Async Middleware

Matthew Weier O'Phinney

MidwestPHP 2019

Terminology

• PHP-FIG (or FIG): Framework Interop Group (standards body)
• PSR-7: HTTP Message interfaces
• PSR-15: HTTP Request Handler/Middleware interfaces
• PSR-17: HTTP Message Factory interfaces
• PSR-14: Event Dispatcher interfaces

Goals

I will demonstrate how async enables:

• Application-specific servers
• Better performance, generally due to...
• Deferred processing.

Node.js

event loop

Why?

PHP: Shared Nothing

• Bootstraps. Every. Request.
• Long-running processes delay the response.

Message Queues

Parallel Processing

Async Programming

Styles of Async Programming

Four general styles:

• Callbacks
• Promises
• async/await
• Coroutines

Deferment patterns

Callbacks

executeSomeAsyncProcess(
    $withData,
    $andA,
    $callbackToExecuteOnCompletion
);
          

function ($error, $result)
{
    if ($error) {
    }
}
            

Callback Hell

doFirst($payload, function ($err, $result) {
    doSecond($result, function ($err, $result) {
        doThird($result, function ($err, $result) {
            // finally got what we needed
        });
    });
});
          

aka the "Pyramid of Doom"

Promises

$promise = someAsyncOperationReturningAPromise($with, $data);
$promise
    ->then($someCallbackToExecuteOnResolution)
    ->then($someAdditionalCallbackToExecuteOnResolutionOfPrevious)
    ->catch($someCallbackToExecuteOnRejection);
          

function then($successCallback = null, $rejectionCallback = null);
            

$promise->then(null, $someCallbackToExecuteOnRejection);
            

async/await

async function ping() {
  const res = await fetch('/api/ping');
  return await res.json();
}
          

let ack = ping();
          

Coroutines

$result = $statement->execute($data);
          

Swoole provides...

• an event loop
• async HTTP, network, and socket clients
• network servers

Swoole features

• Coroutine support for many TCP/UDP and socket operations
• Spawning multiple workers per server
• Spawning separate task workers
• Daemonization of servers

A Basic Web Server

use Swoole\Http\Server as HttpServer;

$server = new HttpServer('127.0.0.1', 9000);
$server->on('start', function ($server) {
    echo "Server started at http://127.0.0.1:9000\n";
});
$server->on('request', function ($request, $response) {
    $response->header('Content-Type', 'text/plain');
    $response->end("Hello World\n");
});
$server->start();
          

Deferment

$server->defer(function () {
    // work to defer
});
          

Task Workers

Prepare the server
for tasks

• Configure the number of task workers to use (required!)
• Register a listener to handle incoming tasks.
• Register a listener to execute on task completion.

Registering task workers

$server->set(['task_worker_num' => 4]);
$server->on('task', function ($server, $taskId, $data) {
    // Handle task

    // Finish task:
    $server->finish('');
});
$server->on('finish', function ($server, $taskId, $returnValue) {
    // Task is complete
});
          

Triggering a task

$server->task($someData);
          

A Basic TaskWorker

class Task {
    public $handler;   // callable
    public $arguments; // array
}

$server->on('task', function ($server, $taskId, $task) {
    if (! $task instanceof Task) {
        $server->finish('');
        return;
    }

    ($task->handler)(...$task->arguments);
    $server->finish('');
});
          

Problems

Code Reloading

or lack thereof

Debugging

Coroutine support in Swoole is incompatible with XDebug and XHProf!

Unit Testing

Mocking Swoole classes is difficult.

One Listener Per Event

$response->end() is Problematic

If you forget to call it:

• the connection will remain open until a network timeout occurs;
• the current process will remain open; which means
• no next tick of the event loop.

Non-Standard Request/Response API

It is none of:

• PSR-7
• Symfony HttpKernel
• zend-http

Swoole Pros and Cons

PSR-15

Request Handlers and Middleware

namespace Psr\Http\Server;
use Psr\Http\Message\ResponseInterface as Response;
use Psr\Http\Message\ServerRequestInterface as Request;

interface RequestHandlerInterface {
    public function handle(Request $request) : Response;
}

interface MiddlewareInterface {
    public function process(
        Request $request,
        RequestHandlerInterface $handler
    ) : Response;
}
          

Middleware Flow

Middleware + Swoole

$server->on('request', function ($request, $response) use ($app) {
    $appResponse = $app->handle(transformRequest($request));
    transformResponse($response, $appResponse);
});
          

Expressive

A middleware application runner, with...

• Dependency Injection wiring abstraction
• Routing abstraction
• Template abstraction
• Error handling abstraction
• Application and per-route pipelines

zend-expressive-swoole

Starting your Expressive+Swoole server

$ ./vendor/bin/zend-expressive-swoole start
          

Configurable Server Features

• Limited hot-code reloading
• Static file serving

Async Applications

• Eliminating bootstrap operations
• Deferred operations

Deferred Operations

Coroutines

$result = $mysqli->query($sql);
while ($data = $result->fetch_assoc()) {
    // ...
}
          

Deferment

$server->defer($callback);
          

Task Workers

$server->task($someData);
          

phly-swoole-taskworker

phly-swoole-taskworker Usage

use Phly\Swoole\TaskWorker\Task;

$server->task(new Task(function ($event) {
    // handle the event
}, $event));
          

Listener deferment

phly/phly-event-dispatcher

$listener = new DeferredListener($server, $listener);

// Where DeferredListener is equivalent to:
function (object $event) use ($server, $listener) : void {
    $server->task(new Task($listener, $event));
}
          

$this->dispatcher->dispatch($someEvent);
            

Pitfalls

Stateful Services

Stateful Services: Templating

$template->addDefaultParam('*', 'user', $user);
          

$metadata = $resourceGenerator
    ->getMetadataMap()
    ->get(Collection::class);
$metadata->setQueryStringArguments(array_merge(
    $metadata->getQueryStringArguments(),
    ['query' => $query]
));
          

Stateful Services: Validation

if (! $validator->isValid($value)) {
    $messages = $validator->getMessages();
}
          

echo implode("
", $validator->getMessages())
            

Stateful Services: Auth

return $handler(
    $request->withAttribute('user', $auth->getIdentity())
);
          

Resolving State Issues

Decoration

class StatelessVariant implements SomeInterface
{
    private $proxy;

    public function __construct(SomeInterface $proxy)
    {
        $this->proxy = $proxy;
    }
}
          

public function morphState($data) : void
{
    throw new CannotChangeStateException();
}
          

Extension

class StatelessVariant extends OriginalClass
{
    public function morphState($data) : void
    {
        throw new CannotChangeStateException();
    }
}
          

Factories as Services

public function __construct(SomeClass $dependency) : void
          

public function __construct(SomeClassFactory $factory) : void
            

$dependency = ($this->factory)();
            

Stateful Messages

Pass stateful data to the service:

$result = $this->router->route(
    $request->getUrl()->getPath()
);
          

$result = $this->router->route(
    $request
);
            

Pass State Via Request Attributes

public function process(
    Request $request,
    RequestHandler $handler
) : Response {
    $result = $this->router->route($request);
    return $handler->handle(
        $request->withAttribute(RouteResult::class, $result)
    );
}
          

Using Request Attributes

$routeResult = $request->getAttribute(RouteResult::class);
return new HtmlResponse($this->renderer->render(
    'some::template',
    [ 'routeResult' => $routeResult ]
));
          

Sessions

Use zend-expressive-session

and its zend-expressive-session-cache adapter

Wrap Up

Benefits

• Eliminating bootstrap operations
• Deferred operations
• Crazy fast performance!

Practices

• Abstract async-specific details.
• Make container services stateless
• Aggregate state in the request
• Avoid the session extension

Resources

• https://www.swoole.co.uk
• https://getexpressive.org
• https://docs.zendframework.com/zend-expressive-swoole/
• https://github.com/phly/phly-swoole-taskworker/
• https://docs.zendframework.com/zend-expressive-session/
• https://docs.zendframework.com/zend-expressive-session-cache/

Thank You!

Contact me at mwop.net

I tweet @mwop