anchor.diff:  
   @InterceptorClass()
   class DecodeJson extends Interceptor {
  -  const DecodeJson();
  +  final Encoding encoding;
  +
  +  const DecodeJson({this.encoding: UTF8});
   
     Future<dynamic> pre(HttpRequest request) async {
  -    String data = await getStringFromBody(request);
  +    String data = await getStringFromBody(request, encoding);
       return JSON.decode(data);
     }
   }
  
positive.code: 
  @InterceptorClass()
  class XWwwFormUrlEncoded extends Interceptor {
    const XWwwFormUrlEncoded();
  
    Future<Map<String, String>> pre(HttpRequest request) async {
      print(request.headers);
      return (await getStringFromBody(request))
          .split("&")
          .map((String part) => part.split("="))
          .map((List<String> part) => <String, String>{part.first: part.last})
  
negative.code: import 'package:http_server/http_server.dart';
  import 'package:mime/mime.dart';
  
  Future<String> getStringFromBody(HttpRequest request, Encoding encoding) async {
    Completer<String> completer = new Completer<String>();
    String allData = "";
    //  TODO: add error
    request.transform(encoding.decoder).listen((String data) => allData += data,
        onDone: () => completer.complete(allData));
    return completer.future;
  }
  