Implement Invalidator::Acknowledge

sync/internal_api/public/base/invalidation_state.h

 // 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.
 
 #ifndef SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_STATE_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_STATE_H_
 
 #include <string>
 
+#include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 class DictionaryValue;
 class Value;
 }  // namespace
 
 namespace syncer {
 
-// Opaque class that represents an ack handle.
-// TODO(dcheng): This is just a refactoring change, so the class is empty for
-// the moment. It will be filled once we start implementing 'reminders'.
+// Opaque class that represents an ack handle. We don't reuse the Tango ack
+// handles to avoid unnecessary dependencies.
 class AckHandle {
  public:
+  static AckHandle CreateUnique();
+  static AckHandle InvalidAckHandle();
+
   bool Equals(const AckHandle& other) const;
 
   scoped_ptr<base::Value> ToValue() const;
+  bool ResetFromValue(const base::Value& value);
 
-  bool ResetFromValue(const base::Value& value);
+ private:
+  AckHandle(const std::string& state);
+
+  std::string state_;

[akalin, 2012/09/17 23:59:54]

since we have complete freedom in what the AckHandle contains, I think it would
be useful to stuff some useful data in there.  I'm thinking some or all of the
following:

ObjectId id_;
base::Time timestamp_;
std::string payload_;
std::string tango_ack_handle_str_; // need better name, may also not be present
(if we synthesize an ackhandle ourselves)
std::string random_bits_;

I feel like this would help us quite a bit in tracking down problems.

[dcheng, 2012/09/25 22:35:06]

I'd prefer to leave this sort of thing out of release builds by default so that
people don't try to start exposing/depending on it, especially since these
fields won't be relevant outside of debugging scenarios. What do you think?

[akalin, 2012/10/01 23:23:08]

We can keep a lid on people trying to expose it, right?  I hope no one will
actually try to parse the string representation.

Unfortunately, I think we'll be spending a significant amount of time debugging
invalidations that the debug info would be useful. :/

 };
 
 struct InvalidationState {
-  std::string payload;
-  AckHandle ack_handle;
+  InvalidationState();
 
   bool Equals(const InvalidationState& other) const;
 
-  // Caller owns the returned DictionaryValue.
   scoped_ptr<base::DictionaryValue> ToValue() const;
+  bool ResetFromValue(const base::DictionaryValue& value);
 
-  bool ResetFromValue(const base::DictionaryValue& value);
+  std::string payload;
+  AckHandle ack_handle;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_BASE_INVALIDATION_STATE_H_