Request/reply with multiple subscribers

nats-multi-reply.go

package main

import(
    "fmt"
    "log"
    "github.com/nats-io/nats"
    "time"
)

func main(){
    nc, err := nats.Connect("nats://192.168.99.100:32772")
    if err != nil {
        log.Fatal(err)
    }
    nc.QueueSubscribe("msg","one",func(msg *nats.Msg){
        fmt.Printf("one heard %s\n", string(msg.Data))
        nc.Publish(msg.Reply, []byte("one is here"))
    })
    nc.QueueSubscribe("msg","two",func(msg *nats.Msg){
        fmt.Printf("two heard %s\n", string(msg.Data))
        nc.Publish(msg.Reply, []byte("two is here"))
    })
    inbox := nats.NewInbox()
    _, err = nc.Subscribe(inbox, func(msg *nats.Msg){
        fmt.Printf("requestor received %s\n", string(msg.Data))
    })
    if err != nil {
        log.Fatal(err)
    }
    err = nc.PublishRequest("msg", inbox, []byte("help"))
    if err != nil {
        log.Fatal(err)
    }
    time.Sleep(1 * time.Second)
}

// Output:
// one heard help
// two heard help
// requestor received one is here
// requestor received two is here

You can use a Request with a timeout from the requestor side and retry on a timeout. That way it does not matter if the subscribers are coming or going or if they fail, just matter if the requestor gets the answer they want. Most situations are non-transactional so this patter works well.