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This is my first gRPC application. I'm attempting to invoke a server-streaming RPC call from a .NET 5 gRPC client (Grpc.Net.Client 2.35.0) which results in the following exception in my local development environment:

Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Error starting gRPC call. HttpRequestException: Requesting HTTP version 2.0 with version policy RequestVersionOrHigher while HTTP/2 is not enabled."

This occurs whether or not the server application is running. Here is the code I'm using to make the call:

using var channel = GrpcChannel.ForAddress(@"http://localhost:5000");
var client = new AlgorithmRunner.AlgorithmRunnerClient(channel);
using var call = client.RunAlgorithm(new RunAlgorithmRequest());

while (await call.ResponseStream.MoveNext())
{

}

My understanding is that .NET 5 gRPC is supposed to have HTTP/2 enabled by default: why does the exception indicate that HTTP/2 is not enabled and how do I resolve it?

Jacob
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3 Answers3

12

After further investigation, this appears related to proxy settings on my machine related to my company's network setup. Specifically, I have the following environment variables defined:

http_proxy https_proxy

.NET populates the HttpClient DefaultProxy from these environment variables. My company proxy appears to be interfering with HTTP/2 (unsupported?), preventing gRPC from working correctly. The workaround for local development is to manually set the default proxy for the HttpClient before making the gRPC call:

HttpClient.DefaultProxy = new WebProxy();
                
using var channel = GrpcChannel.ForAddress(@"http://localhost:5000");
var client = new AlgorithmRunner.AlgorithmRunnerClient(channel);
using var call = client.RunAlgorithm(new RunAlgorithmRequest());

This may represent a general problem with using gRPC through certain types of proxies.

Jacob
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    Thanks, Jacob. This fixed my headache. – Nishant Apr 26 '21 at 12:07
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    The same error seems to happens on client running on Windows7 with no proxy and using https. Seems like Windows7 doesn't support HttpClient using HTTP/2 with TLS. – Dunge Jul 21 '21 at 05:46
  • @Dunge Confirming having another Win7 client spitting out this error – Ray Aug 07 '21 at 18:42
  • @Ray I ended up using grpc-web for Win7 customers. It's just a matter of adding 1-2 lines both in server and client to support it, then you leave an option in the interface to use it or not. – Dunge Aug 08 '21 at 19:26
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    @Dunge Thanks for the idea. I followed https://stackoverflow.com/a/59770858/777985 and replaced Grpc.Net.Client with Grpc.Core, which also only needed a few code adjustments. – Ray Aug 08 '21 at 21:07
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    I had this problem when starting `Grpc` client and service with fiddler running, your answer solves the issue. As soon as Fiddler is closed, the line is not needed. I didn't use `HTTPS` in this tests at all and `HTTP2` was correctly configured. – rvnlord Sep 03 '21 at 20:48
1

I faced the same problem sitting behind a corporate proxy and receiving this error message

An exception of type 'Grpc.Core.RpcException' occurred in System.Private.CoreLib.dll but was not handled in user code: 'Status(StatusCode="Unavailable", Detail="Error starting gRPC call. HttpRequestException: Connection refused SocketException: Connection refused", DebugException="System.Net.Http.HttpRequestException: Connection refused

I fully agree that your suggested workaround with bypassing all proxy settings by overwriting the DefaultProxy is legit and functional.

A slightly better approach would be not to hard code a 'bypass all proxy statement' in your code and use instead the no_proxy environment variable. The purpose of this environment variable is to define a rule for excluding traffic destined to certain hosts

Solution

Activate the env. variable no_proxy for your development setup like

For linux

export no_proxy=localhost,127.0.0.1

For Dockerfile

ENV no_proxy=localhost,127.0.0.1

For a deep dive session about proxy environment variables

It is important when you start your gRPC client application, that you check what the value of the read in environment variables is, because gRPC uses the HttpClient class under the hood, which considers all proxy environment variables. If the no_proxy value is not set, it has not effect.

var noProxy = Environment.GetEnvironmentVariable("no_proxy");
MeltpoolMartin
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If you found this page because your error occurs when Fiddler is running, I found the answer I required (to inspect WCF traffic) below. I only had to configure Fiddler, no code or env changes.

https://stackoverflow.com/a/73398308/5269981

golfalot
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