Make instances of HeaderValue and ContentType immutable

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index feaeb0e4edbd1e7e9066dcc7f782e18df095cdb0..e50dc2acd4ac6461f43c8d8226666b91ba57cd59 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -399,9 +399,7 @@ abstract class HttpHeaders {
  * use code like this:
  *
  *     HttpClientRequest request = ...;
- *     var v = new HeaderValue();
- *     v.value = "text/plain";
- *     v.parameters["q"] = "0.3"
+ *     var v = new HeaderValue("text/plain", {"q": "0.3"});
  *     request.headers.add(HttpHeaders.ACCEPT, v);
  *     request.headers.add(HttpHeaders.ACCEPT, "text/html");
  *
@@ -413,12 +411,16 @@ abstract class HttpHeaders {
  *       HeaderValue v = new HeaderValue.fromString(value);
  *       // Use v.value and v.parameters
  *     });
+ *
+ * An instance of [HeaderValue] is immutable.
  */
 abstract class HeaderValue {
   /**
    * Creates a new header value object setting the value part.
    */
-  factory HeaderValue([String value = ""]) => new _HeaderValue(value);
+  factory HeaderValue([String value = "", Map<String, String> parameters]) {
+    return new _HeaderValue(value, parameters);
+  }
 
   /**
    * Creates a new header value object from parsing a header value
@@ -431,9 +433,9 @@ abstract class HeaderValue {
   }
 
   /**
-   * Gets and sets the header value.
+   * Gets the header value.
    */
-  String value;
+  String get value;
 
   /**
    * Gets the map of parameters.
@@ -473,15 +475,18 @@ abstract class HttpSession implements Map {
 
 
 /**
- * Representation of a content type.
+ * Representation of a content type. An instance of [ContentType] is
+ * immutable.
  */
 abstract class ContentType implements HeaderValue {
   /**
    * Creates a new content type object setting the primary type and
-   * sub type.
+   * sub type and the charset parameter.
    */
-  factory ContentType([String primaryType = "", String subType = ""]) {
-    return new _ContentType(primaryType, subType);
+  factory ContentType([String primaryType = "",
+                       String subType = "",
+                       String charset]) {
+    return new _ContentType(primaryType, subType, charset);
   }
 
   /**
@@ -500,24 +505,19 @@ abstract class ContentType implements HeaderValue {
   }
 
   /**
-   * Gets and sets the content type in the form "primaryType/subType".
-   */
-  String value;
-
-  /**
-   * Gets and sets the primary type.
+   * Gets the primary type.
    */
-  String primaryType;
+  String get primaryType;
 
   /**
-   * Gets and sets the sub type.
+   * Gets the sub type.
    */
-  String subType;
+  String get subType;
 
   /**
-   * Gets and sets the character set.
+   * Gets the character set.
    */
-  String charset;
+  String get charset;
 }