HTTP/2 connection error (PROTOCOL_ERROR): Invalid HTTP/2 connection preface

Change the server configuration of the sample to Kestrel, and then connect aspnetcore grpc-web through Http protocol , The following error occurred:

dbug: Microsoft.AspNetCore.Server.Kestrel[29]
      Connection id "0HLTV45E8MTR4": HTTP/2 connection error.
Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2ConnectionErrorException: HTTP/2 connection error (PROTOCOL_ERROR): Invalid HTTP/2 connection preface.
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.ParsePreface(ReadOnlySequence`1& buffer, SequencePosition& consumed, SequencePosition& examined)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.TryReadPrefaceAsync()
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http2.Http2Connection.ProcessRequestsAsync[TContext](IHttpApplication`1 application)

But using iisexpress to start the service, and the client connects through the http protocol, it works fine

[JamesNK]

This is failing because you are trying to call a HTTP/2 only port without TLS (HTTPS). That isn’t supported by browsers. You either need to use TLS, or change protocols to Microsoft.AspNetCore.Server.Kestrel.Core.HttpProtocols.Http1AndHttp2 (although it will always use HTTP/1.1 because TLS is not available)

[dingsongjie]

Can you provide your appSettings.json and any modifications you made to the sample to change it to Kestrel? This is a scenario we generally expect to work (and has in the past) so having the full context will help identify what might be different now.

I removed all Kestrel related configuration in appsetting, and this is my Program.cs

               .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                    webBuilder.UseKestrel(option =>
                    {
                        option.ListenAnyIP(82, config =>
                        {
                            config.Protocols = Microsoft.AspNetCore.Server.Kestrel.Core.HttpProtocols.Http2;
                            //config.UseHttps();
                        });
                    });
                });

If you start debugging in visual studio in console , do not use IIS EXPRESS , then use javascript grpc-web client to connect it through the http protocol , you will see this error if you set “Microsoft.AspNetCore.Server.Kestrel”: “Debug”

When you set config.UseHttps() , the javascript client will connect success through the https protocol