Helpers

UrlHelper

Zend\Expressive\Helper\UrlHelper provides the ability to generate a URI path based on a given route defined in the Zend\Expressive\Router\RouterInterface. If injected with a route result, and the route being used was also the one matched during routing, you can provide a subset of routing parameters, and any not provided will be pulled from those matched.

Usage

When you have an instance, use either its generate() method, or call the instance as an invokable:

// Using the generate() method:
$url = $helper->generate('resource', ['id' => 'sha1']);

// is equivalent to invocation:
$url = $helper('resource', ['id' => 'sha1']);
```

The signature for both is:

```php
function ($routeName, array $params = []) : string
```

Where:

- `$routeName` is the name of a route defined in the composed router. You may
  omit this argument if you want to generate the path for the currently matched
  request.
- `$params` is an array of substitutions to use for the provided route, with the
  following behavior:
  - If a `RouteResult` is composed in the helper, and the `$routeName` matches
    it, the provided `$params` will be merged with any matched parameters, with
    those provided taking precedence.
  - If a `RouteResult` is not composed, or if the composed result does not match
    the provided `$routeName`, then only the `$params` provided will be used
    for substitutions.
  - If no `$params` are provided, and the `$routeName` matches the currently
    matched route, then any matched parameters found will be used.
    parameters found will be used.
  - If no `$params` are provided, and the `$routeName` does not match the
    currently matched route, or if no route result is present, then no
    substitutions will be made.

Each method will raise an exception if:

- No `$routeName` is provided, and no `RouteResult` is composed.
- No `$routeName` is provided, a `RouteResult` is composed, but that result
  represents a matching failure.
- The given `$routeName` is not defined in the router.

## Creating an instance

In order to use the helper, you will need to instantiate it with the current
`RouterInterface`. The factory `Zend\Expressive\Helper\UrlHelperFactory` has
been provided for this purpose, and can be used trivially with most
dependency injection containers implementing container-interop. Additionally,
it is most useful when injected with the current results of routing, which
requires registering middleware with the application that can inject the route
result. The following steps should be followed to register and configure the helper:

- Register the `UrlHelper` as a service in your container, using the provided
  factory.
- Register the `UrlHelperMiddleware` as a service in your container, using the
  provided factory.
- Register the `UrlHelperMiddleware` as pipeline middleware, immediately
  following the routing middleware.

### Registering the helper service

The following examples demonstrate programmatic registration of the `UrlHelper`
service in your selected dependency injection container.

```php
use Zend\Expressive\Helper\UrlHelper;
use Zend\Expressive\Helper\UrlHelperFactory;

// zend-servicemanager:
$services->setFactory(UrlHelper::class, UrlHelperFactory::class);

// Pimple:
$pimple[UrlHelper::class] = function ($container) {
    $factory = new UrlHelperFactory();
    return $factory($container);
};

// Aura.Di:
$container->set(UrlHelperFactory::class, $container->lazyNew(UrlHelperFactory::class));
$container->set(
    UrlHelper::class,
    $container->lazyGetCall(UrlHelperFactory::class, '__invoke', $container)
);
```

The following dependency configuration will work for all three when using the
Expressive skeleton:

```php
return ['dependencies' => [
    'factories' => [
        UrlHelper::class => UrlHelperFactory::class,
    ],
]]
```

> #### UrlHelperFactory requires RouterInterface
>
> The factory requires that a service named `Zend\Expressive\Router\RouterInterface` is present,
> and will raise an exception if the service is not found.

### Registering the pipeline middleware

To register the `UrlHelperMiddleware` as pipeline middleware following the
routing middleware:

```php
use Zend\Expressive\Helper\UrlHelperMiddleware;

// Programmatically:
$app->pipeRoutingMiddleware();
$app->pipe(UrlHelperMiddleware::class);
$app->pipeDispatchMiddleware();

// Or use configuration:
// [
//     'middleware_pipeline' => [
//         /* ... */
//         Zend\Expressive\Container\ApplicationFactory::ROUTING_MIDDLEWARE,
//         ['middleware' => UrlHelperMiddleware::class],
//         Zend\Expressive\Container\ApplicationFactory::DISPATCH_MIDDLEWARE,
//         /* ... */
//     ],
// ]
//
// Alternately, create a nested middleware pipeline for the routing, UrlHelper,
// and dispatch middleware:
// [
//     'middleware_pipeline' => [
//         /* ... */
//         'routing' => [
//             'middleware' => [
//                 Zend\Expressive\Container\ApplicationFactory::ROUTING_MIDDLEWARE,
//                 UrlHelperMiddleware::class
//                 Zend\Expressive\Container\ApplicationFactory::DISPATCH_MIDDLEWARE,
//             ],
//             'priority' => 1,
//         ],
//         /* ... */
//     ],
// ]

The following dependency configuration will work for all three when using the Expressive skeleton:

return [
    'dependencies' => [
        'factories' => [
            UrlHelper::class => UrlHelperFactory::class,
            UrlHelperMiddleware::class => UrlHelperMiddlewareFactory::class,
        ],
    ],
    'middleware_pipeline' => [
        Zend\Expressive\Container\ApplicationFactory::ROUTING_MIDDLEWARE,
        ['middleware' => UrlHelperMiddleware::class],
        Zend\Expressive\Container\ApplicationFactory::DISPATCH_MIDDLEWARE,
    ],
];

// OR:
return [
    'dependencies' => [
        'factories' => [
            UrlHelper::class => UrlHelperFactory::class,
            UrlHelperMiddleware::class => UrlHelperMiddlewareFactory::class,
        ],
    ],
    'middleware_pipeline' => [
        'routing' => [
            'middleware' => [
                Zend\Expressive\Container\ApplicationFactory::ROUTING_MIDDLEWARE,
                UrlHelperMiddleware::class,
                Zend\Expressive\Container\ApplicationFactory::DISPATCH_MIDDLEWARE,
            ],
            'priority' => 1,
        ],
    ],
];

Skeleton configures helpers

If you started your project using the Expressive skeleton package, the UrlHelper and UrlHelperMiddleware factories are already registered for you, as is the UrlHelperMiddleware pipeline middleware.

Using the helper in middleware

Compose the helper in your middleware (or elsewhere), and then use it to generate URI paths:

use Zend\Expressive\Helper\UrlHelper;

class FooMiddleware
{
    private $helper;

    public function __construct(UrlHelper $helper)
    {
        $this->helper = $helper;
    }

    public function __invoke($request, $response, callable $next)
    {
        $response = $response->withHeader(
            'Link',
            $this->helper->generate('resource', ['id' => 'sha1'])
        );
        return $next($request, $response);
    }
}

Base Path support

If your application is running under a subdirectory, or if you are running pipeline middleware that is intercepting on a subpath, the paths generated by the router may not reflect the base path, and thus be invalid. To accommodate this, the UrlHelper supports injection of the base path; when present, it will be prepended to the path generated by the router.

As an example, perhaps you have middleware running to intercept a language prefix in the URL; this middleware could then inject the UrlHelper with the detected language, before stripping it off the request URI instance to pass on to the router:

use Locale;
use Zend\Expressive\Helper\UrlHelper;

class LocaleMiddleware
{
    private $helper;

    public function __construct(UrlHelper $helper)
    {
        $this->helper = $helper;
    }

    public function __invoke($request, $response, $next)
    {
        $uri = $request->getUri();
        $path = $uri->getPath();
        if (! preg_match('#^/(?P<locale>[a-z]{2,3}([-_][a-zA-Z]{2}|))/#', $path, $matches)) {
            return $next($request, $response);
        }

        $locale = $matches['locale'];
        Locale::setDefault(Locale::canonicalize($locale));
        $this->helper->setBasePath($locale);

        return $next(
            $request->withUri(
                $uri->withPath(substr($path, (strlen($locale) + 1)))
            ),
            $response
        );
    }
}

(Note: if the base path injected is not prefixed with /, the helper will add the slash.)

Paths generated by the UriHelper from this point forward will have the detected language prefix.