Send typed objects through tcp or sockets

Question

I’m having trouble creating a network interface for a very simple game I’ve made in Xna. I would simply need to send objects through a TCP client / Socket. Ex: I have a class named “Player”. In every Player, there’s a field name “Info”, of type “PlayerInfo”. In the client / server, I would need to send every players’ info to every client except the one who sent it (obviously). This is a simple example, but I would need to do that with around 5 – 10 objects, plus sending the player updates (positions, actions …) Is there a simple way to do that with TCP / Sock? Note : I would rate my knowledge in C# and programming as 6/10, so you don’t need to explain everything if you have a solution (Ex : what’s the difference between a variable and a field). I also know about interfaces, libraries and so on… Thanks in advance!

Answer 1

I have one approach I would recommend and two lesser ones which are dependent on many things.

The first one implies you already know how to use the Socket class but have a lot of classes that you need to send through it.

From a transport point of view you should create / take into consideration just one very simple class. Let's call this class MyMessage:

public class MyMessage {
  public byte[] Data { get; set; }
}

Ok. From a TCP point of view all you need to do is make sure you're able to pass instances of this class around (from clients to the server and back). I will not dive into the details of doing that but I will point out that if you manage to do this you transform the nature of the TCP/IP connection from "byte-stream" to "message-stream". What that means is that normally, TCP/IP does not guarantee that chunks of data you send through a connection arrive at the destination in the same formations (they might get joined together or be split apart). The only thing it guarantees is that the bytes of all the chunks will eventually arrive in the same order at the other end of the connection (always).

Now that you have a message-stream up and running you could use .NET good old serialization to encapsulate any class instance inside the Data property. What that does is it serializes object graphs into bytes and vice-versa.

The way you do that (most commonly) is to use the standard library class: System.Runtime.Serialization.Formatters.Binary.BinaryFormatter which can be found in mscorlib.dll like so:

public static class Foo {

  public static Message Serialize(object anySerializableObject) {
    using (var memoryStream = new MemoryStream()) {
      (new BinaryFormatter()).Serialize(memoryStream, anySerializableObject);
      return new Message { Data = memoryStream.ToArray() };
    }
  }

  public static object Deserialize(Message message) {
    using (var memoryStream = new MemoryStream(message.Data))
      return (new BinaryFormatter()).Deserialize(memoryStream);
  }

}

The BinaryFormatter class is able to traverse the tree/graph of objects starting from the root / sentinel provided as the second argument of the Serialize (Stream, object) method and write all of the primitive values plus type information and relative position information to the provided stream. It is also able to do the exact reverse and deserialize an entire object graph as long as the provided stream is positioned accordingly to the place of a former object graph serialization.

There are a few catches here though: you will need to annotate all of your classes with [SerializableAttribute]. If your classes contain fields that are of other classes written by you, and you said they do:

[SerializableAttribute]
public class Player {
  public PlayerInfo Info; 
  //... etc 

then you need to annotate those with [SerializableAttribute] too:

[SerializableAttribute]
public class PlayerInfo { //... etc

If your classes contain fields that are of types written by others (say Microsoft) then those would better be already annotated with the attribute. Most of those which could be serialized already are. Primitive types are naturally serializable. Things that shouldn't be serialized are: FileStreams, Threads, Sockets, etc.

After making sure you have serializable classes all you need to do is serialize their instances, send them, receive them and deserialize them:

class Client {

  public static void SendMovement(Movement movement) {
    Message message = Foo.Serialize(movement);

    socketHelper.SendMessage(message);
  }
  public static void SendPlayer(Player player) {
    Message message = Foo.Serialize(player);

    socketHelper.SendMessage(message);
  }
  // .. etc

  public static void OnMessageReceivedFromServer(Message message) {
    object obj = Foo.Deserialize(message);
    if (obj is Movement)
      Client.ProcessOtherPlayersMovement(obj as Movement);
    else if (obj is Player)
      Client.ProcessOtherPlayersStatusUpdates(obj as Player);
    // .. etc
  }

  public static void ProcessOtherPlayersMovement(Movement movement) {
    //...
  }
  // .. etc

}

While on the server side:

class Server {

  public static void OnMessageReceived(Message message, SocketHelper from, SocketHelper[] all) {
    object obj = Foo.Deserialize( message );
    if (obj is Movement)
      Server.ProcessMovement( obj as Movement );
    else if (obj is Player)
      Server.ProcessPlayer( obj as Player );
    // .. etc

    foreach (var socketHelper in all)
      if (socketHelper != from)
        socketHelper.SendMessage( message );
  }
}

You will need a common assembly project (class library) to be referenced by both executable projects (client and server).

All your classes that need to be passed around will have to be written in that assembly so as that both the server and the client know how to understand each other at this very detailed level.

If the server needs not understand what is being said between the clients and only pass around messages (broadcasting one message to the other N-1 clients) then forget what I said about the common assembly. In that particular case, the server sees only bytes, while the clients have a deeper understanding of the actual messages being sent back and forth.

I said I had three approaches.

The second one involves .NET Remoting which can take a lot of work off your shoulders but which is hard to live with if you don't fully understand it. You can read about it on MSDN, here: http://msdn.microsoft.com/en-us/library/kwdt6w2k(v=vs.100).aspx

The third one would be better only if (now, or in the future) by XNA you mean Windows Phone or another implementation of XNA which does not support the BinaryFormatter class (ExEn with MonoTouch, or others). In that case you would have a hard time if you needed your server (a full blown, good old fashioned .NET application) to reference the common assembly I talked about and also have the game project (which would not be a good old fashioned .NET app but have a rather exotic nature) reference the exact same assembly.

In that case we would need to use and alternate form of serializing and deserializing your objects. You would also need to identically implement two sets of classes in the two worlds (.NET and WP7 or WP8). You could use some form of XML serializers which you would need to map to your classes explicitly (not as powerful as the BinaryFormatter class but more versatile in what the nature of the runtime that host your classes could be).

You can read about the XmlSerializer class on MSDN, here: http://msdn.microsoft.com/en-us/library/system.xml.serialization.xmlserializer.aspx

Answer 2

My personal quick-and-clean solution, using JSON.NET:

class JMessage
{
    public Type Type { get; set; }
    public JToken Value { get; set; }

    public static JMessage FromValue<T>(T value)
    {
        return new JMessage { Type = typeof(T), Value = JToken.FromObject(value) };
    }

    public static string Serialize(JMessage message)
    {
        return JToken.FromObject(message).ToString();
    }

    public static JMessage Deserialize(string data)
    {
        return JToken.Parse(data).ToObject<JMessage>();
    }
}

Now you can serialize your objects like so:

Player player = ...;
Enemy enemy = ...;
string data1 = JMessage.Serialize(JMessage.FromValue(player));
string data2 = JMessage.Serialize(JMessage.FromValue(enemy));

Send that data across the wire and then on the other end you can do something like:

string data = ...;
JMessage message = JMessage.Deserialize(data);
if (message.Type == typeof(Player))
{
    Player player = message.Value.ToObject<Player>();
}
else if (message.Type == typeof(Enemy))
{
    Enemy enemy = message.Value.ToObject<Enemy>();
}
//etc...