Defined custom NotFoundMiddleware for rest routes

module/Rest/src/Middleware/NotFoundMiddleware.php

@@ -0,0 +1,62 @@
+<?php
+namespace Shlinkio\Shlink\Rest\Middleware;
+
+use Acelaya\ZsmAnnotatedServices\Annotation\Inject;
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Shlinkio\Shlink\Rest\Util\RestUtils;
+use Zend\Diactoros\Response\JsonResponse;
+use Zend\I18n\Translator\TranslatorInterface;
+use Zend\Stratigility\MiddlewareInterface;
+
+class NotFoundMiddleware implements MiddlewareInterface
+{
+    /**
+     * @var TranslatorInterface
+     */
+    private $translator;
+
+    /**
+     * NotFoundMiddleware constructor.
+     * @param TranslatorInterface $translator
+     *
+     * @Inject({"translator"})
+     */
+    public function __construct(TranslatorInterface $translator)
+    {
+        $this->translator = $translator;
+    }
+
+    /**
+     * Process an incoming request and/or response.
+     *
+     * Accepts a server-side request and a response instance, and does
+     * something with them.
+     *
+     * If the response is not complete and/or further processing would not
+     * interfere with the work done in the middleware, or if the middleware
+     * wants to delegate to another process, it can use the `$out` callable
+     * if present.
+     *
+     * If the middleware does not return a value, execution of the current
+     * request is considered complete, and the response instance provided will
+     * be considered the response to return.
+     *
+     * Alternately, the middleware may return a response instance.
+     *
+     * Often, middleware will `return $out();`, with the assumption that a
+     * later middleware will return a response.
+     *
+     * @param Request $request
+     * @param Response $response
+     * @param null|callable $out
+     * @return null|Response
+     */
+    public function __invoke(Request $request, Response $response, callable $out = null)
+    {
+        return new JsonResponse([
+            'error' => RestUtils::NOT_FOUND_ERROR,
+            'message' => $this->translator->translate('Requested route does not exist.'),
+        ], 404);
+    }
+}