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This document covers creating an API module in an extension for use with MediaWiki 1.30 and later.

Module creation and registration

All API modules are subclasses of ApiBase , but some types of modules use a derived base class. The method of registration also depends on the module type.

action modules

Modules that provide a value for the main action parameter should subclass ApiBase . They should be registered in extension.json using the APIModules key.

format modules

Modules that provide a value for the main format parameter should subclass ApiFormatBase. They should be registered in extension.json using the APIFormatModules key. It's very uncommon for an extension to need to add a format module.

query submodules

Modules that provide a value for the prop, list, or meta parameters to action=query should subclass ApiQueryBase (if not usable as a generator) or ApiQueryGeneratorBase (if usable as a generator). They should be registered in extension.json using the APIPropModules, APIListModules, or APIMetaModules key.

In all cases, the value for the registration key is an object with the module name (i.e. the value for the parameter) as the key and the class name as the value. Modules may also be registered conditionally using the ApiMain::moduleManager (for action and format modules) and ApiQuery::moduleManager (for query submodules) hooks.

Implementation

Prefix

In the constructor of your API module, when you call parent::__construct() you can specify an optional prefix for your module's parameters. (In the generated documentation for a module this prefix, if any, appears in parentheses in the heading for the module.) If your module is a query submodule then a prefix is required, since a client can invoke multiple submodules each with its own parameters in a single request. For action and format modules, the prefix is optional.

Parameters

Most modules require parameters. These are defined by implementing getAllowedParams(). The return value is an associative array where keys are the (unprefixed) parameter names and values are either the scalar default value for the parameter or an array defining the properties of the parameter using the PARAM_* constants defined by ApiBase.

The example illustrates the syntax and some of the more common PARAM_* constants.

	protected function getAllowedParams() {
		return [
			// An optional parameter with a default value
			'simple' => 'value',

			// A required parameter
			'required' => [
				ApiBase::PARAM_TYPE => 'string',
				ApiBase::PARAM_REQUIRED => true,
			],

			// A parameter accepting multiple values from a list
			'variable' => [
				// The default set of values
				ApiBase::PARAM_DFLT => 'foo|bar|baz',
				// All possible values
				ApiBase::PARAM_TYPE => [ 'foo', 'bar', 'baz', 'quux', 'fred', 'blah' ],
				// Indicate that multiple values are accepted
				ApiBase::PARAM_ISMULTI => true,
				// Use standard "per value" documentation messages
				ApiBase::PARAM_HELP_MSG_PER_VALUE => [],
			],

			// A standard "limit" parameter. It's generally best not to vary from this standard.
			'limit' => [
				ApiBase::PARAM_DFLT => 10,
				ApiBase::PARAM_TYPE => 'limit',
				ApiBase::PARAM_MIN => 1,
				ApiBase::PARAM_MAX => ApiBase::LIMIT_BIG1,
				ApiBase::PARAM_MAX2 => ApiBase::LIMIT_BIG2,
			],
		];
	}

Parameters are documented using MediaWiki's i18n mechanism. See #Documentation for details.

Execution and output

The code actually implementing the module goes in the execute() method. This code will generally use $this→extractRequestParams() to get the input parameters, and will use $this→getResult() to get the ApiResult object to add any output to.

Query prop submodules should use $this→getPageSet() to access the set of pages to operate on.

Query submodules that can be used as generators will also need to implement executeGenerator() which is passed and ApiPageSet that should be filled with the generated pages. In this case, the ApiResult should generally not be used.

Caching

By default API responses are marked as not cacheable ('Cache-Control: private')! For action modules, you can allow caching by calling $this→getMain()→setCacheMode(). This still requires clients pass the maxage or smaxage parameters to actually enable caching. You can force caching by also calling $this→getMain()→setCacheMaxAge().

For query modules, do not call those methods. You can allow caching by instead implementing getCacheMode().

In either case, be sure that private data is not exposed.

Token handling

If your action module changes the wiki in any way, it should require a token of some kind. To have this handled automatically, implement the needsToken() method, returning the token that your module requires (probably the 'csrf' edit token). The API base code will then automatically validate the token that clients provide in API requests in a token parameter.

If you don't want to use a token that is part of core, but rather a custom token with your own permission checks, use ApiQueryTokensRegisterTypes hook to register your token.

Primary database access

If your module accesses the primary database, it should implement the isWriteMode() method to return true.

Returning errors

ApiBase includes several methods for performing various checks, for example,

• If you need to assert that exactly one of a set of parameters was supplied, use $this→requireOnlyOneParameter().
• If you need to assert that at most one of a set of parameters was supplied, use $this→requireMaxOneParameter().
• If you need to assert that at least one of a set of parameters was supplied, use $this→requireAtLeastOneParameter().
• If you need to assert that the user has certain rights, use $this→checkUserRightsAny().
• If you need to assert that the user can take an action on a particular page, use $this→checkTitleUserPermissions().
• If the user is blocked (and that matters to your module), pass the Block object to $this→dieBlocked().

But you will often run into cases where you need to raise an error of your own. The usual way to do that is to call $this→dieWithError(), although if you have a StatusValue with the error information you could pass it to $this→dieStatus() instead.

If you need to issue a warning rather than an error, use $this→addWarning() or $this→addDeprecation() if it's a deprecation warning.

Documentation

The API is documented using MediaWiki's i18n mechanism. Needed messages generally have default names based on the module's "path". For action and format modules, the path is the same as the module's name used during registration. For query submodules, it's the name prefixed with query+.

Every module will need a apihelp-$path-summary message, which should be a one-line description of the module. If additional help text is needed, apihelp-$path-extended-description may be created as well. Each parameter will need a apihelp-$path-param-$name message, and parameters using PARAM_HELP_MSG_PER_VALUE will also need a apihelp-$path-paramvalue-$name-$value for each value.

More details on API documentation are available at API:Localisation .

Extensions may also document their extra API modules on mediawiki.org. This should be located on the extension's main page or, if more space is required, on pages named Extension:<ExtensionName>/API or subpages thereof (e.g. CentralAuth , MassMessage , or StructuredDiscussions ). The API namespace is reserved for the API of MediaWiki core.

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
• APIGetParamDescriptionMessages - 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 prop=, list= and meta= modules
    • If the module is run in generator mode, APIQueryGeneratorAfterExecute will be called instead

List of extensions with API functionality

See Category:API extensions for examples of extensions that add to or extend the API.

Testing your extension

• Visit api.php and navigate to the generated help for your module or query submodule. Your extension's help information should be correct.
  • The example URLs you provided in getExamplesMessages() should appear under "Examples", try clicking them.
  • Omit and mangle URL parameters in the query string, check your extension's response.
• Visit Special:ApiSandbox and interactively explore your API.
• To see additional information about your extension:

api.php?action=paraminfo&modules=myext [try in ApiSandbox]