Make MediaType case-insensitive, following the spec.

lib/src/media_type.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 http_parser.media_type;
 
 import 'package:collection/collection.dart';
 import 'package:string_scanner/string_scanner.dart';
 
+import 'case_insensitive_map.dart';
 import 'scan.dart';
 import 'utils.dart';
 
 /// A regular expression matching a character that needs to be backslash-escaped
 /// in a quoted string.
 final _escapedChar = new RegExp(r'["\x00-\x1F\x7F]');
 
 /// A class representing an HTTP media type, as used in Accept and Content-Type
 /// headers.
 ///
 /// This is immutable; new instances can be created based on an old instance by
 /// calling [change].
 class MediaType {
   /// The primary identifier of the MIME type.
+  ///
+  /// This is always lowercase. 
   final String type;
 
   /// The secondary identifier of the MIME type.
+  ///
+  /// This is always lowercase. 
   final String subtype;
 
   /// The parameters to the media type.
   ///
-  /// This map is immutable.
+  /// This map is immutable and the keys are case-insensitive.
   final Map<String, String> parameters;
 
   /// The media type's MIME type.
   String get mimeType => "$type/$subtype";
 
   /// Parses a media type.
   ///
   /// This will throw a FormatError if the media type is invalid.
   factory MediaType.parse(String mediaType) {
     // This parsing is based on sections 3.6 and 3.7 of the HTTP spec:
@@ skipping 24 matching lines @@
 
         scanner.scan(whitespace);
         parameters[attribute] = value;
       }
 
       scanner.expectDone();
       return new MediaType(type, subtype, parameters);
     });
   }
 
-  MediaType(this.type, this.subtype, [Map<String, String> parameters])
-      : this.parameters = new UnmodifiableMapView(
-          parameters == null ? {} : new Map.from(parameters));
+  MediaType(String type, String subtype, [Map<String, String> parameters])
+      : type = type.toLowerCase(),
+        subtype = subtype.toLowerCase(),
+        parameters = new UnmodifiableMapView(
+            parameters == null ? {} : new CaseInsensitiveMap.from(parameters));
 
   /// Returns a copy of this [MediaType] with some fields altered.
   ///
   /// [type] and [subtype] alter the corresponding fields. [mimeType] is parsed
   /// and alters both the [type] and [subtype] fields; it cannot be passed along
   /// with [type] or [subtype].
   ///
   /// [parameters] overwrites and adds to the corresponding field. If
   /// [clearParameters] is passed, it replaces the corresponding field entirely
   /// instead.
@@ skipping 47 matching lines @@
               value.replaceAllMapped(_escapedChar, (match) => "\\" + match[0]))
           ..write('"');
       } else {
         buffer.write(value);
       }
     });
 
     return buffer.toString();
   }
 }