fix: use sync.Pool for msgId hasher

waku/v2/protocol/relay/waku_relay.go

@@ -6,6 +6,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"hash"
 	"sync"
 
 	"github.com/libp2p/go-libp2p/core/host"
@@ -51,9 +52,22 @@ type WakuRelay struct {
 	subscriptionsMutex sync.Mutex
 }
 
+var sha256Pool = sync.Pool{New: func() interface{} {
+	return sha256.New()
+}}
+
 func msgIdFn(pmsg *pubsub_pb.Message) string {
-	hash := sha256.Sum256(pmsg.Data)
-	return string(hash[:])
+	h, ok := sha256Pool.Get().(hash.Hash)
+	if !ok {
+		h = sha256.New()
+	}
+	defer sha256Pool.Put(h)
+	h.Reset()
+
+	var result [32]byte
+	h.Write(pmsg.Data)
+	h.Sum(result[:0])
+	return string(result[:])
 }
 
 // NewWakuRelay returns a new instance of a WakuRelay struct

waku/v2/protocol/relay/waku_relay_test.go

@@ -5,6 +5,7 @@ import (
 	"crypto/rand"
 	"testing"
 
+	pubsub_pb "github.com/libp2p/go-libp2p-pubsub/pb"
 	"github.com/stretchr/testify/require"
 	"github.com/waku-org/go-waku/tests"
 	"github.com/waku-org/go-waku/waku/v2/protocol/pb"
@@ -53,3 +54,17 @@ func TestWakuRelay(t *testing.T) {
 
 	<-ctx.Done()
 }
+
+func TestMsgID(t *testing.T) {
+	expectedMsgIdBytes := []byte{208, 214, 63, 55, 144, 6, 206, 39, 40, 251, 138, 74, 66, 168, 43, 32, 91, 94, 149, 122, 237, 198, 149, 87, 232, 156, 197, 34, 53, 131, 78, 112}
+
+	topic := "abcde"
+	msg := &pubsub_pb.Message{
+		Data:  []byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
+		Topic: &topic,
+	}
+
+	msgId := msgIdFn(msg)
+
+	require.Equal(t, expectedMsgIdBytes, []byte(msgId))
+}