PHP - echo do other client - php

Question

I`m making an little php server that has 2 clients, on connects to the php (device a) and controls the other (device b).
device a makes a get request to the php. now i want to push that command to device b. is there any way to echo to device b? or to make an request to the device b?
(i only need to send one character to device b)

Answer 1

Pushing to device is possible but depends on your device.
A solution would be websockets, see the following links for further reading:
http://www.websocket.org/
http://code.google.com/p/phpwebsocket/
Another solution would be longpolling which is easy to implement in php:
http://en.wikipedia.org/wiki/Push_technology#Long_polling
Very simple implementation of longpolling on server-side:
$ts = time();
while(true) {
// if there's something new, send the response to the server
// if not, continue with the loop
if($response = getSuperAwesomeResponse()) {
print $response;
break;
}
// timeout after 60 seconds
if( ($ts + 60) > time()) {
break;
}
sleep(1);
}
On the client-side you just need to send some sort of ajax calls

Answer 2

No, unless device B is running a server of some kind (any software that accepts incoming connections really). If that's the case then you can easily make HTTP requests to the device (e.g. even with file_get_contents) or have your own custom connection protocol (with sockets). There are also other options that allow you the same functionality but work in slightly different ways.
If the device is not running any servers then the best you can do is poll the server continuously to see if there are any commands for it. This is easier to set up (the server is already there) but also not efficient.

Answer 3

Device B could open a client connection to the server and wait for incomming data. If data comes in, the client running on device B could echo it.
PHP offers access to network sockets, see http://www.php.net/manual/en/book.sockets.php
Some PHP example code making use of LibEvent and ZMQ, which allows a higher level of access to sockets and queues:
Event-driven Server:
<?php
// 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);
// Define event callback function
$fnc = function ($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($arg[1]);
}
};
// set event flags
event_set($event, $fd, EV_READ | EV_PERSIST, $fnc, array($rep, $base));
// set event base
event_base_set($event, $base);
// enable event
event_add($event);
// start event loop
event_base_loop($base);
ZeroMQ Client:
<?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());
Source, Talk, Video (~22:00).