using System.Collections.Generic;

using System.Diagnostics;

using System.Linq;

using System.Net;

using System.Threading.Tasks;

namespace SharpProxy

{

public static class IPEndPointProvider

{

private static readonly Dictionary<string, IPAddress> _cache = new Dictionary<string, IPAddress>();

private static readonly Dictionary<string, Task<IPAddress>> _retrieving = new Dictionary<string, Task<IPAddress>>();

async public static Task<IPEndPoint> Get(string host, int port)

{

lock (_cache)

{

if (_cache.ContainsKey(host))

return new IPEndPoint(_cache[host], port);

}

Task<IPAddress> addressTask = null;

lock (_retrieving)

{

if (_retrieving.ContainsKey(host))

{

addressTask = _retrieving[host];

}

else

{

addressTask = Dns.GetHostAddressesAsync(host).ContinueWith(task =>

{

IPAddress newIpAddress = null;

if (!task.IsFaulted && task.Result != null)

newIpAddress = task.Result.FirstOrDefault();

lock (_cache)

{

_cache[host] = newIpAddress;

}

return newIpAddress;

});

_retrieving[host] = addressTask;

}

}

var ipAddress = await addressTask;

if (ipAddress == null)

return null;

return new IPEndPoint(ipAddress, port);

}

private static void DnsResolutionError()

{

if (Debugger.IsAttached)

Debugger.Break();

}

}

}