Implement ProtoDatabase::GetEntry

components/leveldb_proto/proto_database_impl.h

Index: components/leveldb_proto/proto_database_impl.h
diff --git a/components/leveldb_proto/proto_database_impl.h b/components/leveldb_proto/proto_database_impl.h
index 4de21e9d4ff805232cfd2b3f33ad0aaa66602c5a..a062270dd780dcf6e3c055f7e3d726c1def1d9e6 100644
--- a/components/leveldb_proto/proto_database_impl.h
+++ b/components/leveldb_proto/proto_database_impl.h
@@ -53,6 +53,9 @@ class ProtoDatabaseImpl : public ProtoDatabase<T> {
       const typename ProtoDatabase<T>::UpdateCallback& callback) override;
   void LoadEntries(
       const typename ProtoDatabase<T>::LoadCallback& callback) override;
+  void GetEntry(
+      const std::string& key,
+      const typename ProtoDatabase<T>::GetCallback& callback) override;
   void Destroy(
       const typename ProtoDatabase<T>::DestroyCallback& callback) override;
 
@@ -97,6 +100,13 @@ void RunLoadCallback(const typename ProtoDatabase<T>::LoadCallback& callback,
 }
 
 template <typename T>
+void RunGetCallback(const typename ProtoDatabase<T>::GetCallback& callback,
+                     const bool* success,
+                     std::unique_ptr<T> entry) {
+  callback.Run(*success, *success ? std::move(entry) : nullptr);
+}
+
+template <typename T>
 void RunDestroyCallback(
     const typename ProtoDatabase<T>::DestroyCallback& callback,
     const bool* success) {
@@ -160,6 +170,24 @@ void LoadEntriesFromTaskRunner(LevelDB* database,
   }
 }
 
+template <typename T>
+void GetEntryFromTaskRunner(LevelDB* database,
+                            const std::string& key,
+                            T* entry,
+                            bool* success) {
+  DCHECK(success);
+  DCHECK(entry);
+
+  std::string serialized_entry;
+  *success = database->Get(key, &serialized_entry);
+
+  if (success && !entry->ParseFromString(serialized_entry)) {
+    *success = false;
+    DLOG(WARNING) << "Unable to parse leveldb_proto entry";
+    // TODO(cjhopman): Decide what to do about un-parseable entries.
+  }
+}
+
 }  // namespace
 
 template <typename T>
@@ -254,6 +282,25 @@ void ProtoDatabaseImpl<T>::LoadEntries(
                  base::Passed(&entries)));
 }
 
+template <typename T>
+void ProtoDatabaseImpl<T>::GetEntry(
+    const std::string& key,
+    const typename ProtoDatabase<T>::GetCallback& callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  bool* success = new bool(false);
+
+  std::unique_ptr<T> entry(new T());
+  // Get this pointer before entry is base::Passed() so we can use it below.
+  T* entry_ptr = entry.get();
+
+  task_runner_->PostTaskAndReply(
+      FROM_HERE,
+      base::Bind(GetEntryFromTaskRunner<T>,
+                 base::Unretained(db_.get()), key, entry_ptr, success),
+      base::Bind(RunGetCallback<T>, callback, base::Owned(success),
+                 base::Passed(&entry)));
+}
+
 }  // namespace leveldb_proto
 
 #endif  // COMPONENTS_LEVELDB_PROTO_PROTO_DATABASE_IMPL_H_