includes/Hooks.php

   1 <?php
   2
   3 /**
   4  * A tool for running hook functions.
   5  *
   6  * Copyright 2004, 2005 Evan Prodromou <evan@wikitravel.org>.
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
  21  *
  22  * @author Evan Prodromou <evan@wikitravel.org>
  23  * @see hooks.txt
  24  * @file
  25  */
  26
  27 /**
  28  * @since 1.18
  29  */
  30 class MWHookException extends MWException {}
  31
  32 /**
  33  * Hooks class.
  34  *
  35  * Used to supersede $wgHooks, because globals are EVIL.
  36  *
  37  * @since 1.18
  38  */
  39 class Hooks {
  40
  41         /**
  42          * Array of events mapped to an array of callbacks to be run
  43          * when that event is triggered.
  44          */
  45         protected static $handlers = array();
  46
  47         /**
  48          * Attach an event handler to a given hook.
  49          *
  50          * @param string $name Name of hook
  51          * @param mixed $callback Callback function to attach
  52          *
  53          * @since 1.18
  54          */
  55         public static function register( $name, $callback ) {
  56                 if ( !isset( self::$handlers[$name] ) ) {
  57                         self::$handlers[$name] = array();
  58                 }
  59
  60                 self::$handlers[$name][] = $callback;
  61         }
  62
  63         /**
  64          * Clears hooks registered via Hooks::register(). Does not touch $wgHooks.
  65          * This is intended for use while testing and will fail if MW_PHPUNIT_TEST is not defined.
  66          *
  67          * @param string $name the name of the hook to clear.
  68          *
  69          * @since 1.21
  70          * @throws MWException if not in testing mode.
  71          */
  72         public static function clear( $name ) {
  73                 if ( !defined( 'MW_PHPUNIT_TEST' ) ) {
  74                         throw new MWException( 'Cannot reset hooks in operation.' );
  75                 }
  76
  77                 unset( self::$handlers[$name] );
  78         }
  79
  80         /**
  81          * Returns true if a hook has a function registered to it.
  82          * The function may have been registered either via Hooks::register or in $wgHooks.
  83          *
  84          * @since 1.18
  85          *
  86          * @param string $name Name of hook
  87          * @return bool True if the hook has a function registered to it
  88          */
  89         public static function isRegistered( $name ) {
  90                 global $wgHooks;
  91                 return !empty( $wgHooks[$name] ) || !empty( self::$handlers[$name] );
  92         }
  93
  94         /**
  95          * Returns an array of all the event functions attached to a hook
  96          * This combines functions registered via Hooks::register and with $wgHooks.
  97          *
  98          * @since 1.18
  99          *
 100          * @param string $name Name of the hook
 101          * @return array
 102          */
 103         public static function getHandlers( $name ) {
 104                 global $wgHooks;
 105
 106                 if ( !self::isRegistered( $name ) ) {
 107                         return array();
 108                 } elseif ( !isset( self::$handlers[$name] ) ) {
 109                         return $wgHooks[$name];
 110                 } elseif ( !isset( $wgHooks[$name] ) ) {
 111                         return self::$handlers[$name];
 112                 } else {
 113                         return array_merge( self::$handlers[$name], $wgHooks[$name] );
 114                 }
 115         }
 116
 117         /**
 118          * Call hook functions defined in Hooks::register and $wgHooks.
 119          *
 120          * For a certain hook event, fetch the array of hook events and
 121          * process them. Determine the proper callback for each hook and
 122          * then call the actual hook using the appropriate arguments.
 123          * Finally, process the return value and return/throw accordingly.
 124          *
 125          * @param string $event Event name
 126          * @param array $args  Array of parameters passed to hook functions
 127          * @return bool True if no handler aborted the hook
 128          *
 129          * @throws MWException
 130          * @throws FatalError
 131          */
 132         public static function run( $event, array $args = array() ) {
 133                 wfProfileIn( 'hook: ' . $event );
 134                 foreach ( self::getHandlers( $event ) as $hook ) {
 135                         // Turn non-array values into an array. (Can't use casting because of objects.)
 136                         if ( !is_array( $hook ) ) {
 137                                 $hook = array( $hook );
 138                         }
 139
 140                         if ( !array_filter( $hook ) ) {
 141                                 // Either array is empty or it's an array filled with null/false/empty.
 142                                 continue;
 143                         } elseif ( is_array( $hook[0] ) ) {
 144                                 // First element is an array, meaning the developer intended
 145                                 // the first element to be a callback. Merge it in so that
 146                                 // processing can be uniform.
 147                                 $hook = array_merge( $hook[0], array_slice( $hook, 1 ) );
 148                         }
 149
 150                         /**
 151                          * $hook can be: a function, an object, an array of $function and
 152                          * $data, an array of just a function, an array of object and
 153                          * method, or an array of object, method, and data.
 154                          */
 155                         if ( $hook[0] instanceof Closure ) {
 156                                 $func = "hook-$event-closure";
 157                                 $callback = array_shift( $hook );
 158                         } elseif ( is_object( $hook[0] ) ) {
 159                                 $object = array_shift( $hook );
 160                                 $method = array_shift( $hook );
 161
 162                                 // If no method was specified, default to on$event.
 163                                 if ( $method === null ) {
 164                                         $method = "on$event";
 165                                 }
 166
 167                                 $func = get_class( $object ) . '::' . $method;
 168                                 $callback = array( $object, $method );
 169                         } elseif ( is_string( $hook[0] ) ) {
 170                                 $func = $callback = array_shift( $hook );
 171                         } else {
 172                                 throw new MWException( 'Unknown datatype in hooks for ' . $event . "\n" );
 173                         }
 174
 175                         // Run autoloader (workaround for call_user_func_array bug)
 176                         // and throw error if not callable.
 177                         if ( !is_callable( $callback ) ) {
 178                                 throw new MWException( 'Invalid callback in hooks for ' . $event . "\n" );
 179                         }
 180
 181                         /*
 182                          * Call the hook. The documentation of call_user_func_array says
 183                          * false is returned on failure. However, if the function signature
 184                          * does not match the call signature, PHP will issue an warning and
 185                          * return null instead. The following code catches that warning and
 186                          * provides better error message.
 187                          */
 188                         $retval = null;
 189                         $badhookmsg = null;
 190                         $hook_args = array_merge( $hook, $args );
 191
 192                         // Profile first in case the Profiler causes errors.
 193                         wfProfileIn( $func );
 194                         set_error_handler( 'Hooks::hookErrorHandler' );
 195                         try {
 196                                 $retval = call_user_func_array( $callback, $hook_args );
 197                         } catch ( MWHookException $e ) {
 198                                 $badhookmsg = $e->getMessage();
 199                         }
 200                         restore_error_handler();
 201                         wfProfileOut( $func );
 202
 203                         // Process the return value.
 204                         if ( is_string( $retval ) ) {
 205                                 // String returned means error.
 206                                 throw new FatalError( $retval );
 207                         } elseif ( $badhookmsg !== null ) {
 208                                 // Exception was thrown from Hooks::hookErrorHandler.
 209                                 throw new MWException(
 210                                         'Detected bug in an extension! ' .
 211                                         "Hook $func has invalid call signature; " . $badhookmsg
 212                                 );
 213                         } elseif ( $retval === null ) {
 214                                 // Null was returned. Error.
 215                                 throw new MWException(
 216                                         'Detected bug in an extension! ' .
 217                                         "Hook $func failed to return a value; " .
 218                                         'should return true to continue hook processing or false to abort.'
 219                                 );
 220                         } elseif ( !$retval ) {
 221                                 wfProfileOut( 'hook: ' . $event );
 222                                 // False was returned. Stop processing, but no error.
 223                                 return false;
 224                         }
 225                 }
 226
 227                 wfProfileOut( 'hook: ' . $event );
 228                 return true;
 229         }
 230
 231         /**
 232          * Handle PHP errors issued inside a hook. Catch errors that have to do with
 233          * a function expecting a reference, and let all others pass through.
 234          *
 235          * This REALLY should be protected... but it's public for compatibility
 236          *
 237          * @since 1.18
 238          *
 239          * @param int $errno Error number (unused)
 240          * @param string $errstr Error message
 241          * @throws MWHookException If the error has to do with the function signature
 242          * @return bool Always returns false
 243          */
 244         public static function hookErrorHandler( $errno, $errstr ) {
 245                 if ( strpos( $errstr, 'expected to be a reference, value given' ) !== false ) {
 246                         throw new MWHookException( $errstr, $errno );
 247                 }
 248                 return false;
 249         }
 250 }