feat(rln): multiple acceptable roots

waku/v2/protocol/rln/rln_relay_builder.go

@@ -36,13 +36,6 @@ func RlnRelayStatic(
 		return nil, err
 	}
 
-	// add members to the Merkle tree
-	for _, member := range group {
-		if err := rlnInstance.InsertMember(member); err != nil {
-			return nil, err
-		}
-	}
-
 	// create the WakuRLNRelay
 	rlnPeer := &WakuRLNRelay{
 		ctx:               ctx,
@@ -55,6 +48,20 @@ func RlnRelayStatic(
 		nullifierLog:      make(map[r.Epoch][]r.ProofMetadata),
 	}
 
+	root, err := rlnPeer.RLN.GetMerkleRoot()
+	if err != nil {
+		return nil, err
+	}
+
+	rlnPeer.validMerkleRoots = append(rlnPeer.validMerkleRoots, root)
+
+	// add members to the Merkle tree
+	for _, member := range group {
+		if err := rlnPeer.insertMember(member); err != nil {
+			return nil, err
+		}
+	}
+
 	// adds a topic validator for the supplied pubsub topic at the relay protocol
 	// messages published on this pubsub topic will be relayed upon a successful validation, otherwise they will be dropped
 	// the topic validator checks for the correct non-spamming proof of the message
@@ -106,6 +113,13 @@ func RlnRelayDynamic(
 		registrationHandler:       registrationHandler,
 	}
 
+	root, err := rlnPeer.RLN.GetMerkleRoot()
+	if err != nil {
+		return nil, err
+	}
+
+	rlnPeer.validMerkleRoots = append(rlnPeer.validMerkleRoots, root)
+
 	// prepare rln membership key pair
 	if memKeyPair == nil && ethAccountPrivateKey != nil {
 		log.Debug("no rln-relay key is provided, generating one")
@@ -130,9 +144,7 @@ func RlnRelayDynamic(
 	}
 
 	handler := func(pubkey r.IDCommitment, index r.MembershipIndex) error {
-		log.Debug("a new key is added", zap.Binary("pubkey", pubkey[:]))
-		// assuming all the members arrive in order
-		return rlnInstance.InsertMember(pubkey)
+		return rlnPeer.insertMember(pubkey)
 	}
 
 	errChan := make(chan error)

waku/v2/protocol/rln/waku_rln_relay.go

@@ -30,6 +30,8 @@ const MAX_EPOCH_GAP = int64(MAX_CLOCK_GAP_SECONDS / r.EPOCH_UNIT_SECONDS)
 
 type RegistrationHandler = func(tx *types.Transaction)
 
+const AcceptableRootWindowSize = 5
+
 type WakuRLNRelay struct {
 	ctx context.Context
 
@@ -52,6 +54,8 @@ type WakuRLNRelay struct {
 	pubsubTopic  string
 	contentTopic string
 
+	validMerkleRoots []r.MerkleNode
+
 	// the log of nullifiers and Shamir shares of the past messages grouped per epoch
 	nullifierLogLock sync.RWMutex
 	nullifierLog     map[r.Epoch][]r.ProofMetadata
@@ -307,6 +311,25 @@ func (r *WakuRLNRelay) MembershipContractAddress() common.Address {
 	return r.membershipContractAddress
 }
 
+func (r *WakuRLNRelay) insertMember(pubkey [32]byte) error {
+	r.log.Debug("a new key is added", zap.Binary("pubkey", pubkey[:]))
+	// assuming all the members arrive in order
+	err := r.RLN.InsertMember(pubkey)
+	if err == nil {
+		newRoot, err := r.RLN.GetMerkleRoot()
+		if err != nil {
+			r.log.Error("inserting member into merkletree", zap.Error(err))
+			return err
+		}
+		r.validMerkleRoots = append(r.validMerkleRoots, newRoot)
+		if len(r.validMerkleRoots) > AcceptableRootWindowSize {
+			r.validMerkleRoots = r.validMerkleRoots[1:]
+		}
+	}
+
+	return err
+}
+
 type SpamHandler = func(message *pb.WakuMessage) error
 
 // this function sets a validator for the waku messages published on the supplied pubsubTopic and contentTopic