rate limiting using token bucket

relayer/relays/beefy/main.go

@@ -3,6 +3,7 @@ package beefy
 import (
 	"context"
 	"fmt"
+	"sync/atomic"
 	"time"
 
 	"golang.org/x/sync/errgroup"
@@ -198,13 +199,27 @@ func (relay *Relay) RateLimitedSync(ctx context.Context) error {
 		return fmt.Errorf("create gateway client: %w", err)
 	}
 
+	var tokens atomic.Uint64
+	tokens.Store(1)
+
+	go refiller(ctx, &tokens, 1, 1, time.Minute*30)
+
 	for {
+		log.Info("Starting check")
+
 		paraNonce, ethNonce, err := relay.queryNonces(ctx, parachainConn, gatewayContract)
 		if err != nil {
-			return fmt.Errorf("require sync: %w", err)
+			return fmt.Errorf("query nonces: %w", err)
 		}
 
-		if paraNonce > ethNonce {
+		log.WithFields(log.Fields{
+			"paraNonce": paraNonce,
+			"ethNonce":  ethNonce,
+		}).Info("Nonces checked")
+
+		if paraNonce > ethNonce && tryConsume(&tokens) {
+			log.Info("Performing sync")
+
 			beefyBlockHash, err := relay.relaychainConn.API().RPC.Beefy.GetFinalizedHead()
 			if err != nil {
 				return fmt.Errorf("fetch latest beefy block: %w", err)
@@ -216,6 +231,12 @@ func (relay *Relay) RateLimitedSync(ctx context.Context) error {
 			}
 
 			relay.doSync(ctx, uint64(header.Number))
+
+			if tokens.Load() > 0 {
+				tokens.Add(^uint64(0))
+			}
+
+			log.Info("Sync completed")
 		}
 
 		// Sleep for 5 minute
@@ -227,6 +248,35 @@ func (relay *Relay) RateLimitedSync(ctx context.Context) error {
 	}
 }
 
+func refiller(ctx context.Context, tokens *atomic.Uint64, refillAmount uint64, maxTokens uint64, refillPeriod time.Duration) {
+	ticker := time.NewTicker(refillPeriod)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			currentTokens := tokens.Load()
+			newTokens := currentTokens + refillAmount
+			tokens.Store(newTokens)
+		}
+	}
+}
+
+func tryConsume(tokens *atomic.Uint64) bool {
+	for {
+		currentTokens := tokens.Load()
+		if currentTokens < 1 {
+			return false
+		}
+
+		if tokens.CompareAndSwap(currentTokens, currentTokens-1) {
+			return true
+		}
+	}
+}
+
 func (relay *Relay) queryNonces(ctx context.Context, parachainConn *parachain.Connection, gatewayContract *contracts.Gateway) (uint64, uint64, error) {
 	data, err := types.HexDecodeString("0xc173fac324158e77fb5840738a1a541f633cbec8884c6a601c567d2b376a0539")
 	if err != nil {