protobuf-net implicit contracts

Question

Does anyone have a working example where protobuf-net can be used as a drop-in replacement for BinaryFormatter? Is that even possible?

Actually I just need a serializer for one message type which looks like

public class A {
  public B[] Bs { get;set; }
  public C[] Cs { get;set; }
}

All types are defined in a different assembly and have a lot of properties. Is there an option to automatically generate proto contracts with all public properties included, for class A and other used types (B, C), so something like

var formatter = ProtoBuf.Serializer.CreateFormatter<A>()

just works?

Answer 1

Firstly, protobuf-net is not intended to be, and does not claim to be, a 100% drop in replacement for BinaryFormatter. It has slightly different features.

Would you be content to do a little reflection? Basically, there is support for ImplicitFields, but currently this is only available via [ProtoContract], and cannot be done conveniently via RuntimeTypeModel, which is a bit of a pain, and is on my list. Although, I should point out that I consider implicit-fields to be a bit risky, and it should only be done if you know the DTO innards won't change! But: to answer your question, you could iterate over the types you expect, and add them to the model manually:

static void Main()
{
    Prepare(typeof(A), typeof(B), typeof(C));
    // if you really want to use IFormatter...
    var formatter = RuntimeTypeModel.Default.CreateFormatter(typeof (A));
    var obj = new A {Bs = new B[] {new B()}};
    using (var ms = new MemoryStream())
    {
        formatter.Serialize(ms, obj);
        ms.Position = 0;
        var clone = formatter.Deserialize(ms);
    }
}
static void Prepare(params Type[] types)
{
    if(types != null) foreach(var type in types) Prepare(type);
}
static void Prepare(Type type)
{
    if(type != null && !RuntimeTypeModel.Default.IsDefined(type))
    {
        Debug.WriteLine("Preparing: " + type.FullName);
        // note this has no defined sort, so invent one
        var props = type.GetProperties(); 
        Array.Sort(props, (x, y) => string.Compare(
            x.Name, y.Name, StringComparison.Ordinal));
        var meta = RuntimeTypeModel.Default.Add(type, false);
        int fieldNum = 1;
        for(int i = 0 ; i < props.Length ; i++)
        {
            meta.Add(fieldNum++, props[i].Name);
        }

    }
}

Note that the use of IFormatter here is entirely unnecessary; you could also use RuntimeTypeModel.Default.Serialize(...) or Serializer.Serialize<T>(...).

As a footnote: I would advise defining the models more ... repeatably. For example:

RuntimeTypeModel.Default.Add(typeof(A)).Add("Bs", "Cs");
RuntimeTypeModel.Default.Add(typeof(B)).Add("Foo");
RuntimeTypeModel.Default.Add(typeof(C)).Add("Bar", "Blap", "Blop");

Answer 2

This is the final version of Prepare function I used:

static void Prepare(params Type[] types)
        {
            foreach (var type in types)
            {
                if (type != null && !RuntimeTypeModel.Default.IsDefined(type))
                {
                    if (type.Namespace.StartsWith("System"))
                        return;

                    Debug.WriteLine("Preparing: " + type.FullName);
                    // note this has no defined sort, so invent one
                    var props = type.GetProperties();
                    Array.Sort(props, (x, y) => string.Compare(
                        x.Name, y.Name, StringComparison.Ordinal));
                    var meta = RuntimeTypeModel.Default.Add(type, false);
                    int fieldNum = 1;
                    for (int i = 0; i < props.Length; i++)
                        if (props[i].CanWrite)
                        {                            
                            meta.Add(fieldNum++, props[i].Name);

                            if (!RuntimeTypeModel.Default.IsDefined(props[i].PropertyType))
                                if (props[i].PropertyType.HasElementType)
                                    Prepare(props[i].PropertyType.GetElementType()); //T[]
                                else if (props[i].PropertyType.IsGenericType)
                                    Prepare(props[i].PropertyType.GetGenericArguments()); //List<T>
                                else
                                    Prepare(props[i].PropertyType);
                        }
                }
            }
        }

If somebody is interested, this is the result of my benchmark (serialize + deserialize):

BinaryFormatter      10000 messages: 2.131s  5028 bytes/msg
Json.NET Bson        10000 messages: 1.679s  1071 bytes/msg
MetSys Bson          10000 messages: 1.581s  1035 bytes/msg
Protobuf             10000 messages: 0.145s   109 bytes/msg
MsgPack              10000 messages: 0.844s   106 bytes/msg

Notes:

• MetSys.Bson library does not handle decimal type well.
• MsgPack library has problems with read-only properties

Thanks Marc for your help and such a great library.