nextcloud-docs/developer_manual/digging_deeper/rest_apis.rst

.. _rest-apis:

=========
REST APIs
=========

.. sectionauthor:: Bernhard Posselt <dev@bernhard-posselt.com>

Offering a RESTful API is not different from creating a :doc:`route <../basics/routing>` and :doc:`controllers <../basics/controllers>` for the web interface.
It is recommended though to inherit from ApiController and add **@CORS** annotations to the methods so that `web applications will also be able to access the API <https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS>`_.

.. code-block:: php

    <?php
    namespace OCA\MyApp\Controller;

    use OCP\AppFramework\ApiController;
    use OCP\AppFramework\Http\Attribute\CORS;
    use OCP\IRequest;

    class AuthorApiController extends ApiController {

        public function __construct($appName, IRequest $request) {
            parent::__construct($appName, $request);
        }

        #[CORS]
        public function index() {

        }

    }

CORS also needs a separate URL for the preflighted **OPTIONS** request that can easily be added by adding the following route:

.. code-block:: php

    <?php
    // appinfo/routes.php
    array(
        'name' => 'author_api#preflighted_cors',
        'url' => '/api/1.0/{path}',
        'verb' => 'OPTIONS',
        'requirements' => array('path' => '.+')
    )


Keep in mind that multiple apps will likely depend on the API interface once it is published and they will move at different speeds to react to changes implemented in the API.
Therefore it is recommended to version the API in the URL to not break existing apps when backwards incompatible changes are introduced::

    /index.php/apps/myapp/api/1.0/resource

Modifying the CORS headers
--------------------------

By default the following values will be used for the preflighted OPTIONS request:

* **Access-Control-Allow-Methods**: 'PUT, POST, GET, DELETE, PATCH'
* **Access-Control-Allow-Headers**: 'Authorization, Content-Type, Accept'
* **Access-Control-Max-Age**: 1728000

To add an additional method or header or allow less headers, simply pass additional values to the parent constructor:

.. code-block:: php

    <?php
    namespace OCA\MyApp\Controller;

    use \OCP\AppFramework\ApiController;
    use \OCP\IRequest;

    class AuthorApiController extends ApiController {

        public function __construct($appName, IRequest $request) {
            parent::__construct(
                $appName,
                $request,
                'PUT, POST, GET, DELETE, PATCH',
                'Authorization, Content-Type, Accept',
                1728000);
        }

    }

.. _ocs-vs-rest:

Relation of REST and OCS
------------------------

There is a close relationship between REST APIs and :ref:`OCS <ocscontroller>`.
Both provide a way to transmit data between the backend of the app in the Nextcloud server and some frontend.

The following combinations of attributes might be relevant for various scenarios:

#. Plain frontend route: ``Controller`` class
#. Plain frontend with CRSF checks disabled: ``Controller`` class and ``#[NoCSRFRequired]`` attribute on the method
#. Plain frontend route with CORS enabled: ``Controller`` class and ``#[CORS]`` and ``#[NoCSRFRequired]`` attributes on the route
#. OCS route: ``OCSController`` class
#. OCS route with CORS enabled: ``OCSController`` class and ``#[CORS]`` attribute on the method

.. warning::
  Adding the ``#[NoCRSFRequired]`` attribute imposes a security risk.
  You should not add this to your controller methods unless you understand the implications and be sure that you absolutely need the attribute.

.. warning::
  Adding the attribute ``#[CORS]`` alone is not sufficient to allow access using CORS.
  The CSRF checker will typically fail, so enabling CORS enforces you to disable the CSRF checker as well.
  Although the disabled CSRF checker in itself is a security issue to consider, adding CORS opens up this even more.
  You should make sure, that you understand the implications completely when enabling CORS and do so only when there is a good use case.

There are different ways a clients might interact with your APIs.
These ways depend on your API configuration (what you allow) and on which route the request is finally made.

- *Access from web frontend* means the user is browses the Nextcloud web frontend with a browser.
- *Access from an external app* indicates that the user is not using the normal browser (as logged in) but directly navigates a certain URL.
  This can be in a new browser tab or an external program (like an Android app or simply a curl command line).
- *Access from external website* means that the user browses some third party web site and data from your Nextcloud server appears.
  The other website has to embed/load/use images, JSON data, or other resources from a URL pointing to the Nextcloud server, to be able to do this.

.. list-table:: Comparison of different API types
    :header-rows: 1
    :align: center

    * - Description
      - 1 (plain)
      - 2 (w/o CSRF)
      - 3 (CORS)
      - 4 (OCS)
      - 5 (OCS+CORS)
    * - URL prefix (relative to server)
      - ``/apps/<appid>/``
      - ``/apps/<appid>/``
      - ``/apps/<appid>/``
      - ``/ocs/v2.php/apps/<appid>/``
      - ``/ocs/v2.php/apps/<appid>/``
    * - Access from web frontend
      - yes
      - yes (CSRF risk)
      - yes (CSRF risk)
      - yes
      - yes (CSRF risk [#]_)
    * - Access from external app
      - ---
      - yes
      - yes
      - yes (with header [#]_)
      - yes
    * - Access from external website
      - ---
      - ---
      - yes
      - ---
      - yes
    * - Encapsulated data
      - no
      - no
      - no
      - yes (JSON or XML)
      - yes (JSON or XML)

Methods from ``Controller`` classes can return ``DataResponse`` objects similar to ``OCSController`` class methods.
For methods of a ``Controller`` class, the data of this response is sent e.g. as JSON as you provide it.
Basically, the output is very similar to what ``json_encode`` would do.
In contrast, the OCS controller will encapsulate the data in an outer shell that provides some more (meta) information.
For example a status code (similar to the HTTP status code) is transmitted at top level.
The actual data is transmitted in the ``data`` property.

As a rule of thumb one can conclude that OCS provides a good way to handle most use cases including sufficient security checks.
The only exception to this is if you want to provide an API for external usage where you have to comply with an externally defined API scheme.
Here, the encapsulation introduced in OCS and CSRF checks might be in your way.

.. [#] Only if you have set ``#[NoCSRFRequired]``.
       OCS controllers have other CSRF checks in place that work with CORS without disabling the CSRF checks completely. 
       Using the ``OCS-APIRequest`` header is a CSRF protection which is compatible with CORS.
.. [#] The OCS controller needs the request header ``OCS-APIRequest`` to be set to ``true``.