Available Game network protocol definition languages and code generation

Question

I've been looking for a good general purpose binary network protocol definition framework to provide a way to write real-time game servers and clients (think World Of Warcraft or Quake III) in multiple languages (e.g. Java backend server and iPhone front-end client written in Objective-C and Cocoa).

I want to support Java Flash clients, iPhone clients and C# clients on windows (and XNA clients on XBOX).

I'm looking for a way to efficiently send/receive messages over a TCP/IP or UDP socket stream connection. I'm not looking for something that can be sent over an HTTP Web Service, like JSON or XML marshalled Objects. Although Hessian's binary web service protocol is a very interesting solution

I want a network protocol format and client/server basic implementation that will allow a client to connect to a server and send any message in the defined protocol and receive any message in the protocol without having to bind to some kind of RPC endpoint. I want a generic stream of any message in my protocol incoming and outgoing. This is so that I can support things like the server sending all clients the positions of various entities in the game every 100 milliseconds.

Answer 1

I want to echo Bill K's suggestion. It's not hard to roll your own protocol.

For the iPhone side, have a look at AsyncSocket which support for delimiter based TCP packets built in, and it's not hard to build a solution which uses packet headers.

If you quickly want to have a testserver to play against AsyncSocket on the iPhone, you can look at Naga (for the java server part) which has ready made stuff both for delimiter based packets and packets with headers. Naga was partially written with networked games in mind.

Answer 2

I disagree with "roll your with simple delimited strings approach": question is, what exactly would be the benefit? Getting to write and maintain more code? The only reasons I could see would be lack of tool support (writing for some odd platform), or specific (very) hard performance or message size constraints. Or, sometimes, really wanting to write a format -- that's ok, but it must be an explicit reason.

Depending on exact needs I would suggest considering JSON, since it can read and write arbitrary messages; has good object binders for Java (just like xml), is easier to read than binary formats, and is all around "good enough" for many use cases.

If message size is very important, Protobuf can work well -- while its size is not always as small as gzipped alternatives (gzip+xml, gzip+json compress very well), it's usually close.

Answer 3

ASN.1 fits the definition of "good general purpose binary network protocol definition framework". It's also standardized by ITU-T, so there's a lot of existing tools and libraries for various languages.

The DER encoding is suitable for efficient network communications, the XER encoding for human-readable (and writable) permanent storage.

Answer 4

The network protocol frameworks I've found are as follows:

1. Google's Protocol Buffer - but it lacks support for things like sending/receiving arbitrary messages from your given protocol.
2. Apache Thrift - an interesting option but it is geared mainly towards RPC instead of generic game client/server socket type connections where the client or server can send messages at any time and not just in response to a client RPC request.
3. Raknet Multiplayer - Raknet provides full multiplayer network library (it's free for indie development with revenue under $250k)
4. Hessian Binary Web Service Protocol - is a HTTP web service binary protocol, it is well-suited to sending binary data without any need to extend the protocol with attachments.

Raknet provides a good game/simulation oriented multiplayer library.

Apache Thrift and Google's protocol buffers seem to be the simplest approaches to using in a game network protocol client/server architecture.

Hessian seems like a great fit if you want to create a web based game server with a Java or flash client using some type of server push technology like COMET. Hessian might provide a really interesting way to support real-time games on the web and even be able to host them on VM web solutions like Google's App engine or Amazon's EC2.

There's some discussion about using various protocol definition frameworks for games and other uses:

• Comparison of Various Serialization Frameworks
• Thrift vs Protocol Buffers - Thrift is declared the better framework because it has a fully supported RPC client/server implementation
• Using Protocol Buffers for client server Game API determining what type of message to decode
• Bi-Directional RPC using thrift

Answer 5

Because you want to use different languages and also because you want something clean/small, I suggest the protocol buffers of google. You need a pre-compile part for the RPC but I really think that's the best option when you begin to mix different languages.. Here's the link: http://code.google.com/apis/protocolbuffers/docs/overview.html

Answer 6

Why not implement UDP directly? Your question mostly mentions what you don't want.. What further form of abstration do you want on top of UDP? Download the Quake III sourcecode and see how they frame game updates over UDP?

The IP protocol has been designed to support multiple devices/OSes in a uniform way, isn't this what you ask for? What protocol has implementations across a huge range of systems, hmm, IP perhaps?

Answer 7

If you do go the route of writing your own protocol, you may want to read the answer I posted here.

In summary it discusses what you should think about when writing a protocol, and list a few tricks for versioning and maintaining backwards and forward compatibility.

Answer 8

Some time ago, I asked a pretty much related question here on SO, that you may want to check out for further pointers: Tools for experimental Protocol design/development?

Answer 9

DIS

Answer 10

If you are really concerned about multiple platforms and language, be sure to take into account endian issues. A binary protocol designed for this use must use network-byte-order, so it needs custom per-data-type serialization functions; you cannot just blindly push C structs into network buffers.

A common solution for this problem at game companies is to have protocol description language or specification in a simple format like XML or python or lua, and then have code generation for each target language that generated packet classes with both data structure and serialization. This specification could use a type system that starts with basic types, then extends to include game-specific types with semantic information, enumerations or more complex structures. For example a data file could look like:

Attack = {
  source = 'objectId',
  target = 'objectId',
  weapon = 'weapon::WEAP_MAIN',
  seed = 'int'
}

This could generate code like:

#define PT_ATTACK 10002

class PacketAttack : public Packet {
  public:
    PacketAttack () : m_packetType(PacketAttack::s_packetType) {}

    ObjectId m_source;
    ObjectId m_target;
    WeaponType m_weapon;
    int m_seed;

   bool Write(Stream* outStream) {
       Packet::Write(outStream);
       outStream << m_source;
       outStream << m_target;
       outStream << m_weapon
       outStream << m_seed;
   }

   bool Read(Stream* inStream);

 static const int s_packetType;
};

This does require some more infrastructure.. streams, packet base classes, safe serialization functions..