Add LwwRegister CRDT

blimp/net/helium/syncable_primitive_serializer.h

Index: blimp/net/helium/syncable_primitive_serializer.h
diff --git a/blimp/net/helium/syncable_primitive_serializer.h b/blimp/net/helium/syncable_primitive_serializer.h
new file mode 100644
index 0000000000000000000000000000000000000000..31130b275aa13940f30fdb7c3d4de627ec00c592
--- /dev/null
+++ b/blimp/net/helium/syncable_primitive_serializer.h
@@ -0,0 +1,67 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[Kevin M, 2016/10/14 17:12:35]

Can you add unit tests for every supported datatype here?

[steimel, 2016/10/17 21:46:00]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BLIMP_NET_HELIUM_SYNCABLE_PRIMITIVE_SERIALIZER_H_
+#define BLIMP_NET_HELIUM_SYNCABLE_PRIMITIVE_SERIALIZER_H_
+
+#include <string>
+
+#include "third_party/protobuf/src/google/protobuf/io/coded_stream.h"
+#include "third_party/protobuf/src/google/protobuf/io/zero_copy_stream_impl_lite.h"
+
+namespace blimp {
+
+// Syncable CRDTs need to serialize their data into CodedOutputStreams. This
+// helper class centralizes that logic into two templated functions, one for
+// serialization and one for deserialization that can be called for any
+// primitive type.
+template <class RegisterType>

[Kevin M, 2016/10/13 22:03:36]

Recommend making these standalone templated functions instead of popping them in
specialized templated classes, so that we get automatic template inference
superpowers.

[steimel, 2016/10/17 21:46:00]

Discussed offline. Changing to overloaded instead.

+class SyncablePrimitiveSerializer {
+ public:
+  static void SerializeSyncablePrimitive(
+      RegisterType& value,
+      google::protobuf::io::ZeroCopyOutputStream* output_stream);
+  static void DeserializeSyncablePrimitive(

[Kevin M, 2016/10/13 22:03:36]

Should this return a bool?

[steimel, 2016/10/17 21:46:00]

Done.

+      RegisterType& value,

[Kevin M, 2016/10/13 22:03:36]

Output parameters should be pointers and located at the end of the parameter
list.

[steimel, 2016/10/17 21:46:00]

Done.

+      google::protobuf::io::ZeroCopyInputStream* input_stream);
+};
+
+// For each type that needs to be (de)serialized, override the template default
+// with a custom implementation.
+template <>
+void SyncablePrimitiveSerializer<int32_t>::SerializeSyncablePrimitive(

[CJ, 2016/10/12 22:32:44]

Pretty sure we could simplify these function names to just
Serialize/Deserialize, since the class name is so descriptive. 

[steimel, 2016/10/17 21:46:00]

Done.

+    int32_t& value,
+    google::protobuf::io::ZeroCopyOutputStream* output_stream) {
+  google::protobuf::io::CodedOutputStream(output_stream)
+      .WriteVarint32((uint32_t)value);
+}
+template <>
+void SyncablePrimitiveSerializer<int32_t>::DeserializeSyncablePrimitive(
+    int32_t& value,
+    google::protobuf::io::ZeroCopyInputStream* input_stream) {
+  google::protobuf::io::CodedInputStream(input_stream)
+      .ReadVarint32((uint32_t*)&value);

[scf, 2016/10/12 23:05:12]

add check?

[steimel, 2016/10/17 21:46:00]

Discussed with Kevin offline. Returning bool instead

+}
+
+template <>
+void SyncablePrimitiveSerializer<std::string>::SerializeSyncablePrimitive(
+    std::string& value,
+    google::protobuf::io::ZeroCopyOutputStream* output_stream) {
+  google::protobuf::io::CodedOutputStream coded_output_stream(output_stream);

[Kevin M, 2016/10/13 22:03:36]

These should take CodedStreams as parameters (there is a pending CL which fixes
this that is in comment limbo ATM, urgh)

[steimel, 2016/10/17 21:46:00]

Done.

+  coded_output_stream.WriteVarint32(value.length());
+  coded_output_stream.WriteString(value);
+}
+template <>
+void SyncablePrimitiveSerializer<std::string>::DeserializeSyncablePrimitive(
+    std::string& value,
+    google::protobuf::io::ZeroCopyInputStream* input_stream) {
+  google::protobuf::io::CodedInputStream coded_input_stream(input_stream);
+  uint32_t length;
+  coded_input_stream.ReadVarint32(&length);

[scf, 2016/10/12 23:05:12]

add check

+  coded_input_stream.ReadString(&value, length);
+}
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_HELIUM_SYNCABLE_PRIMITIVE_SERIALIZER_H_