in lib/src/web_socket_handler.dart [120:132]
Response _htmlResponse(int statusCode, String title, String message) {
title = htmlEscape.convert(title);
message = htmlEscape.convert(message);
return Response(statusCode, body: '''
<!doctype html>
<html>
<head><title>$title</title></head>
<body>
<h1>$title</h1>
<p>$message</p>
</body>
</html>
''', headers: {'content-type': 'text/html'});