Extending the REST API

The eZ Platform REST API comes with a framework that makes it quite easy to extend the API for your own needs.

Requirements

REST routes are required to use the eZ Platform REST API prefix, /api/ezp/v2. You can create new resources below this prefix.

To do so, you will/may need to create

• a Controller that will handle your route actions
• a Route, in your bundle's routing file
• a Controller action
• Optionally, a ValueObjectVisitor (if your Controller returns an object that doesn't already have a converter)
• Optionally, an InputParser

Controller

To create a REST controller, you need to extend the ezpublish_rest.controller.base service, as well as the eZ\Publish\Core\REST\Server\Controller class.

Let's create a very simple controller, that has a sayHello() method, that takes a name as an argument.

Route

As said earlier, your REST routes are required to use the REST URI prefix. To do so, the easiest way is to import your routing file using this prefix.

Using a distinct file for REST routes allows you to use the prefix for all this file's routes without affecting other routes from your bundle.

Next, you need to create the REST route. We need to define the route's controller as a service since our controller was defined as such.

Controller action

Unlike standard Symfony 2 controllers, the REST ones don't return an HttpFoundation\Response object, but a ValueObject. This object will during the kernel run be converted, using a ValueObjectVisitor, to a proper Symfony 2 response. One benefit is that when multiple controllers return the same object, such as a Content item or a Location, the visitor will be re-used.

Let's say that our Controller will return a My\Bundle\RestBundle\Rest\Values\Hello

We will return an instance of this class from our sayHello() controller method.

And that's it. Outputting this object in the Response requires that we create a ValueObjectVisitor.

ValueObjectVisitor

A ValueObjectVisitor will take a Value returned by a REST controller, whatever the class, and will transform it into data that can be converted, either to json or XML. Those visitors are registered as services, and tagged with ezpublish_rest.output.value_object_visitor. The tag attribute says which class this Visitor applies to.

Let's create the service for our ValueObjectVisitor first.

Let's create our visitor next. It must extend the  eZ\Publish\Core\REST\Common\Output\ValueObjectVisitor abstract class, and implement the visit() method.
It will receive as arguments:

• $visitor: The output visitor. Can be used to set custom response headers ( setHeader( $name, $value )), HTTP status code ( setStatus( $statusCode ) )...
• $generator: The actual Response generator. It provides you with a DOM like API.
• $data: the visited data, the exact object you returned from the controller 

Do not hesitate to look into the built-in ValueObjectVisitors, in  eZ/Publish/Core/REST/Server/Output/ValueObjectVisitor , for more examples.

Cache handling

The easiest way to handle cache is to re-use the  CachedValue Value Object. It acts as a proxy, and adds the cache headers, depending on the configuration, for a given object and set of options.

When you want the response to be cached, return an instance of CachedValue, with your Value Object as the argument. You can also pass a location id using the second argument, so that the Response is tagged with it:

Input parser

What we have seen above covers requests that don't require an input payload, such as GET or DELETE. If you need to provide your controller with parameters, either in JSON or XML, the parameter struct requires an Input Parser so that the payload can be converted to an actual ValueObject.

Each payload is dispatched to its Input Parser based on the request's Content-Type header. For example, a request with a Content-Type of application/vnd.ez.api.ContentCreate will be parsed by eZ\Publish\Core\REST\Server\Input\Parser\ContentCreate. This parser will build and return a ContentCreateStruct that can then be used to create content with the Public API.

Those input parsers are provided with a pre-parsed version of the input payload, as an associative array, and don't have to care about the actual format (XML or JSON).

Let's see what it would look like with a Content-Type of application/vnd.my.Greetings, that would send this as XML:

First, we need to create a service with the appropriate tag in services.yml.

The mediaType attribute of the ezpublish_rest.input.parser tag maps our Content Type to the input parser.

Let's implement our parser. It must extend eZ\Publish\Core\REST\Server\Input\Parser, and implement the parse() method. It accepts as an argument the input payload, $data, as an array, and an instance of ParsingDispatcher that can be used to forward parsing of embedded content.

For convenience, we will consider that our input parser returns an instance of our Value\Hello class.

Do not hesitate to look into the built-in InputParsers, in eZ/Publish/Core/REST/Server/Input/Parser, for more examples.

Registering resources in the REST root

You can register newly added resources so that they show up in the REST root resource for automatic discovery.

New resources can be registered with code like this:

with someresource being a unique key.

The router.generate call dynamically renders a URI based on the name of the route and the optional parameters that are passed as the other arguments (in the code above this is the contentId).

The above configuration will add the following entry to the root resource:

<someresource media-type="application/vnd.ez.api.Content+xml" href="/api/ezp/v2/content/objects/2"/>