[Sync] Introduce EntityData and EntityMetadata.

BUG=536895

Review URL: https://codereview.chromium.org/1421663004

Cr-Commit-Position: refs/heads/master@{#356899}

2 files changed, 323 insertions, 0 deletions

diff --git a/sync/internal_api/public/util/proto_value_ptr.h b/sync/internal_api/public/util/proto_value_ptr.h
new file mode 100644
index 0000000..540abd7
--- /dev/null
+++ b/sync/internal_api/public/util/proto_value_ptr.h
@@ -0,0 +1,115 @@
+// Copyright 2015 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_SYNCABLE_ENTRY_PROTO_FIELD_PTR_H_
+#define SYNC_SYNCABLE_ENTRY_PROTO_FIELD_PTR_H_
+
+#include "base/gtest_prod_util.h"
+#include "base/memory/ref_counted.h"
+#include "sync/protocol/attachments.pb.h"
+#include "sync/protocol/sync.pb.h"
+
+namespace syncer_v2 {
+class EntityData;
+}
+
+namespace syncer {
+namespace syncable {
+
+// Default traits struct for ProtoValuePtr - adapts a
+// ::google::protobuf::MessageLite derived type to be used with ProtoValuePtr.
+template <typename T>
+struct DefaultProtoValuePtrTraits {
+  // Deep copy the value from |src| to |dest|.
+  static void CopyValue(T* dest, const T& src) { dest->CopyFrom(src); }
+  // Parse the value from BLOB.
+  static void ParseFromBlob(T* dest, const void* blob, int length) {
+    dest->ParseFromArray(blob, length);
+  }
+  // True if the |value| is a non-default value.
+  static bool HasValue(const T& value) { return value.ByteSize() > 0; }
+  // Default value for the type.
+  static const T& DefaultValue() { return T::default_instance(); }
+};
+
+// This is a smart pointer to a ::google::protobuf::MessageLite derived type
+// that implements immutable, shareable, copy-on-write semantics.
+//
+// Additionally this class helps to avoid storing multiple copies of default
+// instances of the wrapped type.
+//
+// Copying ProtoValuePtr results in ref-counted sharing of the
+// underlying wrapper and the value contained in the wrapper.
+//
+// The public interface includes only immutable access to the wrapped value.
+// The only way to assign a value to ProtoValuePtr is through a
+// private SetValue function which is called from EntryKernel. That results
+// in stopping sharing the previous value and creating a wrapper to the new
+// value.
+template <typename T, typename Traits = DefaultProtoValuePtrTraits<T>>
+class ProtoValuePtr {
+ private:
+  // Immutable shareable ref-counted wrapper that embeds the value.
+  class Wrapper : public base::RefCountedThreadSafe<Wrapper> {
+   public:
+    Wrapper(const T& value) { Traits::CopyValue(&value_, value); }
+    const T& value() const { return value_; }
+    // Create wrapper by deserializing a BLOB.
+    static Wrapper* ParseFromBlob(const void* blob, int length) {
+      Wrapper* wrapper = new Wrapper;
+      Traits::ParseFromBlob(&wrapper->value_, blob, length);
+      return wrapper;
+    }
+
+   private:
+    friend class base::RefCountedThreadSafe<Wrapper>;
+    Wrapper() {}
+    ~Wrapper() {}
+
+    T value_;
+  };
+
+  ProtoValuePtr() {}
+  ~ProtoValuePtr() {}
+
+ public:
+  const T& value() const {
+    return wrapper_ ? wrapper_->value() : Traits::DefaultValue();
+  }
+
+  const T* operator->() const {
+    const T& wrapped_instance = value();
+    return &wrapped_instance;
+  }
+
+ private:
+  friend class syncer_v2::EntityData;
+  friend struct EntryKernel;
+  FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, BasicTest);
+  FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, SharingTest);
+  FRIEND_TEST_ALL_PREFIXES(ProtoValuePtrTest, ParsingTest);
+
+  void set_value(const T& new_value) {
+    if (Traits::HasValue(new_value)) {
+      wrapper_ = new Wrapper(new_value);
+    } else {
+      // Don't store default value.
+      wrapper_ = nullptr;
+    }
+  }
+
+  void load(const void* blob, int length) {
+    wrapper_ = Wrapper::ParseFromBlob(blob, length);
+  }
+
+  scoped_refptr<Wrapper> wrapper_;
+};
+
+typedef ProtoValuePtr<sync_pb::EntitySpecifics> EntitySpecificsPtr;
+typedef ProtoValuePtr<sync_pb::AttachmentMetadata> AttachmentMetadataPtr;
+
+}  // namespace syncable
+}  // namespace syncer
+
+#endif  // SYNC_SYNCABLE_ENTRY_PROTO_FIELD_PTR_H_
diff --git a/sync/internal_api/public/util/proto_value_ptr_unittest.cc b/sync/internal_api/public/util/proto_value_ptr_unittest.cc
new file mode 100644
index 0000000..4479b5d
--- /dev/null
+++ b/sync/internal_api/public/util/proto_value_ptr_unittest.cc
@@ -0,0 +1,208 @@
+// Copyright 2015 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 "sync/internal_api/public/util/proto_value_ptr.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace syncer {
+namespace syncable {
+
+namespace {
+
+// TestValue class is used as a template argument with ProtoValuePtr<T>
+class TestValue {
+ public:
+  TestValue() : value_(0), is_initialized_(false), is_default_(false) {}
+  explicit TestValue(int value)
+      : value_(value), is_initialized_(true), is_default_(false) {}
+
+  ~TestValue() { g_delete_count++; }
+
+  static void ResetCounters() {
+    g_copy_count = 0;
+    g_parse_count = 0;
+    g_delete_count = 0;
+  }
+
+  static int copy_count() { return g_copy_count; }
+  static int parse_count() { return g_parse_count; }
+  static int delete_count() { return g_delete_count; }
+
+  int value() const { return value_; }
+  bool is_initialized() const { return is_initialized_; }
+  bool is_default() const { return is_default_; }
+
+  // TestValue uses the default traits struct with ProtoValuePtr<TestValue>.
+  // The following 4 functions are expected by the traits struct to exist
+  // in this class.
+  void CopyFrom(const TestValue& from) {
+    // Expected to always copy from an initialized instance
+    // to an uninitialized one.
+    // Not expected either value to be default.
+    ASSERT_FALSE(is_initialized());
+    ASSERT_FALSE(is_default());
+    ASSERT_TRUE(from.is_initialized());
+    ASSERT_FALSE(from.is_default());
+    value_ = from.value();
+    is_initialized_ = true;
+    g_copy_count++;
+  }
+
+  void ParseFromArray(const void* blob, int length) {
+    // Similarly to CopyFrom this is expected to be called on
+    // an uninitialized instance.
+    ASSERT_FALSE(is_initialized());
+    ASSERT_FALSE(is_default());
+    // The blob is an address of an integer
+    ASSERT_EQ(static_cast<int>(sizeof(int)), length);
+    value_ = *static_cast<const int*>(blob);
+    is_initialized_ = true;
+    g_parse_count++;
+  }
+
+  int ByteSize() const { return is_initialized() ? sizeof(int) : 0; }
+
+  static const TestValue& default_instance() {
+    static TestValue default_instance;
+    default_instance.is_default_ = true;
+    return default_instance;
+  }
+
+ private:
+  static int g_copy_count;
+  static int g_parse_count;
+  static int g_delete_count;
+
+  int value_;
+  bool is_initialized_;
+  bool is_default_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestValue);
+};
+
+// Static initializers.
+int TestValue::g_copy_count = 0;
+int TestValue::g_parse_count = 0;
+int TestValue::g_delete_count = 0;
+
+}  // namespace
+
+typedef ProtoValuePtr<TestValue> TestPtr;
+
+class ProtoValuePtrTest : public testing::Test {
+ public:
+  void SetUp() override { TestValue::ResetCounters(); }
+
+  static bool WrappedValuesAreShared(const TestPtr& ptr1, const TestPtr& ptr2) {
+    const TestValue& wrapped_value_1 = ptr1.value();
+    const TestValue& wrapped_value_2 = ptr2.value();
+    // Compare addresses.
+    return &wrapped_value_1 == &wrapped_value_2;
+  }
+};
+
+TEST_F(ProtoValuePtrTest, BasicTest) {
+  // Basic assignment and default value.
+  TestValue t1(1);
+  {
+    TestPtr ptr1;
+    EXPECT_TRUE(ptr1->is_default());
+
+    ptr1.set_value(t1);
+    EXPECT_FALSE(ptr1->is_default());
+    EXPECT_EQ(1, ptr1->value());
+  }
+
+  EXPECT_EQ(1, TestValue::copy_count());
+  EXPECT_EQ(1, TestValue::delete_count());
+}
+
+TEST_F(ProtoValuePtrTest, SharingTest) {
+  // Sharing between two pointers.
+  TestValue empty;
+  TestValue t2(2);
+  TestValue t3(3);
+  {
+    TestPtr ptr2;
+    TestPtr ptr3;
+
+    EXPECT_TRUE(ptr2->is_default());
+    EXPECT_TRUE(ptr3->is_default());
+    EXPECT_EQ(0, TestValue::copy_count());
+    EXPECT_EQ(0, TestValue::delete_count());
+
+    ptr2.set_value(t2);
+    EXPECT_EQ(1, TestValue::copy_count());
+    EXPECT_EQ(0, TestValue::delete_count());
+
+    ptr3 = ptr2;
+    // Both |ptr2| and |ptr3| now share the same value "2".
+    // No additional copies expected.
+    EXPECT_EQ(1, TestValue::copy_count());
+    EXPECT_EQ(0, TestValue::delete_count());
+    EXPECT_FALSE(ptr3->is_default());
+    EXPECT_EQ(2, ptr3->value());
+    EXPECT_TRUE(WrappedValuesAreShared(ptr2, ptr3));
+
+    // Stop sharing - |ptr2| is "3" and |ptr3| is still "2".
+    ptr2.set_value(t3);
+    EXPECT_FALSE(WrappedValuesAreShared(ptr2, ptr3));
+    EXPECT_EQ(3, ptr2->value());
+    EXPECT_EQ(2, ptr3->value());
+    // No extra copies or deletions expected.
+    EXPECT_EQ(2, TestValue::copy_count());
+    EXPECT_EQ(0, TestValue::delete_count());
+
+    // |ptr3| still has the old value.
+    EXPECT_EQ(2, ptr3->value());
+
+    // Share again. Both values are "3".
+    ptr3 = ptr2;
+    EXPECT_EQ(3, ptr3->value());
+    // This should have resulted in deleting the wrapper for the value "2".
+    EXPECT_EQ(1, TestValue::delete_count());
+    // No extra copies expected.
+    EXPECT_EQ(2, TestValue::copy_count());
+
+    // Set default value to one of the pointers.
+    ptr2.set_value(empty);
+    EXPECT_TRUE(ptr2->is_default());
+    // The other one is still intact.
+    EXPECT_FALSE(ptr3->is_default());
+    EXPECT_EQ(3, ptr3->value());
+    // No extra copies or deletions expected.
+    EXPECT_EQ(1, TestValue::delete_count());
+    EXPECT_EQ(2, TestValue::copy_count());
+
+    // Copy the default value between the pointers.
+    ptr3 = ptr2;
+    EXPECT_TRUE(ptr3->is_default());
+    // The wrapper for "3" is now deleted.
+    EXPECT_EQ(2, TestValue::delete_count());
+  }
+
+  // No extra deletions expected upon leaving the scope.
+  EXPECT_EQ(2, TestValue::delete_count());
+}
+
+TEST_F(ProtoValuePtrTest, ParsingTest) {
+  int v1 = 21;
+
+  {
+    TestPtr ptr1;
+
+    ptr1.load(&v1, sizeof(int));
+
+    EXPECT_EQ(1, TestValue::parse_count());
+    EXPECT_EQ(0, TestValue::copy_count());
+
+    EXPECT_EQ(v1, ptr1->value());
+  }
+
+  EXPECT_EQ(1, TestValue::delete_count());
+}
+
+}  // namespace syncable
+}  // namespace syncer