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[RateLimiter] Document reserve() method and rename to RateLimiter #14435

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Merged
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Oct 17, 2020
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[RateLimiter] Document reserve() method and rename to RateLimiter #14435

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45 changes: 35 additions & 10 deletions rate_limiter.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -124,12 +124,13 @@ the number of requests to the API::

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpKernel\Exception\TooManyRequestsHttpException;
use Symfony\Component\RateLimiter\Limiter;
use Symfony\Component\RateLimiter\RateLimiter;

class ApiController extends AbstractController
{
// the variable name must be: "rate limiter name" + "limiter" suffix
public function index(Limiter $anonymousApiLimiter)
// if you're using autowiring for your services
public function index(RateLimiter $anonymousApiLimiter)
{
// create a limiter based on a unique identifier of the client
// (e.g. the client's IP address, a username/email, an API key, etc.)
Expand Down Expand Up @@ -158,35 +159,59 @@ the number of requests to the API::
for the :ref:`kernel.request event <component-http-kernel-kernel-request>`
and check the rate limiter once for all requests.

In other scenarios you may want instead to wait as long as needed until a new
token is available. In those cases, use the ``wait()`` method::
Wait until a Token is Available
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Instead of dropping a request or process when the limit has been reached,
you might want to wait until a new token is available. This can be achieved
using the ``reserve()`` method::

// src/Controller/ApiController.php
namespace App\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\RateLimiter\Limiter;
use Symfony\Component\RateLimiter\RateLimiter;

class ApiController extends AbstractController
{
public function registerUser(Request $request, Limiter $authenticatedApiLimiter)
public function registerUser(Request $request, RateLimiter $authenticatedApiLimiter)
{
$apiKey = $request->headers->get('apikey');
$limiter = $authenticatedApiLimiter->create($apiKey);

// this blocks the application until the given number of tokens can be consumed
do {
$limit = $limiter->consume(1);
$limit->wait();
} while (!$limit->isAccepted());
$limiter->reserve(1)->wait();

// optional, pass a maximum wait time (in seconds), a MaxWaitDurationExceededException
// is thrown if the process has to wait longer. E.g. to wait at most 20 seconds:
//$limiter->reserve(1, 20)->wait();
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Is this example correct? I would expect it to be:

$limiter->reserve(1)->wait(20);

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Unfortunately, yes. I would also prefer your way, but the goal of max time is avoid reserving a token if we know the wait time is longer than its value. So the reserve() method must be aware of the max wait time.

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@javiereguiluz javiereguiluz Oct 17, 2020 •
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Thinking out loud: what if we had these methods instead?

reserve(int $tokens = 1);
reserveAndWait(int $tokens = 1, float $maxTime);


reserve();
reserve(2);
reserveAndWait();
reserveAndWait(2);
reserveAndWait(1, 20);

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In any case, I'm merging your nice PR because this discussion is something to discuss (or not) in the code repository instead of here. Thanks!


// ...
}

// ...
}

The ``reserve()`` method is able to reserve a token in the future. Only use
this method if you're planning to wait, otherwise you will block other
processes by reserving unused tokens.

.. note::

Not all strategies allow reservering tokens in the future. These
strategies may throw an ``ReserveNotSupportedException`` when calling
``reserve()``.

In these cases, you can use ``consume()`` together with ``wait()``, but
there is no guarantee that a token is available after the wait::

// ...
do {
$limit = $limiter->consume(1);
$limit->wait();
} while (!$limit->isAccepted());

Rate Limiter Storage and Locking
--------------------------------

Expand Down