如何使用 protobuf-net 为反序列化目的嵌入类型信息？

Question

我希望能够以保留/嵌入类型信息的方式序列化 IMessage 的具体实例（类似于 Json.NET 中可用的内容），以便在反序列化时可以使用类型信息将这些具体实例具体化。我很清楚下面的反序列化方法不起作用。任何有关如何更改它们以使其正常工作的指导将不胜感激。

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);
  }
}

阐明一点：序列化的事件被写入持久性。阅读它们时，使用带有泛型参数的反序列化方法不是一个可行的选择（最好的办法是将类型信息指定为常规参数或使用通用协定，在这种情况下为 IMessage）。

Answer 1

有两种方法可以解决这个问题；我最不首选的选项是使用DynamicType=true - 这更昂贵并且限制了可移植性/版本控制，但不需要预先知道数据。我的 preferred 选项是为每个接口声明一个固定标识符，使其能够识别数据本身。如下所示。

对于信息，DontAskWrapper 是因为 Serialize() 使用 GetType()；这意味着它不会发现接口基础。我怀疑我可以改进它，但这适用于今天的 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);
        }
    }
}

---

没有属性也是一样的：

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);
}

请注意，在两种情况中，TypeModel 应该被缓存并重新使用；它是线程安全的，因此可以被不同的线程积极地并行使用，等等。