Using custom header value for error messages

Author: mmoreram

README.md

@@ -128,6 +128,11 @@ your application
 php vendor/bin/server run 0.0.0.0:8000 --adapter='My\Namespace\Adapter"
 ```
 
+### Custom response output
+
+You can internally use the `x-server-message` header for custom server messages.
+The server will remove this server value before returning the response content.
+
 ## Workers
 
 This server creates a single worker by default. A simple PHP thread that will 
@@ -224,4 +229,4 @@ Some first steps for you!
 or
 
 - [Try a demo](https://github.com/driftphp/demo)
-- [Install the skeleton](https://github.com/driftphp/skeleton)
+- [Install the skeleton](https://github.com/driftphp/skeleton)

src/Application.php

@@ -212,6 +212,13 @@ private function toServerResponse(
             ->applyResponseEncoding($response, $request->getHeaderLine('Accept-encoding'))
             ->then(function (ResponseInterface $response) use ($request, $from) {
                 $to = microtime(true);
+                $responseMessage = '';
+                if ($response->hasHeader('x-server-message')) {
+                    $responseMessage = $response->getHeader('x-server-message');
+                    $responseMessage = ($responseMessage[0] ?? '') ? \strval($responseMessage[0]) : '';
+                    $response = $response->withoutHeader('x-server-message');
+                }
+
                 $serverResponse =
                     new ServerResponseWithMessage(
                         $response,
@@ -220,7 +227,7 @@ private function toServerResponse(
                             $request->getUri()->getPath(),
                             $request->getMethod(),
                             $response->getStatusCode(),
-                            '',
+                            $responseMessage,
                             TimeFormatter::formatTime($to - $from)
                         )
                     );