dart server: retrieve data from Request

I was trying to create a simple dart server, glad it's working, but...

   Future<Response> _echoHandler(Request request) async{
    final message = await request.readAsString();
    print(message);
    return Response.ok('$message\n');
  }

this is how that message looks like

----------------------------116375419757550841191749
Content-Disposition: form-data; name="message"

asdf
----------------------------116375419757550841191749--

Postman testing

I want to extract this message.