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  PhpIPCMessageQueue
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What Is It

	These files define a php class 'ipc_message_queue.php'.
	It is intended to be used a lightweight inter-process Message Queue communication mechanism.

	The class wraps System V IPC Queue functionality, which is managed by the Operating System.
	IPC Queues are usually managed with a small amount of memory, and lack a method to persist
	message contents between reboots.

	This example consists of:

		README
			This file
		ipc_message_queue.php
			PHP class that wraps System V IPC-Q functions
		errno.php
			defines system error-numbers which might be received by IPC functions
		examples/rand
			command-line example, sends and receives random numbers
		examples/sys
			example started with a sysv-init script

Use

	Subclass ipc_message_queue, redefining as needed:
		- the constructor (which sets the message-queue key)
		- the message-received function (which processes received messages)

	---8<---
	<?php
	require_once('ipc_message_queue.php');

	// a number of queues can exist simultaneously in the system; each has it's own Unique Key (an integer).
	$queue_key = 123;

	// messages are sent with a type-identifier (integer). This value, used in the constructor,
	// defines which types to listen for. Alternately, set to MSG_TYPE_ANY to receive all msg types
	$msg_type  = 99;

	class MyListener extends ipc_message_queue {
		public function __construct() {
			parent::__construct($queue_key, $msg_type, 33, 33, '0666');
			}
		protected function msg_received($type,$msg) {
			print($msg);
			}
		}
	// instantiate an instance, which will create the Q if it does not already exist
	$q = new MyListener();

	// kill Queue (deletes messages, any listening server will stop)
	$q->deletequeue();

	// client; send message
	$q->send_message($options['message']);

	// run in server mode
	become_daemon('/var/run/myq.pid',33,33);
	$q->process_messages();
	--->8---


Security

	If, when trying to create an IPC Queue as a non-root user, there is a message about CAP_IPC_OWNER, then you can
	add this capability to the PHP binary file like this (setcap is in package libcap2-bin, see https://sites.google.com/site/fullycapable/):

		> sudo /sbin/setcap cap_ipc_owner=ep /usr/bin/php5

	check capabilities:

		> /sbin/getcap /usr/bin/php5

		/usr/bin/php5 = cap_ipc_owner+ep

	Capabilities discussions, critiques, ...
		http://en.wikipedia.org/wiki/Capability-based_security#POSIX_Capabilities
		http://www.linuxjournal.com/article/5737
		http://lwn.net/Articles/212962/
		http://www.gentoo.org/proj/en/hardened/capabilities.xml