HttpRequestException: Unable to get subchannel from HttpRequestMessage - .Net 7 - using Fiddler Everywhere

[rizi]

What version of gRPC and what language are you using?

Grpc.Net.Client/Grpc.Net.ClientFactory 2.53.0, C#

What operating system (Linux, Windows,...) and version?

Windows 10 Enterprise (22H2)

What runtime / compiler are you using (e.g. .NET Core SDK version dotnet --info)

.Net 7.0.400,

What did you do?

We are creating a grpc client as described here: https://learn.microsoft.com/en-us/aspnet/core/grpc/netstandard?view=aspnetcore-7.0.

Using the gRCP client works as expected as long as there is no proxy running (like Fiddler Everywhere), as soon as I start Fiddler Everywhere which supports HTTP 2 and gRPC capturing, we get an exception (see the section What did you see instead?),
is the configuration of the grpc client registration correct?

builder.Services
    .AddGrpcClient<Greeter.GreeterClient>(o =>
    {
        o.Address = new Uri("https://someAddress:5001");
    })
   .ConfigureChannel(options =>
                                               {
                                                   options.Credentials = new SslCredentials();

                                                   options.HttpHandler = new SocketsHttpHandler
                                                                         {
                                                                             PooledConnectionIdleTimeout = Timeout.InfiniteTimeSpan,
                                                                             KeepAlivePingDelay = TimeSpan.FromSeconds(50),
                                                                             KeepAlivePingTimeout = TimeSpan.FromSeconds(20),
                                                                             KeepAlivePingPolicy = HttpKeepAlivePingPolicy.Always,
                                                                             EnableMultipleHttp2Connections = true
                                                                         };
                                               });

What did you expect to see?

I would expect that the gRPC call successfully runs through the proxy and finally returns the result.

What did you see instead?

I see the following exception (note that 127.0.0.1:8866 is the address of fiddler, so the call is forwarded to the proxy)

Connection id "0HMT23GS5CF6U", Request id "0HMT23GS5CF6U:00000001": An unhandled exception was thrown by the application.

Error: Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: Unable to get subchannel from HttpRequestMessage. (127.0.0.1:8866) InvalidOperationException: Unable to get subchannel from HttpRequestMessage.", DebugException="System.Net.Http.HttpRequestException: Unable to get subchannel from HttpRequestMessage. (127.0.0.1:8866)")
---> System.Net.Http.HttpRequestException: Unable to get subchannel from HttpRequestMessage. (127.0.0.1:8866)
---> System.InvalidOperationException: Unable to get subchannel from HttpRequestMessage.
 at Grpc.Net.Client.Balancer.Internal.BalancerHttpHandler.OnConnect(SocketsHttpConnectionContext context, CancellationToken cancellationToken)
 at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)

This issue seems very similar: #2116

Note: using HttpClientHandler instead of SocketsHttpHandler does not cause an exception and the result from the gRPC call is returned correctly.

However the gRPC call is not captured by Fiddler and it is not an option, because the HttpClientHandler does not provide properties like PooledConnectionIdleTimeout , EnableMultipleHttp2Connections , KeepAlivePingPolicy, ...

Any help would highly be appreciated.

[JamesNK]

A limitation of gRPC load balancing is it doesn't work well with proxies. There isn't an ETA on when this will be fixed.

Configuring HttpClientHandler disables load balancing which is why it starts working.

[rizi]

A limitation of gRPC load balancing is it doesn't work well with proxies. There isn't an ETA on when this will be fixed.

Configuring HttpClientHandler disables load balancing which is why it starts working.

Can load balancing be deactivated using the SocketsHttpHandler?
If so are there any disadvantages?

Br

[JamesNK]

Can load balancing be deactivated using the SocketsHttpHandler? If so are there any disadvantages?

Yes, the latest version supports this: #2312 (comment)