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Yii2 Advanced Rate Limiter

Advanced Rate Limiter is a Yii2's filter to enforce or monitor request rate limits.

In contrast to Yii2's built-in RateLimiter, Advanced Rate Limiter:

• allows you to define multiple, independent rate limit definitions
  • by controller action, and
  • by an identifier such as an IP address, user ID, other identifiers relevant to your application, or a combination thereof;
• provides support for customizing the type of response to a checked or exceeded rate limit such as:
  • sending a 429 Too Many Requests HTTP response,
  • triggering a Yii2 Event,
  • setting rate-limit HTTP headers, and/or
  • executing your own Callable or anonymous function;
• provides support for storing and managing the allowance and timestamp values for each rate limit (Yii2's built-in RateLimiter requires you to implement the storage yourself);
• allows you to customize the prefix of rate-limit HTTP headers instead of the hardcoded X-Rate-Limit- prefix used by the built-in RateLimiter;
• provides support for sending the Retry-After HTTP header indicating how many seconds the client should wait before retrying.

For license information check the LICENSE-file.

Installation

The preferred way to install this extension is through composer.

or add

to the require section of your composer.json file.

Usage

Introduction

This Rate Limiter is an implementation of the leaky bucket algorithm.

In general, you will configure the rate limiter as a behavior on any Controller class you want to rate limit. For example,

Advanced Example:

Storage

In order to assign one or more rate limits, you must be able to store an integer allowance value and a timestamp for each configured rate limit.

Default Allowance Storage in Cache

The RateLimiter uses an allowanceStorage component for storing the rate limit values. By default, the AllowanceCacheStorage component stores the allowance data in the cache component you specify. If no cache is specified, an instance of yii\caching\DummyCache will be used.

You can specify a cache component in several ways:

Implement Your Own Storage Layer

However, you may use your own storage layer implementation by implementing AllowanceStorageInterface and referencing your implementation in RateLimiter's allowanceStorage component.

For example:

Defining Rate Limits

A single RateLimiter can have one or more separate rate limits defined. For example, you may wish to provide one rate limit for each IP address and a different rate limit for each authenticated user, especially when this is not always a one-to-one mapping.

A simple rate limit can be defined like the following:

By returning an identifier value, you can enforce the defined rate limit on a per-identifier basis, such as per IP address. Or you may leave the identifier unspecified in order to apply the defined rate limit globally.

You can also implement your own rate limit definition by referencing an implementation of the RateLimitInterface:

You will need to implement the getRateLimit($context) method to return a RateLimit object or an array of its properties (limit, window, and optionally an identifier such as a user ID, and optionally an active boolean).

Defining Responses

There can be any number of responses to an exceeded rate limit. A couple of predefined response types can be attached as behaviors of the RateLimiter. For example:

A more advanced example with some additional configuration options set:

You may also attach your own event handlers to the RateLimiter object to look for RateLimiter::EVENT_RATE_LIMITS_EXCEEDED or RateLimiter::EVENT_RATE_LIMITS_CHECKED events:

Alternatively, you can attach event handlers using the on() method:

See Yii's Events page for more information about attaching Event handlers.

Filtering Events

If the only and except properties of the handlers are not enough for filtering, your custom event handler can set $event->handled to true to prevent any other handler from being invoked.

For example, if you want to whitelist an IP address:

Events

RateLimitsCheckedEvent

The RateLimitsCheckedEvent is triggered whenever a set of defined rate limits are checked. The RateLimitsExceededEvent is triggered whenever one or more of the defined rate limits are exceeded. The predefined responses attached to the RateLimiter as behaviors all work by registering themselves as event handlers and looking for these events.

Both events include the following properties:

• $context - the Context object containing the yii\web\Request and $action
• $time - the current unix timestamp
• $rateLimits - an array of RateLimitResult objects. Only those rate limits that were exceeded are included in the RateLimitsExceededEvent.

Predefined responses such as the RateLimitHeadersHandler will make use of the rate information in order to output the appropriate values in the HTTP headers. In the case of RateLimitHeadersHandler, the information from multiple rate limits may be combined together in order to compute one set of HTTP header values.

Other responses, such as the TooManyRequestsHttpExceptionHandler, will not care what or how many rate limits were exceeded. It will just throw the TooManyRequestsHttpException no matter what.

Some responses are triggered whenever rate limits are checked, such as the RateLimitHeadersHandler which will add its HTTP headers to every response to indicate to the client how it is doing with respect to its rate limits.

Other responses, such as the TooManyRequestsHttpExceptionHandler will only apply when rate limits are exceeded.

Order of Responses

The order in which responses are added matters.

Response handlers are executed in the order in which they are attached to the RateLimiter. This means that an exception-throwing handler, like TooManyRequestsHttpException, must come after header-setting handlers, like RateLimitHeadersHandler.

Recipes

See Recipes

See Also

• Yii's Rate Limiter Docs

• Yii's Event Docs

• Leaky Bucket Algorithm