Question about nats pub/sub

[karanpratapsingh]

Hey, I had a question, why don’t I see Received: 1 as output?

package main

import (
	"fmt"

	"github.com/nats-io/nats.go"
)

func main() {
	wait := make(chan bool)

	nc, err := nats.Connect(nats.DefaultURL)
	topic := "topic"

	if err != nil {
		fmt.Println(err)
	}
	nc.Publish(topic, []byte("1"))

	nc.Subscribe(topic, func(m *nats.Msg) {
		fmt.Printf("Received: %s\n", string(m.Data))
	})

	nc.Publish(topic, []byte("2"))
	nc.Publish(topic, []byte("3"))

	<-wait
}

Output:

Received: 2
Received: 3

[derekcollison]

When you subscribe you queue up the interest to the system, but you do that after you send []byte("1"), so when the system processes that message there is no interest in "topic".

[karanpratapsingh]

Thanks @derekcollison , makes perfect sense. I think Basic Usage in readme might need to be updated as I was running the example from there and couldn't figure out what was I doing wrong. Then I ran the basic usage from nats.js in node and it worked as subscribe came before publish (if this is as expected then feel free to close this issue).

Also, I just migrate from Kafka to Nats for one of my projects, It's pretty cool. Thanks!

[Vanlius]

When you subscribe you queue up the interest to the system, but you do that after you send []byte("1"), so when the system processes that message there is no interest in "topic".

What about 'limitedPolicy' and 'WorkQueuePolicy' if The Retention in Jetstream is not InterestPolicy?

[derekcollison]

These are separate issues in my opinion.

JetStream allows you to persist messages, so the "interest" is JetStream itself, so users can come along at a later date and consume a message. JetStream can also be used to do global flow control, and if you need a globally ordered set of messages.