Content Negotiation

The API system has built-in content negotiation capabilities.

By default, only the JSON-LD and JSON formats are enabled. However API Platform Core supports many more formats and can be extended.

The framework natively supports JSON-LD (and Hydra), GraphQL, JSON:API, HAL, YAML, CSV, HTML (API docs), raw JSON and raw XML. Using the raw JSON or raw XML formats is discouraged, prefer using JSON-LD instead, which provides more feature and is as easy to use.

API Platform also supports JSON Merge Patch (RFC 7396) the JSON:API PATCH formats, as well as Problem Details (RFC 7807), Hydra and JSON:API error formats.

Watch the Formats screencast

API Platform Core will automatically detect the best resolving format depending on:

• enabled formats (see below)
• the requested format, specified in either the Accept HTTP header or as an extension appended to the URL

Available formats are:

If the client’s requested format is not specified, the response format will be the first format defined in the formats configuration key (see below). If the request format is not supported, an Unsupported Media Type error will be returned.

Examples showcasing how to use the different mechanisms are available in the API Platform test suite.

The first required step is to configure allowed formats. The following configuration will enable the support of XML (built-in) and of a custom format called myformat and having application/vnd.myformat as MIME type.

# api/config/packages/api_platform.yaml
api_platform:
    formats:
        jsonld:   ['application/ld+json']
        jsonhal:  ['application/hal+json']
        jsonapi:  ['application/vnd.api+json']
        json:     ['application/json']
        xml:      ['application/xml', 'text/xml']
        yaml:     ['application/x-yaml']
        csv:      ['text/csv']
        html:     ['text/html']
        myformat: ['application/vnd.myformat']

To enable GraphQL support, read the dedicated chapter.

Because the Symfony Serializer component is able to serialize objects in XML, sending an Accept HTTP header with the text/xml string as value is enough to retrieve XML documents from our API. However API Platform knows nothing about the myformat format. We need to register an encoder and optionally a normalizer for this format.

By default, API Platform supports JSON Merge Patch and JSON:API PATCH formats. Support for the JSON:API PATCH format is automatically enabled if JSON:API support is enabled. JSON Merge Patch support must be enabled explicitly:

# api/config/packages/api_platform.yaml
api_platform:
    patch_formats:
        json:     ['application/merge-patch+json']
        jsonapi:  ['application/vnd.api+json']

When support for at least one PATCH format is enabled, an Accept-Patch HTTP header containing the list of supported patch formats is automatically added to all HTTP responses for items.

API Platform will try to send to the client the error format matching with the format request with the Accept HTTP headers (or the URL extension). For instance, if a client request a JSON-LD representation of a resource, and an error occurs, then API Platform will serialize this error using the Hydra format (Hydra is a vocabulary for JSON-LD containing a standard representation of API errors).

Available formats can also be configured:

# api/config/packages/api_platform.yaml
api_platform:
    error_formats:
        jsonproblem:                   ['application/problem+json']
        jsonld:                        ['application/ld+json']      # Hydra error formats
        jsonapi:                       ['application/vnd.api+json']

Support for specific formats can also be configured at resource and operation level using the input_formats and output_formats attributes. input_formats controls the formats accepted in request bodies while output_formats controls formats available for responses.

The formats attribute can be used as a shortcut, it sets both the input_formats and output_formats in one time.

<?php
// api/src/Entity/Book.php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;

 #[ApiResource(formats: ['xml', 'jsonld', 'csv' => ['text/csv']])]
class Book
{
    // ...
}

In the example above, xml or jsonld will be allowed and there is no need to specify the MIME types as they are already defined in the configuration. Additionally the csv format is added with the MIME type text/csv.

It is also important to notice that the usage of this attribute will override the formats defined in the configuration, therefore this configuration might disable the json or the html on this resource for example.

You can specify different accepted formats at operation level too, it’s especially convenient for to configure formats available for the PATCH method:

<?php
// api/src/Entity/Book.php

namespace App\Entity;

use ApiPlatform\Core\Annotation\ApiResource;

#[ApiResource(
    formats: ['jsonld', 'csv' => ['text/csv']],
    itemOperations: [
        'patch' => [
            'input_formats' => [
                'json' => ['application/merge-patch+json'],
            ],
        ],
    ],
)]
class Book
{
    // ...
}

resources:
    App\Entity\Book:
        attributes:
            formats:
               0: 'jsonld' # format already defined in the config
               csv: 'text/csv'
        itemOperations:
            get:
                formats:
                    json: ['application/merge-patch+json'] # works also with "application/merge-patch+json"

<resources xmlns="https://api-platform.com/schema/metadata"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="https://api-platform.com/schema/metadata
           https://api-platform.com/schema/metadata/metadata-2.0.xsd">
    <resource class="App\Entity\Greeting">
        <attribute name="formats">
            <attribute>jsonld</attribute> <!-- format already defined in the config -->
            <attribute name="csv">text/csv</attribute>
        </attribute>

        <itemOperations>
            <itemOperation name="get">
                <attribute name="input_formats">
                    <attribute name="json">
                        <attribute>application/merge-patch+json</attribute>
                    </attribute>
                    <!-- works also with <attribute name="json">application/merge-patch+json</attribute> -->
                </attribute>
            </itemOperation>
        </itemOperations>
    </resource>
</resources>

The API Platform content negotiation system is extendable. You can add support for formats not available by default by creating custom normalizer and encoders. Refer to the Symfony documentation to learn how to create and register such classes.

Then, register the new format in the configuration:

# api/config/packages/api_platform.yaml
api_platform:
    formats:
        # ...
        myformat: ['application/vnd.myformat']

API Platform Core will automatically call the serializer with your defined format name as format parameter during the deserialization process (myformat in the example). It will then return the result to the client with the requested MIME type using its built-in responder. For non-standard formats, a vendor, vanity or unregistered MIME type should be used.

Using composition is the recommended way to implement a custom normalizer. You can use the following template to start your own implementation of CustomItemNormalizer:

# api/config/services.yaml
services:
    'App\Serializer\CustomItemNormalizer':
        arguments: [ '@api_platform.serializer.normalizer.item' ]
        # Uncomment if you don't use the autoconfigure feature
        #tags: [ 'serializer.normalizer' ]
    
    # ...

<?php
// api/src/Serializer/CustomItemNormalizer.php

namespace App\Serializer;

use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

final class CustomItemNormalizer implements NormalizerInterface, DenormalizerInterface
{
    private $normalizer;

    public function __construct(NormalizerInterface $normalizer)
    {
        if (!$normalizer instanceof DenormalizerInterface) {
            throw new \InvalidArgumentException('The normalizer must implement the DenormalizerInterface');
        }

        $this->normalizer = $normalizer;
    }

    public function denormalize($data, $class, $format = null, array $context = [])
    {
        return $this->normalizer->denormalize($data, $class, $format, $context);
    }

    public function supportsDenormalization($data, $type, $format = null)
    {
        return $this->normalizer->supportsDenormalization($data, $type, $format);
    }

    public function normalize($object, $format = null, array $context = [])
    {
        return $this->normalizer->normalize($object, $format, $context);
    }

    public function supportsNormalization($data, $format = null)
    {
        return $this->normalizer->supportsNormalization($data, $format);
    }
}

For example if you want to make the csv format work for even complex entities with a lot of hierarchy, you have to flatten or remove overly complex relations:

<?php
// api/src/Serializer/CustomItemNormalizer.php

namespace App\Serializer;

use Symfony\Component\Serializer\Normalizer\DenormalizerInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

class CustomItemNormalizer implements NormalizerInterface, DenormalizerInterface
{
    // ...

    public function normalize($object, $format = null, array $context = [])
    {
        $result = $this->normalizer->normalize($object, $format, $context);

        if ('csv' !== $format || !is_array($result)) {
            return $result;
        }

        foreach ($result as $key => $value) {
            if (is_array($value) && array_keys(array_keys($value)) === array_keys($value)) {
                unset($result[$key]);
            }
        }

        return $result;
    }

    // ...
}

Adding support for standard formats upstream is welcome! We’ll be glad to merge new encoders and normalizers in API Platform Core.