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- public static DateTime GetNetworkTime()
- {
- //default Windows time server
- const string ntpServer = "time.windows.com";
- // NTP message size - 16 bytes of the digest (RFC 2030)
- var ntpData = new byte[48];
- //Setting the Leap Indicator, Version Number and Mode values
- ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)
- var addresses = Dns.GetHostEntry(ntpServer).AddressList;
- //The UDP port number assigned to NTP is 123
- var ipEndPoint = new IPEndPoint(addresses[0], 123);
- //NTP uses UDP
- var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
- socket.Connect(ipEndPoint);
- socket.Send(ntpData);
- socket.Receive(ntpData);
- socket.Close();
- //Offset to get to the "Transmit Timestamp" field (time at which the reply
- //departed the server for the client, in 64-bit timestamp format."
- const byte serverReplyTime = 40;
- //Get the seconds part
- ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);
- //Get the seconds fraction
- ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);
- //Convert From big-endian to little-endian
- intPart = SwapEndianness(intPart);
- fractPart = SwapEndianness(fractPart);
- var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);
- //**UTC** time
- var networkDateTime = (new DateTime(1900, 1, 1)).AddMilliseconds((long)milliseconds);
- return networkDateTime;
- }
- // stackoverflow.com/a/3294698/162671
- static uint SwapEndianness(ulong x)
- {
- return (uint) (((x & 0x000000ff) << 24) +
- ((x & 0x0000ff00) << 8) +
- ((x & 0x00ff0000) >> 8) +
- ((x & 0xff000000) >> 24));
- }
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