V8Js

V8Js is a PHP extension for Google's V8 Javascript engine.

The extension allows you to execute Javascript code in a secure sandbox from PHP. The executed code can be restricted using a time limit and/or memory limit. This provides the possibility to execute untrusted code with confidence.

Minimum requirements

• V8 Javascript Engine library (libv8) master https://github.com/v8/v8/ (trunk)

  V8 is Google's open source Javascript engine. V8 is written in C++ and is used in Google Chrome, the open source browser from Google. V8 implements ECMAScript as specified in ECMA-262, 5th edition. This extension makes use of V8 isolates to ensure separation between multiple V8Js instances and uses the new isolate-based mechanism to throw exceptions, hence the need for 3.24.6 or above.

• PHP 5.3.3+

  This embedded implementation of the V8 engine uses thread locking so it should work with ZTS enabled. However, this has not been tested yet.

Compiling latest version

For some very first steps, instead of compiling manually you might want to try out the V8Js docker image. It has v8, v8js and php-cli pre-installed so you can give it a try with PHP in "interactive mode". There is no Apache, etc. running however.

Building on Microsoft Windows is a bit more involved, see README.Win32.md file for a quick run through. Building on GNU/Linux and MacOS X is straight forward, see README.Linux.md and README.MacOS.md files for a walk through with platform specific notes.

PHP API

<?php
class V8Js
{
    /* Constants */

    const V8_VERSION = '';

    const FLAG_NONE = 1;
    const FLAG_FORCE_ARRAY = 2;

    const DEBUG_AUTO_BREAK_NEVER = 1;
    const DEBUG_AUTO_BREAK_ONCE = 2;
    const DEBUG_AUTO_BREAK_ALWAYS = 3;

    /* Methods */

    /**
     * Initializes and starts V8 engine and Returns new V8Js object with it's own V8 context.
     * @param string $object_name
     * @param array $variables
     * @param array $extensions
     * @param bool $report_uncaught_exceptions
     */
    public function __construct($object_name = "PHP", array $variables = NULL, array $extensions = NULL, $report_uncaught_exceptions = TRUE)
    {}

    /**
     * Provide a function or method to be used to load required modules. This can be any valid PHP callable.
     * The loader function will receive the normalised module path and should return Javascript code to be executed.
     * @param callable $loader
     */
    public function setModuleLoader(callable $loader)
    {}

    /**
     * Compiles and executes script in object's context with optional identifier string.
     * A time limit (milliseconds) and/or memory limit (bytes) can be provided to restrict execution. These options will throw a V8JsTimeLimitException or V8JsMemoryLimitException.
     * @param string $script
     * @param string $identifier
     * @param int $flags
     * @param int $time_limit in milliseconds
     * @param int $memory_limit in bytes
     * @return mixed
     */
    public function executeString($script, $identifier = '', $flags = V8Js::FLAG_NONE, $time_limit = 0, $memory_limit = 0)
    {}

    /**
     * Compiles a script in object's context with optional identifier string.
     * @param $script
     * @param string $identifier
     * @return resource
     */
    public function compileString($script, $identifier = '')
    {}

    /**
     * Executes a precompiled script in object's context.
     * A time limit (milliseconds) and/or memory limit (bytes) can be provided to restrict execution. These options will throw a V8JsTimeLimitException or V8JsMemoryLimitException.
     * @param resource $script
     * @param int $flags
     * @param int $time_limit
     * @param int $memory_limit
     */
    public function executeScript($script, $flags = V8Js::FLAG_NONE, $time_limit = 0 , $memory_limit = 0)
    {}

    /**
     * Set the time limit (in milliseconds) for this V8Js object
     * works similar to the set_time_limit php
     * @param int $limit
     */
    public function setTimeLimit($limit)
    {}

    /**
     * Set the memory limit (in bytes) for this V8Js object
     * @param int $limit
     */
    public function setMemoryLimit($limit)
    {}

    /**
     * Returns uncaught pending exception or null if there is no pending exception.
     * @return V8JsScriptException|null
     */
    public function getPendingException()
    {}

    /**
     * Clears the uncaught pending exception
     */
    public function clearPendingException()
    {}

    /**
     * Starts V8 debug agent for use with Google Chrome Developer Tools (Eclipse Plugin)
     * @param string $agent_name
     * @param int $port
     * @param int $auto_break
     * @return bool
     */
    public function startDebugAgent($agent_name = "V8Js", $port = 9222, $auto_break = V8Js::DEBUG_AUTO_BREAK_NEVER)
    {}

    /** Static methods **/

    /**
     * Registers persistent context independent global Javascript extension.
     * NOTE! These extensions exist until PHP is shutdown and they need to be registered before V8 is initialized.
     * For best performance V8 is initialized only once per process thus this call has to be done before any V8Js objects are created!
     * @param string $extension_name
     * @param string $code
     * @param array $dependencies
     * @param bool $auto_enable
     * @return bool
     */
    public static function registerExtension($extension_name, $code, array $dependencies, $auto_enable = FALSE)
    {}

    /**
     * Returns extensions successfully registered with V8Js::registerExtension().
     * @return array|string[]
     */
    public static function getExtensions()
    {}
}

final class V8JsScriptException extends Exception
{
    /**
     * @return string
     */
    final public function getJsFileName( ) {}

    /**
     * @return int
     */
    final public function getJsLineNumber( ) {}
    /**
     * @return int
     */
    final public function getJsStartColumn( ) {}
    /**
     * @return int
     */
    final public function getJsEndColumn( ) {}

    /**
     * @return string
     */
    final public function getJsSourceLine( ) {}
    /**
     * @return string
     */
    final public function getJsTrace( ) {}
}

final class V8JsTimeLimitException extends Exception
{
}

final class V8JsMemoryLimitException extends Exception
{
}

Javascript API

    // Print a string.
    print(string);

    // Dump the contents of a variable.
    var_dump(value);

    // Terminate Javascript execution immediately.
    exit();

    // CommonJS Module support to require external code.
    // This makes use of the PHP module loader provided via V8Js::setModuleLoader (see PHP API above).
    require("path/to/module");

The JavaScript in operator, when applied to a wrapped PHP object, works the same as the PHP isset() function. Similarly, when applied to a wrapped PHP object, JavaScript delete works like PHP unset.

<?php
class Foo {
  var $bar = null;
}
$v8 = new V8Js();
$v8->foo = new Foo;
// This prints "no"
$v8->executeString('print( "bar" in PHP.foo ? "yes" : "no" );');
?>

PHP has separate namespaces for properties and methods, while JavaScript has just one. Usually this isn't an issue, but if you need to you can use a leading $ to specify a property, or __call to specifically invoke a method.

<?php
class Foo {
	var $bar = "bar";
	function bar($what) { echo "I'm a ", $what, "!\n"; }
}

$foo = new Foo;
// This prints 'bar'
echo $foo->bar, "\n";
// This prints "I'm a function!"
$foo->bar("function");

$v8 = new V8Js();
$v8->foo = new Foo;
// This prints 'bar'
$v8->executeString('print(PHP.foo.$bar, "\n");');
// This prints "I'm a function!"
$v8->executeString('PHP.foo.__call("bar", ["function"]);');
?>

Mapping Rules

Native Arrays

Despite the common name the concept of arrays is very different between PHP and JavaScript. In JavaScript an array is a contiguous collection of elements indexed by integral numbers from zero on upwards. In PHP arrays can be sparse, i.e. integral keys need not be contiguous and may even be negative. Besides PHP arrays may not only use integral numbers as keys but also strings (so-called associative arrays). Contrary JavaScript arrays allow for properties to be attached to arrays, which isn't supported by PHP. Those properties are not part of the arrays collection, for example Array.prototype.forEach method doesn't "see" these.

Generally PHP arrays are mapped to JavaScript "native" arrays if this is possible, i.e. the PHP array uses contiguous numeric keys from zero on upwards. Both associative and sparse arrays are mapped to JavaScript objects. Those objects have a constructor also called "Array", but they are not native arrays and don't share the Array.prototype, hence they don't (directly) support the typical array functions like join, forEach, etc. PHP arrays are immediately exported value by value without live binding. This is if you change a value on JavaScript side or push further values onto the array, this change is not reflected on PHP side.

If JavaScript arrays are passed back to PHP the JavaScript array is always converted to a PHP array. If the JavaScript array has (own) properties attached, these are also converted to keys of the PHP array.

Native Objects

PHP objects passed to JavaScript are mapped to native JavaScript objects which have a "virtual" constructor function with the name of the PHP object's class. This constructor function can be used to create new instances of the PHP class as long as the PHP class doesn't have a non-public __construct method. All public methods and properties are visible to JavaScript code and the properties are live-bound, i.e. if a property's value is changed by JavaScript code, the PHP object is also affected.

If a native JavaScript object is passed to PHP the JavaScript object is mapped to a PHP object of V8Object class. This object has all properties the JavaScript object has and is fully mutable. If a function is assigned to one of those properties, it's also callable by PHP code. The executeString function can be configured to always map JavaScript objects to PHP arrays by setting the V8Js::FLAG_FORCE_ARRAY flag. Then the standard array behaviour applies that values are not live-bound, i.e. if you change values of the resulting PHP array, the JavaScript object is not affected.

PHP Objects implementing ArrayAccess, Countable

The above rule that PHP objects are generally converted to JavaScript objects also applies to PHP objects of ArrayObject type or other classes, that implement both the ArrayAccess and the Countable interface -- even so they behave like PHP arrays.

This behaviour can be changed by enabling the php.ini flag v8js.use_array_access. If set, objects of PHP classes that implement the aforementioned interfaces are converted to JavaScript Array-like objects. This is by-index access of this object results in immediate calls to the offsetGet or offsetSet PHP methods (effectively this is live-binding of JavaScript against the PHP object). Such an Array-esque object also supports calling every attached public method of the PHP object + methods of JavaScript's native Array.prototype methods (as long as they are not overloaded by PHP methods).