Get Bitcoin nodes on onion domains

Program.cs

using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace seeds
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var list = await GetAsync();
        }

        private static async Task<List<string>> GetAsync()
        {
            var ret = new List<string>();

            using (var httpClient = new HttpClient())
            {
                httpClient.BaseAddress = new Uri("https://bitnodes.21.co/api/v1/");

                using (var response = await httpClient.GetAsync("snapshots/latest/", HttpCompletionOption.ResponseContentRead))
                {
                    if (response.StatusCode != HttpStatusCode.OK)
                        throw new HttpRequestException(response.StatusCode.ToString());
                    var responseString = await response.Content.ReadAsStringAsync();
                    var json = (JObject)JsonConvert.DeserializeObject(responseString);
                    foreach(JProperty node in json["nodes"])
                    {
                        if( !node.Name.ToString().Contains(".onion") )
                            continue;
                        var userAgent = ((JArray)node.Value)[1].ToString();
                        if( userAgent.Contains("Satoshi:0.16") || userAgent.Contains("Satoshi:0.17"))
                        {
                            ret.Add(node.Name);
                        }
                    }
                }
            }

            return ret;
        }
    }
}

Program2.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Sockets;
using System.Threading.Tasks;

namespace seeds
{
    class Program
    {
        static async Task Main(string[] args)
        {
            var dns = new []
            {
                "testnet-seed.bitcoin.jonasschnelli.ch",
                "seed.tbtc.petertodd.org",
                "seed.testnet.bitcoin.sprovoost.nl",
                "testnet-seed.bluematt.me",
            };

            var hs = new HashSet<IPAddress>();
            var i = 0;
            while(true)
            {
                var source = dns[i++ % dns.Length];
                try{
                    var dnsServer = Dns.GetHostAddresses(source);

                    foreach(var ip in dnsServer.Where(x=>x.AddressFamily==AddressFamily.InterNetworkV6))
                    {
                        if(hs.Contains(ip)) continue;
                        var bytes = ip.GetAddressBytes();
                        if(bytes[0] == 0xfd && bytes[1] == 0x87){
                            Console.WriteLine(ip.ToString());
                            hs.Add(ip);
                        }
                    }
                    await Task.Delay(3000);
                }
                catch(Exception)
                {
                    Console.WriteLine("Error: " + source);
                    await Task.Delay(1000);
                }
            }
        }
    }
}