Broadcasting messages with Server-Sent events

Question

I want to implement a simple Server-Sent events app where clients listen to a php file like this

<script src="eventsource.js"></script>
<script>
  var es = new EventSource('../sse.php');

  es.onmessage = function (event) {
    var data = JSON.parse(event.data);
    console.log('msg: ' + event.data);
  };

  es.onopen = function () {
    console.log('connected');
  }
</script>

but then i need to be able to broadcast a message and every connected client gets it simultaneously.

The php file will be triggered by another request and it will "echo" some SSE data to all clients.

Is this possible? Is there another route i can take?

Thank you in advance

JeffS · Accepted Answer · 2013-01-09 17:07:02Z

7

PHP is not going to be great for this. If you have lots of clients waiting for this event, you're going to require an instance of the PHP interpreter (and probably an apache thread) for each client that's waiting.

What you might consider doing is having an event driven server handle this. Node.JS and Tornado (Python) are two environments I've used in the past in similar circumstances. If you use Node.js, you may want to look into socket.io for this -- it doesn't use Server Sent Events, but would make what you want very simple.

You could have two webservers side by side, your current server (I'm assuming Apache) and one written by you to handle the clients waiting for updates. Whenever the PHP server wants to send a message to waiting clients, the PHP server notifies the other server (AMQP, ZeroMQ, redis Pub/Sub or a simple HTTP request on a non-public interface would all be good choices), and that server passes on the message to any waiting clients.

You can see a very simple version of what I'm talking about using node.js + socket.io (Which could easily be replaced by SSE) on github.

edited Jan 9, 2013 at 17:07

answered Jan 8, 2013 at 21:07

JeffS

2,7672 gold badges19 silver badges24 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

JeffS Over a year ago

If people are interested, I could up an implementation like what I was talking about it sometime later this week

kbariotis Over a year ago

i would be intrested although i am right now trying to implement it. So don't bother loosing your time unless you really want it. :) thank you

kbariotis Over a year ago

wonderfull and also got the point. Great implementation! Also found this which is another great implementation using also PHP for the server and Coffeescript for the client. Thanks a lot @JeffS

kapil das Over a year ago

Is there any way to do multicast using Server Sent Events?

JeffS Over a year ago

No, there's no way to do true multicast sse. Sse requires one tcp connection to the server per client. You can obviously simulate multicast by having a simple server setup that sends the same messages to all connected clients.

seyed · Accepted Answer · 2013-01-09 20:20:52Z

1

important EDIT: (after a day)

after testing i found this is so bad solution.

test case:

clients: run 8 clients (in one browser(Chromium,(k)ubuntu), one tab, 8 iframe).
Server API: Apache 2.0 Handler
PHP Version 5.3.10-1ubuntu3.4

result:

6 SSE-connections opened. but 2 SSE-connections left pending. other pages in server cannot be open until close SSE-clients.

but server can handle many clients by ajax (repeat ajax every 1 second).

Old Answer:

use share memory.

sse.php

<?php

header("Content-Type: text/event-stream\n\n");
header('Cache-Control: no-cache');

$key = "987654";
$permissions = 0666;
$size = 1024;

//Create or open the shared memory segment.
$segment = shm_attach($key, $size, $permissions);

$msg = ' null ';
$last_time = 0;
$time = 0;
while (1) {

    if (shm_has_var($segment, 0)) {
        $time = shm_get_var($segment, 0);
    }
    if (shm_has_var($segment, 0)) {
        $msg = shm_get_var($segment, 1);
    }
    $now = time();
    if ($last_time < $time) {
        $last_time = $time;
        echo 'data: msg(' . $msg . ') time(' . $time . ')';
        echo "\n\n";
    }

    ob_flush();
    flush();
    sleep(1);
}

trigger.php

<?php 
if (isset($_GET['msg'])) {

    $key = "987654";// TODO: how to generate suitable key?
    $permissions = 0666;
    $size = 1024;

    $segment = shm_attach($key, $size, $permissions);

    $time = time();
    $msg = $_GET['msg'];

    shm_put_var($segment, 0, $time);
    shm_put_var($segment, 1, $msg);
    echo $time;
}

disadvantage of this way:

one second delay
long time open connections. and this cause non-Scalability.

in my implementation sse.php send only last message in a second. but you can improve it and use database. (if trigger.php called 3 times in a second, then only last message saved)

edited Jan 9, 2013 at 20:20

answered Jan 8, 2013 at 20:47

seyed

2,1151 gold badge23 silver badges27 bronze badges

3 Comments

seyed Over a year ago

I interested to this question. and will +1 better solutions. :D

JeffS Over a year ago

The results of your testing are almost certainly do to the way apache handles connections, with at least one thread per connection, threads are too heavy weight for this. That's why the alternate solution I proposed actually avoids using apache (and PHP) for the piece that's going to have a lot of long, open connections to it.

oif_vet Over a year ago

You are also limited in the amount of open sockets per domain by the browser. You may recall the problem of domain sharding for assets. Same thing.

bwlee · Accepted Answer · 2013-08-19 23:13:44Z

0

To the number limit, it is because of the browser limit number of connections to same server, you can change that by reconfiguration. There is same default number (6) in firefox.

Also, I have wonder how to handle the disconnect event on the server side, if too many clients use SSE, it is necessary to manage the connections, even when other resource such as sockets to other services used.

answered Aug 19, 2013 at 23:13

bwlee

3533 silver badges10 bronze badges

Comments

Naftali · Accepted Answer · 2013-01-07 19:22:20Z

-1

All of the page will not get the same message simultaneously.

They will only get the message once they are connected.

If you want, you can look into WebSockets and/or Node.JS which could allow for more "instant" messaging.

answered Jan 7, 2013 at 19:22

Naftali

147k41 gold badges247 silver badges304 bronze badges

2 Comments

kbariotis Over a year ago

Basically i would like to have a file (or a structure) to listen to POST requests, edit them and them send data to all connected clients that listen to server events. How would you recomend to implement this?

Kornel Over a year ago

SSE is as instant as WebSockets in server->client communication. Might be actually even slightly faster due to lower overhead and quicker handshake.

Collectives™ on Stack Overflow

Broadcasting messages with Server-Sent events

4 Answers 4

5 Comments

3 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

3 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related