Extracted middleware and handlers

src/Http/Middleware/NotFoundHandler.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace NoccyLabs\Mercureact\Http\Middleware;
+
+use Psr\Http\Message\ServerRequestInterface;
+use React\Http\Message\Response;
+use React\Promise\Promise;
+use React\Promise\PromiseInterface;
+
+class NotFoundHandler
+{
+    /**
+     * Resolves unhandled requests with a 404 error
+     * 
+     * @param ServerRequestInterface $request
+     * @return PromiseInterface
+     */
+    public function __invoke(ServerRequestInterface $request): PromiseInterface
+    {
+        return new Promise(
+            function ($resolve) { 
+                $resolve(Response::plaintext("Not found")->withStatus(404));
+            }
+        );
+    }
+
+}