Slim3/DRY - How to handle errors/exceptions correctly without duplicating code?

Question

I'm working on a fairly large JSON API using Slim3. My controllers/actions are currently littered with the following:

return $response->withJson([
    'status' => 'error',
    'data' => null,
    'message' => 'Username or password was incorrect'
]);

At certain points in the application anything can go wrong and the response needs to be appropriate. But one thing that is common is the error responses are always the same. The status is always error, the data is optional (in the case of form validation errors data will contain those) and message is set to indicate to the user or consumer of the API what went wrong.

I smell code duplication. How can I reduce the code duplication?

From the top of my head all I could think of doing was creating a custom exception, something like App\Exceptions\AppException that takes option data and the message will be obtained form $e->getMessage().

<?php

namespace App\Exceptions;

class AppException extends Exception
{
    private $data;

    public function __construct($message, $data = null, $code = 0, $previous = null)
    {
        $this->data = $data;
        parent::__construct($message, $code, $previous);
    }

    public function getData()
    {
        return $this->data;
    }
}

Following that create middleware that calls $next wrapped in a try/catch:

$app->add(function($request, $response, $next) {

  try {
    return $next($request, $response);
  }
  catch(\App\Exceptions\AppException $e)
  {
    $container->Logger->addCritical('Application Error: ' . $e->getMessage());
    return $response->withJson([
      'status' => 'error',
      'data' => $e->getData(),
      'message' => $e->getMessage()
    ]);
  }
  catch(\Exception $e)
  {
    $container->Logger->addCritical('Unhandled Exception: ' . $e->getMessage());
    $container->SMSService->send(getenv('ADMIN_MOBILE'), "Shit has hit the fan! Run to your computer and check the error logs. Beep. Boop.");
    return $response->withJson([
      'status' => 'error',
      'data' => null,
      'message' => 'It is not possible to perform this action right now'
    ]);
  }
});

Now all I have to do at points in the code is to throw new \App\Exceptions\AppException("Username or password incorrect", null).

My only issue with this is it feels like I'm using exceptions for the wrong reasons and it may make debugging a little more difficult.

Any suggestions on reducing the duplicates and cleaning up error responses?

Answer 1

You can achieve similar similar results by creating an error handler which outputs JSON.

namespace Slim\Handlers;

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

final class ApiError extends \Slim\Handlers\Error
{
    public function __invoke(Request $request, Response $response, \Exception $exception)
    {
        $status = $exception->getCode() ?: 500;
        $data = [
            "status" => "error",
            "message" => $exception->getMessage(),
        ];
        $body = json_encode($data, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT);
        return $response
                   ->withStatus($status)
                   ->withHeader("Content-type", "application/json")
                   ->write($body);
    }
}

You must also configure Slim to use your custom error handler.

$container = $app->getContainer();

$container["errorHandler"] = function ($container) {
    return new Slim\Handlers\ApiError;
};

Check Slim API Skeleton for example implemention.