docs/hooks.txt

   1 HOOKS.DOC
   2
   3 This document describes how event hooks work in MediaWiki; how to add
   4 hooks for an event; and how to run hooks for an event.
   5
   6 ==Glossary==
   7
   8 event
   9      Something that happens with the wiki. For example: a user logs
  10      in. A wiki page is saved. A wiki page is deleted. Often there are
  11      two events associated with a single action: one before the code
  12      is run to make the event happen, and one after. Each event has a
  13      name, preferably in CamelCase. For example, 'UserLogin',
  14      'ArticleSave', 'ArticleSaveComplete', 'ArticleDelete'.
  15
  16 hook
  17      A clump of code and data that should be run when an event
  18      happens. This can be either a function and a chunk of data, or an
  19      object and a method.
  20
  21 hook function
  22      The function part of a hook.
  23
  24 ==Rationale==
  25
  26 Hooks allow us to decouple optionally-run code from code that is run
  27 for everyone. It allows MediaWiki hackers, third-party developers and
  28 local administrators to define code that will be run at certain points
  29 in the mainline code, and to modify the data run by that mainline
  30 code. Hooks can keep mainline code simple, and make it easier to
  31 write extensions. Hooks are a principled alternative to local patches.
  32
  33 Consider, for example, two options in MediaWiki. One reverses the
  34 order of a title before displaying the article; the other converts the
  35 title to all uppercase letters. Currently, in MediaWiki code, we
  36 would handle this as follows (note: not real code, here):
  37
  38     function showAnArticle($article) {
  39         global $wgReverseTitle, $wgCapitalizeTitle;
  40
  41         if ($wgReverseTitle) {
  42             wfReverseTitle($article);
  43         }
  44
  45         if ($wgCapitalizeTitle) {
  46            wfCapitalizeTitle($article);
  47         }
  48
  49         # code to actually show the article goes here
  50     }
  51
  52 An extension writer, or a local admin, will often add custom code to
  53 the function -- with or without a global variable. For example,
  54 someone wanting email notification when an article is shown may add:
  55
  56     function showAnArticle($article) {
  57         global $wgReverseTitle, $wgCapitalizeTitle;
  58
  59         if ($wgReverseTitle) {
  60             wfReverseTitle($article);
  61         }
  62
  63         if ($wgCapitalizeTitle) {
  64            wfCapitalizeTitle($article);
  65         }
  66
  67         # code to actually show the article goes here
  68
  69         if ($wgNotifyArticle) {
  70            wfNotifyArticleShow($article));
  71         }
  72     }
  73
  74 Using a hook-running strategy, we can avoid having all this
  75 option-specific stuff in our mainline code. Using hooks, the function
  76 becomes:
  77
  78     function showAnArticle($article) {
  79
  80         if (wfRunHooks('ArticleShow', array(&$article))) {
  81
  82             # code to actually show the article goes here
  83
  84             wfRunHooks('ArticleShowComplete', array(&$article));
  85         }
  86     }
  87
  88 We've cleaned up the code here by removing clumps of weird,
  89 infrequently used code and moving them off somewhere else. It's much
  90 easier for someone working with this code to see what's _really_ going
  91 on, and make changes or fix bugs.
  92
  93 In addition, we can take all the code that deals with the little-used
  94 title-reversing options (say) and put it in one place. Instead of
  95 having little title-reversing if-blocks spread all over the codebase
  96 in showAnArticle, deleteAnArticle, exportArticle, etc., we can
  97 concentrate it all in an extension file:
  98
  99     function reverseArticleTitle($article) {
 100         # ...
 101     }
 102
 103     function reverseForExport($article) {
 104         # ...
 105     }
 106
 107 The setup function for the extension just has to add its hook
 108 functions to the appropriate events:
 109
 110     setupTitleReversingExtension() {
 111         global $wgHooks;
 112
 113         $wgHooks['ArticleShow'][] = 'reverseArticleTitle';
 114         $wgHooks['ArticleDelete'][] = 'reverseArticleTitle';
 115         $wgHooks['ArticleExport'][] = 'reverseForExport';
 116     }
 117
 118 Having all this code related to the title-reversion option in one
 119 place means that it's easier to read and understand; you don't have to
 120 do a grep-find to see where the $wgReverseTitle variable is used, say.
 121
 122 If the code is well enough isolated, it can even be excluded when not
 123 used -- making for some slight savings in memory and load-up
 124 performance at runtime. Admins who want to have all the reversed
 125 titles can add:
 126
 127     require_once('extensions/ReverseTitle.php');
 128
 129 ...to their LocalSettings.php file; those of us who don't want or need
 130 it can just leave it out.
 131
 132 The extensions don't even have to be shipped with MediaWiki; they
 133 could be provided by a third-party developer or written by the admin
 134 him/herself.
 135
 136 ==Writing hooks==
 137
 138 A hook is a chunk of code run at some particular event. It consists of:
 139
 140   * a function with some optional accompanying data, or
 141   * an object with a method and some optional accompanying data.
 142
 143 Hooks are registered by adding them to the global $wgHooks array for a
 144 given event. All the following are valid ways to define hooks:
 145
 146       $wgHooks['EventName'][] = 'someFunction'; # function, no data
 147       $wgHooks['EventName'][] = array('someFunction', $someData);
 148       $wgHooks['EventName'][] = array('someFunction'); # weird, but OK
 149
 150       $wgHooks['EventName'][] = $object; # object only
 151       $wgHooks['EventName'][] = array($object, 'someMethod');
 152       $wgHooks['EventName'][] = array($object, 'someMethod', $someData);
 153       $wgHooks['EventName'][] = array($object); # weird but OK
 154
 155 When an event occurs, the function (or object method) will be called
 156 with the optional data provided as well as event-specific parameters.
 157 The above examples would result in the following code being executed
 158 when 'EventName' happened:
 159
 160       # function, no data
 161       someFunction($param1, $param2)
 162       # function with data
 163       someFunction($someData, $param1, $param2)
 164
 165       # object only
 166       $object->onEventName($param1, $param2)
 167       # object with method
 168       $object->someMethod($param1, $param2)
 169       # object with method and data
 170       $object->someMethod($someData, $param1, $param2)
 171
 172 Note that when an object is the hook, and there's no specified method,
 173 the default method called is 'onEventName'. For different events this
 174 would be different: 'onArticleSave', 'onUserLogin', etc.
 175
 176 The extra data is useful if we want to use the same function or object
 177 for different purposes. For example:
 178
 179       $wgHooks['ArticleSaveComplete'][] = array('ircNotify', 'TimStarling');
 180       $wgHooks['ArticleSaveComplete'][] = array('ircNotify', 'brion');
 181
 182 This code would result in ircNotify being run twice when an article is
 183 saved: once for 'TimStarling', and once for 'brion'.
 184
 185 Hooks can return three possible values:
 186
 187   * true: the hook has operated successfully
 188   * "some string": an error occurred; processing should
 189           stop and the error should be shown to the user
 190   * false: the hook has successfully done the work
 191            necessary and the calling function should skip
 192
 193 The last result would be for cases where the hook function replaces
 194 the main functionality. For example, if you wanted to authenticate
 195 users to a custom system (LDAP, another PHP program, whatever), you
 196 could do:
 197
 198     $wgHooks['UserLogin'][] = array('ldapLogin', $ldapServer);
 199
 200     function ldapLogin($username, $password) {
 201         # log user into LDAP
 202         return false;
 203     }
 204
 205 Returning false makes less sense for events where the action is
 206 complete, and will normally be ignored.
 207
 208 ==Using hooks==
 209
 210 A calling function or method uses the wfRunHooks() function to run
 211 the hooks related to a particular event, like so:
 212
 213     class Article {
 214         # ...
 215         function protect() {
 216             global $wgUser;
 217             if (wfRunHooks('ArticleProtect', array(&$this, &$wgUser))) {
 218                 # protect the article
 219                 wfRunHooks('ArticleProtectComplete', array(&$this, &$wgUser));
 220             }
 221         }
 222
 223 wfRunHooks() returns true if the calling function should continue
 224 processing (the hooks ran OK, or there are no hooks to run), or false
 225 if it shouldn't (an error occurred, or one of the hooks handled the
 226 action already). Checking the return value matters more for "before"
 227 hooks than for "complete" hooks.
 228
 229 Note that hook parameters are passed in an array; this is a necessary
 230 inconvenience to make it possible to pass reference values (that can
 231 be changed) into the hook code. Also note that earlier versions of
 232 wfRunHooks took a variable number of arguments; the array() calling
 233 protocol came about after MediaWiki 1.4rc1.
 234
 235 ==Events and parameters==
 236
 237 This is a list of known events and parameters; please add to it if
 238 you're going to add events to the MediaWiki code.
 239
 240 'ArticleDelete': before an article is deleted
 241 $article: the article (object) being deleted
 242 $user: the user (object) deleting the article
 243 $reason: the reason (string) the article is being deleted
 244
 245 'ArticleDeleteComplete': after an article is deleted
 246 $article: the article that was deleted
 247 $user: the user that deleted the article
 248 $reason: the reason the article was deleted
 249
 250 'ArticleProtect': before an article is protected
 251 $article: the article being protected
 252 $user: the user doing the protection
 253 $protect: boolean whether this is a protect or an unprotect
 254 $reason: Reason for protect
 255 $moveonly: boolean whether this is for move only or not
 256
 257 'ArticleProtectComplete': after an article is protected
 258 $article: the article that was protected
 259 $user: the user who did the protection
 260 $protect: boolean whether it was a protect or an unprotect
 261 $reason: Reason for protect
 262 $moveonly: boolean whether it was for move only or not
 263
 264 'ArticleSave': before an article is saved
 265 $article: the article (object) being saved
 266 $user: the user (object) saving the article
 267 $text: the new article text
 268 $summary: the article summary (comment)
 269 $isminor: minor flag
 270 $iswatch: watch flag
 271 $section: section #
 272
 273 'ArticleSaveComplete': after an article is saved
 274 $article: the article (object) saved
 275 $user: the user (object) who saved the article
 276 $text: the new article text
 277 $summary: the article summary (comment)
 278 $isminor: minor flag
 279 $iswatch: watch flag
 280 $section: section #
 281
 282 'BlockIp': before an IP address or user is blocked
 283 $block: the Block object about to be saved
 284 $user: the user _doing_ the block (not the one being blocked)
 285
 286 'BlockIpComplete': after an IP address or user is blocked
 287 $block: the Block object that was saved
 288 $user: the user who did the block (not the one being blocked)
 289
 290 'EmailUser': before sending email from one user to another
 291 $to: address of receiving user
 292 $from: address of sending user
 293 $subject: subject of the mail
 294 $text: text of the mail
 295
 296 'EmailUserComplete': after sending email from one user to another
 297 $to: address of receiving user
 298 $from: address of sending user
 299 $subject: subject of the mail
 300 $text: text of the mail
 301
 302 'LogPageValidTypes': action being logged.
 303 $type: array of strings
 304
 305 'LogPageLogName': name of the logging page(s).
 306 $typeText: array of strings
 307
 308 'LogPageLogHeader': strings used by wfMsg as a header.
 309 $headerText: array of strings
 310
 311 'TitleMoveComplete': after moving an article (title)
 312 $old: old title
 313 $nt: new title
 314 $user: user who did the move
 315 $pageid: database ID of the page that's been moved
 316 $redirid: database ID of the created redirect
 317
 318 'UnknownAction': An unknown "action" has occured (useful for defining
 319                  your own actions)
 320 $action: action name
 321 $article: article "acted on"
 322
 323 'UnwatchArticle': before a watch is removed from an article
 324 $user: user watching
 325 $article: article object to be removed
 326
 327 'UnwatchArticle': after a watch is removed from an article
 328 $user: user that was watching
 329 $article: article object removed
 330
 331 'UserLoginComplete': after a user has logged in
 332 $user: the user object that was created on login
 333
 334 'UserLogout': before a user logs out
 335 $user: the user object that is about to be logged out
 336
 337 'UserLogoutComplete': after a user has logged out
 338 $user: the user object _after_ logout (won't have name, ID, etc.)
 339
 340 'WatchArticle': before a watch is added to an article
 341 $user: user that will watch
 342 $article: article object to be watched
 343
 344 'WatchArticleComplete': after a watch is added to an article
 345 $user: user that watched
 346 $article: article object watched
 347
 348 'CategoryPageView': before viewing a categorypage in CategoryPage::view
 349 $catpage: CategoryPage instance
 350
 351
 352 More hooks might not be available but undocumented.