PSR-15 Queue

MiddlewareQueue

Table of Contents

The MiddlewareQueue manages the middlewares involved in processing a server request. It makes sure they are called in first-in, first-out (FIFO) order, i.e. the same order they were added to the queue. It also ensures all middlewares are implementing the PSR-15: HTTP Server Request Handlers specification for the Psr\Http\Server\MiddlewareInterface.

When instantiating a MiddlewareQueue it defaults to being empty. But you can optionally pass an iterable set of middlewares to the constructor which are then put into the queue. To demonstrate, the following examples both have exactly the same result.

Examples:

use OCC\PSR15\MiddlewareQueue;

$middlewares = [
    new MiddlewareOne(),
    new MiddlewareTwo()
];

$queue = new MiddlewareQueue($middlewares);
use OCC\PSR15\MiddlewareQueue;

$queue = new MiddlewareQueue();

$queue->enqueue(new MiddlewareOne());
$queue->enqueue(new MiddlewareTwo());

The MiddlewareQueue is based on a OCC\Basics\DataStructures\StrictQueue.

Methods

The MiddlewareQueue provides a set of API methods, with MiddlewareQueue::enqueue() and MiddlewareQueue::dequeue() being the most relevant ones. The former will add a new item at the end of the queue while the latter removes and returns the first item from the queue.

For a complete API documentation have a look at the StrictQueue.

Adding a Middleware

Invoking MiddlewareQueue::enqueue() will add a middleware at the end of the queue. The only argument must be a middleware object implementing the Psr\Http\Server\MiddlewareInterface . If the given argument does not meet the criterion an OCC\Basics\DataStructures\Exceptions\InvalidDataTypeException is thrown.

Have a look at the AbstractMiddleware for an easy way to create your own middlewares!

Fetching the next in line

Calling MiddlewareQueue::dequeue() will return the first middleware from the queue, i.e. the oldest one on the queue. Also, this middleware is removed from the queue.

If the queue is empty a RuntimeException is thrown, so make sure to check the queue's length (e.g. with count() ) before trying to dequeue an item!

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