How to Get the Current Network Time from an NTP Server using C#?

Retrieving Network Time from an NTP Server with C#

This guide demonstrates a simple method for obtaining the current time from an NTP (Network Time Protocol) server using C#.

Here's the C# code:

using System;
using System.Net;
using System.Net.Sockets;

public static class NetworkTime
{
    public static DateTime GetNetworkTime()
    {
        const string ntpServer = "time.windows.com"; // Or another NTP server
        const int ntpDataSize = 48;
        const int serverReplyTimeOffset = 40;

        byte[] ntpData = new byte[ntpDataSize];
        IPAddress[] addresses = Dns.GetHostEntry(ntpServer).AddressList;

        using (Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
        {
            IPEndPoint ipEndPoint = new IPEndPoint(addresses[0], 123);
            socket.Connect(ipEndPoint);
            socket.ReceiveTimeout = 3000; // 3-second timeout
            socket.Send(ntpData);
            socket.Receive(ntpData);
        }

        ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTimeOffset);
        ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTimeOffset + 4);
        intPart = SwapEndianness(intPart);
        fractPart = SwapEndianness(fractPart);

        long milliseconds = (long)(intPart * 1000) + (long)((fractPart * 1000) / 0x100000000L);
        DateTime networkDateTime = new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddMilliseconds(milliseconds);

        return networkDateTime.ToLocalTime();
    }

    static uint SwapEndianness(ulong x)
    {
        return (uint)(((x & 0x000000ff) << 24) +
                       ((x & 0x0000ff00) << 8) +
                       ((x & 0x00ff0000) >> 8) +
                       ((x & 0xff000000) >> 24));
    }
}

Remember to add using System.Net; and using System.Net.Sockets; to your project. This improved version uses more descriptive variable names and clarifies the SwapEndianness function's return type for better readability and maintainability. A timeout is also added to the socket receive operation to prevent indefinite blocking.

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