I’m working with on C# client library using gRpc. This is not a web based library where there’s a need for envoy or other application to help work with HTTP2. Instead this was on a C# client using tcp/ip.

Everything was working fine on my machine until the machine was relocated (not that this specifically was the problem as I later found out others were having similar problems, some times intermittently) at which point I found that the client would exception with the message “UNAVAILABLE: Trying to connect an http1.x server”.

Note: if you turn on all exceptions within Visual Studio, you’ll firstly see an exception where grpc tries to get a Value from a Nullable when it’s null (this was the call to Native.grpcsharp_batch_context_recv_message_length). This is a red herring, it’s simple that the nullable is null which seems to be expected behaviour, maybe should be handled in the gRPC .NET library code.

Testing the client on another machine demonstrated the problem was seemingly network related, turns out it was HTTP proxy related to be precise.

This doesn’t seem to be too well documented from what I could tell, but setting the ChannelOption grpc.enable_http_proxy to 0 (see https://grpc.github.io/grpc/core/group__grpc__arg__keys.html) fixed the problem.

var channel = new ManagedChannel(
   host, 
   port, 
   ChannelCredentials.Insecure,
   new []{ new ChannelOption("grpc.enable_http_proxy", 0)} );