Helium: Initial proto and Syncable interface definition

blimp/net/helium/syncable_unittest.cc

+// 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.
+
+#include "blimp/net/helium/syncable.h"
+
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blimp {
+namespace {
+
+// This is a sample implementation that demostrates the implementation
+// of the SyncableMember and SyncableObject
+
+// For simplicity of this example, the ChangeSet will be an integer.
+class IntValueSyncable : public SyncableMember<int> {
+ public:
+  explicit IntValueSyncable(SyncableObject* parent)
+      : SyncableMember(parent), value_(0) {
+    last_modified_ = parent_clock();
+  }
+
+  bool ModifiedSince(const VectorClock& from) override {

[perumaal, 2016/10/04 00:07:37]

This seems backward.
The parent seems to know how to manage its child member Syncables. If so, the
delegation from the parent to child back to parent seems confusing/backwards.

parent::ApplyChangeset calls child::ModifiedSince which calls
parent::parent_clock()::local_revision().

All of this information is available from the parent itself (as in, it maintains
the master vector clock).

In a way, I am wondering if we can remove all the 'child members have a direct
pointer to their parent' which seems dangerous in general and looks like an
inversion in separation of concerns.

From the parent's perspective, one could presumably write code that had all the
vector clock logic isolated within the parent object itself instead of having to
seep it through the children - where the logic becomes distributed between the
parent and each of the child members.

[scf, 2016/10/04 17:07:20]

`parent::ApplyChangeset calls child::ModifiedSince which calls
parent::parent_clock()::local_revision().

All of this information is available from the parent itself (as in, it maintains
the master vector clock).
`

false. ModifiedSince uses it own clock to check if it was modified since the
last sync. 

Look at line 53. It gets modified every time we set the value. Thus it belongs
here imo.

Again, related to the clock comment, we will use a clock generator and remove
the notion of parent here. hang tight for the next diff :)

+    return from.local_revision() < last_modified_.local_revision();
+  }
+
+  std::unique_ptr<int> CreateChangesetToCurrent(
+      const VectorClock& from) override {
+    return base::MakeUnique<int>(value_);
+  }
+
+  void ApplyChangeset(const VectorClock& from,
+                      const VectorClock& to,
+                      std::unique_ptr<int> changeset) override {
+    // Restore the value
+    value_ = *changeset;
+
+    // Update our clock to the latest clock
+    last_modified_ = to;
+  }
+
+  void ReleaseCheckpointsBefore(const VectorClock& checkpoint) override {
+    last_modified_ = checkpoint;
+  }
+
+  void SetValue(int value) {
+    value_ = value;
+
+    // Increment the parent clock and update our last_modified_ value
+    last_modified_ = IncrementParentClock();
+  }
+
+  int value() { return value_; }
+
+ private:
+  // The last time this object was changed
+  VectorClock last_modified_;
+  int32_t value_;
+
+  DISALLOW_COPY_AND_ASSIGN(IntValueSyncable);
+};
+
+class ParentObjectSyncable : public SyncableObject {
+ public:
+  explicit ParentObjectSyncable(VectorClock clock)
+      : SyncableObject(clock), child1_(this), child2_(this) {}
+
+  std::unique_ptr<proto::ChangesetMessage> CreateChangesetToCurrent(
+      const VectorClock& from) override {
+    std::unique_ptr<proto::ChangesetMessage> changeset =
+        base::MakeUnique<proto::ChangesetMessage>();
+
+    proto::TestChangesetMessage* bm = changeset->mutable_test();
+
+    if (child1_.ModifiedSince(from)) {
+      std::unique_ptr<int> value1 = child1_.CreateChangesetToCurrent(from);
+      bm->set_value1(*value1);
+    }
+
+    if (child2_.ModifiedSince(from)) {
+      std::unique_ptr<int> value2 = child2_.CreateChangesetToCurrent(from);
+      bm->set_value2(*value2);
+    }
+
+    return changeset;
+  }
+
+  void ApplyChangeset(
+      const VectorClock& from,
+      const VectorClock& to,
+      std::unique_ptr<proto::ChangesetMessage> changeset) override {
+    proto::TestChangesetMessage bm = changeset->test();
+
+    int child1_value = bm.value1();
+    if (child1_value != 0) {
+      child1_.ApplyChangeset(from, to, base::MakeUnique<int>(child1_value));
+    }
+
+    int child2_value = bm.value2();
+    if (child2_value != 0) {
+      child2_.ApplyChangeset(from, to, base::MakeUnique<int>(child2_value));
+    }
+  }
+
+  void ReleaseCheckpointsBefore(const VectorClock& checkpoint) override {
+    child1_.ReleaseCheckpointsBefore(checkpoint);
+    child2_.ReleaseCheckpointsBefore(checkpoint);
+  }
+
+  IntValueSyncable& get_child1() { return child1_; }
+  IntValueSyncable& get_child2() { return child2_; }
+
+ private:
+  IntValueSyncable child1_;
+  IntValueSyncable child2_;
+
+  DISALLOW_COPY_AND_ASSIGN(ParentObjectSyncable);
+};
+
+class SyncableTest : public testing::Test {
+ public:
+  SyncableTest()
+      : last_sync_local_(),
+        last_sync_remote_(),
+        parent_local_(last_sync_local_),
+        parent_remote_(last_sync_remote_) {}
+
+  ~SyncableTest() override {}
+
+ protected:
+  VectorClock last_sync_local_;
+  VectorClock last_sync_remote_;
+  ParentObjectSyncable parent_local_;
+  ParentObjectSyncable parent_remote_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SyncableTest);
+};
+
+TEST_F(SyncableTest, CreateAndApplyChangesetTest) {
+  // Lets modify a children object
+  parent_local_.get_child1().SetValue(123);
+
+  // At this point |child1| and |parentObject| should have its clock incremented
+  // whereas |child2| should still be the same.
+  EXPECT_TRUE(parent_local_.get_child1().ModifiedSince(last_sync_local_));
+  EXPECT_FALSE(parent_local_.get_child2().ModifiedSince(last_sync_local_));
+
+  std::unique_ptr<proto::ChangesetMessage> changeset =
+      parent_local_.CreateChangesetToCurrent(last_sync_local_);
+
+  VectorClock local_clock = parent_local_.clock();
+  VectorClock remote_clock = local_clock.Invert();
+
+  parent_remote_.ApplyChangeset(last_sync_remote_, remote_clock,
+                                std::move(changeset));
+  last_sync_local_ = local_clock;
+  parent_local_.ReleaseCheckpointsBefore(local_clock);
+  EXPECT_FALSE(parent_local_.get_child1().ModifiedSince(last_sync_local_));
+  EXPECT_FALSE(parent_local_.get_child2().ModifiedSince(last_sync_local_));
+
+  EXPECT_EQ(123, parent_remote_.get_child1().value());
+  EXPECT_EQ(0, parent_remote_.get_child2().value());
+}
+
+}  // namespace
+}  // namespace blimp