Fix for https://github.com/micro/go-micro/issues/2687

server/rpc_events.go

@@ -127,6 +127,27 @@ func (s *rpcServer) reSubscribe(config Options) {
 		if s.subscribers[sb] != nil {
 			continue
 		}
+		// If we've already created a broker subscription for this topic
+		// (from a different Subscriber entry) then don't create another
+		// broker.Subscribe. We still need to register the subscriber with
+		// the router so it receives dispatched messages.
+		var already bool
+		for other, subs := range s.subscribers {
+			if other.Topic() == sb.Topic() && subs != nil {
+				already = true
+				break
+			}
+		}
+		if already {
+			// register with router only
+			if err := s.router.Subscribe(sb); err != nil {
+				config.Logger.Logf(log.WarnLevel, "Unable to subscribing to topic: %s, error: %s", sb.Topic(), err)
+				continue
+			}
+			// mark this subscriber as having no broker subscription
+			s.subscribers[sb] = nil
+			continue
+		}
 		var opts []broker.SubscribeOption
 		if queue := sb.Options().Queue; len(queue) > 0 {
 			opts = append(opts, broker.Queue(queue))

server/rpc_events_test.go

@@ -0,0 +1,219 @@
+package server
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"go-micro.dev/v5/broker"
+	"go-micro.dev/v5/registry"
+)
+
+// TestSubscriberNoDuplicates verifies that when multiple subscribers are registered
+// for the same topic with different queues, each handler is called exactly once
+// per published message (no duplicate deliveries).
+func TestSubscriberNoDuplicates(t *testing.T) {
+	// Create a memory broker
+	memBroker := broker.NewMemoryBroker()
+	if err := memBroker.Connect(); err != nil {
+		t.Fatalf("Failed to connect broker: %v", err)
+	}
+	defer memBroker.Disconnect()
+
+	// Create a memory registry
+	memRegistry := registry.NewMemoryRegistry()
+
+	// Create server with memory broker and registry
+	srv := NewRPCServer(
+		Broker(memBroker),
+		Registry(memRegistry),
+		Name("test.service"),
+		Id("test-1"),
+		Address("127.0.0.1:0"),
+	)
+
+	// Track handler invocations
+	var countA, countB, countC int32
+
+	// Handler functions
+	handlerA := func(ctx context.Context, msg *TestMessage) error {
+		atomic.AddInt32(&countA, 1)
+		return nil
+	}
+
+	handlerB := func(ctx context.Context, msg *TestMessage) error {
+		atomic.AddInt32(&countB, 1)
+		return nil
+	}
+
+	handlerC := func(ctx context.Context, msg *TestMessage) error {
+		atomic.AddInt32(&countC, 1)
+		return nil
+	}
+
+	// Register three subscribers with same topic but different queues
+	topic := "EVENT_1"
+
+	subA := srv.NewSubscriber(topic, handlerA, SubscriberQueue("A"))
+	if err := srv.Subscribe(subA); err != nil {
+		t.Fatalf("Failed to subscribe A: %v", err)
+	}
+
+	subB := srv.NewSubscriber(topic, handlerB, SubscriberQueue("B"))
+	if err := srv.Subscribe(subB); err != nil {
+		t.Fatalf("Failed to subscribe B: %v", err)
+	}
+
+	subC := srv.NewSubscriber(topic, handlerC, SubscriberQueue("C"))
+	if err := srv.Subscribe(subC); err != nil {
+		t.Fatalf("Failed to subscribe C: %v", err)
+	}
+
+	// Start the server (this will trigger reSubscribe)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Failed to start server: %v", err)
+	}
+	defer srv.Stop()
+
+	// Give server time to establish subscriptions
+	time.Sleep(100 * time.Millisecond)
+
+	// Publish a message to the topic
+	if err := memBroker.Publish(topic, &broker.Message{
+		Header: map[string]string{
+			"Micro-Topic": topic,
+			"Content-Type": "application/json",
+		},
+		Body: []byte(`{"value":"test"}`),
+	}); err != nil {
+		t.Fatalf("Failed to publish message: %v", err)
+	}
+
+	// Give handlers time to process
+	time.Sleep(200 * time.Millisecond)
+
+	// Verify each handler was called exactly once
+	if got := atomic.LoadInt32(&countA); got != 1 {
+		t.Errorf("Handler A called %d times, expected 1", got)
+	}
+	if got := atomic.LoadInt32(&countB); got != 1 {
+		t.Errorf("Handler B called %d times, expected 1", got)
+	}
+	if got := atomic.LoadInt32(&countC); got != 1 {
+		t.Errorf("Handler C called %d times, expected 1", got)
+	}
+}
+
+// TestSubscriberMultipleTopics verifies that subscribers for different topics
+// each receive their respective messages correctly.
+func TestSubscriberMultipleTopics(t *testing.T) {
+	// Create a memory broker
+	memBroker := broker.NewMemoryBroker()
+	if err := memBroker.Connect(); err != nil {
+		t.Fatalf("Failed to connect broker: %v", err)
+	}
+	defer memBroker.Disconnect()
+
+	// Create a memory registry
+	memRegistry := registry.NewMemoryRegistry()
+
+	// Create server
+	srv := NewRPCServer(
+		Broker(memBroker),
+		Registry(memRegistry),
+		Name("test.service"),
+		Id("test-2"),
+		Address("127.0.0.1:0"),
+	)
+
+	// Track handler invocations
+	var count1, count2 int32
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	// Handler functions
+	handler1 := func(ctx context.Context, msg *TestMessage) error {
+		atomic.AddInt32(&count1, 1)
+		wg.Done()
+		return nil
+	}
+
+	handler2 := func(ctx context.Context, msg *TestMessage) error {
+		atomic.AddInt32(&count2, 1)
+		wg.Done()
+		return nil
+	}
+
+	// Register subscribers for different topics
+	topic1 := "TOPIC_1"
+	topic2 := "TOPIC_2"
+
+	sub1 := srv.NewSubscriber(topic1, handler1)
+	if err := srv.Subscribe(sub1); err != nil {
+		t.Fatalf("Failed to subscribe to topic1: %v", err)
+	}
+
+	sub2 := srv.NewSubscriber(topic2, handler2)
+	if err := srv.Subscribe(sub2); err != nil {
+		t.Fatalf("Failed to subscribe to topic2: %v", err)
+	}
+
+	// Start the server
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Failed to start server: %v", err)
+	}
+	defer srv.Stop()
+
+	// Give server time to establish subscriptions
+	time.Sleep(100 * time.Millisecond)
+
+	// Publish messages to different topics
+	if err := memBroker.Publish(topic1, &broker.Message{
+		Header: map[string]string{
+			"Micro-Topic": topic1,
+			"Content-Type": "application/json",
+		},
+		Body: []byte(`{"value":"test1"}`),
+	}); err != nil {
+		t.Fatalf("Failed to publish to topic1: %v", err)
+	}
+
+	if err := memBroker.Publish(topic2, &broker.Message{
+		Header: map[string]string{
+			"Micro-Topic": topic2,
+			"Content-Type": "application/json",
+		},
+		Body: []byte(`{"value":"test2"}`),
+	}); err != nil {
+		t.Fatalf("Failed to publish to topic2: %v", err)
+	}
+
+	// Wait for handlers to be called
+	done := make(chan struct{})
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+		// Success
+	case <-time.After(2 * time.Second):
+		t.Fatal("Timeout waiting for handlers to be called")
+	}
+
+	// Verify each handler was called exactly once
+	if got := atomic.LoadInt32(&count1); got != 1 {
+		t.Errorf("Handler 1 called %d times, expected 1", got)
+	}
+	if got := atomic.LoadInt32(&count2); got != 1 {
+		t.Errorf("Handler 2 called %d times, expected 1", got)
+	}
+}
+
+// TestMessage is a test message type
+type TestMessage struct {
+	Value string `json:"value"`
+}