System.ArgumentOutOfRangeException when using test server in combination with Yarp

[Erwinvandervalk]

Describe the bug

I'm creating a test server for my application and another testserver for the reverse proxy. When I call the proxy, it should forward the call to the application, but instead, I get the following exception:

System.ArgumentOutOfRangeException

To Reproduce

I've included a test project that gives the error for me.
yarp.zip

Yarp.ReverseProxy.Forwarder.HttpForwarder[48]
      ResponseBodyDestination: The destination reported an error when copying the response body.
      System.ArgumentOutOfRangeException:  (Parameter 'count')
      Actual value was 0.
         at Microsoft.AspNetCore.TestHost.ResponseBodyReaderStream.VerifyBuffer(Byte[] buffer, Int32 offset, Int32 count)
         at Microsoft.AspNetCore.TestHost.ResponseBodyReaderStream.ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken)
         at Yarp.ReverseProxy.Forwarder.StreamCopier.CopyAsync(Stream input, Stream output, Int64 promisedContentLength, StreamCopierTelemetry telemetry, ActivityCancellationTokenSource activityToken, CancellationToken cancellation)

Further technical details

Yarp 1.1.0
testhost 6.0.5

[MihaZupan]

Hey, this looks like a the same kind of issue as #1665 and #1657. It's a bug that manifests when using Yarp 1.1.0 with some stream implementations.
I've filed an issue in AspNetCore to track fixing the TestHost.

[Erwinvandervalk]

Thanks Miha. Fingers crossed it can / will be fixed :)

[karelz]

Triage: Closing as external -- tracked by dotnet/aspnetcore#41692