Workaround for PlatformNotSupportedException

* Address https://github.com/dotnet/corefx/issues/26840

Author: cnblogs-dudu

Enyim.Caching/Configuration/MemcachedClientConfiguration.cs

@@ -47,7 +47,7 @@ public MemcachedClientConfiguration(
             Servers = new List<DnsEndPoint>();
             foreach (var server in options.Servers)
             {
-                Servers.Add(new DnsEndPoint(server.Address, server.Port));
+                    Servers.Add(new DnsEndPoint(server.Address, server.Port));
             }
 
             SocketPool = new SocketPoolConfiguration();

Enyim.Caching/Memcached/MemcachedNode.cs

@@ -35,8 +35,7 @@ public class MemcachedNode : IMemcachedNode
         public MemcachedNode(
             DnsEndPoint endpoint, 
             ISocketPoolConfiguration socketPoolConfig,
-            ILogger logger
-            )
+            ILogger logger)
         {
             this.endPoint = endpoint;
             this.config = socketPoolConfig;

Enyim.Caching/Memcached/PooledSocket.cs

@@ -46,8 +46,7 @@ public PooledSocket(DnsEndPoint endpoint, TimeSpan connectionTimeout, TimeSpan r
                 : (int)receiveTimeout.TotalMilliseconds;
 
             socket.ReceiveTimeout = rcv;
-            socket.SendTimeout = rcv;
-            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+            socket.SendTimeout = rcv;            
 
             ConnectWithTimeout(socket, endpoint, timeout);
 
@@ -59,8 +58,21 @@ public PooledSocket(DnsEndPoint endpoint, TimeSpan connectionTimeout, TimeSpan r
 
         private void ConnectWithTimeout(Socket socket, DnsEndPoint endpoint, int timeout)
         {
+            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
             var args = new SocketAsyncEventArgs();
-            args.RemoteEndPoint = endpoint;
+
+            //Workaround for https://github.com/dotnet/corefx/issues/26840
+            if (!IPAddress.TryParse(endpoint.Host, out var address))
+            {
+                address = Dns.GetHostAddresses(endpoint.Host).FirstOrDefault(ip => ip.AddressFamily == AddressFamily.InterNetwork);
+                if (address == null)
+                    throw new ArgumentException(String.Format("Could not resolve host '{0}'.", endpoint.Host));
+                args.RemoteEndPoint = new IPEndPoint(address, endpoint.Port);
+            }
+            else
+            {
+                args.RemoteEndPoint = endpoint;
+            }
 
             using (var mres = new ManualResetEventSlim())
             {