Add handling of HTTP '100 Continue' intermediate response

sdk/lib/io/http_impl.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 const int _OUTGOING_BUFFER_SIZE = 8 * 1024;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
@@ skipping 1271 matching lines @@
         (incoming) {
           // Only handle one incoming response at the time. Keep the
           // stream paused until the response have been processed.
           _subscription.pause();
           // We assume the response is not here, until we have send the request.
           if (_nextResponseCompleter == null) {
             throw new HttpException(
                 "Unexpected response (unsolicited response without request).",
                 uri: _currentUri);
           }
-          _nextResponseCompleter.complete(incoming);
-          _nextResponseCompleter = null;
+
+          // Check for status code '100 Continue'. In that case just
+          // consume that response as the final response will follow
+          // it. There is currently no API for the client to wait for
+          // the '100 Continue' response.
+          if (incoming.statusCode == 100) {
+            incoming.drain().then((_) {
+              _subscription.resume();
+            }).catchError((error, [StackTrace stackTrace]) {
+              _nextResponseCompleter.completeError(
+                  new HttpException(error.message, uri: _currentUri),
+                  stackTrace);
+              _nextResponseCompleter = null;
+            });
+          } else {
+            _nextResponseCompleter.complete(incoming);
+            _nextResponseCompleter = null;
+          }
         },
         onError: (error, [StackTrace stackTrace]) {
           if (_nextResponseCompleter != null) {
             _nextResponseCompleter.completeError(
                 new HttpException(error.message, uri: _currentUri),
                 stackTrace);
             _nextResponseCompleter = null;
           }
         },
         onDone: () {
@@ skipping 1512 matching lines @@
   const _RedirectInfo(this.statusCode, this.method, this.location);
 }
 
 String _getHttpVersion() {
   var version = Platform.version;
   // Only include major and minor version numbers.
   int index = version.indexOf('.', version.indexOf('.') + 1);
   version = version.substring(0, index);
   return 'Dart/$version (dart:io)';
 }