Add handling of HTTP header "Expires"

runtime/bin/http.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.
 
 /**
  * HTTP status codes.
  */
 interface HttpStatus {
   static final int CONTINUE = 100;
   static final int SWITCHING_PROTOCOLS = 101;
@@ skipping 159 matching lines @@
    */
   int statusCode;
 
   /**
    * Gets and sets the reason phrase. If no reason phrase is explicitly
    * set a default reason phrase is provided.
    */
   String reasonPhrase;
 
   /**
+   * Gets and sets the expiry date. The value of this property will
+   * reflect the "Expires" header
+   */
+  Date expires;
+
+  /**
    * Sets a header on the response. NOTE: If the same header name is
    * set more than once only the last value will be part of the
    * response.
    */
   void setHeader(String name, String value);
 
   /**
    * Returns the response headers.
    */
   Map<String, String> get headers();
@@ skipping 169 matching lines @@
    * the request body is not known in advance this -1.
    */
   int get contentLength();
 
   /**
    * Returns the keep alive state of the connection.
    */
   bool get keepAlive();
 
   /**
+   * Returns the date value for the "Expires" header. Returns null if
+   * the response has no "Expires" header. Throws a HttpException if
+   * the response has an "Expires" header which is not formatted as a
+   * valid HTTP date.
+   */
+  Date get expires();
+
+  /**
    * Returns the response headers.
    */
   Map<String, String> get headers();
 
   /**
    * Returns the input stream for the response. This is used to read
    * the response data.
    */
   InputStream get inputStream();
 }
 
 
 class HttpException implements Exception {
   const HttpException([String this.message = ""]);
   String toString() => "HttpException: $message";
   final String message;
 }