While waiting for a connection in Frankfurt I had a quick look at what it would take to make ZeroMQ and libevent co-exist in PHP and it was actually quite easy. Well, easy after Mikko Koppanen added a way to get the underlying socket fd from the ZeroMQ PHP extension. To get this working, install the PHP ZeroMQ extension and the PHP libevent extension. First, a little event-driven server that listens on loopback port 5555 and waits for 10 messages and then exits.

Server.php

<?php
    function print_line($fd, $events, $arg) {
        static $msgs = 1; 
        echo "CALLBACK FIRED" . PHP_EOL;
        if($arg[0]->getsockopt (ZMQ::SOCKOPT_EVENTS) & ZMQ::POLL_IN) {
            echo "Got incoming data" . PHP_EOL;
            var_dump ($arg[0]->recv());
            $arg[0]->send("Got msg $msgs");
        if($msgs++ >= 10) event_base_loopexit($arg[1]);
        }
    }

    // create base and event
    $base = event_base_new();
    $event = event_new();

    // Allocate a new context
    $context = new ZMQContext();

    // Create sockets
    $rep = $context->getSocket(ZMQ::SOCKET_REP);

    // Connect the socket
    $rep->bind("tcp://127.0.0.1:5555");

    // Get the stream descriptor
    $fd = $rep->getsockopt(ZMQ::SOCKOPT_FD);

    // set event flags
    event_set($event, $fd, EV_READ | EV_PERSIST, "print_line", array($rep, $base));

    // set event base
    event_base_set($event, $base);

    // enable event
    event_add($event);

    // start event loop
    event_base_loop($base);

Client.php

<?php
    // Create new queue object
    $queue = new ZMQSocket(new ZMQContext(), ZMQ::SOCKET_REQ, "MySock1");
    $queue->connect("tcp://127.0.0.1:5555");

    // Assign socket 1 to the queue, send and receive
    var_dump($queue->send("hello there!")->recv());

You will notice when you run it that the server gets a couple of events that are not actually incoming messages. Right now ZeroMQ doesn't expose the nature of these events, but they are the socket initialization and client connect. You will also get one for the client disconnect. A future version of the ZeroMQ library will expose these so you can properly catch when clients connect to your server.

There really isn't much else to say. The code should be self-explanatory. If not, see the PHP libevent docs and the PHP ZeroMQ docs. And if you build something cool with this, please let me know.