protobuf-net 是否支持 C# 9 位置记录类型？

Question

I'm trying to use protobuf-net with C# positional record types, and I've encountered this exception:

10:18:48.048 [EROR] #010 (Microsoft.AspNetCore.Server.Kestrel) Connection id ""0HM4NDHMUB3C6"", Request id ""0HM4NDHMUB3C6:00000003"": An unhandled exception was thrown by the application.
Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. ProtoException: No parameterless constructor found for Bidirectional.Demo.Common.Contracts.Server.GetServerProcessI
nfo.GetServerProcessInfoResponse", DebugException="ProtoBuf.ProtoException: No parameterless constructor found for Bidirectional.Demo.Common.Contracts.Server.GetServerProcessInfo.GetServerProcessInfoResp
onse
   at ProtoBuf.Internal.ThrowHelper.ThrowProtoException(String message, Exception inner) in /_/src/protobuf-net.Core/Internal/ThrowHelper.cs:line 70
   at ProtoBuf.Meta.TypeModel.ThrowCannotCreateInstance(Type type, Exception inner) in /_/src/protobuf-net.Core/Meta/TypeModel.cs:line 1666
   at proto_12(State& , GetServerProcessInfoResponse )
   at ProtoBuf.Internal.Serializers.SimpleCompiledSerializer`1.ProtoBuf.Serializers.ISerializer<T>.Read(State& state, T value)
   at ProtoBuf.ProtoReader.State.ReadAsRoot[T](T value, ISerializer`1 serializer)
   at ProtoBuf.ProtoReader.State.DeserializeRoot[T](T value, ISerializer`1 serializer)
   at ProtoBuf.Meta.TypeModel.Deserialize[T](ReadOnlySequence`1 source, T value, Object userState)
   at ProtoBuf.Grpc.Configuration.ProtoBufMarshallerFactory.ContextualDeserialize[T](DeserializationContext context)

This is what GetServerProcessInfoResponse looks like:

[ProtoContract]
public record GetServerProcessInfoResponse(
    [property: ProtoMember(1)] TimeSpan TotalProcessorTime,
    [property: ProtoMember(2)] TimeSpan UserProcessorTime,
    [property: ProtoMember(3)] TimeSpan PrivilegedProcessorTime,
    [property: ProtoMember(4)] string CurrentMemoryUsage,
    [property: ProtoMember(5)] string PeakMemoryUsage,
    [property: ProtoMember(6)] int ActiveThreads
);

The code works fine if I change GetServerProcessInfoResponse into a regular C# class with gettable and settable properties. I was hoping however that records could work too, because they avoid a whole lot of nullability warnings. System.Text.Json has support for deserializing records for example, which has to work against the same limitations.

I couldn't find anything in the docs, issues or here on StackOverflow, so maybe I'm bad at searching, or maybe the answer isn't out there yet. :-)

The protobuf-net repository also doesn't seem to have any unit tests that try to serialize / deserialize a c# record, it only contains "RecordTypeTests" which seems to be checking if records can be cloned?

Answer 1

Yes, in two different ways.

With your existing code, the simplest option is to tell protobuf-net to perform voodoo to get past the fact there is no available constructor; fortunately, this is simple:

[ProtoContract(SkipConstructor = true)]
public record GetServerProcessInfoResponse(
    [property: ProtoMember(1)] TimeSpan TotalProcessorTime,
    [property: ProtoMember(2)] TimeSpan UserProcessorTime,
    [property: ProtoMember(3)] TimeSpan PrivilegedProcessorTime,
    [property: ProtoMember(4)] string CurrentMemoryUsage,
    [property: ProtoMember(5)] string PeakMemoryUsage,
    [property: ProtoMember(6)] int ActiveThreads
);

However, With recent builds of the v3 code, it will also infer what you are trying to do specifically in the case of purely positional records , ie the following should work too, and mean more or less the same thing (as a minute detail: it will actually use the constructor in this case, instead of creating an instance via voodoo and then stomping the values):

public record GetServerProcessInfoResponse(
    TimeSpan TotalProcessorTime,
    TimeSpan UserProcessorTime,
    TimeSpan PrivilegedProcessorTime,
    string CurrentMemoryUsage,
    string PeakMemoryUsage,
    int ActiveThreads
);

Answer 2

Records will work , and as comments and Marc's answer here shows, the issue is with the constructor, not that it is a record type.

Record types are just classes, with compiler-generated code and attributes.

To show a different way to get to where you want, you could just add the parameterless constructor. Yes, it's a little bit more work than just the naive record declaration, but if you're stuck with a version of ProtoBuf that doesn't support parameterized constructors, and you don't want to bypass the constructors like Marc showed, here's a different option:

[ProtoContract]
public record GetServerProcessInfoResponse(
    [property: ProtoMember(1)] TimeSpan TotalProcessorTime,
    [property: ProtoMember(2)] TimeSpan UserProcessorTime,
    [property: ProtoMember(3)] TimeSpan PrivilegedProcessorTime,
    [property: ProtoMember(4)] string CurrentMemoryUsage,
    [property: ProtoMember(5)] string PeakMemoryUsage,
    [property: ProtoMember(6)] int ActiveThreads
)
{
    public GetServerProcessInfoResponse() : this(default, default, default, default, default, default) { }
}

This lets you use the basic positional record declaration, but allows you to add the parameterless constructor that ProtoBuf <3 wants.