Detect sync server communication errors

chrome/browser/sync/sessions/sync_session.h

 // Copyright (c) 2011 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.
 
 // A class representing an attempt to synchronize the local syncable data
 // store with a sync server. A SyncSession instance is passed as a stateful
 // bundle to and from various SyncerCommands with the goal of converging the
 // client view of data with that of the server. The commands twiddle with
 // session status in response to events and hiccups along the way, set and
 // query session progress with regards to conflict resolution and applying
@@ skipping 94 matching lines @@
   // Builds a thread-safe and read-only copy of the current session state.
   SyncSessionSnapshot TakeSnapshot() const;
 
   // Builds and sends a snapshot to the session context's listeners.
   void SendEventNotification(SyncEngineEvent::EventCause cause);
 
   // Returns true if this session contains data that should go through the sync
   // engine again.
   bool HasMoreToSync() const;
 
+  // Returns true if there we did not detect any errors in this session.
+  //
+  // There are many errors that could prevent a sync cycle from succeeding.
+  // These include invalid local state, inability to contact the server,
+  // inability to authenticate with the server, and server errors.  What they
+  // have in common is that the we either need to take some action and then
+  // retry the sync cycle or, in the case of transient errors, retry after some
+  // backoff timer has expired.  Most importantly, the SyncScheduler should not
+  // assume that the original action that triggered the sync cycle (ie. a nudge
+  // or a notification) has been properly serviced.
+  //
+  // This function also returns false if SyncShare has not been called on this
+  // session yet, or if ResetTransientState() has been called on this session
+  // since the last call to SyncShare.
+  bool Succeeded() const;
+
   // Collects all state pertaining to how and why |s| originated and unions it
   // with corresponding state in |this|, leaving |s| unchanged.  Allows |this|
   // to take on the responsibilities |s| had (e.g. certain data types) in the
   // next SyncShare operation using |this|, rather than needed two separate
   // sessions.
   void Coalesce(const SyncSession& session);
 
   // Compares the routing_info_, workers and payload map with the passed in
   // session. Purges types from the above 3 which are not in session. Useful
   // to update the sync session when the user has disabled some types from
@@ skipping 95 matching lines @@
 
  private:
   SyncSession* session_;
   DISALLOW_COPY_AND_ASSIGN(ScopedSetSessionWriteTransaction);
 };
 
 }  // namespace sessions
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_SESSIONS_SYNC_SESSION_H_