aonurdemir/page.html

## page.html
<html>
<head>
   <meta charset="UTF-8">
   <title>Server-sent events demo</title>
</head>
<body>
  <button>Close the connection</button>

  <ul>
  </ul>

<script>
  var button = document.querySelector('button');
  var evtSource = new EventSource('http://127.0.0.1:3000');
  console.log(evtSource.withCredentials);
  console.log(evtSource.readyState);
  console.log(evtSource.url);
  var eventList = document.querySelector('ul');

  evtSource.onopen = function() {
    console.log("Connection to server opened.");
  };

  evtSource.onmessage = function(e) {
    var newElement = document.createElement("li");

    newElement.textContent = "message: " + e.data;
    eventList.appendChild(newElement);
  };

  evtSource.onerror = function() {
    console.log("EventSource failed.");
  };

  button.onclick = function() {
    console.log('Connection closed');
    evtSource.close();
  };

  // evtSource.addEventListener("ping", function(e) {
  //   var newElement = document.createElement("li");
  //
  //   var obj = JSON.parse(e.data);
  //   newElement.innerHTML = "ping at " + obj.time;
  //   eventList.appendChild(newElement);
  // }, false);
</script>
</body>
</html>

## sse.go
// Copyright (c) 2017 Ismael Celis

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package main

import (
	"fmt"
	"log"
	"net/http"
	"time"
)

// Example SSE server in Golang.
//     $ go run sse.go

type Broker struct {

	// Events are pushed to this channel by the main events-gathering routine
	Notifier chan []byte

	// New client connections
	newClients chan chan []byte

	// Closed client connections
	closingClients chan chan []byte

	// Client connections registry
	clients map[chan []byte]bool
}

func NewServer() (broker *Broker) {
	// Instantiate a broker
	broker = &Broker{
		Notifier:       make(chan []byte, 1),
		newClients:     make(chan chan []byte),
		closingClients: make(chan chan []byte),
		clients:        make(map[chan []byte]bool),
	}

	// Set it running - listening and broadcasting events
	go broker.listen()

	return
}

func (broker *Broker) ServeHTTP(rw http.ResponseWriter, req *http.Request) {

	// Make sure that the writer supports flushing.
	//
	flusher, ok := rw.(http.Flusher)

	if !ok {
		http.Error(rw, "Streaming unsupported!", http.StatusInternalServerError)
		return
	}

	rw.Header().Set("Content-Type", "text/event-stream")
	rw.Header().Set("Cache-Control", "no-cache")
	rw.Header().Set("Connection", "keep-alive")
	rw.Header().Set("Access-Control-Allow-Origin", "*")

	// Each connection registers its own message channel with the Broker's connections registry
	messageChan := make(chan []byte)

	// Signal the broker that we have a new connection
	broker.newClients <- messageChan

	// Remove this client from the map of connected clients
	// when this handler exits.
	defer func() {
		broker.closingClients <- messageChan
	}()

	// Listen to connection close and un-register messageChan
	// notify := rw.(http.CloseNotifier).CloseNotify()
	notify := req.Context().Done()

	go func() {
		<-notify
		broker.closingClients <- messageChan
	}()

	for {

		// Write to the ResponseWriter
		// Server Sent Events compatible
		fmt.Fprintf(rw, "data: %s\n\n", <-messageChan)

		// Flush the data immediatly instead of buffering it for later.
		flusher.Flush()
	}

}

func (broker *Broker) listen() {
	for {
		select {
		case s := <-broker.newClients:

			// A new client has connected.
			// Register their message channel
			broker.clients[s] = true
			log.Printf("Client added. %d registered clients", len(broker.clients))
		case s := <-broker.closingClients:

			// A client has dettached and we want to
			// stop sending them messages.
			delete(broker.clients, s)
			log.Printf("Removed client. %d registered clients", len(broker.clients))
		case event := <-broker.Notifier:

			// We got a new event from the outside!
			// Send event to all connected clients
			for clientMessageChan, _ := range broker.clients {
				clientMessageChan <- event
			}
		}
	}

}

func main() {

	broker := NewServer()

	go func() {
		for {
			time.Sleep(time.Second * 2)
			eventString := fmt.Sprintf("the time is %v", time.Now())
			log.Println("Receiving event")
			broker.Notifier <- []byte(eventString)
		}
	}()

	log.Fatal("HTTP server error: ", http.ListenAndServe("localhost:3000", broker))

}
	<html>
	<head>
	<meta charset="UTF-8">
	<title>Server-sent events demo</title>
	</head>
	<body>
	<button>Close the connection</button>

	<ul>
	</ul>

	<script>
	var button = document.querySelector('button');
	var evtSource = new EventSource('http://127.0.0.1:3000');
	console.log(evtSource.withCredentials);
	console.log(evtSource.readyState);
	console.log(evtSource.url);
	var eventList = document.querySelector('ul');

	evtSource.onopen = function() {
	console.log("Connection to server opened.");
	};

	evtSource.onmessage = function(e) {
	var newElement = document.createElement("li");

	newElement.textContent = "message: " + e.data;
	eventList.appendChild(newElement);
	};

	evtSource.onerror = function() {
	console.log("EventSource failed.");
	};

	button.onclick = function() {
	console.log('Connection closed');
	evtSource.close();
	};

	// evtSource.addEventListener("ping", function(e) {
	// var newElement = document.createElement("li");
	//
	// var obj = JSON.parse(e.data);
	// newElement.innerHTML = "ping at " + obj.time;
	// eventList.appendChild(newElement);
	// }, false);
	</script>
	</body>
	</html>
	// Copyright (c) 2017 Ismael Celis

	// Permission is hereby granted, free of charge, to any person obtaining a copy
	// of this software and associated documentation files (the "Software"), to deal
	// in the Software without restriction, including without limitation the rights
	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	// copies of the Software, and to permit persons to whom the Software is
	// furnished to do so, subject to the following conditions:

	// The above copyright notice and this permission notice shall be included in all
	// copies or substantial portions of the Software.

	// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	// SOFTWARE.

	package main

	import (
	"fmt"
	"log"
	"net/http"
	"time"
	)

	// Example SSE server in Golang.
	// $ go run sse.go

	type Broker struct {

	// Events are pushed to this channel by the main events-gathering routine
	Notifier chan []byte

	// New client connections
	newClients chan chan []byte

	// Closed client connections
	closingClients chan chan []byte

	// Client connections registry
	clients map[chan []byte]bool
	}

	func NewServer() (broker *Broker) {
	// Instantiate a broker
	broker = &Broker{
	Notifier: make(chan []byte, 1),
	newClients: make(chan chan []byte),
	closingClients: make(chan chan []byte),
	clients: make(map[chan []byte]bool),
	}

	// Set it running - listening and broadcasting events
	go broker.listen()

	return
	}

	func (broker Broker) ServeHTTP(rw http.ResponseWriter, req http.Request) {

	// Make sure that the writer supports flushing.
	//
	flusher, ok := rw.(http.Flusher)

	if !ok {
	http.Error(rw, "Streaming unsupported!", http.StatusInternalServerError)
	return
	}

	rw.Header().Set("Content-Type", "text/event-stream")
	rw.Header().Set("Cache-Control", "no-cache")
	rw.Header().Set("Connection", "keep-alive")
	rw.Header().Set("Access-Control-Allow-Origin", "*")

	// Each connection registers its own message channel with the Broker's connections registry
	messageChan := make(chan []byte)

	// Signal the broker that we have a new connection
	broker.newClients <- messageChan

	// Remove this client from the map of connected clients
	// when this handler exits.
	defer func() {
	broker.closingClients <- messageChan
	}()

	// Listen to connection close and un-register messageChan
	// notify := rw.(http.CloseNotifier).CloseNotify()
	notify := req.Context().Done()

	go func() {
	<-notify
	broker.closingClients <- messageChan
	}()

	for {

	// Write to the ResponseWriter
	// Server Sent Events compatible
	fmt.Fprintf(rw, "data: %s\n\n", <-messageChan)

	// Flush the data immediatly instead of buffering it for later.
	flusher.Flush()
	}

	}

	func (broker *Broker) listen() {
	for {
	select {
	case s := <-broker.newClients:

	// A new client has connected.
	// Register their message channel
	broker.clients[s] = true
	log.Printf("Client added. %d registered clients", len(broker.clients))
	case s := <-broker.closingClients:

	// A client has dettached and we want to
	// stop sending them messages.
	delete(broker.clients, s)
	log.Printf("Removed client. %d registered clients", len(broker.clients))
	case event := <-broker.Notifier:

	// We got a new event from the outside!
	// Send event to all connected clients
	for clientMessageChan, _ := range broker.clients {
	clientMessageChan <- event
	}
	}
	}

	}

	func main() {

	broker := NewServer()

	go func() {
	for {
	time.Sleep(time.Second * 2)
	eventString := fmt.Sprintf("the time is %v", time.Now())
	log.Println("Receiving event")
	broker.Notifier <- []byte(eventString)
	}
	}()

	log.Fatal("HTTP server error: ", http.ListenAndServe("localhost:3000", broker))

	}