issue 17992 Added extra params to message

pkg/shelf/lib/src/message.dart

 // Copyright (c) 2014, 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 shelf.message;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:collection/wrappers.dart';
 import 'package:http_parser/http_parser.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 /// Represents logic shared between [Request] and [Response].
 abstract class Message {
   /// The HTTP headers.
   ///
   /// The value is immutable.
   final Map<String, String> headers;
 
   /// The streaming body of the message.
   ///
   /// This can be read via [read] or [readAsString].
   final Stream<List<int>> _body;
 
-  Message(UnmodifiableMapView<String, String> headers, this._body)
-      : this.headers = headers;
+  /// Extra parameters for handlers to pass data to downstream handlers

[nweiz, 2014/04/08 21:33:50]

I don't know that everyone will have the same intuition for which direction is
"upstream" and which is "downstream". It's especially confusing because during
request handling, this will be passed to inner handlers, but during response
handling it will be passed to outer handlers. Maybe just "other handlers" is
best.

[andersmholmgren, 2014/04/08 22:16:36]

My bad, clearly I was thinking of request context when I wrote this comment.
Will amend

+  /// TODO: less sucky name
+  ///
+  /// The value is immutable.
+  final Map<String, Object> extraParams;

[nweiz, 2014/04/08 21:33:50]

I like "context" as a name here.

[andersmholmgren, 2014/04/08 22:16:36]

+1. That's the best name. It came to me a day after submitting this but I
couldn't figure out how to add a comment to my own review.

Other options are handlerContext, appContext etc

+
+
+  Message(UnmodifiableMapView<String, String> headers, this._body,
+          [ UnmodifiableMapView<String, Object> extraParams ])
+      : this.headers = headers,
+        this.extraParams = extraParams;
 
   /// The contents of the content-length field in [headers].
   ///
   /// If not set, `null`.
   int get contentLength {
     if (_contentLengthCache != null) return _contentLengthCache;
     if (!headers.containsKey('content-length')) return null;
     _contentLengthCache = int.parse(headers['content-length']);
     return _contentLengthCache;
   }
@@ skipping 47 matching lines @@
   /// Otherwise the encoding is taken from the Content-Type header. If that
   /// doesn't exist or doesn't have a "charset" parameter, UTF-8 is used.
   ///
   /// This calls [read] internally, which can only be called once.
   Future<String> readAsString([Encoding encoding]) {
     if (encoding == null) encoding = this.encoding;
     if (encoding == null) encoding = UTF8;
     return Chain.track(encoding.decodeStream(read()));
   }
 }