troubles using grpc-web client from .net framework

im running this on Win10 21H2 (Build 19044.1415) and trying to make a call from the .net framework to my .net 6 greeter service

Server

using web.Services;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddGrpc();

var app = builder.Build();
app.UseGrpcWeb();

// Configure the HTTP request pipeline.
app.MapGrpcService<GreeterService>().EnableGrpcWeb();
app.MapGet("/", () => "Communication with gRPC endpoints must be made through a gRPC client.");

app.Run();

client project

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<OutputType>Exe</OutputType>
		<TargetFrameworks>net48;net6.0</TargetFrameworks>
		<ImplicitUsings>enable</ImplicitUsings>
		<LangVersion>10.0</LangVersion>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Google.Protobuf" Version="3.19.1" />
		<PackageReference Include="Grpc.Net.Client" Version="2.41.0" />
		<PackageReference Include="Grpc.Net.Client.Web" Version="2.41.0" />
		<PackageReference Include="Grpc.Tools" Version="2.42.0">
			<PrivateAssets>all</PrivateAssets>
			<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
		</PackageReference>
	</ItemGroup>

	<ItemGroup Condition="$(TargetFramework) == 'net48'" >
		<PackageReference Include="System.Net.Http" Version="4.3.4" />
	</ItemGroup>

	<ItemGroup>
		<Protobuf Include="..\Proto\greet.proto" GrpcServices="Client" Link="Proto\greet.proto" />
	</ItemGroup>

</Project>

client code

using Grpc.Net.Client;
using Greet;
using Grpc.Net.Client.Web;

var version =
#if NET48
    "net48";
#else
    "net6.0";
#endif

var handler = new GrpcWebHandler(new HttpClientHandler());
var options = new GrpcChannelOptions {HttpHandler = handler};

var channel = GrpcChannel.ForAddress("http://localhost:5001", options);
var client = new Greeter.GreeterClient(channel);

var result = await client.SayHelloAsync(new HelloRequest { Name = version });
Console.WriteLine(result.Message);

which works fine with net6

dotnet run --framework net6.0
Hello net6.0

but fails on .net framework 4.8

dotnet run --framework net48

Unhandled Exception: Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: An error occurred while sending the request. WebException: The server committed a protocol violation. Section=ResponseStatusLine", DebugException="System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: The server committed a protocol violation. Section=ResponseStatusLine
   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)
...

any hint would be highly appreciated

[ThorstenReichert]

@JamesNK indeed, changing the appsettings json from

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

to

{ "Kestrel": { "EndpointDefaults": { "Protocols": "Http1AndHttp2" }}}

solved the issue for me, thanks a lot!

[JamesNK]

.NET Framework only supports HTTP/1.1 (unless WinHttpHandler is configured). That’s fine, because gRPC-Web works over HTTP/1.1. An ASP.NET Core gRPC project is configured by default to HTTP/2 only. This is most likely your problem

You’re both sending non-TLS requests (i.e. the address is http and not https). That means the .NET Framework client is sending HTTP/1.1 to a server that expects HTTP/2.

To fix this, you must either use TLS and allow HTTP/1.1 and 2 (TLS allows negotiation between the client and server of which to use) or have a separate HTTP/1.1 only http port.