Keep around a copy of the http.Request that triggered each Response.

pkg/http/lib/src/io_client.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library io_client;
 
 import 'dart:io';
 
 import 'base_client.dart';
 import 'base_request.dart';
@@ skipping 54 matching lines @@
     };
 
     connection.onResponse = (response) {
       var headers = <String>{};
       response.headers.forEach((key, value) => headers[key] = value);
 
       completer.complete(new StreamedResponse(
           wrapInputStream(response.inputStream),
           response.statusCode,
           response.contentLength,
+          request: request,
           headers: headers,
           isRedirect: response.isRedirect,
           persistentConnection: response.persistentConnection,
           reasonPhrase: response.reasonPhrase));
     };
 
     return completer.future;
   }
 
   /// Closes the client. This terminates all active connections. If a client
   /// remains unclosed, the Dart process may not terminate.
   void close() {
     if (_inner != null) _inner.shutdown(force: true);
     _inner = null;
   }
 }