SignalR. An HTTP/2 connection could not be established

Question

I have SignalR server (hub) and C# client.

Target Framework: net6.0.

The server uses let's encrypt certificates.

After upgrading SignalR client from 6.0.10 to 7.0.12, the error "An HTTP/2 connection could not be established because the server did not complete the HTTP/2 handshake" appeared on one of the client computers (Windows Server 2012 R2).

Error occurs when calling StartAsync

_hubConnection = new HubConnectionBuilder().WithUrl($"{_setting.HubUrl}/hubs/tariff")
  .AddJsonProtocol(options => options.PayloadSerializerOptions.PropertyNamingPolicy = null).Build();
await _hubConnection.StartAsync(); // <-- Exception HttpRequestException

There are no errors when testing local client. How to fix this problem? Maybe there are options to forcefully disable http/2?

Stacktrace:

! An HTTP/2 connection could not be established because the server did not complete the HTTP/2 handshake. System.Net.Http.HttpRequestException: An HTTP/2 connection could not be established because the server did not complete the HTTP/2 handshake. at System.Net.Http.HttpConnectionPool.ReturnHttp2Connection(Http2Connection connection, Boolean isNewConnection) at System.Net.Http.HttpConnectionPool.AddHttp2ConnectionAsync(HttpRequestMessage request) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining) at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) at System.Threading.Tasks.Task1.TrySetResult(TResult result) at System.Runtime.CompilerServices.AsyncValueTaskMethodBuilder1.SetResult(TResult result) at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining) at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.SetExistingTaskResult(Task1 task, TResult result) at System.Net.Http.ConnectHelper.EstablishSslConnectionAsync(SslClientAuthenticationOptions sslOptions, HttpRequestMessage request, Boolean async, Stream stream, CancellationToken cancellationToken) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining) at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.SetExistingTaskResult(Task1 task, TResult result) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder.SetResult() at System.Net.Security.SslStream.ForceAuthenticationAsync[TIOAdapter](TIOAdapter adapter, Boolean receiveFirst, Byte[] reAuthenticationData, Boolean isApm) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining) at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.SetExistingTaskResult(Task1 task, TResult result) at System.Net.Security.SslStream.ReceiveBlobAsync[TIOAdapter](TIOAdapter adapter) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.Tasks.AwaitTaskContinuation.RunOrScheduleAction(IAsyncStateMachineBox box, Boolean allowInlining) at System.Threading.Tasks.Task.RunContinuations(Object continuationObject) at System.Runtime.CompilerServices.AsyncValueTaskMethodBuilder1.SetResult(TResult result) at System.Net.Security.SslStream.<FillHandshakeBufferAsync>g__InternalFillHandshakeBufferAsync|189_0[TIOAdapter](TIOAdapter adap, ValueTask1 task, Int32 minSize) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.ExecutionContextCallback(Object s) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext(Thread threadPoolThread) at System.Runtime.CompilerServices.AsyncTaskMethodBuilder1.AsyncStateMachineBox1.MoveNext() at System.Threading.ThreadPool.<>c.<.cctor>b__87_0(Object state) at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.InvokeContinuation(Action1 continuation, Object state, Boolean forceAsync, Boolean requiresExecutionContextFlow) at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.OnCompleted(SocketAsyncEventArgs _) at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pNativeOverlapped) --- End of stack trace from previous location --- at System.Threading.Tasks.TaskCompletionSourceWithCancellation1.WaitWithCancellationAsync(CancellationToken cancellationToken) at System.Net.Http.HttpConnectionPool.GetHttp2ConnectionAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken) at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken) at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.Internal.AccessTokenHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.Internal.LoggingHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) at System.Net.Http.HttpClient.g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.NegotiateAsync(Uri url, HttpClient httpClient, ILogger logger, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.GetNegotiationResponseAsync(Uri uri, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.SelectAndStartTransport(TransferFormat transferFormat, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.StartAsyncCore(TransferFormat transferFormat, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnection.StartAsync(TransferFormat transferFormat, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnectionFactory.ConnectAsync(EndPoint endPoint, CancellationToken cancellationToken) at Microsoft.AspNetCore.Http.Connections.Client.HttpConnectionFactory.ConnectAsync(EndPoint endPoint, CancellationToken cancellationToken) at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsyncCore(CancellationToken cancellationToken) at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsyncInner(CancellationToken cancellationToken) at Microsoft.AspNetCore.SignalR.Client.HubConnection.StartAsync(CancellationToken cancellationToken) at ...

Answer 1

The IIS version is 8.5 in Windows Server 2012 R2.

And the HTTP/2 Support was introduced in IIS 10.0 ( Windows Server 2016 +).

Solution

1. So you need to upgrade the windows server system.

2. If you don't want to upgrade it, you can think about using NGINX.

It acts as a front-end reverse proxy, accepting HTTP/2 connections and forwarding them as HTTP/1.1 connections to your backend server. This allows clients to connect to NGINX using HTTP/2, while your application server (such as one running on Windows Server 2012 R2) still uses HTTP/1.1.