fix handler function response

README.md

@@ -73,12 +73,15 @@ $server->start(
     function (
         string $request,
         string $connect
-    ) {
+    ): ?string
+    {
         printf(
             'connection: %s request: %s',
             $connect,
             $request
         );
+
+        return null; // null|string response
     }
 );
 ```

src/Server.php

@@ -145,6 +145,14 @@ class Server
                     $request,
                     $connect
                 );
+
+                if ($response)
+                {
+                    fwrite(
+                        $incoming,
+                        $response
+                    );
+                }
             }
 
             fclose(