dotnetcore dns lookup for srv records

SrvLookup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Threading.Tasks;
using DnsClient;

namespace
{
    public class DnsSrvClient
    {
        public static async Task<IEnumerable<IPEndPoint>> Lookup(string host)
        {
            var nameservers = NameServer.ResolveNameServers(skipIPv6SiteLocal: true, fallbackToGooglePublicDns: false);
            var dns = new LookupClient(nameservers?.ToArray());
            var queryResponse = await dns.QueryAsync(host, QueryType.SRV);

            var records = queryResponse.Answers.SrvRecords().ToList();

            if (records.Count == 0)
            {
                throw new Exception($"no SRV records for {host}");
            }

            var arecords = queryResponse.Additionals.ARecords().ToLookup(r => r.DomainName);
            if (arecords.Count == 0)
            {
                // my docker containers on macos (docker desktop 2.0.0.3) always hit this branch
                var tasks = records.Select(srv => dns.QueryAsync(srv.Target, QueryType.A));
                var results = await Task.WhenAll(tasks.ToArray());
                arecords = results
                    .SelectMany(rs => rs.Answers.ARecords())
                    .ToLookup(r => r.DomainName);
            }

            var topPriority = records
                .OrderBy(srv => srv.Priority)
                .ThenByDescending(srv => srv.Weight)
                .GroupBy(srv => srv.Priority)
                .First();

            return topPriority
                .Where(srv => arecords.Contains(srv.Target))
                .Select(srv => new IPEndPoint(arecords[srv.Target].First().Address, srv.Port));
        }
    }
}

uses https://github.com/MichaCo/DnsClient.NET

heed the warning though.. ideally an app would cache the list of results and rotate through them according to rfc 2782