.Net WebAPI returning Protocol Buffer: Protocol message contained a tag with an invalid wire type

Question

I have a *.proto file that defines two messages: MyRequest and MyResponse. This is defined in a common .NET Standard 2.0 library and uses the following NuGet packages:

    <PackageReference Include="Google.Protobuf" Version="3.18.0" />
    <PackageReference Include="Grpc" Version="2.40.0" />
    <PackageReference Include="Grpc.Tools" Version="2.40.0">

The Server

I have a .NET Framework (4.8) WebAPI and the following Action Method:

[HttpPost]
public async Task<IHttpActionResult> FetchSomeData()
{
    using (var ms = new MemoryStream(2048))
    {
        await content.CopyToAsync(ms).ConfigureAwait(false);
        byte[] bytes = ms.ToArray();
        MyRequest request = MyRequest.Parser.ParseFrom(bytes);

        MyResponse response = await SomeMethodAsync(request).ConfigureAwait(false);
        byte[] responseByteArray = response.ToByteArray();
        return this.Ok(responseByteArray);
    }
}

So this successfully receives a MyRequest object sent via HttpPost, and based on the data in that object, generates a MyResponse object and returns that.

The Client

I have a .Net 5 client that consumes this service with an HttpClient:

// Prepare Request
MyRequest webRequest = new() { ... };
byte[] byteArray = webRequest.ToByteArray();
ByteArrayContent byteContent = new(byteArray);

// Send data
HttpClient client = this.HttpClientFactory.CreateClient("Blah");
HttpResponseMessage webResponse = await client.PostAsync(new Uri("...", UriKind.Relative), byteContent).ConfigureAwait(false);

// Read response
HttpContent content = webResponse.Content;
byte[] webMethodResponseAsByteArray = await content.ReadAsByteArrayAsync().ConfigureAwait(false);
MyResponse webMethodResponse = MyResponse.Parser.ParseFrom(webMethodResponseAsByteArray);

The HttpClient "Blah" is only configured with a base URL and security token.

However....when I call the ParseFrom on the last line I get the following exception:

Google.Protobuf.InvalidProtocolBufferException
  HResult=0x80131620
  Message=Protocol message contained a tag with an invalid wire type.
  Source=Google.Protobuf
  StackTrace:
   at Google.Protobuf.UnknownFieldSet.MergeFieldFrom(ParseContext& ctx)
   at Google.Protobuf.UnknownFieldSet.MergeFieldFrom(UnknownFieldSet unknownFields, ParseContext& ctx)
   at namespace.MyResponse.pb::Google.Protobuf.IBufferMessage.InternalMergeFrom(ParseContext& input) in ....

Not sure how to solve this one...

Answer 1

I solved the problem I was facing by changing the .NET Framework (4.8) Server's method:

From

[HttpPost]
public async Task<IHttpActionResult> FetchSomeData()
{
    using (var ms = new MemoryStream(2048))
    {
        await content.CopyToAsync(ms).ConfigureAwait(false);
        byte[] bytes = ms.ToArray();
        MyRequest request = MyRequest.Parser.ParseFrom(bytes);

        MyResponse response = await SomeMethodAsync(request).ConfigureAwait(false);
        byte[] responseByteArray = response.ToByteArray();
        return this.Ok(responseByteArray);
    }
}

TO

[HttpPost]
public async Task<HttpResponseMessage FetchSomeData()
{
    using (var ms = new MemoryStream(2048))
    {
        await content.CopyToAsync(ms).ConfigureAwait(false);
        byte[] bytes = ms.ToArray();
        MyRequest request = MyRequest.Parser.ParseFrom(bytes);

        MyResponse response = await SomeMethodAsync(request).ConfigureAwait(false);
        byte[] responseByteArray = response.ToByteArray();
        var result = new HttpResponseMessage(HttpStatusCode.OK)
        {
           Content = new ByteArrayContent(responseByteArray),
        };
        return result;
    }
}

However, also considering the gRPC approach mentioned by @MarcGravell (see comments/conversation).