendGroup, blockNumber hexutil.Uint64) {
+	consensusFinalizedBlock.WithLabelValues(group.Name).Set(float64(blockNumber))
+}
+
 func RecordGroupConsensusCount(group *BackendGroup, count int) {
 	consensusGroupCount.WithLabelValues(group.Name).Set(float64(count))
 }
@@ -418,12 +458,20 @@ func RecordBackendLatestBlock(b *Backend, blockNumber hexutil.Uint64) {
 	backendLatestBlockBackend.WithLabelValues(b.Name).Set(float64(blockNumber))
 }
 
+func RecordBackendSafeBlock(b *Backend, blockNumber hexutil.Uint64) {
+	backendSafeBlockBackend.WithLabelValues(b.Name).Set(float64(blockNumber))
+}
+
+func RecordBackendFinalizedBlock(b *Backend, blockNumber hexutil.Uint64) {
+	backendFinalizedBlockBackend.WithLabelValues(b.Name).Set(float64(blockNumber))
+}
+
+func RecordBackendUnexpectedBlockTags(b *Backend, unexpected bool) {
+	backendUnexpectedBlockTagsBackend.WithLabelValues(b.Name).Set(boolToFloat64(unexpected))
+}
+
 func RecordConsensusBackendBanned(b *Backend, banned bool) {
-	v := float64(0)
+	consensusBannedBackends.WithLabelValues(b.Name).Set(boolToFloat64(banned))
-	if banned {
-		v = float64(1)
-	}
-	consensusBannedBackends.WithLabelValues(b.Name).Set(v)
 }
 
 func RecordConsensusBackendPeerCount(b *Backend, peerCount uint64) {
@@ -431,11 +479,7 @@ func RecordConsensusBackendPeerCount(b *Backend, peerCount uint64) {
 }
 
 func RecordConsensusBackendInSync(b *Backend, inSync bool) {
-	v := float64(0)
+	consensusInSyncBackend.WithLabelValues(b.Name).Set(boolToFloat64(inSync))
-	if inSync {
-		v = float64(1)
-	}
-	consensusInSyncBackend.WithLabelValues(b.Name).Set(v)
 }
 
 func RecordConsensusBackendUpdateDelay(b *Backend, delay time.Duration) {
@@ -446,10 +490,13 @@ func RecordBackendNetworkLatencyAverageSlidingWindow(b *Backend, avgLatency time
 	avgLatencyBackend.WithLabelValues(b.Name).Set(float64(avgLatency.Milliseconds()))
 }
 
-func RecordBackendNetworkRequestCountSlidingWindow(b *Backend, count uint) {
+func RecordBackendNetworkErrorRateSlidingWindow(b *Backend, rate float64) {
-	requestCountBackend.WithLabelValues(b.Name).Set(float64(count))
+	networkErrorRateBackend.WithLabelValues(b.Name).Set(rate)
 }
 
-func RecordBackendNetworkErrorCountSlidingWindow(b *Backend, count uint) {
+func boolToFloat64(b bool) float64 {
-	networkErrorCountBackend.WithLabelValues(b.Name).Set(float64(count))
+	if b {
+		return 1
+	}
+	return 0
 }

proxyd/proxyd/rewriter.go

@@ -10,6 +10,8 @@ import (
 
 type RewriteContext struct {
 	latest    hexutil.Uint64
+	safe      hexutil.Uint64
+	finalized hexutil.Uint64
 }
 
 type RewriteResult uint8
@@ -180,11 +182,13 @@ func rewriteTag(rctx RewriteContext, current string) (string, bool, error) {
 	}
 
 	switch *bnh.BlockNumber {
-	case rpc.SafeBlockNumber,
+	case rpc.PendingBlockNumber,
-		rpc.FinalizedBlockNumber,
-		rpc.PendingBlockNumber,
 		rpc.EarliestBlockNumber:
 		return current, false, nil
+	case rpc.FinalizedBlockNumber:
+		return rctx.finalized.String(), true, nil
+	case rpc.SafeBlockNumber:
+		return rctx.safe.String(), true, nil
 	case rpc.LatestBlockNumber:
 		return rctx.latest.String(), true, nil
 	default:

proxyd/proxyd/rewriter_test.go

@@ -326,33 +326,33 @@ func TestRewriteRequest(t *testing.T) {
 		{
 			name: "eth_getBlockByNumber finalized",
 			args: args{
-				rctx: RewriteContext{latest: hexutil.Uint64(100)},
+				rctx: RewriteContext{latest: hexutil.Uint64(100), finalized: hexutil.Uint64(55)},
 				req:  &RPCReq{Method: "eth_getBlockByNumber", Params: mustMarshalJSON([]string{"finalized"})},
 				res:  nil,
 			},
-			expected: RewriteNone,
+			expected: RewriteOverrideRequest,
 			check: func(t *testing.T, args args) {
 				var p []string
 				err := json.Unmarshal(args.req.Params, &p)
 				require.Nil(t, err)
 				require.Equal(t, 1, len(p))
-				require.Equal(t, "finalized", p[0])
+				require.Equal(t, hexutil.Uint64(55).String(), p[0])
 			},
 		},
 		{
 			name: "eth_getBlockByNumber safe",
 			args: args{
-				rctx: RewriteContext{latest: hexutil.Uint64(100)},
+				rctx: RewriteContext{latest: hexutil.Uint64(100), safe: hexutil.Uint64(50)},
 				req:  &RPCReq{Method: "eth_getBlockByNumber", Params: mustMarshalJSON([]string{"safe"})},
 				res:  nil,
 			},
-			expected: RewriteNone,
+			expected: RewriteOverrideRequest,
 			check: func(t *testing.T, args args) {
 				var p []string
 				err := json.Unmarshal(args.req.Params, &p)
 				require.Nil(t, err)
 				require.Equal(t, 1, len(p))
-				require.Equal(t, "safe", p[0])
+				require.Equal(t, hexutil.Uint64(50).String(), p[0])
 			},
 		},
 		{

proxyd/proxyd/tools/mockserver/handler/handler.go

@@ -95,7 +95,7 @@ func (mh *MockedHandler) Handler(w http.ResponseWriter, req *http.Request) {
 	resBody := ""
 	if batched {
 		resBody = "[" + strings.Join(responses, ",") + "]"
-	} else {
+	} else if len(responses) > 0 {
 		resBody = responses[0]
 	}