How to inject the @request into a service?

When I try to inject the @request into any of my services, I get this exception:

ScopeWideningInjectionException: Scope Widening Injection detected: The definition "service.navigation" references the service "request" which belongs to a narrower scope. Generally, it is safer to either move "service.navigation" to scope "request" or alternatively rely on the provider pattern by injecting the container itself, and requesting the service "request" each time it is needed. In rare, special cases however that might not be necessary, then you can set the reference to strict=false to get rid of this error.

What is the best way to proceed? Should I try to set this strict=false and how, or should I NOT inject the request service, but rather pass it to the service through my controller each time I call functions I need?

Other possibility would be to inject the kernel and take it from there, but in my service I am using only @router and @request, so injecting the whole kernel would be irrational.

In Symfony 2.4, this has changed. Now, you can inject the 'request_stack' service.

For example:

use Symfony\Component\HttpFoundation\RequestStack;

class MyService
{

    protected $request;

    public function setRequest(RequestStack $request_stack)
    {
        $this->request = $request_stack->getCurrentRequest();
    }

}

In your config.yml:

services:
    my.service:
        class: Acme\DemoBundle\MyService
        calls:
            - [setRequest, ["@request_stack"]]

Full documentation is here: http://symfony.com/blog/new-in-symfony-2-4-the-request-stack

I think there may have been some misunderstanding about what the official documentation says. In most cases you do want to inject the request directly with a scope="request" attribute on the service element. This makes the Scope Widening go away.

<service 
    id="zayso_core.openid.rpx" 
    class="Zayso\CoreBundle\Component\OpenidRpx" public="true" scope="request">

or in yml

zayso_core.openid.rpx: 
    class: Zayso\CoreBundle\Component\OpenidRpx
    public: true
    scope: request

It's only in specific special cases such as Twig extensions where you need to inject the container.

And kernel is not even mentioned in the page on scopes. Injecting the kernel is far worse (conceptually) than injecting a container.

UPDATE: For S2.4 and newer, use @Blowski's answer below.

NB: This answer was written back in 2012, when Symfony 2.0 was out and then it was the good way to do! Please don't downvote any more :)

Today I went through same problem myself, so here are my 5 cents. According to the official documentation it is usually not required to inject request into your services. In your service class you can pass kernel container (injecting it is not a big overhead, as it sounds), and then access request like this:

public function __construct(\AppKernel $kernel)
{
    $this->kernel = $kernel;
}

public function getRequest()
{
    if ($this->kernel->getContainer()->has('request')) {
        $request = $this->kernel->getContainer()->get('request');
    } else {
        $request = Request::createFromGlobals();
    }
    return $request;
}

This code is also working fine when service is accessed in CLI (eg, during unit-testing).

The best way i found to make a service use the request service, not rely on the whole container and still not be required to have the request scope, was to make a RequestInjector service which takes the container. then you inject that into the service that wants to use the request object

class RequestInjector{

    protected $container;

    public function __construct(Container $container){

         $this->container = $container;
   }

    public function getRequest(){

        return $this->container->get('request');
    }
}

class SomeService{

    protected $requestInjector;

    public function __construct(RequestInjector $requestInjector){

        $this->requestInjector = $requestInjector;

    }
}     

for services.yml

request_injector:
    class: RequestInjector
    public: false
    arguments: ['@service_container']

some_service:
    class: SomeService
    arguments: ['@request_injector']