Follow the redirect rules from RFC 2616

sdk/lib/io/http_impl.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.
 
 // The close queue handles graceful closing of HTTP connections. When
 // a connection is added to the queue it will enter a wait state
 // waiting for all data written and possibly socket shutdown from
 // peer.
 class _CloseQueue {
   _CloseQueue() : _q = new Set<_HttpConnectionBase>();
@@ skipping 1268 matching lines @@
     extends _HttpRequestResponseBase implements HttpClientResponse {
   _HttpClientResponse(_HttpClientConnection connection)
       : super(connection) {
     _connection = connection;
   }
 
   int get statusCode => _statusCode;
   String get reasonPhrase => _reasonPhrase;
 
   bool get isRedirect {
-    return statusCode == HttpStatus.MOVED_PERMANENTLY ||
-           statusCode == HttpStatus.FOUND ||
-           statusCode == HttpStatus.SEE_OTHER ||
-           statusCode == HttpStatus.TEMPORARY_REDIRECT;
+    var method = _connection._request._method;
+    if (method == "GET" || method == "HEAD") {
+      return statusCode == HttpStatus.MOVED_PERMANENTLY ||
+             statusCode == HttpStatus.FOUND ||
+             statusCode == HttpStatus.SEE_OTHER ||
+             statusCode == HttpStatus.TEMPORARY_REDIRECT;
+    } else if (method == "POST") {
+      return statusCode == HttpStatus.SEE_OTHER;
+    }
+    return false;
   }
 
   List<Cookie> get cookies {
     if (_cookies != null) return _cookies;
     _cookies = new List<Cookie>();
     List<String> values = _headers["set-cookie"];
     if (values != null) {
       values.forEach((value) {
         _cookies.add(new Cookie.fromSetCookieValue(value));
       });
@@ skipping 36 matching lines @@
           Uri redirectUrl = new Uri.fromString(location[0]);
           for (int i = 0; i < _connection._redirects.length; i++) {
             if (_connection._redirects[i].location.toString() ==
                 redirectUrl.toString()) {
               throw new RedirectLoopException(_connection._redirects);
             }
           }
         }
         // Drain body and redirect.
         inputStream.onData = inputStream.read;
-        _connection.redirect();
+        if (_statusCode == HttpStatus.SEE_OTHER &&
+            _connection._method == "POST") {
+          _connection.redirect("GET");
+        } else {
+          _connection.redirect();
+        }
       } else {
         throw new RedirectLimitExceededException(_connection._redirects);
       }
     } else if (statusCode == HttpStatus.UNAUTHORIZED) {
       _handleUnauthorized();
     } else if (_connection._onResponse != null) {
       _connection._onResponse(this);
     }
   }
 
@@ skipping 918 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }