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

pkg/http/lib/src/response.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 response;
 
 import 'dart:io';
 import 'dart:scalarlist';
 
+import 'base_request.dart';
 import 'base_response.dart';
 import 'streamed_response.dart';
 import 'utils.dart';
 
 /// An HTTP response where the entire response body is known in advance.
 class Response extends BaseResponse {
   /// The bytes comprising the body of this response.
   final Uint8List bodyBytes;
 
   /// The body of the response as a string. This is converted from [bodyBytes]
   /// using the `charset` parameter of the `Content-Type` header field, if
   /// available. If it's unavailable or if the encoding name is unknown,
   /// [Encoding.ISO_8859_1] is used by default, as per [RFC 2616][].
   ///
   /// [RFC 2616]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html
   String get body => decodeString(bodyBytes, _encodingForHeaders(headers));
 
   /// Creates a new HTTP response with a string body.
   Response(
       String body,
       int statusCode,
-      {Map<String, String> headers: const <String>{},
+      {BaseRequest request: null,

[Bob Nystrom, 2012/11/29 23:57:04]

null is the default default value, so you can omit it here. Just:

   {BaseRequest request,

[nweiz, 2012/11/30 00:08:54]

Done.

+       Map<String, String> headers: const <String>{},
        bool isRedirect: false,
        bool persistentConnection: true,
        String reasonPhrase})
     : this.bytes(
         encodeString(body, _encodingForHeaders(headers)),
         statusCode,
+        request: request,
         headers: headers,
         isRedirect: isRedirect,
         persistentConnection: persistentConnection,
         reasonPhrase: reasonPhrase);
 
   /// Create a new HTTP response with a byte array body.
   Response.bytes(
       List<int> bodyBytes,
       int statusCode,
-      {Map<String, String> headers: const <String>{},
+      {BaseRequest request: null,
+       Map<String, String> headers: const <String>{},
        bool isRedirect: false,
        bool persistentConnection: true,
        String reasonPhrase})
     : bodyBytes = toUint8List(bodyBytes),
       super(
         statusCode,
         bodyBytes.length,
+        request: request,
         headers: headers,
         isRedirect: isRedirect,
         persistentConnection: persistentConnection,
         reasonPhrase: reasonPhrase);
 
   /// Creates a new HTTP response by waiting for the full body to become
   /// available from a [StreamedResponse].
   static Future<Response> fromStream(StreamedResponse response) {
     return consumeInputStream(response.stream).transform((body) {
       return new Response.bytes(
           body,
           response.statusCode,
+          request: response.request,
           headers: response.headers,
           isRedirect: response.isRedirect,
           persistentConnection: response.persistentConnection,
           reasonPhrase: response.reasonPhrase);
     });
   }
 }
 
 /// Returns the encoding to use for a response with the given headers. This
 /// defaults to [Encoding.ISO_8859_1] if the headers don't specify a charset or
 /// if that charset is unknown.
 Encoding _encodingForHeaders(Map<String, String> headers) =>
   encodingForCharset(_contentTypeForHeaders(headers).charset);
 
 /// Returns the [ContentType] object for the given headers. Defaults to
 /// `application/octet-stream`.
 ContentType _contentTypeForHeaders(Map<String, String> headers) {
   var contentType = headers[HttpHeaders.CONTENT_TYPE];
   if (contentType != null) return new ContentType.fromString(contentType);
   return new ContentType("application", "octet-stream");
 }