CODEWITHSUNDEEP
c#protocol-buffersprotobuf-net
ElRoro
ElRoro

Reputation: 213

Is there a way to deserialize an unknown object with a DescriptorProto?

I want to find a way to deserialize an unknown object with a DescriptorProto. When I serialize a Person, it's not a problem because I know its type. But when I deserialize, I don't know the type of object I receive so how with DescriptorProto, which define the structure of the proto, I can create an object like an ExpandObject?

This is my class : 

    class Person
    {
        [ProtoMember(1)]
        public int Id { get; set; }
        [ProtoMember(2)]
        public string Name { get; set; }
    }

I create an object Person with some values, serialize it and create my .proto :

var person = new Person
{
   Id = 12345,
   Name = "Fred"
};
using (var file = File.Create(@"C:\temp\protobuf\person.bin"))
{
   Serializer.Serialize(file, person);
   file.SetLength(file.Position);
}
string proto = Serializer.GetProto<Person>();
File.WriteAllText(@"C:\temp\protobuf\person.proto", proto);

After i create my FileDescriptor with this following command line :

protoc.exe person.proto --descriptor_set_out=person.pb

Finally i want to deserialize my person.bin with the description of person.pb like this :

byte[] payload = System.IO.File.ReadAllBytes(@"C:\temp\protobuf\person.pb");
FileDescriptorSet fileDescriptorSet = FileDescriptorSet.ParseFrom(payload);
FileDescriptorProto fileDescriptorProto = fileDescriptorSet.GetFile(0);
DescriptorProto requestDescriptor = fileDescriptorProto.GetMessageType(0);

/**
             requestDescriptor : 

            {name: "Person"
                field {
                  name: "Id"
                  number: 1
                  label: LABEL_OPTIONAL
                  type: TYPE_INT32
                  default_value: "0"
                }
                field {
                  name: "Name"
                  number: 2
                  label: LABEL_OPTIONAL
                  type: TYPE_STRING
                }
             }

             **/

object youhou;
using (var file = File.OpenRead(@"C:\temp\protobuf\person.bin"))
{
    //youhou = Serializer.Deserialize<Person>(file);
    // I don't know **Person** so i can't do this
}

At first, I wanted to create a Dictionary of string, object instead of Person but it's impossible to serialize it.

Upvotes: 2

Views: 1604

Answers (1)

Marc Gravell
Marc Gravell

Reputation: 1062855

I'm answering this specifically from the perspective of protobuf-net (tags); if you use the Google C# API, things will be different.

There's a couple of different things here; protobuf-net does not currently have an API to load things specifically taking a descriptor, however! It does have an Extensible base class which can be used to deserialize any arbitrary payload, along with the static methods on Extensible such as Extensible.GetValue<int>(1). So; that gives you the ability to read (or write) an arbitrary payload. You might need to create a non-abstract class to play with, but class Foo : Extensible {} should suffice, then Serializer.Deserialize<Foo>(source).

So; the second part is how to parse a descriptor. For that, see the protobuf-net.Reflection package. This includes the usual descriptor types you would expect, including FileDescriptorSet, so: you can use protobuf-net's regular Serializer.Deserialize<FileDescriptorSet>(source) to get a descriptor-set, from which you can pull apart the model in the usual way and discover the properties, to use with Extensible.

Upvotes: 2

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