Reverse engineering using PHP

BANGALORE, INDIA: A good documentation of source code is necessary as it helps others to evaluate your application, to make it error free. But with so much code being written it becomes difficult to document each and every program. PHP 5 has an in-built feature called 'Reflection,' which allows you to reverse engineer different classes, functions or extensions.

It also gives information on objects, starting and ending line numbers of a class or function, parameters and creates documents. It is an object oriented extension to the existing PHP core engine. Using this feature, you no longer need to go through hundreds of pages of documentation to find out about any class or function.

A common scenario where you can use 'Reflection' is, when you have an encoded script to work on and you don't want to go through its manual. It also helps in understanding how a particular code is working. Now let's define a class 'first' with a function called 'display' and second function called 'second' which inherits the parent class.

class first {

public function display($text) {

// Display the argument passed

echo $text;

} }

class second extends first {

private function bar(first &$baz) {

// do something

} }

$child = new second('hello world');

$child->display('test');

?>

Save this code with '.php' extension and run the script by issuing the command “php .php”. The output of the above script will be “test”. Now, let's do reverse engineering of our code. Add the following lines at the end of the program:

$sec_refl = new ReflectionClass('second'); echo "\n", "Reflection of Second Class: ", "\n"; echo "This class is abstract: ", (int)$sec_refl->isAbstract(), "\n";

echo "This class is final: ", (int)$sec_refl->isFinal(), "\n";

echo "This class is actually an interface: ", (int)$sec_refl->isInterface(), "\n"; echo "\$second is an object of this class: ", (int)$sec_refl->isInstance($sec), "\n"; $first_refl = new ReflectionClass('first');

echo "\n", "Reflection of First Class: ", "\n" ; echo "This class inherits from First : ", (int)$sec_refl-> isSubclassOf ($first_refl), "\n";

$reflect = new ReflectionClass('second'); foreach($reflect->getMethods() as $reflectmethod) {

echo " {$reflectmethod->getName()}()\n"; echo " ", str_repeat("-", strlen($reflectmethod->getName()) + 2), "\n"; foreach($reflectmethod->getParameters() as $num => $param) {

echo "Param $num: \$", $param->getName(), "\n"; echo "Passed by

reference: ", (int)$param->isPassedByReference(), "\n"; echo "Can be null: ", (int)$param->allowsNull(), "\n";

echo "Class type: ";

if ($param->getClass()) {

echo $param->getClass()->getName();

} else { echo "N/A"; } echo "\n\n"; }}

In these lines we have created two new instances of Reflection class for each class and passed both the classes as a parameter. Then we formatted the output using some inbuilt function along with the Reflection Class. There is another way of doing this, ie by simply giving a single line “echo $sec_refl” (for second class), however, the output will be a bit confusing. The output after adding the above code is:

Output of the first display function:

Sample Text Argument

Reflection of Second Class:

This class is abstract: 0

This class is final: 0

This class is actually an interface: 0

$second is an object of this class: 1

...

In the output you can clearly see whether a class is an abstract class or not, or whether there's any object, etc. Further you can also see the description of each method for the 'second' class: like the number of arguments, class type, name of the arguments passed, etc.