Method interception in PHP 5.*

Question

Hi everybody,

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 multidimensionnal 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 ???

Thanks in advance, Rolf

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 '<a href="?">Either</a> | <a href="?parent=Mum">Mum</a> | <a href="?parent=Dad">Dad</a> <br />';

$child = new Child();
$child->speak();*