API Reference

The following make up the primary API of Stratigility.

Middleware

Zend\Stratigility\MiddlewarePipe is the primary application interface, and has been discussed previously. Its API is:

namespace Zend\Stratigility;

use Interop\Http\Middleware\DelegateInterface;
use Interop\Http\Middleware\MiddlewareInterface as InteropMiddlewareInterface;
use Interop\Http\Middleware\ServerMiddlewareInterface;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;

class MiddlewarePipe implements MiddlewareInterface, ServerMiddlewareInterface
{
    public function pipe(
        string|callable|InteropMiddlewareInterface|ServerRequestInterface $path,
        callable|InteropMiddlewareInterface|ServerRequestInterface $middleware = null
    );

    public function __invoke(
        ServerRequestInterface,
        ResponseInterface $response,
        callable $out = null
    ) :  ResponseInterface;

    public function process(
        ServerRequestInterface $request,
        DelegateInterface $delegate
    ) : ResponseInterface;
}

pipe() takes up to two arguments. If only one argument is provided, $middleware will be assigned that value, and $path will be re-assigned to the value /; this is an indication that the $middleware should be invoked for any path. If $path is provided, the $middleware will only be executed for that path and any subpaths.

Request path changes when path matched

When you pipe middleware using a path (other than '' or '/'), the middleware is dispatched with a request that strips the matched segment(s) from the start of the path.

If, for example, you executed $pipeline->pipe('/api', $api), and this was matched via a URI with the path /api/users/foo, the $api middleware will receive a request with the path /users/foo. This allows middleware segregated by path to be re-used without changes to its own internal routing.

Middleware is executed in the order in which it is piped to the MiddlewarePipe instance.

The MiddlewarePipe is itself middleware, and can be executed in stacks that expect the __invoke() signature (via the __invoke() signature), or stacks expecting http-interop middleware signatures (via the process() method).

When executing the MiddlewarePipe via its __invoke() method, if $out is not provided, an instance of Zend\Stratigility\FinalHandler will be created and used in the event that the pipe stack is exhausted (MiddlewarePipe passes the $response instance it receives to FinalHandler as well, so that the latter can determine if the response it receives is new).

$out is no longer optional

Starting in version 1.3.0, we now raise a deprecation notice if no argument is passed for the $out argument to __invoke(); starting in version 2.0.0, the argument will be required. Always pass a Next instance, a Zend\Stratigility\NoopFinalHandler instance, or a custom callback; we no longer recommend the FinalHandler implementation.

When using __invoke(), the callable $out argument should use the signature:

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;

function (
    ServerRequestInterface $request,
    ResponseInterface $response
) : ResponseInterface

Within Stratigility, Zend\Stratigility\Next provides such an implementation.

Starting in version 1.3.0, MiddlewarePipe also implements the http-interop ServerMiddlewareInterface, and thus provides a process() method. This method requires a ServerRequestInterface instance and an Interop\Http\Middleware\DelegateInterface instance on invocation; the latter can be a Next instance, as it also implements that interface.

Internally, for both __invoke() and process(), MiddlewarePipe creates an instance of Zend\Stratigility\Next, feeding it its queue, executes it, and returns its response.

Response prototype

Starting in version 1.3.0, you can compose a "response prototype" in the MiddlewarePipe. When present, any callable middleware piped to the instance will be wrapped in a decorator (see the section on middleware decorators, below) such that it will now conform to http-interop middleware interfaces.

To use this functionality, inject the prototype before piping middleware:

$pipeline = new MiddlewarePipe();
$pipeline->setResponsePrototype(new Response());

Next

Zend\Stratigility\Next is primarily an implementation detail of middleware, and exists to allow delegating to middleware registered later in the stack. It is implemented both as a functor and as an Interop\Http\Middleware\DelegateInterface.

Functor invocation

Because Psr\Http\Message's interfaces are immutable, if you make changes to your Request and/or Response instances, you will have new instances, and will need to make these known to the next middleware in the chain. Next expects these arguments for every invocation. Additionally, if an error condition has occurred, you may pass an optional third argument, $err, representing the error condition.

class Next
{
    public function __invoke(
        Psr\Http\Message\ServerRequestInterface $request,
        Psr\Http\Message\ResponseInterface $response
    ) : Psr\Http\Message\ResponseInterface;
}

You should always either capture or return the return value of $next() when calling it in your application. The expected return value is a response instance, but if it is not, you may want to return the response provided to you.

$err argument

Technically, Next::__invoke() accepts a third, optional argument, $err. However, as of version 1.3.0, this argument is deprecated, and usage will raise a deprecation notice during runtime. We will be removing the argument entirely starting with version 2.0.0.

$response argument

Using the $response argument is unsafe when using delegation, as an inner layer could return an entirely different response, ignoring any changes you may have introduced previously. Additionally, when manipulating the response from an inner layer, you may be inheriting unwanted context.

As such, we recommend ignoring the $response argument and doing one of the following:

  • For innermost middleware that will be returning a response without delegation, we recommend instantiating and returning a concrete response instance. Diactoros provides a number of convenient custom responses.
  • For middleware delegating to another layer, operate on the returned response instead:
$response = $next($request, $response);
return $response->withHeader('X-Foo', 'Bar');

Delegate invocation

  • Since 1.3.0.

When invoked as a DelegateInterface, the process() method will be invoked, and passed a ServerRequestInterface instance only. If you need to return a response, you will need to:

  • Compose a response prototype in the middleware to use to build a response, or a canned response to return, OR
  • Create and return a concrete response type, OR
  • Operate on a response returned by invoking the delegate.

Providing an altered request:

// Standard invokable:
function ($request, $response, $next) use ($bodyParser)
{
    $bodyParams = $bodyParser($request);
    return $next(
        $request->withBodyParams($bodyParams), // Next will pass the new
        $response                              // request instance
    );
}

// http-interop invokable:
function ($request, DelegateInterface $delegate) use ($bodyParser)
{
    $bodyParams = $bodyParser($request);

    // Provide a new request instance to the delegate:
    return $delegate->process(
        $request->withBodyParams($bodyParams)
    );
}

Returning a response to complete the request

If your middleware does not need to delegate to another layer, it's time to return a response.

While we pass a response when using Next as a functor, we recommend creating a new response, or providing your middleware with a response prototype; this will ensure that the response is specific for your context.

use Interop\Http\Middleware\DelegateInterface;
use Zend\Diactoros\Response;

$prototype = new Response();

// Standard invokable signature:
function ($request, $response, $next) use ($prototype)
{
    $response = $prototype->withAddedHeader('Cache-Control', [
        'public',
        'max-age=18600',
        's-maxage=18600',
    ]);
    return $response;
}

// http-interop invokable signature:
function ($request, DelegateInterface $delegate) use ($prototype)
{
    $response = $prototype->withAddedHeader('Cache-Control', [
        'public',
        'max-age=18600',
        's-maxage=18600',
    ]);
    return $response;
}

Delegation

If your middleware is not capable of returning a response, or a particular path in the middleware cannot return a response, return the result of executing the delegate.

If using the legacy middleware signature, invoke the $next argument:

return $next($request, $response);

If using a DelegateInterface, invoke its process() method:

return $delegate->process($request);

Middleware should always return a response, and, if it cannot, return the result of delegation.

Raising an error condition

  • Deprecated as of 1.3.0; please use exceptions and a error handling middleware such as the ErrorHandler to handle error conditions in your application instead.

To raise an error condition, pass a non-null value as the third argument to $next():

function ($request, $response, $next)
{
    try {
        // try some operation...
    } catch (Exception $e) {
        return $next($request, $response, $e); // Next registered error middleware will be invoked
    }
}

FinalHandler

  • Deprecated starting with 1.3.0. Use Zend\Stratigility\NoopFinalHandler or a custom handler guaranteed to return a response instead.

Zend\Stratigility\FinalHandler is a default implementation of middleware to execute when the stack exhausts itself. It expects three arguments when invoked: a request instance, a response instance, and an error condition (or null for no error). It returns a response.

FinalHandler allows two optional arguments during instantiation

  • $options, an array of options with which to configure itself. These options currently include:
  • env, the application environment. If set to "production", no stack traces will be provided.
  • onerror, a callable to execute if an error is passed when FinalHandler is invoked. The callable is invoked with the error (which will be null in the absence of an error), the request, and the response, in that order.
  • Psr\Http\Message\ResponseInterface $response; if passed, it will compare the response passed during invocation against this instance; if they are different, it will return the response from the invocation, as this indicates that one or more middleware provided a new response instance.

Internally, FinalHandler does the following on invocation:

  • If $error is non-null, it creates an error response from the response provided at invocation, ensuring a 400 or 500 series response is returned.
  • If the response at invocation matches the response provided at instantiation, it returns it without further changes. This is an indication that some middleware at some point in the execution chain called $next() with a new response instance.
  • If the response at invocation does not match the response provided at instantiation, or if no response was provided at instantiation, it creates a 404 response, as the assumption is that no middleware was capable of handling the request.

HTTP Messages

Zend\Stratigility\Http\Request

  • Deprecated in 1.3.0; to be removed in 2.0.0.

Zend\Stratigility\Http\Request acts as a decorator for a Psr\Http\Message\ServerRequestInterface instance. The primary reason is to allow composing middleware such that you always have access to the original request instance.

As an example, consider the following:

$app1 = new Middleware();
$app1->pipe('/foo', $fooCallback);

$app2 = new Middleware();
$app2->pipe('/root', $app1);

$server = Server::createServer($app2 /* ... */);

In the above, if the URI of the original incoming request is /root/foo, what $fooCallback will receive is a URI with a past consisting of only /foo. This practice ensures that middleware can be nested safely and resolve regardless of the nesting level.

If you want access to the full URI — for instance, to construct a fully qualified URI to your current middleware — Zend\Stratigility\Http\Request contains a method, getOriginalRequest(), which will always return the original request provided to the application:

function ($request, $response, $next)
{
    $location = $request->getOriginalRequest()->getUri()->getPath() . '/[:id]';
    $response = $response->setHeader('Location', $location);
    $response = $response->setStatus(302);
    return $response;
}

Zend\Stratigility\Http\Response

  • Deprecated in 1.3.0; to be removed in 2.0.0.

Zend\Stratigility\Http\Response acts as a decorator for a Psr\Http\Message\ResponseInterface instance, and also implements Zend\Stratigility\Http\ResponseInterface, which provides the following convenience methods:

  • write(), which proxies to the write() method of the composed response stream.
  • end(), which marks the response as complete; it can take an optional argument, which, when provided, will be passed to the write() method. Once end() has been called, the response is immutable and will throw an exception if a state mutating method like withHeader is called.
  • isComplete() indicates whether or not end() has been called.

Additionally, it provides access to the original response created by the server via the method getOriginalResponse().

Middleware

Stratigility provides several concrete middleware implementations.

ErrorHandler and NotFoundHandler

These two middleware allow you to provide handle PHP errors and exceptions, and 404 conditions, respectively. You may read more about them in the error handling chapter.

OriginalMessages

This callable middleware can be used as the outermost layer of middleware in order to set the original request, URI, and response instances as request attributes for inner layers. See the v2 migration chapter for more details.

Middleware Decorators

Starting in version 1.3.0, we offer the ability to work with http-interop middleware. Internally, if a response prototype is composed in the MiddlewarePipe, callable middleware piped to the MiddlewarePipe will be wrapped in one of these decorators.

Two versions exist:

  • Zend\Stratigility\Middleware\CallableMiddlewareWrapper will wrap a callable using the legacy interface; as such, it also requires a response instance:
$middleware = new CallableMiddlewareWrapper($middleware, $response);
  • Zend\Stratigility\Middleware\CallableMiddlewareWrapper will wrap a callable that defines exactly two arguments, with the second type-hinting on Interop\Http\Middleware\DelegateInterface:
$middleware = new CallableMiddlewareWrapper(
  function ($request, DelegateInterface $delegate) {
      // ...
  }
);

You can manually decorate callable middleware using these decorators, or simply let MiddlewarePipe do the work for you. To let MiddlewarePipe handle this, however, you must compose a response prototype prior to piping middleware using the legacy middleware signature.

Delegates

In addition to Zend\Stratigility\Next, Stratigility provides another Interop\Http\Middleware\DelegateInterface implementation, Zend\Stratigility\Delegate\CallableDelegateDecorator.

This class can be used to wrap a callable $next instance for use in passing to a ServerMiddlewareInterface::process() method as a delegate; the primary use case is adapting functor middleware to work as http-interop middleware.

As an example:

use Interop\Http\Middleware\DelegateInterface;
use Interop\Http\Middleware\ServerMiddlewareInterface;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Zend\Stratigility\Delegate\CallableDelegateDecorator;

class TimestampMiddleware implements ServerMiddlewareInterface
{
    public function __invoke(
        ServerRequestInterface $request,
        ResponseInterface $response,
        callable $next
    ) {
        return $this->process($request, new CallableDelegateDecorator($next, $response));
    }

    public function process(
        ServerRequestInterface $request,
        DelegateInterface $delegate
    ) {
        $response = $delegate->process($request);
        return $response->withHeader('X-Processed-Timestamp', time());
    }
}

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