includes/StubObject.php

   1 <?php
   2 /**
   3  * Delayed loading of global objects.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  */
  22 use Wikimedia\ObjectFactory;
  23
  24 /**
  25  * Class to implement stub globals, which are globals that delay loading the
  26  * their associated module code by deferring initialisation until the first
  27  * method call.
  28  *
  29  * Note on reference parameters:
  30  *
  31  * If the called method takes any parameters by reference, the __call magic
  32  * here won't work correctly. The solution is to unstub the object before
  33  * calling the method.
  34  *
  35  * Note on unstub loops:
  36  *
  37  * Unstub loops (infinite recursion) sometimes occur when a constructor calls
  38  * another function, and the other function calls some method of the stub. The
  39  * best way to avoid this is to make constructors as lightweight as possible,
  40  * deferring any initialisation which depends on other modules. As a last
  41  * resort, you can use StubObject::isRealObject() to break the loop, but as a
  42  * general rule, the stub object mechanism should be transparent, and code
  43  * which refers to it should be kept to a minimum.
  44  */
  45 class StubObject {
  46         /** @var null|string */
  47         protected $global;
  48
  49         /** @var null|string */
  50         protected $class;
  51
  52         /** @var null|callable */
  53         protected $factory;
  54
  55         /** @var array */
  56         protected $params;
  57
  58         /**
  59          * @param string|null $global Name of the global variable.
  60          * @param string|callable|null $class Name of the class of the real object
  61          *                               or a factory function to call
  62          * @param array $params Parameters to pass to constructor of the real object.
  63          */
  64         public function __construct( $global = null, $class = null, $params = [] ) {
  65                 $this->global = $global;
  66                 if ( is_callable( $class ) ) {
  67                         $this->factory = $class;
  68                 } else {
  69                         $this->class = $class;
  70                 }
  71                 $this->params = $params;
  72         }
  73
  74         /**
  75          * Returns a bool value whenever $obj is a stub object. Can be used to break
  76          * a infinite loop when unstubbing an object.
  77          *
  78          * @param object $obj Object to check.
  79          * @return bool True if $obj is not an instance of StubObject class.
  80          */
  81         public static function isRealObject( $obj ) {
  82                 return is_object( $obj ) && !$obj instanceof self;
  83         }
  84
  85         /**
  86          * Unstubs an object, if it is a stub object. Can be used to break a
  87          * infinite loop when unstubbing an object or to avoid reference parameter
  88          * breakage.
  89          *
  90          * @param object &$obj Object to check.
  91          * @return void
  92          */
  93         public static function unstub( &$obj ) {
  94                 if ( $obj instanceof self ) {
  95                         $obj = $obj->_unstub( 'unstub', 3 );
  96                 }
  97         }
  98
  99         /**
 100          * Function called if any function exists with that name in this object.
 101          * It is used to unstub the object. Only used internally, PHP will call
 102          * self::__call() function and that function will call this function.
 103          * This function will also call the function with the same name in the real
 104          * object.
 105          *
 106          * @param string $name Name of the function called
 107          * @param array $args Arguments
 108          * @return mixed
 109          */
 110         public function _call( $name, $args ) {
 111                 $this->_unstub( $name, 5 );
 112                 return call_user_func_array( [ $GLOBALS[$this->global], $name ], $args );
 113         }
 114
 115         /**
 116          * Create a new object to replace this stub object.
 117          * @return object
 118          */
 119         public function _newObject() {
 120                 $params = $this->factory
 121                         ? [ 'factory' => $this->factory ]
 122                         : [ 'class' => $this->class ];
 123                 return ObjectFactory::getObjectFromSpec( $params + [
 124                         'args' => $this->params,
 125                         'closure_expansion' => false,
 126                 ] );
 127         }
 128
 129         /**
 130          * Function called by PHP if no function with that name exists in this
 131          * object.
 132          *
 133          * @param string $name Name of the function called
 134          * @param array $args Arguments
 135          * @return mixed
 136          */
 137         public function __call( $name, $args ) {
 138                 return $this->_call( $name, $args );
 139         }
 140
 141         /**
 142          * This function creates a new object of the real class and replace it in
 143          * the global variable.
 144          * This is public, for the convenience of external callers wishing to access
 145          * properties, e.g. eval.php
 146          *
 147          * @param string $name Name of the method called in this object.
 148          * @param int $level Level to go in the stack trace to get the function
 149          *   who called this function.
 150          * @return object The unstubbed version of itself
 151          * @throws MWException
 152          */
 153         public function _unstub( $name = '_unstub', $level = 2 ) {
 154                 static $recursionLevel = 0;
 155
 156                 if ( !$GLOBALS[$this->global] instanceof self ) {
 157                         return $GLOBALS[$this->global]; // already unstubbed.
 158                 }
 159
 160                 if ( get_class( $GLOBALS[$this->global] ) != $this->class ) {
 161                         $caller = wfGetCaller( $level );
 162                         if ( ++$recursionLevel > 2 ) {
 163                                 throw new MWException( "Unstub loop detected on call of "
 164                                         . "\${$this->global}->$name from $caller\n" );
 165                         }
 166                         wfDebug( "Unstubbing \${$this->global} on call of "
 167                                 . "\${$this->global}::$name from $caller\n" );
 168                         $GLOBALS[$this->global] = $this->_newObject();
 169                         --$recursionLevel;
 170                         return $GLOBALS[$this->global];
 171                 }
 172         }
 173 }