Example of using Redis PubSub and EventSource with golang

redis-eventsource.go

package main

import (
  eventsource "github.com/antage/eventsource/http"
  redis "github.com/vmihailenco/redis"
  "log"
  "net/http"
)

func haltOnErr(err error){
  if err != nil { panic(err) }
}

type subscriptionHandler struct {
  index map[string]subscription
}

// maps a url to a redis Subscribe channel
type subscription struct {
  pubsub  * redis.PubSubClient
  es      eventsource.EventSource
  ch      chan * redis.Message
  pubChan string
}

func createSubscription(sh * subscriptionHandler, pubChan * string){
  log.Printf("creating channel %s",*pubChan)

  pubsub, err := redis.NewTCPClient(":6379","",-1).PubSubClient()
  haltOnErr(err)

  ch, err := pubsub.Subscribe(*pubChan)
  haltOnErr(err)

  es := eventsource.New(nil)

  sh.index[*pubChan] = subscription{pubsub, es, ch, *pubChan}
}

// listen for published events and send to the EventSource
func listen(index subscription){
  for {
    msg := <-index.ch
    index.es.SendMessage(msg.Message, "", "")
    log.Printf("message has been sent on %s (consumers: %d)", index.pubChan, index.es.ConsumersCount())
  }
}

func (sh *subscriptionHandler) ServeHTTP(resp http.ResponseWriter, req *http.Request){
  pubChan := req.URL.Path[1:]
  _, ok := sh.index[pubChan]

  if ! ok {
    createSubscription(sh, &pubChan)
    defer sh.index[pubChan].pubsub.Close()
    defer sh.index[pubChan].es.Close()
  }

  log.Printf("subscribed to %s",pubChan)

  go listen(sh.index[pubChan])

  sh.index[pubChan].es.ServeHTTP(resp,req)
}

func main() {
  streamer := new(subscriptionHandler)
  streamer.index = make(map[string]subscription)

  http.Handle("/events/", streamer)

  err := http.ListenAndServe(":8080", nil)
  haltOnErr(err)
}

streamer.js

// https://github.com/Yaffle/EventSource
function listen(channel){
  var source;

  if (!!window.EventSource) {
    source = new EventSource('/events/'+channel);
  } else {
    // Result to xhr polling :(
  }
  source.addEventListener('message', function(e) {
    console.log(e.data);
  }, false);

  source.addEventListener('open', function(e) {
    console.log("opened channel on "+channel)
  }, false);

  source.addEventListener('error', function(e) {
    if (e.readyState == EventSource.CLOSED) {
      console.log("closed channel on "+channel)
    }
  }, false);
}

There is no need to pass immutable strings as pointers. You can also use redis to handle the subscriptions instead of a global variable.