Grpc client in .net standard fails when called from .net framework, but not .net core 3.1

Question

This is my setup:

• A: .Net Standard version=2.0 (gRPC Client library)
• B: .Net Framework version=4.8 (web application - uses the client library)
• C: .Net Core version=3.1 (WPF application - uses the client library)
• D: .Net Core version=3.1 (gRPC Server, my own creation)
• E: .Net Core Version=3 or 5 - I'm not sure. (gRPC Server, production)

Error = "HTTP/2 over TLS was not negotiated on an HTTP/2-only endpoint."

So... Someone else implemented this Grpc Server (E). I can call this one with both applications. No errors.

But to get a nice development environment for developing the two applications, I got the proto-file from the production server and developed my own implementation (D). I use this for testing error handling in the clients - I can control which responses the server gives.

I implemented two exactly alike unit tests, which are in fact integration tests. One in a .net framework project and one in a .net core project.

And it works for .net core test, but not the .net framework.

However, if I inject a WinHttpHandler instead of the HttpClientHandler , then it works. I really do not want to have to inject a handler (it's not even an interface).

Also the production gRPC server works, as mentioned before. But I do not know why mine fails and the production gRPC server works.

I think somehow my own implementation of the gRPC service is wrong (or lacking) but I do not know what I am missing.

Please help!

Answer 1

Grpc.Net.Client only works on .NET Framework (as opposed to .NET Core and .NET5+) with limitations. The reason is that .NET Framework doesn't really have a HTTP/2 implementation, which is a requirement for gRPC protocol (but not for grpc-web, it that's an option for you).

Grpc.Net.Client works on .NET Framework to some extent with WinHttpHandler (as you've discovered). The limitations are documented here:

• https://docs.microsoft.com/en-us/aspnet/core/grpc/supported-platforms?view=aspnetcore-6.0.net-grpc-client-requirements
• https://docs.microsoft.com/en-us/aspnet/core/grpc/netstandard?view=aspnetcore-6.0.net-framework

Answer 2

Actually, I had this in my appsetting.json (which I had copied from another project):

"Kestrel": {
    "EndpointDefaults": {
      "Protocols": "Http2"
    }

Of cause, deleting that from the file solved my problem.