API:Extensions

Creating API modules in extensions
Extensions can also add API modules. Create a new class that inherits ApiBase (for a top-level module), ApiQueryBase (for a non-generator submodule of action=query) or ApiQueryGeneratorBase (for a submodule of action=query with generator functionality) and implement the methods execute, getAllowedParams, getParamDescription, getDescription and getVersion.

A generator module is somewhat like UNIX piping, where the output of one module is the input of another. For example: You can ask for a list of all pages with, and you can enumerate images on specific pages (by specifying page titles) with. can also act as a generator, so you can "pipe" it to. By convention when a module acts as a generator its parameters, often the same as in its regular mode, are prefixed with ' '. Thus api.php?action=query&generator=allpages&gaplimit=8&prop=images&imlimit=15 generates a list of the first 8 wiki pages, and from them shows up to 12 images in total. Generator modules also need to implement executeGenerator.

When you've created your new class, you need to register it with the API by adding it to $wgAPIModules (top-level modules, selected using action=), $wgAPIPropModules (prop= modules), $wgAPIMetaModules (meta= modules) or $wgAPIListModules (list= modules), like this:

It's possible to override core modules.

Extending core modules
Since MediaWiki 1.14, it's possible to extend core modules' functionality using the following hooks:
 * APIGetAllowedParams to add or modify the module's parameter list
 * APIGetParamDescription to add or modify the module's parameter descriptions
 * APIAfterExecute to do something after the module has been executed (but before the result has been output)
 * Use APIQueryAfterExecute for,   and   modules
 * If the module is run in generator mode, APIQueryGeneratorAfterExecute will be called instead

List of extensions with API functionality
See API extensions for examples of extensions that add or extend to the API.

Caching
By default ApiMain leaves caching of API calls up to the callee ('Cache-Control: private')! To modify this behavior for high volume requests add the following somewhere in your execute method:

Returning errors
Some errors will be automatically generated if certain conditions that you set up are not met; for example, if the user fails to provide a title, then the "missingparam" error will be thrown if you have set getAllowedParams as follows:

Sometimes the types of error conditions set up by the methods supplied by ApiBase will not suffice and you will have to set up your own conditions. E.g., if you wanted to prevent the client from using interwiki links (e.g. MediaWiki) as titles, you might use: That would throw the error defined in messageMap. See documentation for ApiBase::dieUsage, ApiBase::dieUsageMsg, and ApiBase::getPossibleErrors. For an example of how the latter is done, see ApiEditPage::getPossibleErrors.

Sample API extension
This is an example API extension that receives  (i.e. an emoticon) as a parameter and outputs various data (viz. reply emoticons and predictions) in response. For example:

to generate: To install it requires the usual procedure, i.e. copying the following three files into $IP/extensions/SampleApiExtension and adding to the end of LocalSettings.php: