ERR_CONNECTION_REFUSED with Example Blazor Project gRPC Web Server

What version of gRPC and what language are you using?

Grpc.AspNetCore = 2.41.0 Grpc.AspNetCore.Web = 2.41.0

What operating system (Linux, Windows,…) and version?

MacOS 11.2.3

What runtime / compiler are you using (e.g. .NET Core SDK version dotnet --info)

Version: 6.0.101

What did you do?

Ran server project and connected to the endpoint with RPC client (BloomRPC) using both gRPC-web and gRPC

What did you expect to see?

The same, successful response using both protocols

What did you see instead?

Using BloomRPC I tested the gRPC GetWeatherForecasts endpoint using straight gRPC and it worked. Used gRPC-web and it errored with the following response:

{ “error”: “full url: http://0.0.0.0:5000/weather.WeatherForecasts/GetWeatherForecasts, code: 2, err: Http response at 400 or 500 level” }

with the status ERR_CONNECTION_REFUSED

I have also replicated the same issue using the client application, running locally, as well as BloomRPC

Anything else we should know about your project / environment?

I have also built a PoC project separately from the test project and am experiencing the same issue but with different details of implementation.

From what I have researched around the issue, I would guess it’s issue specific to MacOS (possibly to do with the changes you need to make to the server as described here: https://docs.microsoft.com/en-us/aspnet/core/grpc/troubleshoot?view=aspnetcore-3.0#unable-to-start-aspnet-core-grpc-app-on-macos), which is different to CORS or url related issues as described here: https://github.com/grpc/grpc-dotnet/issues/1126

As per above Microsoft docs, I added the following to the ConfigureWebHostDefaults in Server/Program.cs - all other code is unchanged from latest repo version (7d081d7c2682c792971d851e9e88d11a8728a2aa)

webBuilder.UseKestrel(options => { // Setup a HTTP/2 endpoint without TLS. options.ListenLocalhost(5000, o => o.Protocols = HttpProtocols.Http2); });

[tenglandct]

I tried again after updating to 12.1 and it also failed, however, I did a bit more looking around at what could be different between the 2 projects and found that I had also added in the following block into appsettings.json:

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

Removing that, as well as the Kestrel web host config block, fixed the issue for me.

I agree it looks like the workaround either needs updating or removing with a caveat about TLS on macOS in general (as I could not build the site whilst still trying to serve to an https address as well as the http one)

[hmih]

AAAAAAA Oh my god, I’ve been banging my head against the wall for 2 days on a stupid CORS preflight headers issue and removing the Kestrel configuration worked for me. The setup of my project is grpc-web server and blazor wasm grpc-web client. I’m on a MacOS M1 13 with everything latest. The official Microsoft documentation does not refer to this issue and it’s been a huge pain in the ass. Thank you @tenglandct . I’m also referring #998 (same error) because maybe some lonely search result explorer will find this fix.