diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index 3c0ce56..6b9f40d 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -40,4 +40,4 @@ jobs:
         run:  ./vendor/bin/phpunit tests --testdox
 
       - name: Run static analysis
-        run: ./vendor/bin/phpstan analyse src --level 6 --no-progress --no-interaction
\ No newline at end of file
+        run: ./vendor/bin/phpstan analyse src --no-progress --no-interaction
diff --git a/composer.json b/composer.json
index 476fb3b..c96a64f 100644
--- a/composer.json
+++ b/composer.json
@@ -20,7 +20,7 @@
   },
   "autoload": {
     "psr-4": {
-      "Borsch\\": "src/"
+      "Borsch\\RequestHandler\\": "src/"
     }
   },
   "autoload-dev": {
@@ -28,4 +28,4 @@
       "BorschTest\\": "tests/"
     }
   }
-}
\ No newline at end of file
+}
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..ad2c08d
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,3 @@
+parameters:
+    level: 6
+    treatPhpDocTypesAsCertain: false
diff --git a/src/Emitter.php b/src/Emitter.php
new file mode 100644
index 0000000..f60c969
--- /dev/null
+++ b/src/Emitter.php
@@ -0,0 +1,62 @@
+<?php declare(strict_types=1);
+
+namespace Borsch\RequestHandler;
+
+use Psr\Http\Message\{ResponseInterface, StreamInterface};
+use function header, sprintf, ucwords;
+
+class Emitter implements EmitterInterface
+{
+
+    /**
+     * @link https://github.com/http-interop/response-sender/blob/master/src/functions.php
+     */
+    public function emit(ResponseInterface $response): void
+    {
+        $this->emitHeaders($response);
+        $this->emitStatusLine($response);
+        $this->emitBody($response->getBody());
+    }
+
+    private function emitHeaders(ResponseInterface $response): void
+    {
+        foreach ($response->getHeaders() as $name => $values) {
+            foreach ($values as $value) {
+                header(sprintf(
+                    '%s: %s',
+                    ucwords($name, '-'), $value),
+                    false
+                );
+            }
+        }
+    }
+
+    private function emitStatusLine(ResponseInterface $response): void
+    {
+        $http_line = sprintf(
+            'HTTP/%s %s %s',
+            $response->getProtocolVersion(),
+            $response->getStatusCode(),
+            $response->getReasonPhrase()
+        );
+
+        header($http_line, true, $response->getStatusCode());
+    }
+
+    private function emitBody(StreamInterface $stream): void
+    {
+        if ($stream->isSeekable()) {
+            $stream->rewind();
+        }
+
+        if (!$stream->isReadable()) {
+            echo $stream;
+            return;
+        }
+
+        $length = 1024 * 8;
+        while (!$stream->eof()) {
+            echo $stream->read($length);
+        }
+    }
+}
diff --git a/src/EmitterInterface.php b/src/EmitterInterface.php
new file mode 100644
index 0000000..12ee33c
--- /dev/null
+++ b/src/EmitterInterface.php
@@ -0,0 +1,16 @@
+<?php declare(strict_types=1);
+
+namespace Borsch\RequestHandler;
+
+use Psr\Http\Message\ResponseInterface;
+
+interface EmitterInterface
+{
+
+    /**
+     * Emits the given response.
+     *
+     * @param ResponseInterface $response The response to emit.
+     */
+    public function emit(ResponseInterface $response): void;
+}
diff --git a/src/RequestHandler/RequestHandler.php b/src/RequestHandler.php
similarity index 71%
rename from src/RequestHandler/RequestHandler.php
rename to src/RequestHandler.php
index 14d08c0..ba8b513 100644
--- a/src/RequestHandler/RequestHandler.php
+++ b/src/RequestHandler.php
@@ -1,11 +1,11 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Borsch\RequestHandler;
 
-use Borsch\RequestHandler\Exception\RequestHandlerRuntimeException;
 use Psr\Http\Message\{ResponseInterface, ServerRequestInterface};
 use Psr\Http\Server\MiddlewareInterface;
 use SplStack;
+use function get_class, gettype, is_object;
 
 class RequestHandler implements RequestHandlerInterface
 {
@@ -44,6 +44,13 @@ public function handle(ServerRequestInterface $request): ResponseInterface
             throw RequestHandlerRuntimeException::emptyStack();
         }
 
-        return $this->stack->shift()->process($request, $this);
+        $middleware = $this->stack->shift();
+        if (!$middleware instanceof MiddlewareInterface) {
+            throw RequestHandlerRuntimeException::invalidMiddleware(
+                (string)(is_object($middleware) ? get_class($middleware) : gettype($middleware))
+            );
+        }
+
+        return $middleware->process($request, $this);
     }
 }
diff --git a/src/RequestHandler/Emitter.php b/src/RequestHandler/Emitter.php
deleted file mode 100644
index f55032f..0000000
--- a/src/RequestHandler/Emitter.php
+++ /dev/null
@@ -1,40 +0,0 @@
-<?php
-
-namespace Borsch\RequestHandler;
-
-use Psr\Http\Message\ResponseInterface;
-
-class Emitter
-{
-
-    /**
-     * @link https://github.com/http-interop/response-sender/blob/master/src/functions.php
-     */
-    public function emit(ResponseInterface $response): void
-    {
-        $http_line = sprintf('HTTP/%s %s %s',
-            $response->getProtocolVersion(),
-            $response->getStatusCode(),
-            $response->getReasonPhrase()
-        );
-
-        header($http_line, true, $response->getStatusCode());
-
-        foreach ($response->getHeaders() as $name => $values) {
-            foreach ($values as $value) {
-                header(sprintf('%s: %s', $name, $value), false);
-            }
-        }
-
-        $stream = $response->getBody();
-
-        if ($stream->isSeekable()) {
-            $stream->rewind();
-        }
-
-        $length = 1024 * 8;
-        while (!$stream->eof()) {
-            echo $stream->read($length);
-        }
-    }
-}
diff --git a/src/RequestHandler/Exception/RequestHandlerRuntimeException.php b/src/RequestHandler/Exception/RequestHandlerRuntimeException.php
deleted file mode 100644
index 7caa458..0000000
--- a/src/RequestHandler/Exception/RequestHandlerRuntimeException.php
+++ /dev/null
@@ -1,18 +0,0 @@
-<?php
-
-namespace Borsch\RequestHandler\Exception;
-
-use Psr\Http\Message\ResponseInterface;
-use RuntimeException;
-
-class RequestHandlerRuntimeException extends RuntimeException
-{
-
-    public static function emptyStack(): self
-    {
-        return new self(sprintf(
-            'The middleware stack is empty and no %s has been returned',
-            ResponseInterface::class
-        ));
-    }
-}
\ No newline at end of file
diff --git a/src/RequestHandler/RequestHandlerInterface.php b/src/RequestHandlerInterface.php
similarity index 85%
rename from src/RequestHandler/RequestHandlerInterface.php
rename to src/RequestHandlerInterface.php
index f111e4a..f39d4e4 100644
--- a/src/RequestHandler/RequestHandlerInterface.php
+++ b/src/RequestHandlerInterface.php
@@ -1,4 +1,4 @@
-<?php
+<?php declare(strict_types=1);
 
 namespace Borsch\RequestHandler;
 
@@ -11,8 +11,8 @@ interface RequestHandlerInterface extends PsrRequestHandlerInterface
 {
 
     /**
-     * Add a middleware to the request handler.
+     * Add middleware to the request handler.
      * Must return itself to allow method chaining (if desired).
      */
     public function middleware(MiddlewareInterface $middleware): RequestHandlerInterface;
-}
\ No newline at end of file
+}
diff --git a/src/RequestHandlerRunner.php b/src/RequestHandlerRunner.php
new file mode 100644
index 0000000..8a06182
--- /dev/null
+++ b/src/RequestHandlerRunner.php
@@ -0,0 +1,51 @@
+<?php declare(strict_types=1);
+
+namespace Borsch\RequestHandler;
+
+use Psr\Http\Message\{ResponseInterface, ServerRequestInterface};
+use Psr\Http\Server\RequestHandlerInterface;
+use Throwable;
+
+final class RequestHandlerRunner implements RequestHandlerRunnerInterface
+{
+
+    /** @var callable(): ServerRequestInterface */
+    private $server_request_factory;
+
+    /** @var callable(Throwable $e): ResponseInterface */
+    private $error_response_factory;
+
+    /**
+     * @param callable(): ServerRequestInterface $server_request_factory
+     * @param callable(Throwable $e): ResponseInterface $error_response_factory
+     */
+    public function __construct(
+        private readonly RequestHandlerInterface $handler,
+        private readonly EmitterInterface $emitter,
+        callable $server_request_factory,
+        callable $error_response_factory,
+    ) {
+        $this->server_request_factory = $server_request_factory;
+        $this->error_response_factory = $error_response_factory;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function run(): void
+    {
+        try {
+            $request = ($this->server_request_factory)();
+        } catch (Throwable $e) {
+            $this->emitter->emit(
+                ($this->error_response_factory)($e)
+            );
+
+            return;
+        }
+
+        $this->emitter->emit(
+            $this->handler->handle($request)
+        );
+    }
+}
diff --git a/src/RequestHandlerRunnerInterface.php b/src/RequestHandlerRunnerInterface.php
new file mode 100644
index 0000000..bcb5911
--- /dev/null
+++ b/src/RequestHandlerRunnerInterface.php
@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace Borsch\RequestHandler;
+
+interface RequestHandlerRunnerInterface
+{
+
+    /**
+     * Run the request handler.
+     * This method should handle the request and send the response.
+     */
+    public function run(): void;
+}
diff --git a/src/RequestHandlerRuntimeException.php b/src/RequestHandlerRuntimeException.php
new file mode 100644
index 0000000..4556acb
--- /dev/null
+++ b/src/RequestHandlerRuntimeException.php
@@ -0,0 +1,29 @@
+<?php declare(strict_types=1);
+
+namespace Borsch\RequestHandler;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use RuntimeException;
+use function sprintf;
+
+class RequestHandlerRuntimeException extends RuntimeException
+{
+
+    public static function emptyStack(): self
+    {
+        return new self(sprintf(
+            'The middleware stack is empty and no %s has been returned',
+            ResponseInterface::class
+        ));
+    }
+
+    public static function invalidMiddleware(string $middleware): self
+    {
+        return new self(sprintf(
+            'The middleware "%s" must implement %s',
+            $middleware,
+            MiddlewareInterface::class
+        ));
+    }
+}