Nested Types in C# generated code causes serilization issue

[arun kumar]

All,

I am new to the usage of proto buffer with C sharp.. All I try is to get the input in XML and convert to C# object and then using google protobuf to serialize and deserialize. 

While converting the xml input to C# object, i am getting below because of nested types 

--------------------------------

Unhandled Exception: System.InvalidOperationException: There was an error reflecting type 'SCL.PC.ClientIdentifier'. ---> System.InvalidOperationException: SCL.PC.ClientIdentifier+Types cannot be serialized. Static types cannot be used as parameters or return types.

----------------------------------

It complains Types cannot be serialized. Please help me out 

[Marc Gravell]

And can we see some code that actually demonstrates this problem? That would really help here.

[arun kumar]

@Marc Gravell,

I auto-generated ".cs" files from each ".proto" file. . Whereever a message declared inside another message in proto, auto-generated cs file is generated as " Nested Types " and Types class is generated as static. (I guess , its how the generator defined)

And, I am trying to convert my xml data into CS object using XMLSerializer , it complains 

There was an error reflecting type 'SCL.PC.ClientIdentifier'. ---> System.InvalidOperationException: SCL.PC.ClientIdentifier+Types cannot be serialized. Static types cannot be used as parameters or return types.

All I am trying to do is ,

Converting XML data --> CS Object (IMessage) --> proto buf Serialize into stream 

Is there any way, to convert the xml data to IMessageObject.. I can see MessageParser has ParseJson object.  Likewise, anything available for xml ? 

 

   var serializer = new XmlSerializer(typeof(SCL.PC.ClientIdentifier));

Auto-Generated CS File :

public sealed partial class ClientIdentifier : pb::IMessage<ClientIdentifier> {

    private static readonly pb::MessageParser<ClientIdentifier> _parser = new pb::MessageParser<ClientIdentifier>(() => new ClientIdentifier());

    private pb::UnknownFieldSet _unknownFields;

    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]

    public static pb::MessageParser<ClientIdentifier> Parser { get { return _parser; } }

---

    #region Nested types

    /// <summary>Container for nested types declared in the ClientIdentifier message type.</summary>

    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]

    public static partial class Types {

      public enum Context {

        /// <summary>

        /// The client's identifier consists of a functional identifier (FID) in big-endian format.  Valid values range from 0x00000000 to 0xFFFFFFFF.

        /// </summary>

        [pbr::OriginalName("CFID")] Cfid = 0,

        /// <summary>

        /// The client's identifier consists of an ASCII-encoded serial number.

        /// </summary>

        [pbr::OriginalName("CSN")] Csn = 1,

      }

    }

    #endregion

  }

  #endregion

[Marc Gravell]

Can you show any of your XmlSerializer code here, so can understand it? I wouldn't expect the presence of a static type to break XmlSerializer, I admit! But also: protobuf code doesn't usually guarantee anything other than that it should work with the corresponding protobuf library.

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[Arun]

I am not able to initialize XmlSerializer class itself. It is failing saying "static Types cannot be serialized "

--

-- Arun

[Marc Gravell]

K, I took the tiny bit of code you posted, and added something that uses it with XmlSerializer, which basically meant implementing the interface (with NIEs) and adding:

using System;
using System.Xml.Serialization;
using pb = global::Google.Protobuf;
using pbr = global::Google.Protobuf.Reflection;

static class Program
{
    static void Main()
    {
        var ser = new XmlSerializer(typeof(ClientIdentifier));
        var obj = new ClientIdentifier();
        ser.Serialize(Console.Out, obj);
    }
}

---

And here's the thing: it works fine! So: if anyone is going to be able to help you here, you're going to need to meet us half way, by *showing us the code that doesn't work*.

--

Regards,

Marc

[Arun]

I did the same but it throwing the error.. I dont know what I am making mistake here . All my application are 3.5 .net version, 

Please find  actual CS file which I am trying to serialize. 

--

-- Arun

[Marc Gravell]

OK; that helps a bit; now, I've tried that with:

using Google.Protobuf;
using SCL.PC;
using System;
using System.Xml.Serialization;

static class P
{
    static void Main()
    {
        var obj = new ClientIdentifier
        {
            Context = ClientIdentifier.Types.Context.Cfid,
            Value = ByteString.CopyFrom(00, 01, 02, 03)
        };
        var ser = new XmlSerializer(obj.GetType());
        ser.Serialize(Console.Out, obj);
    }
}

---

I **cannot** reproduce the error you're seeing, but I *do* get another error, as shown below.

This tells me, ultimately, that your model *isn't going to work with XmlSerializer*. And that's fine - the code is only *tested* against the specific API it is designed for - Google's protobuf library in this case.

If XmlSerializer on some down-level version of .NET has *even more* problems, that's... unexpected, but not amazingly surprising.

If you want to use multiple serializers, usually you should have a serialization DTO model *per serializer* - one that is designed for use with that serializer.

However, there may be another option *if you want*. Google's generated code that is contributing to the pain here. Looking at your generated code, it looks like your schema is something like:

syntax = "proto3";
message ClientIdentifier {
  Context context = 1;
  bytes value = 2;
}
enum Context {
  Cfid = 0;
  Csn = 1;
}

Now, I can run that through protobuf-net's tooling (https://protogen.marcgravell.com/#g50e914251fc5d16b94cdc695c8ebac20) which gives me the simpler code (attached); if I then run that with the tweaked code:

static class P
{
    static void Main()
    {
        var obj = new ClientIdentifier
        {
            Context = Context.Cfid,
            Value = new byte[] { 00, 01, 02, 03 }
        };
        var ser = new XmlSerializer(obj.GetType());
        ser.Serialize(Console.Out, obj);
    }
}

it now all works fine in my version of .NET, and I'm *guessing* that it'll work in yours too. This is using a **different library**, specifically protobuf-net rather than Google.ProtoBuf, but: the key point here is that they both implement the same specification so should be interchangeable.

Up to you!

---

XmlSerializer exception.

Unhandled exception. System.InvalidOperationException: There was an error reflecting type 'SCL.PC.ClientIdentifier'.
 ---> System.InvalidOperationException: To be XML serializable, types which inherit from IEnumerable must have an implementation of Add(System.Object) at all levels of their inheritance hierarchy. Google.Protobuf.ByteString does not implement Add(System.Object).
   at System.Xml.Serialization.TypeScope.GetEnumeratorElementType(Type type, TypeFlags& flags)
   at System.Xml.Serialization.TypeScope.ImportTypeDesc(Type type, MemberInfo memberInfo, Boolean directReference)
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throwOnError)
   at System.Xml.Serialization.StructModel.GetPropertyModel(PropertyInfo propertyInfo)
   at System.Xml.Serialization.StructModel.GetFieldModel(MemberInfo memberInfo)
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportStructLikeMapping(StructModel model, String ns, Boolean openModel, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportElement(TypeModel model, XmlRootAttribute root, String defaultNamespace, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type, XmlRootAttribute root, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at P.Main() in C:\Users\marc\source\repos\ConsoleApp14\Program.cs:line 16

--

Regards,

Marc

[Arun]

Thanks Marc for your analysis..   Thanks for clarifying  me that generated code for my proto files does not suitable for all serialized API, I was thinking the other way. 

And, generated code through protobuf-net's tooling works very well . But, I am not able to generated code for all my proto's even though , "  my dependant proto files are in same folder " 

" Paths should be relative to the import paths, not rooted
Parameter name: name
   at Google.Protobuf.Reflection.FileDescriptorSet.Add(String name, Boolean includeInOutput, TextReader source, FileDescriptorProto fromFile)
   at protogen.Program.Main(String[] args) ".  

And , thanks for the solution by giving this clue , --> generated code *tested* against the specific API it is designed for - Google's protobuf library  .. 

I am converting my input to object via Google's protobuf library JSON parser and it works fine. It sounds may insane, This is what I doing now, xml --> json --> CS object --> serialize and writing to stream

Thanks for your help !!! Much appreciated ! 

--

-- Arun