How to embed type information for de-/serialization purposes using protobuf-net?

I'd like to be able to serialize concrete instances of IMessage in such a way that the type information is retained/embedded (akin to what's available in e.g. Json.NET), so that upon deserialization that type information can be used to materialize those concrete instances. I'm well aware that the de-/serialization methods below don't work. Any guidance would be appreciated on how to change them so they do work.

public interface IMessage {}
public interface IEvent : IMessage {}
[ProtoContract]
public class DogBarkedEvent : IEvent {
  [ProtoMember(0)]
  public string NameOfDog { get; set; }
  [ProtoMember(1)]
  public int Times { get; set; }
}

//Somewhere in a class far, far away
public byte[] Serialize(IMessage message) {
  using(var stream = new MemoryStream()) {
    ProtoBuf.Serializer.Serialize<IMessage>(stream, message);
    return stream.ToArray();
  }
}

public IMessage Deserialize(byte[] data) {
  using(var stream = new MemoryStream(data)) {
    return ProtoBuf.Serializer.Deserialize<IMessage>(stream);
  }
}

To shed a little light: The serialized events get written to persistence. When reading them, u开发者_开发知识库sage of a deserialization method with a generic argument is not a viable option (the best that can be done is specifying the type information as a regular parameter or using the common contract, IMessage in this case).

There are two ways of approaching this; my least preferred option is to use DynamicType=true - this is more expensive and limits portability/versioning, but places no demands on knowing the data up-front. My preferred option is to declare a fixed identifier per interface, allowing it to recognise the data itself. This is shown below.

For info, DontAskWrapper is because Serialize() uses GetType(); which means it won't spot the interface base. I suspect I can improve that, but this works for today on v2:

using System.Diagnostics;
using System.IO;
using NUnit.Framework;
using ProtoBuf;
using ProtoBuf.Meta;

namespace Examples.Issues
{
    [TestFixture]
    public class SO7078615
    {
        [ProtoContract] // treat the interface as a contract
        // since protobuf-net *by default* doesn't know about type metadata, need to use some clue
        [ProtoInclude(1, typeof(DogBarkedEvent))]
        // other concrete messages here; note these can also be defined at runtime - nothing *needs*
        // to use attributes
        public interface IMessage { }
        public interface IEvent : IMessage { }

        [ProtoContract] // removed (InferTagFromName = true) - since you are already qualifying your tags
        public class DogBarkedEvent : IEvent
        {
            [ProtoMember(1)] // .proto tags are 1-based; blame google ;p
            public string NameOfDog { get; set; }
            [ProtoMember(2)]
            public int Times { get; set; }
        }

        [ProtoContract]
        class DontAskWrapper
        {
            [ProtoMember(1)]
            public IMessage Message { get; set; }
        }

        [Test]
        public void RoundTripAnUnknownMessage()
        {
            IMessage msg = new DogBarkedEvent
            {
                  NameOfDog = "Woofy", Times = 5
            }, copy;
            var model = TypeModel.Create(); // could also use the default model, but
            using(var ms = new MemoryStream()) // separation makes life easy for my tests
            {
                var tmp = new DontAskWrapper {Message = msg};
                model.Serialize(ms, tmp);
                ms.Position = 0;
                string hex = Program.GetByteString(ms.ToArray());
                Debug.WriteLine(hex);

                var wrapper = (DontAskWrapper)model.Deserialize(ms, null, typeof(DontAskWrapper));
                copy = wrapper.Message;
             }
            // check the data is all there
            Assert.IsInstanceOfType(typeof(DogBarkedEvent), copy);
            var typed = (DogBarkedEvent)copy;
            var orig = (DogBarkedEvent)msg;
            Assert.AreEqual(orig.Times, typed.Times);
            Assert.AreEqual(orig.NameOfDog, typed.NameOfDog);
        }
    }
}

And here's the same thing without attributes:

public interface IMessage { }
public interface IEvent : IMessage { }
public class DogBarkedEvent : IEvent
{
    public string NameOfDog { get; set; }
    public int Times { get; set; }
}
class DontAskWrapper
{
    public IMessage Message { get; set; }
}

[Test]
public void RoundTripAnUnknownMessage()
{
    IMessage msg = new DogBarkedEvent
    {
        NameOfDog = "Woofy",
        Times = 5
    }, copy;
    var model = TypeModel.Create();
    model.Add(typeof (DogBarkedEvent), false).Add("NameOfDog", "Times");
    model.Add(typeof (IMessage), false).AddSubType(1, typeof (DogBarkedEvent));
    model.Add(typeof (DontAskWrapper), false).Add("Message");


    using (var ms = new MemoryStream())
    {
        var tmp = new DontAskWrapper { Message = msg };
        model.Serialize(ms, tmp);
        ms.Position = 0;
        string hex = Program.GetByteString(ms.ToArray());
        Debug.WriteLine(hex);

        var wrapper = (DontAskWrapper)model.Deserialize(ms, null, typeof(DontAskWrapper));
        copy = wrapper.Message;
    }
    // check the data is all there
    Assert.IsInstanceOfType(typeof(DogBarkedEvent), copy);
    var typed = (DogBarkedEvent)copy;
    var orig = (DogBarkedEvent)msg;
    Assert.AreEqual(orig.Times, typed.Times);
    Assert.AreEqual(orig.NameOfDog, typed.NameOfDog);
}

Note that in both cases the TypeModel should be cached and re-used; it is thread-safe, so can be aggressively used in parallel by different threads, etc.