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FlatBuffers Introduction

Introduction

Google FlatBuffers is a cross-platform serialization library that can be used to efficiently serialize and deserialize data. FlatBuffers files are compact and efficient to access, making them ideal for use in games, mobile applications, and other performance-critical applications.

FlatBuffers uses a schema-based approach to serialization. Schemas are defined in a language-agnostic format called FlatBuffer IDL, which is similar to Protocol Buffers. Schemas define the structure of the data that will be serialized, including the names and types of fields.

Once a schema is defined, the FlatBuffers compiler can be used to generate code for a variety of programming languages, including C++, Python, Java, Go, and C#. This generated code provides a simple and efficient way to serialize and deserialize data in the defined schema.

FlatBuffers syntax

FlatBuffers syntax is a simple language that is used to define the structure of data that will be serialized. Schemas are defined in .fbs files, and each schema defines a single root type. The root type is the type of object that will be the top-level object in the serialized data.

Here is an example of a FlatBuffer schema for a simple monster object:

monster {
  name: string;
  hp: short;
  mana: short;
}

root_type monster;

This schema defines a monster object with three fields: name, hp, and mana. The root_type keyword specifies that the monster object is the root type of the schema.

In addition to the basic data types shown in the example above, FlatBuffers also supports a number of other data types, including:

  • Arrays
  • Vectors
  • Unions
  • Structs
  • Tables
  • Enums

FlatBuffers also supports a number of features that make it ideal for use in games and other performance-critical applications, such as:

  • Zero-copy serialization
  • Compact binary format
  • Support for multiple programming languages

Here is an example of a FlatBuffer schema for a more complex monster object:

monster {
  name: string;
  hp: short;
  mana: short;

  // An array of items.
  items: [ubyte];

  // A vector of weapons.
  weapons: [Weapon];

  // A union of equipment.
  equipment: Equipment;

  // A struct.
  position: Vec3;
}

enum Equipment {
  None,
  Sword,
  Shield
}

struct Vec3 {
  x: float;
  y: float;
  z: float;
}

This schema defines a monster object with a number of additional fields, including an array of items, a vector of weapons, a union of equipment, and a struct for the monster’s position.

Sure. Here is the rest of my answer on how to use FlatBuffers with C++ and Python:

Using FlatBuffers with C++

Once you have generated the C++ code for your schema, you can use it to serialize and deserialize FlatBuffers in your C++ code. To serialize a FlatBuffer, you use the flatbuffers::FlatBufferBuilder class. To deserialize a FlatBuffer, you use the flatbuffers::Verifier class.

Here is an example of how to serialize a monster object in C++:

#include "monster_generated.h"

int main() {
  // Create a new `monster` object.
  MyGame::Monster monster;
  monster.name = "My Monster";
  monster.hp = 100;
  monster.mana = 50;

  // Serialize the `monster` object to a FlatBuffer buffer.
  flatbuffers::FlatBufferBuilder builder;
  flatbuffers::Offset<MyGame::Monster> monsterOffset = MyGame::Monster::Pack(builder, &monster);

  // Finish the buffer and get a pointer to the serialized data.
  uint8_t* buffer = builder.GetBufferPointer();

  // ...

  // To deserialize the `monster` object, you would use the following code:

  // Create a `monster` object from the serialized data.
  MyGame::Monster monster;
  flatbuffers::Verifier verifier(buffer, builder.GetSize());
  if (verifier.VerifyBuffer<MyGame::Monster>(monsterOffset)) {
    // The buffer is valid, and the `monster` object is now populated.
  } else {
    // The buffer is invalid.
  }

  // ...

  // You can also use the FlatBuffers generated code to access the fields of a FlatBuffer object directly. For example, to get the name of the monster object, you would use the following code:

  std::string monsterName = monster.name()->str();

  // ...
}

Using FlatBuffers with Python

To use FlatBuffers in Python, you first need to install the FlatBuffers Python library. Once you have installed the library, you can use it to serialize and deserialize FlatBuffers in your Python code.

Here is an example of how to serialize a monster object in Python:

import monster_generated as fbs

def main():
  # Create a new `monster` object.
  monster = fbs.Monster()
  monster.name = "My Monster"
  monster.hp = 100
  monster.mana = 50

  # Serialize the `monster` object to a FlatBuffer buffer.
  builder = fbs.FlatBufferBuilder()
  monster_offset = fbs.Monster.Pack(builder, monster)

  # Finish the buffer and get a pointer to the serialized data.
  buffer = builder.GetBufferPointer()

  # ...

  # To deserialize the `monster` object, you would use the following code:

  # Create a `monster` object from the serialized data.
  monster = fbs.Monster()
  verifier = fbs.Verifier(buffer, builder.GetSize())
  if verifier.VerifyBuffer(monster, monster_offset):
    # The buffer is valid, and the `monster` object is now populated.
  else:
    # The buffer is invalid.

  # You can also use the FlatBuffers generated code to access the fields of a FlatBuffer object directly. For example, to get the name of the monster object, you would use the following code:

  monster_name = monster.name

  # ...

if __name__ == "__main__":
  main()

High level interface

there are other classes that can be used to serialize and deserialize FlatBuffers, in addition to flatbuffers::FlatBufferBuilder and flatbuffers::Verifier.

  • flatbuffers::FlatBufferSerializer: This class provides a higher-level interface for serializing FlatBuffers. It allows you to serialize FlatBuffer objects to a variety of output streams, such as files, memory buffers, and network sockets.
  • flatbuffers::FlatBufferDeserializer: This class provides a higher-level interface for deserializing FlatBuffers. It allows you to deserialize FlatBuffer objects from a variety of input streams, such as files, memory buffers, and network sockets.
  • flatbuffers::FlatBufferRoot: This class is a base class for all FlatBuffer root types. It provides helper methods for accessing the fields of a FlatBuffer object and for serializing and deserializing the object.

Here is an example of how to use the flatbuffers::FlatBufferSerializer class to serialize a monster object to a file:

#include "monster_generated.h"

int main() {
  // Create a new `monster` object.
  MyGame::Monster monster;
  monster.name = "My Monster";
  monster.hp = 100;
  monster.mana = 50;

  // Create a FlatBuffer serializer.
  flatbuffers::FlatBufferSerializer serializer;

  // Serialize the `monster` object to the file "monster.bin".
  serializer.SerializeToFile("monster.bin", &monster);

  return 0;
}

Here is an example of how to use the flatbuffers::FlatBufferDeserializer class to deserialize a monster object from a file:

#include "monster_generated.h"

int main() {
  // Create a FlatBuffer deserializer.
  flatbuffers::FlatBufferDeserializer deserializer;

  // Deserialize the `monster` object from the file "monster.bin".
  MyGame::Monster monster;
  if (!deserializer.DeserializeFromFile("monster.bin", &monster)) {
    // The file could not be deserialized.
    return 1;
  }

  // The `monster` object is now populated with the data from the file.

  return 0;
}

Here is an example of how to use the flatbuffers::FlatBufferRoot class to access the fields of a monster object:

#include "monster_generated.h"

int main() {
  // Create a `monster` object.
  MyGame::Monster monster;
  monster.name = "My Monster";
  monster.hp = 100;
  monster.mana = 50;

  // Get the name of the monster object.
  std::string monsterName = monster.name()->str();

  // Get the HP of the monster object.
  int monsterHp = monster.hp();

  // Get the mana of the monster object.
  int monsterMana = monster.mana();

  // ...
}

The flatbuffers::FlatBufferSerializer, flatbuffers::FlatBufferDeserializer, and flatbuffers::FlatBufferRoot classes provide a more convenient and flexible way to serialize and deserialize FlatBuffers than the flatbuffers::FlatBufferBuilder and flatbuffers::Verifier classes. However, the flatbuffers::FlatBufferBuilder and flatbuffers::Verifier classes are still useful for more advanced tasks, such as serializing and deserializing partial FlatBuffers.

How to include

To include or import other FlatBuffers files in a .fbs file, you can use the include directive. The include directive allows you to reference the contents of another .fbs file, as if those contents were defined in the current file.

To use the include directive, simply add a line to the top of your .fbs file that looks like this:

include "other_file.fbs";

This will tell the FlatBuffers compiler to include the contents of the file other_file.fbs in the current file.

You can use the include directive to include any type of FlatBuffers definition, including root types, enums, unions, structs, and tables. You can also use the include directive to include other .fbs files that are nested within folders.

Here is an example of a .fbs file that includes another .fbs file:

// monster.fbs

include "weapon.fbs";

monster {
  name: string;
  hp: short;
  mana: short;
  weapon: Weapon;
}

root_type monster;

This .fbs file includes the weapon.fbs file, which defines a Weapon type. The monster type in this file has a field called weapon, which is of type Weapon.

When you compile the monster.fbs file, the FlatBuffers compiler will automatically include the contents of the weapon.fbs file. This means that you will be able to use the Weapon type in your code, as if it were defined in the monster.fbs file.

The include directive is a powerful tool that allows you to reuse FlatBuffers definitions across multiple files. This can make your code more modular and easier to maintain.

Project

Here are some famous projects that use FlatBuffers:

  • Cocos2d-x: Cocos2d-x is a popular open source game engine that uses FlatBuffers to serialize all of its game data. FlatBuffers helps Cocos2d-x to achieve high performance and low memory usage.
  • Facebook: Facebook uses FlatBuffers for client-server communication in their Android app. FlatBuffers helps Facebook to reduce the size of their serialized data and improve the performance of their app.
  • Google: Google uses FlatBuffers in a variety of projects, including the Google Play Games SDK, the TensorFlow Serving system, and the Android browser. FlatBuffers helps Google to achieve high performance and low memory usage in these projects.
  • Netflix: Netflix uses FlatBuffers to serialize the data that is streamed to their devices. FlatBuffers helps Netflix to reduce the size of their streamed data and improve the performance of their streaming service.
  • Spotify: Spotify uses FlatBuffers to serialize the data that is stored on their users’ devices. FlatBuffers helps Spotify to reduce the size of the stored data and improve the performance of their app.

These are just a few examples of the many famous projects that use FlatBuffers. FlatBuffers is a popular choice for serialization because it is fast, efficient, and easy to use.

Here are some of the reasons why these projects use FlatBuffers instead of other serialization and deserialization methods:

  • Performance: FlatBuffers is very fast, both for serialization and deserialization. This is important for high-performance applications such as games and streaming services.
  • Efficiency: FlatBuffers produces very compact serialized data. This is important for applications that need to reduce the size of their data, such as mobile apps and streaming services.
  • Ease of use: FlatBuffers is easy to use and integrate into existing code. This is important for projects of all sizes.

In addition to the above, FlatBuffers also has a number of other features that make it a good choice for serialization, including:

  • Zero-copy serialization: FlatBuffers uses zero-copy serialization, which means that there is no need to copy data between buffers when serializing or deserializing data. This improves performance and reduces memory usage.
  • Compact binary format: FlatBuffers produces a very compact binary format, which reduces the size of serialized data.
  • Support for multiple programming languages: FlatBuffers is supported by a wide range of programming languages, including C++, Java, Python, Go, and C#. This makes it easy to use FlatBuffers in projects that use multiple programming languages.

Compare with Protobuf

Protocol buffers (protobuf) is another popular serialization library that is similar to FlatBuffers. However, there are a few reasons why some projects choose to use FlatBuffers instead of protobuf:

  • Performance: FlatBuffers is generally faster than protobuf for both serialization and deserialization. This is because FlatBuffers uses a zero-copy serialization mechanism, while protobuf does not.
  • Efficiency: FlatBuffers produces more compact serialized data than protobuf. This is because FlatBuffers uses a more efficient binary encoding format.
  • Ease of use: FlatBuffers is generally easier to use than protobuf. This is because FlatBuffers has a simpler syntax and does not require as much configuration.

However, protobuf also has some advantages over FlatBuffers:

  • Maturity: Protobuf is a more mature technology than FlatBuffers. It has been around for longer and has a larger community of users and contributors.
  • Language support: Protobuf supports a wider range of programming languages than FlatBuffers.
  • Schema evolution: Protobuf has better support for schema evolution than FlatBuffers. This means that it is easier to make changes to protobuf schemas without breaking existing applications.

Ultimately, the best choice for serialization will depend on the specific needs of the project. If performance and efficiency are the top priorities, then FlatBuffers is a good choice. If maturity, language support, and schema evolution are more important, then protobuf is a good choice.

Here are some specific examples of when a project might choose to use FlatBuffers instead of protobuf:

  • A high-performance game that needs to minimize serialization and deserialization overhead.
  • A mobile app that needs to reduce the size of its data.
  • A project that needs to be easy to maintain and integrate with existing code.

Here are some specific examples of when a project might choose to use protobuf instead of FlatBuffers:

  • A project that needs to support a wide range of programming languages.
  • A project that needs to frequently evolve its schema.
  • A project that needs to be compatible with existing protobuf applications.

Overall, both FlatBuffers and protobuf are excellent serialization libraries. The best choice for a project will depend on its specific needs.

Summary

FlatBuffers is a powerful and efficient serialization library that can be used in a variety of programming languages. By using FlatBuffers, you can reduce the size of your serialized data and improve the performance of your applications.