Custom ParamConverter

Sep 1, 2016

4mn

Thierry T.

Summary

•

Introduction

•

The basics

•

A token in a header

•

Creation of the Paramconverter

•

Service statement

•

Use in the controller

Introduction

The following article is aimed at developers who have already used the ParamConverter, and who understand its basic principles.

It was written in order to explain how to solve the following issue: I needed to pass a token into a custom header, and to be able to get it back in the controllers. The goal was to avoid repeating the acquisition of the header in each one of the controllers.

The basics

The ParamConverter is a magic tool. From a controller, you just need to type-hint the argument to obtain an instance of a class based on the id in the url.

<?php

/**
 * @Route("/post/{post}")
 */
public function getAction(Post $post)
{
    return new Response($post->getTitle());
}

In my example, Symfony has recognised the post token in the route. In the method signature, the $post variable is type hinted by the Post class. Through ParamConverter, Symfony will try to create an instance of the Post class and to assign it to the $post variable.

I would refer you to the documentation for the basic usage of the ParamConverter: http://symfony.com/doc/current/bundles/SensioFrameworkExtraBundle/annotations/converters.html

But what if the value I am looking for is not found in the url, for example in a header?

A token in a header

Let’s take another example:

<?php

/**
 * @Route("/token")
 */
public function isTokenValidAction($token)
{
    return $this->get('app.service')->isValid($token);
}

The value of the token must pass through an x-token header. I will then create a ParamConverter in order to fetch the token from the header and not from the url.

Creation of the Paramconverter

All ParamConverters must implement the Sensio\Bundle\FrameworkExtraBundle\Request\ParamConverter\ParamConverterInterface.

There are the apply(Request $request, ConfigurationInterface $configuration); and supports(ConfigurationInterface $configuration); methods.

supports verifies that the ParamConveter can be applied with the data provided in $configuration. It will result in true if all is good, otherwise it will be false. In this case, the ParamConverter moves to another converter. It is possible to sort ParamConverters by priority.
*apply *will apply a business rule. In our case, we will need to search for the token in the request and replace the value in the request’s attributes.

Structure example:

<?php

namespace AppBundle\Request\ParamConverter;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\ConfigurationInterface;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
use Sensio\Bundle\FrameworkExtraBundle\Request\ParamConverter\ParamConverterInterface;
use Symfony\Component\HttpFoundation\Request;

class TokenConverter implements ParamConverterInterface
{
    /**
     * {@inheritdoc}
     */
    public function apply(Request $request, ConfigurationInterface $configuration)
    {

    }

    /**
     * {@inheritdoc}
     */
    public function supports(ConfigurationInterface $configuration)
    {

    }
}

I begin with the supports method*. *Here, I don’t have any reference class. I will then work on the name of the variable.

public function supports(ConfigurationInterface $configuration)
{
    return $configuration->getName() === "token";
}

The method must return true or false.

Then, I work on the apply method . It’s here that I’ll fetch the token’s value. Since I have access to the current request, I can proceed as follow:

public function apply(Request $request, ConfigurationInterface $configuration)
{
    $request->attributes->set($configuration->getName(), $request->headers->get('x-token'));

    return true;
}

During the building of the controller, Symfony will fetch all the values of the controller’s arguments in the *attributes *variable of the request. This is why I assign the token’s value in the *attributes *variable through the ParameterBag method.

My custom ParamConverter is complete. I can now use it.

Service statement

A compiler pass will read the services with the "request.param_converter" tag. We can define a priority and a name. If there’s a priority, they will be sorted in this order.

<service id="token_converter" class="AppBundle\Request\ParamConverter\CrmTokenConverter">
    <tag name="request.param_converter" converter="token" />
</service>

Use in the controller

In order to use it in my controller, I add the *ParamConverter *annotation to my controller with the *name *option and the converter name given in the service.

<?php

/**
 * @Route("/token")
 * @ParamConverter(name="token", converter="token")
 */
public function isTokenValidAction($token)
{
    return $this->get('app.service')->isValid($token);
}