How to create NATS push consumer using jscontext.newConsumer() in Golang

While creating js context AddConsumer(topic.ID(), &nats.ConsumerConfig{}) creating pull consumer, Is there any way to create a push consumer using addconsumer

The documentation is very bad about this part, and the errors are not very descriptive. I spent hours figuring it out. Here is what I found...

To create a push consumer using AddConsumer you must provide the DeliverySubject parameter, it can be anything, and for simplicity it can be the same as the consumer name. The documentation for this part is very bad and does not explain how it should be used.

The following is a full working example that creates a consumer and subscribes to certain subject from that consumer.

nc, err := nats.Connect("nats://localhost:4222")
if err != nil {
	log.Fatalf("could not connect to nats: %s", err)
}

js, err := nc.JetStream()
if err != nil {
	log.Fatal("Could not get jetstream:", err)
}

streamName := "TEST_STREAM"
_, err = js.AddStream(&nats.StreamConfig{
	Name:      streamName,
	Subjects:  []string{"test.>"},
	Retention: nats.InterestPolicy,
	Replicas:  1,
})

if err != nil {
	fmt.Printf("error creating stream %q: %s\n", streamName, err)
	return
}

groupName := "group-1"
consumerName := fmt.Sprintf("%s-consumer", groupName)
_, err = js.AddConsumer(
	streamName,
	&nats.ConsumerConfig{
		Name:           consumerName,
		Durable:        consumerName,
		DeliverSubject: consumerName,
		DeliverGroup:   groupName,
	},
)

if err != nil {
	fmt.Printf("error creating consumer %q: %s\n", consumerName, err)
	return
}

subject := "test.resource.created"
_, err = js.QueueSubscribe(
	subject,
	groupName,
	func(msg *nats.Msg) { 
		fmt.Printf("Jetstream - received %q: %q\n", msg.Subject, msg.Data) 
	},
	nats.Bind(streamName, consumerName),
)

if err != nil {
	fmt.Printf("error subscribing to %q: %s\n", subject, err)
}

delivery group is provided so that several app instances can subscribe to the same consumer and the event will only be delivered to one of them (at random). That is, if you want to scale the app horizontally.

If you want to restrict what events the consumer receives. Then you should provide SubjectFilter to consumer config. Each consumer will persist all events that their filter matches, or all the events from the stream if no filter is provided.

After creating the consumer, You can then subscribe to it using any JetStream subscribe method (js.SubscribeSync, js.QueueSubscribeSync, js.Subscribe, js.QueueSubscribe, ...) but you MUST provide nats option to bind the subscription to a consumer, this is done using nats.Bind(streamName, consumerName)

You can leave the subject name an empty string when subscribing to subscribe to all events from the consumer.

Create a Consumer.

js.AddConsumer("ORDERS", &nats.ConsumerConfig{
	Durable: "MONITOR",
})

AddConsumer adds a consumer to a stream.

AddConsumer(stream string, cfg *ConsumerConfig, opts ...JSOpt) (*ConsumerInfo, error)