Fix one case that can make sync backend stuck in auth error state.

sync/engine/net/server_connection_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/engine/net/server_connection_manager.h"
 
 #include <errno.h>
 
 #include <ostream>
 #include <string>
@@ skipping 215 matching lines @@
   active_connection_ = NULL;
 }
 
 bool ServerConnectionManager::SetAuthToken(const std::string& auth_token) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (previously_invalidated_token != auth_token) {
     auth_token_.assign(auth_token);
     previously_invalidated_token = std::string();
     return true;
   }
+
+  // This could happen in case like server outage/bug. E.g. token returned by
+  // first request is considered invalid by sync server and because
+  // of token server's caching policy, etc, same token is returned on second
+  // request. Need to notify sync frontend again to request new token,
+  // otherwise backend will stay in SYNC_AUTH_ERROR state while frontend thinks
+  // everything is fine and takes no actions.
+  SetServerStatus(HttpResponse::SYNC_AUTH_ERROR);
   return false;
 }
 
 void ServerConnectionManager::OnInvalidationCredentialsRejected() {
   InvalidateAndClearAuthToken();
   SetServerStatus(HttpResponse::SYNC_AUTH_ERROR);
 }
 
 void ServerConnectionManager::InvalidateAndClearAuthToken() {
   DCHECK(thread_checker_.CalledOnValidThread());
   // Copy over the token to previous invalid token.
   if (!auth_token_.empty()) {
     previously_invalidated_token.assign(auth_token_);
     auth_token_ = std::string();
   }
 }
 
 void ServerConnectionManager::SetServerStatus(
     HttpResponse::ServerConnectionCode server_status) {
-  if (server_status_ == server_status)
+  // SYNC_AUTH_ERROR is permanent error. Need to notify observer to take
+  // action externally to resolve.
+  if (server_status != HttpResponse::SYNC_AUTH_ERROR &&
+      server_status_ == server_status) {
     return;
+  }
   server_status_ = server_status;
   NotifyStatusChanged();
 }
 
 void ServerConnectionManager::NotifyStatusChanged() {
   DCHECK(thread_checker_.CalledOnValidThread());
   FOR_EACH_OBSERVER(ServerConnectionEventListener, listeners_,
      OnServerConnectionEvent(
          ServerConnectionEvent(server_status_)));
 }
@@ skipping 106 matching lines @@
 
 std::ostream& operator << (std::ostream& s, const struct HttpResponse& hr) {
   s << " Response Code (bogus on error): " << hr.response_code;
   s << " Content-Length (bogus on error): " << hr.content_length;
   s << " Server Status: "
     << HttpResponse::GetServerConnectionCodeString(hr.server_status);
   return s;
 }
 
 }  // namespace syncer