Resolve IP addresses in ConnectCallback example

Author: antonfirsov

snippets/csharp/System.Net.Http/SocketsHttpHandler/ConnectCallback/program.cs

@@ -1,8 +1,9 @@
-using System;
+using System;
 using System.IO;
 using System.Net;
 using System.Net.Http;
 using System.Net.Sockets;
+using System.Threading;
 using System.Threading.Tasks;
 
 class HttpClientHandler_SecureExample
@@ -14,14 +15,17 @@ static async Task Main()
 
         handler.ConnectCallback = async (ctx, ct) =>
         {
+            DnsEndPoint dnsEndPoint = ctx.DnsEndPoint;
+            IPAddress[] addresses = await Dns.GetHostAddressesAsync(dnsEndPoint.Host, dnsEndPoint.AddressFamily, ct);
             var s = new Socket(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
             try
             {
                 s.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
                 s.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, 5);
                 s.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, 5);
                 s.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, 5);
-                await s.ConnectAsync(ctx.DnsEndPoint, ct);
+
+                await s.ConnectAsync(addresses, dnsEndPoint.Port, ct);
                 return new NetworkStream(s, ownsSocket: true);
             }
             catch