Method interception in PHP 5.* - php

Question

I'm implementing a Log system for PHP, and I'm a bit stuck.
All the configuration is defined in an XML file, that declares every method to be logged. XML is well parsed and converted into a multidimensional array (classname => array of methods). So far, so good.
Let's take a simple example:
#A.php
class A {
public function foo($bar) {
echo ' // Hello there !';
}
public function bar($foo) {
echo " $ù$ùmezf$z !";
}
}
#B.php
class B {
public function far($boo) {
echo $boo;
}
}
Now, let's say I've this configuration file:
<interceptor>
<methods class="__CLASS_DIR__A.php">
<method name="foo">
<log-level>INFO</log-level>
<log-message>Transaction init</log-message>
</method>
</methods>
<methods class="__CLASS_DIR__B.php">
<method name="far">
<log-level>DEBUG</log-level>
<log-message>Useless</log-message>
</method>
</methods>
</interceptor>
The thing I'd like AT RUNTIME ONLY (once the XML parser has done his job) is:
#Logger.php (its definitely NOT a final version) -- generated by the XML parser
class Logger {
public function __call($name,$args) {
$log_level = args[0];
$args = array_slice($args,1);
switch($method_name) {
case 'foo':
case 'far':
//case .....
//write in log files
break;
}
//THEN, RELAY THE CALL TO THE INITIAL METHOD
}
}
#"dynamic" A.php
class A extends Logger {
public function foo($log_level, $bar) {
parent::foo($log_level, $bar);
echo ' // Hello there !';
}
public function bar($foo) {
echo " $ù$ùmezf$z !";
}
}
#"dynamic" B.php
class B extends Logger {
public function far($log_level, $boo) {
parent::far($log_level, $bar);
echo $boo;
}
}
The big challenge here is to transform A and B into their "dynamic" versions, once the XML parser has completed its job.
The ideal would be to achieve that without modifying the code of A and B at all (I mean, in the files) - or at least find a way to come back to their original versions once the program is finished.
To be clear, I wanna find the most proper way to intercept method calls in PHP.
What are your ideas about it?
PS: and of course, there should be NO CONSEQUENCE on the client code (no different if interception is enabled or not).

Answer 1

You could use eval() to actually define the classes, but you should be very careful. The eval() function can be very dangerous.
Something like this:
$parentName = 'Bar';
eval('class Foo extends ' . $parentName . ' { }');
http://php.net/eval

Answer 2

This solution once again uses eval, but I'll post it for your consideration anyway because I think it's a really nice way of dynamic inheritance.
The method here is to use an intermediary class which extends some default class that can be changed (in this instance to a different class also extending the default).
I'm uncertain as to what it is in your setup that is not allowing for this kind of working -- if you clarify this I could perhaps provide a better recommendation.
<?php
/*
* One of the following classes will be the superclass of the Child
*/
class Ancestor {
function speak() {
echo 'Ancestor <br />';
}
}
class Mum extends Ancestor {
function speak() {
parent::speak();
echo 'Mum <br />';
}
}
class Dad extends Ancestor {
function speak() {
parent::speak();
echo 'Dad <br />';
}
}
/*
* Decide on which class we wish to make the superclass of our Child
*/
$parentClass = null;
if (isset($_GET['parent'])) {
$parentClass = $_GET['parent'];
if (!class_exists($parentClass)) {
$parentClass = "Ancestor";
}
}
if (!is_null($parentClass)) {
eval("class ChildParent extends $parentClass {};");
} else {
class ChildParent extends Ancestor {};
}
if (class_exists('ChildParent')) {
class Child extends ChildParent
{
function speak() {
parent::speak();
echo 'Child <br />';
}
}
}
/*
* Show what's going on
*/
echo 'Either | Mum | Dad <br />';
$child = new Child();
$child->speak();*