Aspnetcore.docs: Use streaming in ASP.NET Core SignalR with IAsyncEnumerable

[cuzzlor]

Issue description

Following the IAsyncEnumerable example code from here:
https://docs.microsoft.com/en-us/aspnet/core/signalr/streaming?view=aspnetcore-3.0

I can't get the .Net client to bind...

System.IO.InvalidDataException: Invocation provides 2 argument(s) but target expects 3.
   at Microsoft.AspNetCore.SignalR.Protocol.NewtonsoftJsonHubProtocol.BindArguments(JsonTextReader reader, IReadOnlyList`1 paramTypes)
   at Microsoft.AspNetCore.SignalR.Protocol.NewtonsoftJsonHubProtocol.ParseMessage(Utf8BufferTextReader textReader, IInvocationBinder binder)
Exception thrown: 'Microsoft.AspNetCore.SignalR.HubException' in System.Private.CoreLib.dll
An unhandled exception of type 'Microsoft.AspNetCore.SignalR.HubException' occurred in System.Private.CoreLib.dll
Failed to invoke 'Counter' due to an error on the server.

If I add a second cancellationToken...

var channel = await connection.StreamAsChannelAsync<int>("Counter", 100, 1000, tokenSource.Token, tokenSource.Token);

I get...

The client attempted to invoke the non-streaming 'Counter' method with a streaming invocation.

Software versions

Client

<PackageReference Include="Microsoft.AspNetCore.SignalR.Client" Version="3.0.0-preview3-19153-02" />

Server

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

  <PropertyGroup>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <RootNamespace>IAsyncEnumerable_demo</RootNamespace>
  </PropertyGroup>

</Project>

Check the .NET target framework(s) being used, and include the version number(s).

• [x] .NET Core 3 Preview 3
• [ ] .NET Framework
• [ ] .NET Standard

If using the .NET Core SDK, include dotnet --info output. If using .NET Framework without the .NET Core SDK, include info from Visual Studio's Help > About Microsoft Visual Studio dialog.

dotnet --info output or About VS info

D:\dev> dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview3-010431
 Commit:    d72abce213

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17134
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview3-010431\

Host (useful for support):
  Version: 3.0.0-preview3-27503-5
  Commit:  3844df9537

.NET Core SDKs installed:
  2.1.4 [C:\Program Files\dotnet\sdk]
  2.1.101 [C:\Program Files\dotnet\sdk]
  2.1.104 [C:\Program Files\dotnet\sdk]
  2.1.201 [C:\Program Files\dotnet\sdk]
  2.1.202 [C:\Program Files\dotnet\sdk]
  2.1.504 [C:\Program Files\dotnet\sdk]
  2.1.505 [C:\Program Files\dotnet\sdk]
  2.1.601 [C:\Program Files\dotnet\sdk]
  3.0.100-preview3-010431 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview3-19153-02 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview3-27503-5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview3-27504-2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[BrennanConroy]

I believe this feature went in right after preview3 branching. So it will be available in preview4 or nightly bits.

Looks like we were a little over-eager to write docs for it, sorry.

[cuzzlor]

Thanks for confirming!

[mgnsm]

@BrennanConroy: I am getting the same exception using the latest version (3.1.1) of Microsoft.AspNetCore.SignalR.Client, i.e. I can't seem to bind to a hub method that accepts a CancellationToken.

Is this the expected current behavior? If I can't use a CancellationToken in the hub, how do I then determine when a (.NET) client disconnects from the stream?

Why hasn't the docs been updated and why isn't the .NET client code included in the downloadable code sample?

[BrennanConroy]

I am getting the same exception

What exception? There were multiple listed.

The .NET client code can be seen in the docs at https://docs.microsoft.com/aspnet/core/signalr/streaming?view=aspnetcore-3.1#net-client

[mgnsm]

I can confirm that the sample code works as expected.

The reason why I got an InvalidDataException with the message "Invocation provides 2 argument(s) but target expects 3" in the client was because I unintentionally returned a Channel<T> from the streaming method in the hub instead of a ChannelReader<T>. :flushed:

[BrennanConroy]

This is an old doc issue from before the streaming feature was release. I think there are no actionable items left.