pkg/shelf: change helper method on Request and Response

pkg/shelf/lib/src/message.dart

Index: pkg/shelf/lib/src/message.dart
diff --git a/pkg/shelf/lib/src/message.dart b/pkg/shelf/lib/src/message.dart
index 1b2e966c4660b3375519c985a459362257e00408..1522e1301aac2ca2af36caec47af853ddbec111f 100644
--- a/pkg/shelf/lib/src/message.dart
+++ b/pkg/shelf/lib/src/message.dart
@@ -5,14 +5,13 @@
 library shelf.message;
 
 import 'dart:async';
-import 'dart:collection';
 import 'dart:convert';
 
-// TODO(kevmoo): use UnmodifiableMapView from SDK once 1.4 ships
-import 'package:collection/wrappers.dart' as pc;
 import 'package:http_parser/http_parser.dart';
 import 'package:stack_trace/stack_trace.dart';
 
+import 'shelf_unmodifiable_map.dart';
+
 /// Represents logic shared between [Request] and [Response].
 abstract class Message {
   /// The HTTP headers.
@@ -43,9 +42,10 @@ abstract class Message {
   /// If [headers] is `null`, it is treated as empty.
   Message(this._body, {Map<String, String> headers,
         Map<String, Object> context})
-      : this.headers = _getIgnoreCaseMapView(headers),
-        this.context = new pc.UnmodifiableMapView(
-            context == null ? const {} : new Map.from(context));
+      : this.headers = new ShelfUnmodifiableMap<String>(headers,
+            ignoreKeyCase: true),
+        this.context = new ShelfUnmodifiableMap<Object>(context,
+            ignoreKeyCase: false);
 
   /// The contents of the content-length field in [headers].
   ///
@@ -112,18 +112,8 @@ abstract class Message {
     if (encoding == null) encoding = UTF8;
     return Chain.track(encoding.decodeStream(read()));
   }
-}
-
-/// Creates on an unmodifiable map of [headers] with case-insensitive access.
-Map<String, String> _getIgnoreCaseMapView(Map<String, String> headers) {
-  if (headers == null) return const {};
-  // TODO(kevmoo) generalize this model with a 'canonical map' to align with
-  // similiar implementation in http pkg [BaseRequest].
-  var map = new LinkedHashMap<String, String>(
-      equals: (key1, key2) => key1.toLowerCase() == key2.toLowerCase(),
-      hashCode: (key) => key.toLowerCase().hashCode);
-
-  map.addAll(headers);
 
-  return new pc.UnmodifiableMapView<String, String>(map);
+  /// Creates a new [Message] by copying existing values and applying specified
+  /// changes.
+  Message change({Map<String, String> headers, Map<String, Object> context});
 }