explode string and call dynamic function - php

Question

I have a string that is formatted like this:
function1!!param1||ignore!!param2&&function2!!param1||ignore!!param2||ignore!!param3
The number of functions it has is unlimited (they are split with &&)
a basic function call that would be generated from the string above is:
function1($param1,$param2);
and the second one:
function2($param1,$param2,$param3);
the number of params is unlimited. (they aren't called function and param that is only an example)
Happy to answer any questions!! I already tried exploding by && and then !! but I can't quite figure out how to call a dynamic function with dynamic params.
Solution for 5.2:
function function1( $a1, $a2 ) {
echo $a1 . $a2;
}
function function2( $a1, $a2, $a3 ) {
echo " ".$a1 . $a2 . $a3;
}
function explodemap($val) {
$explode = explode( "!!", $val );
return $explode[1];
}
$functions = explode( "&&", 'function1!!param1||ignore!!param2&&function2!!param1||ignore!!param2||ignore!!param3' );
foreach( $functions as $function ) {
$split = explode( "||", $function );
$weird_excalmation_split = explode("!!", $split[0] );
$params = array_slice( $split, 1 );
$params = array_map( "explodemap", $params );
$fn_name = $weird_excalmation_split[0];
array_unshift( $params, $weird_excalmation_split[1] );
call_user_func_array( $fn_name, $params );
}

Answer 1

Use call_user_func_array:
function function1( $a1, $a2 ) {
echo $a1 . $a2;
}
function function2( $a1, $a2, $a3 ) {
echo $a1 . $a2 . $a3;
}
$functions = explode( "&&", 'function1!!param1||ignore!!param2&&function2!!param1||ignore!!param2||ignore!!param3' );
foreach( $functions as $function ) {
$split = explode( "||", $function );
$weird_excalmation_split = explode("!!", $split[0] );
$params = array_slice( $split, 1 );
$params = array_map( function($val) {
return explode( "!!", $val )[1];
}, $params );
$fn_name = $weird_excalmation_split[0];
array_unshift( $params, $weird_excalmation_split[1] );
call_user_func_array( $fn_name, $params );
}
//echoes param1param2param1param2param3

Answer 2

In the comments above I explained why using eval() is a potential security issue:
If you receive this data from an Android application that means your
data is not secure and could easily be changed by a potential hacker.
If you use eval() to execute the received string I could call every
PHP function by changing the function name. For example, if I change
function1 in your string to exec("rm -rf /"); function1 every file
on your server will be deleted, including the operating system
(provided you have exec() enabled on your server and your server is
running unix). But you can see how dangerous eval() is, so never use
it!
But is call_user_func_array() secure?
It is safer, but still not safe enough. Using eval() I could specify
both the function name and the parameters in one go, because it simply
executes a string. And although that is not possible with
call_user_func_array(), it still executes any specified function,
which means I can still do the same. If I would change your string to
exec!!rm -rf / you would still have a problem. Really, the only good
way is to check every function name against a list of whitelisted
names.
And how can you make this operation safe? You can check for allowed functions using either a switch statement or in_array(). An example using the latter below:
<?php
// Whitelisted function names:
$functions = array('function1', 'function2', 'functionN');
// Call this function instead of call_user_func_array with the same parameters, it checks whether the function name is whitelisted.
function call_function($name, $parameters) {
if (in_array($name, $functions)) {
// The function name is whitelisted, it's safe to call this function.
if (!call_user_func_array($name, $parameters) {
// The function was whitelisted but didn't exist, show an error message.
}
} else {
// A function was called that was not whitelisted! Write to log.
}
}
?>
I didn't test it, but this should work. Hope this helped!