feat: WithLocalPublication option to enable local only publishing on a topic (#481)

* feat: WithLocalPublication option to enable local only publishing on a topic

* docs: improve comment on WithLocalPublication option

pubsub.go

@@ -221,6 +221,7 @@ type Message struct {
 	ID            string
 	ReceivedFrom  peer.ID
 	ValidatorData interface{}
+	Local bool
 }
 
 func (m *Message) GetFrom() peer.ID {
@@ -1066,7 +1067,7 @@ func (p *PubSub) handleIncomingRPC(rpc *RPC) {
 				continue
 			}
 
-			p.pushMsg(&Message{pmsg, "", rpc.from, nil})
+			p.pushMsg(&Message{pmsg, "", rpc.from, nil, false})
 		}
 	}
 
@@ -1165,7 +1166,9 @@ func (p *PubSub) checkSigningPolicy(msg *Message) error {
 func (p *PubSub) publishMessage(msg *Message) {
 	p.tracer.DeliverMessage(msg)
 	p.notifySubs(msg)
-	p.rt.Publish(msg)
+	if !msg.Local {
+		p.rt.Publish(msg)
+	}
 }
 
 type addTopicReq struct {

topic.go

@@ -215,6 +215,7 @@ type ProvideKey func() (crypto.PrivKey, peer.ID)
 type PublishOptions struct {
 	ready     RouterReady
 	customKey ProvideKey
+	local bool
 }
 
 type PubOpt func(pub *PublishOptions) error
@@ -307,7 +308,7 @@ func (t *Topic) Publish(ctx context.Context, data []byte, opts ...PubOpt) error
 		}
 	}
 
-	return t.p.val.PushLocal(&Message{m, "", t.p.host.ID(), nil})
+	return t.p.val.PushLocal(&Message{m, "", t.p.host.ID(), nil, pub.local})
 }
 
 // WithReadiness returns a publishing option for only publishing when the router is ready.
@@ -319,6 +320,18 @@ func WithReadiness(ready RouterReady) PubOpt {
 	}
 }
 
+// WithLocalPublication returns a publishing option to notify in-process subscribers only.
+// It prevents message publication to mesh peers.
+// Useful in edge cases where the msg needs to be only delivered to the in-process subscribers,
+// e.g. not to spam the network with outdated msgs.
+// Should not be used specifically for in-process pubsubing.
+func WithLocalPublication(local bool) PubOpt {
+	return func(pub *PublishOptions) error {
+		pub.local = local
+		return nil
+	}
+}
+
 // WithSecretKeyAndPeerId returns a publishing option for providing a custom private key and its corresponding peer ID
 // This option is useful when we want to send messages from "virtual", never-connectable peers in the network
 func WithSecretKeyAndPeerId(key crypto.PrivKey, pid peer.ID) PubOpt {

topic_test.go

@@ -1019,3 +1019,48 @@ func TestTopicRelayPublishWithKey(t *testing.T) {
 		}
 	}
 }
+
+func TestWithLocalPublication(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	const topic = "test"
+
+	hosts := getNetHosts(t, ctx, 2)
+	pubsubs := getPubsubs(ctx, hosts)
+	topics := getTopics(pubsubs, topic)
+	connectAll(t, hosts)
+
+	payload := []byte("pubsub smashes")
+
+	local, err := topics[0].Subscribe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	remote, err := topics[1].Subscribe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = topics[0].Publish(ctx, payload, WithLocalPublication(true))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	remoteCtx, cancel := context.WithTimeout(ctx, time.Millisecond*100)
+	defer cancel()
+
+	msg, err := remote.Next(remoteCtx)
+	if msg != nil || err == nil {
+		t.Fatal("unexpected msg")
+	}
+
+	msg, err = local.Next(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !msg.Local || !bytes.Equal(msg.Data, payload) {
+		t.Fatal("wrong message")
+	}
+}