chimera/routing

A collection of reusable PSR-15 components that connects Chimera to any framework

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0.4.0 2021-02-24 20:42 UTC

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Last update: 2021-10-18 08:47:44 UTC


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The term Chimera (/kɪˈmɪərə/ or /kaɪˈmɪərə/) has come to describe any mythical or fictional animal with parts taken from various animals, or to describe anything composed of very disparate parts, or perceived as wildly imaginative, implausible, or dazzling.

There are many many amazing libraries in the PHP community and with the creation and adoption of the PSRs we don't necessarily need to rely on full stack frameworks to create a complex and well designed software. Choosing which components to use and plugging them together can sometimes be a little challenging.

The goal of this set of packages is to make it easier to do that (without compromising the quality), allowing you to focus on the behaviour of your software.

This particular package provides PSR-15 middleware and reusable request handlers that help you to expose command and query handlers using HTTP as the web mechanism.

Installation

You probably won't depend directly on this package, but it is available on Packagist, and can be installed it using Composer:

composer require chimera/routing

PHP Configuration

In order to make sure that we're dealing with the correct data, we're using assert(), which is a very interesting feature in PHP but not often used. The nice thing about assert() is that we can (and should) disable it in production mode so that we don't have useless statements.

So, for production mode, we recommend you to set zend.assertions to -1 in your php.ini. For development you should leave zend.assertions as 1 and set assert.exception to 1, which will make PHP throw an AssertionError when things go wrong.

Check the documentation for more information: https://secure.php.net/manual/en/function.assert.php

Components

Extension points

The packages that extend this library should implement two basic interfaces, they're used to abstract how each routing library works:

  • Chimera\Routing\RouteParamsExtractor: returns the list of parameters of the matched route
  • Chimera\Routing\UriGenerator: generate routes based on the given arguments

Route parameters extraction middleware

This middleware uses an implementation of Chimera\Routing\RouteParamsExtractor to put the parameters of the matched route in a standard attribute, so that other components can retrieve them.

Request handlers

  • Chimera\Handler\CreateAndFetch: executes a command to create a resource and immediately a query, returning an unformatted response with the query result and location header - intended to be used to handle POST requests
  • Chimera\Handler\CreateOnly: executes a command to create a resource, returning an empty response with the location header - intended to be used to handle POST requests (variation of the previous one but can also be used in asynchronous APIs)
  • Chimera\Handler\ExecuteAndFetch: executes a command to modify a resource and immediately a query, returning an unformatted response with the query result - intended to be used to handle PUT or PATCH requests
  • Chimera\Handler\ExecuteOnly: executes a command to modify or remove a resource, returning an empty response - intended to be used to handle PUT, PATCH, or DELETE requests (can also be used in asynchronous APIs)
  • Chimera\Handler\FetchOnly: executes a query to fetch a resource, returning an unformatted response with the query result - intended to be used to handle GET requests

Usage

Middleware pipeline

As mentioned above content negotiation is not a responsibility of the request handlers. It's expected that you configure lcobucci/content-negotiation-middleware to process such task and it should be put in the very beginning of the pipeline, so that it can process any unformatted response.

The Chimera\Routing\RouteParamsExtractor middleware should be put right after the middleware responsible for matching routes (which changes for each implementation).

So a middleware pipeline in a Zend Expressive v3 application would look like this - considering that all services are properly configured in the DI container:

<?php
declare(strict_types=1);

use Chimera\Routing\RouteParamsExtraction;
use Lcobucci\ContentNegotiation\ContentTypeMiddleware;
use Psr\Container\ContainerInterface;
use Zend\Expressive\Application;
use Zend\Expressive\Handler\NotFoundHandler;
use Zend\Expressive\Helper\BodyParams;
use Zend\Expressive\Helper\ServerUrlMiddleware;
use Zend\Expressive\Helper\UrlHelperMiddleware;
use Zend\Expressive\MiddlewareFactory;
use Zend\Expressive\Router\Middleware\DispatchMiddleware;
use Zend\Expressive\Router\Middleware\ImplicitHeadMiddleware;
use Zend\Expressive\Router\Middleware\ImplicitOptionsMiddleware;
use Zend\Expressive\Router\Middleware\MethodNotAllowedMiddleware;
use Zend\Expressive\Router\Middleware\RouteMiddleware;
use Zend\Stratigility\Middleware\ErrorHandler;

return function (Application $app, MiddlewareFactory $factory, ContainerInterface $container) : void {
    $app->pipe(ErrorHandler::class);
    $app->pipe(ServerUrlMiddleware::class);

    // Handles content negotiation, ensuring that the response format is the best one
    // according to what was requested via the `Accept` header
    $app->pipe(ContentTypeMiddleware::class);

    $app->pipe(RouteMiddleware::class);

    // Puts the matched arguments in a standard place (must be executed after the
    // `Zend\Expressive\Router\Middleware\RouteMiddleware` middleware, otherwise
    // matched routed info is not available)
    $app->pipe(RouteParamsExtraction::class);

    // It's quite important to add this one to the list, so that we ensure
    // that the request body is properly parsed and can be retrieved via
    // `ServerRequestInterface#getParsedBody()` - used by the `HttpRequest` input
    $app->pipe(BodyParams::class);

    $app->pipe(ImplicitHeadMiddleware::class);
    $app->pipe(ImplicitOptionsMiddleware::class);
    $app->pipe(MethodNotAllowedMiddleware::class);
    $app->pipe(UrlHelperMiddleware::class);
    $app->pipe(DispatchMiddleware::class);
    $app->pipe(NotFoundHandler::class);
};

Routes

The main idea of this package is to move your application's behaviour to the command and query handlers, which allows them to be reused by different delivery mechanism. This means that the logic of the request handlers are pretty much reusable, therefore you end up having less code to maintain.

Considering that you have configured the command and query buses with the correct handlers and also that you have mapped the instances of the request handlers in your dependency injection container, you just need to configure the PSR-15 router to add the handlers to the correct endpoint.

In a Zend Expressive v3 application the config/routes.php would look like this:

<?php

declare(strict_types=1);

use Psr\Container\ContainerInterface;
use Zend\Expressive\Application;
use Zend\Expressive\MiddlewareFactory;

/**
 * Considering you have the following services in your DI container:
 *
 * - `album.list` => new FetchOnly(
 *     new ExecuteQuery(**query bus**, **message creation strategy**, MyApi\FetchAlbumList::class),
 *     ResponseInterface::class
 * );
 * - `album.find_one` => new FetchOnly(
 *     new ExecuteQuery(**query bus**, **message creation strategy**, MyApi\FindAlbum::class),
 *     ResponseInterface::class
 * );
 * - `album.create` => new CreateOnly(
 *     new ExecuteCommand(**command bus**, **message creation strategy**, MyApi\CreateAlbum::class),
 *     ResponseInterface::class,
 *     'album.find_one',
 *     UriGenerator::class,
 *     IdentifierGenerator::class,
 *     201
 * );
 * - `album.update_album` => new ExecuteAndFetch(
 *     new ExecuteCommand(**command bus**, **message creation strategy**, MyApi\UpdateAlbum::class),
 *     new ExecuteQuery(**query bus**, **message creation strategy**, MyApi\FindAlbum::class),
 *     ResponseInterface::class
 * );
 */
return function (Application $app, MiddlewareFactory $factory, ContainerInterface $container) : void {
    $app->get('/album', 'album.list', 'album.list');
    $app->post('/album', 'album.create', 'album.create');
    $app->get('/album/{id}', 'album.find_one', 'album.find_one');
    $app->patch('/album/{id}', 'album.update_album', 'album.update_album');
};

License

MIT, see LICENSE.