Add LwwRegister CRDT

blimp/net/helium/lww_register_serializer.h

Index: blimp/net/helium/lww_register_serializer.h
diff --git a/blimp/net/helium/lww_register_serializer.h b/blimp/net/helium/lww_register_serializer.h
new file mode 100644
index 0000000000000000000000000000000000000000..c1329ba92065b350d221f4dd7958afd9195af768
--- /dev/null
+++ b/blimp/net/helium/lww_register_serializer.h
@@ -0,0 +1,71 @@
+// Copyright 2016 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 BLIMP_NET_HELIUM_LWW_REGISTER_SERIALIZER_H_
+#define BLIMP_NET_HELIUM_LWW_REGISTER_SERIALIZER_H_
+
+#include "base/logging.h"
+#include "blimp/common/proto/helium.pb.h"
+
+namespace blimp {
+
+// Each type of LwwRegister has it's own way of serializing and deserializing
+// data into/from the LwwRegisterChangesetMessage. This template class extracts
+// that logic out into this file.
+template <class RegisterType>
+class LwwRegisterSerializer {
+ public:
+  static void SerializeLwwRegister(
+      RegisterType& state,
+      proto::LwwRegisterChangesetMessage* changeset);
+  static void DeserializeLwwRegister(
+      RegisterType& state,
+      proto::LwwRegisterChangesetMessage* changeset);
+};
+
+// NOTREACHED for any unsupported types.
+template <class RegisterType>

[scf, 2016/10/10 19:45:47]

I prefer removing this code so you get a compiler error instead of runtime
error.

[Kevin M, 2016/10/10 20:50:21]

+1

[steimel, 2016/10/11 16:39:17]

Done.

+void LwwRegisterSerializer<RegisterType>::SerializeLwwRegister(
+    RegisterType& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  NOTREACHED() << "Serializing unsupported LwwRegister type.";
+}
+template <class RegisterType>
+void LwwRegisterSerializer<RegisterType>::DeserializeLwwRegister(
+    RegisterType& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  NOTREACHED() << "Deserializing unsupported LwwRegister type.";
+}
+
+// For each type that needs to be (de)serialized, override the template default
+// with a custom implementation.
+template <>
+void LwwRegisterSerializer<int32_t>::SerializeLwwRegister(

[Kevin M, 2016/10/10 20:50:21]

Since we'll be serializing primitive data types all the time, I recommend moving
these functions into a common library which, given a value and a
CodedOutputStream, will the value to the stream using the appropriate Write
method. 

[steimel, 2016/10/11 16:39:17]

Gotcha. I'll do that when I make the change to CodedOutputStreams

+    int32_t& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  changeset->set_integer_value(state);
+}
+template <>
+void LwwRegisterSerializer<int32_t>::DeserializeLwwRegister(
+    int32_t& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  state = changeset->integer_value();
+}
+
+template <>
+void LwwRegisterSerializer<std::string>::SerializeLwwRegister(
+    std::string& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  changeset->set_string_value(state);
+}
+template <>
+void LwwRegisterSerializer<std::string>::DeserializeLwwRegister(
+    std::string& state,
+    proto::LwwRegisterChangesetMessage* changeset) {
+  state = changeset->string_value();
+}
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_HELIUM_LWW_REGISTER_SERIALIZER_H_