Change DNS using HttpClient

httpClientWithCustomDns.cs

using System.Net;
using System.Net.Sockets;

namespace PocHttpClientCustomDns
{
    // https://stackoverflow.com/questions/58547451/is-it-possible-to-set-custom-dns-resolver-in-cs-httpclient
    // https://learn.microsoft.com/en-us/dotnet/api/system.net.http.socketshttphandler.connectcallback?view=net-5.0#System_Net_Http_SocketsHttpHandler_ConnectCallback
    // https://csharpforums.net/threads/httpclient-custom-dns-ip.7486/#post-26692
    // https://stackoverflow.com/questions/71638441/how-to-improve-slow-dns-with-httpclient
    // https://stackoverflow.com/questions/37384945/how-to-force-ipv6-or-ipv4-for-httpwebrequest-or-webrequest-c-sharp/70475741#70475741

    public class UnitTest1
    {
        [Fact]
        public async Task Test1()
        {
            var dummyDnsHandler = new SocketsHttpHandler
            {
                ConnectCallback = async (context, cancellationToken) =>
                {
                    IPAddress ipAddress = IPAddress.Parse("127.0.0.1");

                    try
                    {
                        // Use DNS to look up the IP address(es) of the target host
                        IPHostEntry ipHostEntry = await Dns.GetHostEntryAsync(context.DnsEndPoint.Host, cancellationToken);

                        // Filter for IPv4 addresses only
                        ipAddress = ipHostEntry.AddressList.First /*OrDefault*/(i => i.AddressFamily == AddressFamily.InterNetwork);
                    }
                    catch (System.Net.Http.HttpRequestException e)
                    {
                        // swallow, expected, not found
                        // No such host is known
                    }
                    catch (Exception e)
                    {
                        // swallow
                    }

                    // Fail the connection if there aren't any IPV4 addresses
                    if (ipAddress == null)
                    {
                        throw new Exception($"No IP4 address for {context.DnsEndPoint.Host}");
                    }

                    // Open the connection to the target host/port
                    TcpClient tcp = new();
                    await tcp.ConnectAsync(ipAddress, context.DnsEndPoint.Port, cancellationToken);

                    // Return the NetworkStream to the caller
                    return tcp.GetStream();
                }
            };

            using var http = new HttpClient(dummyDnsHandler);
            var rsp = await http.GetAsync("https://goasdfsadfasdfasdfasdfogle.com");
            Assert.True(rsp.IsSuccessStatusCode);
        }
    }
}