api.nuget.org connection tester

00_api.nuget.org test.md

This app will try to connect to api.nuget.org with HttpClient, expliciting passing each value of the SslProtocols enumeration.

Note that as the docs say, SslProtocol.None actually means "use the operating system defaults". It does not mean "do not use encryption".

If this app shows that Tls12 has failed, try the recommendations from this blog post: https://devblogs.microsoft.com/nuget/deprecating-tls-1-0-and-1-1-on-nuget-org/

If this app shows that Tls12 worked, but None failed, the most common reason is that Windows TLS 1.3 is enabled, however is incompatible with api.nuget.org's CDN provider's implementation. You should disable TLS 1.3 so that Windows no longer attempts to use TLS 1.3 when talking to nuget.org. See dotnet/runtime#40679

api.nuget.org-tls-test.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net472;net6.0</TargetFrameworks>
    <RootNamespace>tls_test</RootNamespace>
  </PropertyGroup>

  <ItemGroup>
    <Reference Include="System.Net.Http" Condition=" '$(TargetFrameworkIdentifier)' == '.NETFramework' " />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Net.Http;
using System.Security.Authentication;
using System.Threading.Tasks;

namespace tls_test
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var sslProtocols = (SslProtocols[])Enum.GetValues(typeof(SslProtocols));

            foreach (var protocol in sslProtocols)
            {
                var successful = await TestProtocolAsync(protocol);
                var status = successful ? "worked" : "failed";

                Console.WriteLine(protocol + " " + status);
            }
        }

        private static async Task<bool> TestProtocolAsync(SslProtocols protocol)
        {
            try
            {
                var httpMessageHandler = new HttpClientHandler()
                {
                    SslProtocols = protocol
                };
                var client = new HttpClient(httpMessageHandler);
                var request = new HttpRequestMessage(HttpMethod.Get, "https://api.nuget.org/v3/index.json");
                var response = await client.SendAsync(request);
                return true;
            }
            catch
            {
                return false;
            }
        }
    }
}