Synchronise Time C#

Question

I have a program in C# .net that is deployed on different machines. I want all instances of this program to use a "DateTime" variable that is synchronized with windows time server.

What is the best way to do that ?

Answer 1

Update Begin

Another approach which I could think of is to expose a service which would return a UTC time in the machine it is running and use the same across other app running in other machines.

Update End

If you are aware of authoritive time server which supports Simple Network Time Protocol (SNTP) you can read the time using the Code documented at @ http://dotnet-snippets.com/snippet/simple-network-time-ntp-protocol-client/571

Placing the code below for reference.

/*
 * A C# SNTP Client
 * 
 * Copyright (C)2001-2003 Valer BOCAN <vbocan@dataman.ro>
 * All Rights Reserved
 * 
 * You may download the latest version from http://www.dataman.ro
 * Last modified: September 20, 2003
 *  
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, and/or sell copies of the Software, and to permit persons
 * to whom the Software is furnished to do so, provided that the above
 * copyright notice(s) and this permission notice appear in all copies of
 * the Software and that both the above copyright notice(s) and this
 * permission notice appear in supporting documentation.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
 * OF THIRD PARTY RIGHTS. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * HOLDERS INCLUDED IN THIS NOTICE BE LIABLE FOR ANY CLAIM, OR ANY SPECIAL
 * INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES WHATSOEVER RESULTING
 * FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
 * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
 * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Disclaimer
 * ----------
 * Although reasonable care has been taken to ensure the correctness of this
 * implementation, this code should never be used in any application without
 * proper verification and testing. I disclaim all liability and responsibility
 * to any person or entity with respect to any loss or damage caused, or alleged
 * to be caused, directly or indirectly, by the use of this SNTPClient class.
 *
 * Comments, bugs and suggestions are welcome.
 *
 * Update history:
 * September 20, 2003
 * - Renamed the class from NTPClient to SNTPClient.
 * - Fixed the RoundTripDelay and LocalClockOffset properties.
 *   Thanks go to DNH <dnharris@csrlink.net>.
 * - Fixed the PollInterval property.
 *   Thanks go to Jim Hollenhorst <hollenho@attbi.com>.
 * - Changed the ReceptionTimestamp variable to DestinationTimestamp to follow the standard
 *   more closely.
 * - Precision property is now shown is seconds rather than milliseconds in the
 *   ToString method.
 * 
 * May 28, 2002
 * - Fixed a bug in the Precision property and the SetTime function.
 *   Thanks go to Jim Hollenhorst <hollenho@attbi.com>.
 * 
 * March 14, 2001
 * - First public release.
 */

namespace InternetTime
{
    using System;
    using System.Net;
    using System.Net.Sockets;
    using System.Runtime.InteropServices;

    // Leap indicator field values
    public enum _LeapIndicator
    {
        NoWarning,      // 0 - No warning
        LastMinute61,   // 1 - Last minute has 61 seconds
        LastMinute59,   // 2 - Last minute has 59 seconds
        Alarm           // 3 - Alarm condition (clock not synchronized)
    }

    //Mode field values
    public enum _Mode
    {
        SymmetricActive,    // 1 - Symmetric active
        SymmetricPassive,   // 2 - Symmetric pasive
        Client,             // 3 - Client
        Server,             // 4 - Server
        Broadcast,          // 5 - Broadcast
        Unknown             // 0, 6, 7 - Reserved
    }

    // Stratum field values
    public enum _Stratum
    {
        Unspecified,            // 0 - unspecified or unavailable
        PrimaryReference,       // 1 - primary reference (e.g. radio-clock)
        SecondaryReference,     // 2-15 - secondary reference (via NTP or SNTP)
        Reserved                // 16-255 - reserved
    }

    /// <summary>
    /// SNTPClient is a C# class designed to connect to time servers on the Internet and
    /// fetch the current date and time. Optionally, it may update the time of the local system.
    /// The implementation of the protocol is based on the RFC 2030.
    /// 
    /// Public class members:
    ///
    /// LeapIndicator - Warns of an impending leap second to be inserted/deleted in the last
    /// minute of the current day. (See the _LeapIndicator enum)
    /// 
    /// VersionNumber - Version number of the protocol (3 or 4).
    /// 
    /// Mode - Returns mode. (See the _Mode enum)
    /// 
    /// Stratum - Stratum of the clock. (See the _Stratum enum)
    /// 
    /// PollInterval - Maximum interval between successive messages
    /// 
    /// Precision - Precision of the clock
    /// 
    /// RootDelay - Round trip time to the primary reference source.
    /// 
    /// RootDispersion - Nominal error relative to the primary reference source.
    /// 
    /// ReferenceID - Reference identifier (either a 4 character string or an IP address).
    /// 
    /// ReferenceTimestamp - The time at which the clock was last set or corrected.
    /// 
    /// OriginateTimestamp - The time at which the request departed the client for the server.
    /// 
    /// ReceiveTimestamp - The time at which the request arrived at the server.
    /// 
    /// Transmit Timestamp - The time at which the reply departed the server for client.
    /// 
    /// RoundTripDelay - The time between the departure of request and arrival of reply.
    /// 
    /// LocalClockOffset - The offset of the local clock relative to the primary reference
    /// source.
    /// 
    /// Initialize - Sets up data structure and prepares for connection.
    /// 
    /// Connect - Connects to the time server and populates the data structure.
    /// It can also update the system time.
    /// 
    /// IsResponseValid - Returns true if received data is valid and if comes from
    /// a NTP-compliant time server.
    /// 
    /// ToString - Returns a string representation of the object.
    /// 
    /// -----------------------------------------------------------------------------
    /// Structure of the standard NTP header (as described in RFC 2030)
    ///                       1                   2                   3
    ///   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |LI | VN  |Mode |    Stratum    |     Poll      |   Precision   |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                          Root Delay                           |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                       Root Dispersion                         |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                     Reference Identifier                      |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                                                               |
    ///  |                   Reference Timestamp (64)                    |
    ///  |                                                               |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                                                               |
    ///  |                   Originate Timestamp (64)                    |
    ///  |                                                               |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                                                               |
    ///  |                    Receive Timestamp (64)                     |
    ///  |                                                               |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                                                               |
    ///  |                    Transmit Timestamp (64)                    |
    ///  |                                                               |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                 Key Identifier (optional) (32)                |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ///  |                                                               |
    ///  |                                                               |
    ///  |                 Message Digest (optional) (128)               |
    ///  |                                                               |
    ///  |                                                               |
    ///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /// 
    /// -----------------------------------------------------------------------------
    /// 
    /// SNTP Timestamp Format (as described in RFC 2030)
    ///                         1                   2                   3
    ///     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    /// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /// |                           Seconds                             |
    /// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /// |                  Seconds Fraction (0-padded)                  |
    /// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /// 
    /// </summary>

    public class SNTPClient
    {
        // SNTP Data Structure Length
        private const byte SNTPDataLength = 48;
        // SNTP Data Structure (as described in RFC 2030)
        byte []SNTPData = new byte[SNTPDataLength];

        // Offset constants for timestamps in the data structure
        private const byte offReferenceID        = 12;
        private const byte offReferenceTimestamp = 16;
        private const byte offOriginateTimestamp = 24;
        private const byte offReceiveTimestamp   = 32;
        private const byte offTransmitTimestamp  = 40;

        // Leap Indicator
        public _LeapIndicator LeapIndicator
        {
            get
            {
                // Isolate the two most significant bits
                byte val = (byte)(SNTPData[0] >> 6);
                switch(val)
                {
                    case 0: return _LeapIndicator.NoWarning;
                    case 1: return _LeapIndicator.LastMinute61;
                    case 2: return _LeapIndicator.LastMinute59;
                    case 3: goto default;
                    default:
                            return _LeapIndicator.Alarm;
                }
            }
        }

        // Version Number
        public byte VersionNumber
        {
            get
            {
                // Isolate bits 3 - 5
                byte val = (byte)((SNTPData[0] & 0x38) >> 3);
                return val;
            }
        }

        // Mode
        public _Mode Mode
        {
            get
            {
                // Isolate bits 0 - 3
                byte val = (byte)(SNTPData[0] & 0x7);
                switch(val)
                {
                    case 0: goto default;
                    case 6: goto default;
                    case 7: goto default;
                    default:
                        return _Mode.Unknown;
                    case 1:
                        return _Mode.SymmetricActive;
                    case 2:
                        return _Mode.SymmetricPassive;
                    case 3:
                        return _Mode.Client;
                    case 4:
                        return _Mode.Server;
                    case 5:
                        return _Mode.Broadcast;
                }
            }
        }

        // Stratum
        public _Stratum Stratum
        {
            get
            {
                byte val = (byte)SNTPData[1];
                if(val == 0) return _Stratum.Unspecified;
                else
                    if(val == 1) return _Stratum.PrimaryReference;
                else
                    if(val <= 15) return _Stratum.SecondaryReference;
                else
                    return _Stratum.Reserved;
            }
        }

        // Poll Interval (in seconds)
        public uint PollInterval
        {
            get 
            {
                // Thanks to Jim Hollenhorst <hollenho@attbi.com>
                return (uint)(Math.Pow(2, (sbyte)SNTPData[2]));
            }
        }

        // Precision (in seconds)
        public double Precision
        {
            get
            {
                // Thanks to Jim Hollenhorst <hollenho@attbi.com>
                return (Math.Pow(2, (sbyte)SNTPData[3]));
            }
        }

        // Root Delay (in milliseconds)
        public double RootDelay
        {
            get
            {
                int temp = 0;
                temp = 256 * (256 * (256 * SNTPData[4] + SNTPData[5]) + SNTPData[6]) + SNTPData[7];
                return 1000 * (((double)temp) / 0x10000);
            }
        }

        // Root Dispersion (in milliseconds)
        public double RootDispersion
        {
            get
            {
                int temp = 0;
                temp = 256 * (256 * (256 * SNTPData[8] + SNTPData[9]) + SNTPData[10]) + SNTPData[11];
                return 1000 * (((double)temp) / 0x10000);
            }
        }

        // Reference Identifier
        public string ReferenceID
        {
            get
            {
                string val = "";
                switch(Stratum)
                {
                    case _Stratum.Unspecified:
                        goto case _Stratum.PrimaryReference;
                    case _Stratum.PrimaryReference:
                        val += (char)SNTPData[offReferenceID + 0];
                        val += (char)SNTPData[offReferenceID + 1];
                        val += (char)SNTPData[offReferenceID + 2];
                        val += (char)SNTPData[offReferenceID + 3];
                    break;
                    case _Stratum.SecondaryReference:
                        switch(VersionNumber)
                        {
                            case 3: // Version 3, Reference ID is an IPv4 address
                                string Address = SNTPData[offReferenceID + 0].ToString() + "." +
                                                 SNTPData[offReferenceID + 1].ToString() + "." +
                                                 SNTPData[offReferenceID + 2].ToString() + "." +
                                                 SNTPData[offReferenceID + 3].ToString();
                                try
                                    {
                                    IPHostEntry Host = Dns.GetHostEntry(Address);
                                    val = Host.HostName + " (" + Address + ")";
                                }
                                catch(Exception)
                                {
                                    val = "N/A";
                                }
                                break;
                            case 4: // Version 4, Reference ID is the timestamp of last update
                                DateTime time = ComputeDate(GetMilliSeconds(offReferenceID));
                                // Take care of the time zone
                                TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
                                val = (time + offspan).ToString();
                                break;
                            default:
                                val = "N/A";
                                break;
                        }
                        break;
                }

                return val;
            }
        }

        // Reference Timestamp
        public DateTime ReferenceTimestamp
        {
            get
            {
                DateTime time = ComputeDate(GetMilliSeconds(offReferenceTimestamp));
                // Take care of the time zone
                TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
                return time + offspan;
            }
        }

        // Originate Timestamp (T1)
        public DateTime OriginateTimestamp
        {
            get
            {
                return ComputeDate(GetMilliSeconds(offOriginateTimestamp));
            }
        }

        // Receive Timestamp (T2)
        public DateTime ReceiveTimestamp
        {
            get
            {
                DateTime time = ComputeDate(GetMilliSeconds(offReceiveTimestamp));
                // Take care of the time zone
                TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
                return time + offspan;
            }
        }

        // Transmit Timestamp (T3)
        public DateTime TransmitTimestamp
        {
            get
            {
                DateTime time = ComputeDate(GetMilliSeconds(offTransmitTimestamp));
                // Take care of the time zone
                TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
                return time + offspan;
            }
            set
            {
                SetDate(offTransmitTimestamp, value);
            }
        }

        // Destination Timestamp (T4)
        public DateTime DestinationTimestamp;

        // Round trip delay (in milliseconds)
        public int RoundTripDelay
        {
            get
            {
                // Thanks to DNH <dnharris@csrlink.net>
                TimeSpan span = (DestinationTimestamp - OriginateTimestamp) - (ReceiveTimestamp - TransmitTimestamp);
                return (int)span.TotalMilliseconds;
            }
        }

        // Local clock offset (in milliseconds)
        public int LocalClockOffset
        {
            get
            {
                // Thanks to DNH <dnharris@csrlink.net>
                TimeSpan span = (ReceiveTimestamp - OriginateTimestamp) + (TransmitTimestamp - DestinationTimestamp);
                return (int)(span.TotalMilliseconds / 2);
            }
        }

        // Compute date, given the number of milliseconds since January 1, 1900
        private DateTime ComputeDate(ulong milliseconds)
        {
            TimeSpan span = TimeSpan.FromMilliseconds((double)milliseconds);
            DateTime time = new DateTime(1900, 1, 1);
            time += span;
            return time;
        }

        // Compute the number of milliseconds, given the offset of a 8-byte array
        private ulong GetMilliSeconds(byte offset)
        {
            ulong intpart = 0, fractpart = 0;

            for(int i = 0; i <= 3; i++)
            {
                intpart = 256 * intpart + SNTPData[offset + i]; 
            }
            for(int i = 4; i<=7; i++)
            {
                fractpart = 256 * fractpart + SNTPData[offset + i];
            }
            ulong milliseconds = intpart * 1000 + (fractpart * 1000) / 0x100000000L;
            return milliseconds;
        }

        // Compute the 8-byte array, given the date
        private void SetDate(byte offset, DateTime date)
        {
            ulong intpart = 0, fractpart = 0;
            DateTime StartOfCentury = new DateTime(1900, 1, 1, 0, 0, 0);    // January 1, 1900 12:00 AM

            ulong milliseconds = (ulong)(date - StartOfCentury).TotalMilliseconds;
            intpart = milliseconds / 1000;
            fractpart=((milliseconds % 1000) * 0x100000000L) / 1000;

            ulong temp = intpart;
            for(int i = 3; i >= 0; i--)
            {
                SNTPData[offset + i] = (byte) (temp % 256);
                temp = temp / 256;
            }

            temp = fractpart;
            for(int i = 7; i >=4; i--)
            {
                SNTPData[offset + i] = (byte) (temp % 256);
                temp = temp / 256;
            }
        }

        // Initialize the NTPClient data
        private void Initialize()
        {
            // Set version number to 4 and Mode to 3 (client)
            SNTPData[0] = 0x1B;
            // Initialize all other fields with 0
            for(int i = 1; i < 48; i++)
            {
                SNTPData[i] = 0;
            }
            // Initialize the transmit timestamp
            TransmitTimestamp = DateTime.Now;
        }

        public SNTPClient(string host)
        {
            TimeServer = host;
        }

        // Connect to the time server and update system time
        public void Connect(bool UpdateSystemTime)
        {
            try {
                // Resolve server address
                IPHostEntry hostadd = Dns.GetHostEntry(TimeServer);
                IPEndPoint EPhost = new IPEndPoint(hostadd.AddressList[0], 123);

                //Connect the time server
                UdpClient TimeSocket = new UdpClient();
                TimeSocket.Connect(EPhost);

                // Initialize data structure
                Initialize();
                TimeSocket.Send(SNTPData, SNTPData.Length);
                SNTPData = TimeSocket.Receive(ref EPhost);
                if(!IsResponseValid())
                {
                    throw new Exception("Invalid response from " + TimeServer);
                }
                DestinationTimestamp = DateTime.Now;
            } catch(SocketException e)
              {
                throw new Exception(e.Message);
              }

            // Update system time
            if(UpdateSystemTime)
            {
                SetTime();
            }
        }

        // Check if the response from server is valid
        public bool IsResponseValid()
        {
            if(SNTPData.Length < SNTPDataLength || Mode != _Mode.Server)
            {
                return false;
            }
            else
            {
                return true;
            }
        }

        // Converts the object to string
        public override string ToString()
        {
            string str;

            str = "Leap Indicator: ";
            switch(LeapIndicator)
            {
                case _LeapIndicator.NoWarning:
                    str += "No warning";
                    break;
                case _LeapIndicator.LastMinute61:
                    str += "Last minute has 61 seconds";
                    break;
                case _LeapIndicator.LastMinute59:
                    str += "Last minute has 59 seconds";
                    break;
                case _LeapIndicator.Alarm:
                    str += "Alarm Condition (clock not synchronized)";
                    break;
            }
            str += "\r\nVersion number: " + VersionNumber.ToString() + "\r\n";
            str += "Mode: ";
            switch(Mode)
            {
                case _Mode.Unknown:
                    str += "Unknown";
                    break;
                case _Mode.SymmetricActive:
                    str += "Symmetric Active";
                    break;
                case _Mode.SymmetricPassive:
                    str += "Symmetric Pasive";
                    break;
                case _Mode.Client:
                    str += "Client";
                    break;
                case _Mode.Server:
                    str += "Server";
                    break;
                case _Mode.Broadcast:
                    str += "Broadcast";
                    break;
            }
            str += "\r\nStratum: ";
            switch(Stratum)
            {
                case _Stratum.Unspecified:
                case _Stratum.Reserved:
                    str += "Unspecified";
                    break;
                case _Stratum.PrimaryReference:
                    str += "Primary Reference";
                    break;
                case _Stratum.SecondaryReference:
                    str += "Secondary Reference";
                    break;
            }
            str += "\r\nLocal time: " + TransmitTimestamp.ToString();
            str += "\r\nPrecision: " + Precision.ToString() + " s";
            str += "\r\nPoll Interval: " + PollInterval.ToString() + " s";
            str += "\r\nReference ID: " + ReferenceID.ToString();
            str += "\r\nRoot Delay: " + RootDelay.ToString() + " ms";
            str += "\r\nRoot Dispersion: " + RootDispersion.ToString() + " ms";
            str += "\r\nRound Trip Delay: " + RoundTripDelay.ToString() + " ms";
            str += "\r\nLocal Clock Offset: " + LocalClockOffset.ToString() + " ms";
            str += "\r\n";

            return str;
        }

        // SYSTEMTIME structure used by SetSystemTime
        [StructLayoutAttribute(LayoutKind.Sequential)]
        private struct SYSTEMTIME
            {
                public short year;
                public short month;
                public short dayOfWeek;
                public short day;
                public short hour;
                public short minute;
                public short second;
                public short milliseconds;
            }

        [DllImport("kernel32.dll")]
                static extern bool SetLocalTime(ref SYSTEMTIME time);


        // Set system time according to transmit timestamp
        private void SetTime()
        {
            SYSTEMTIME st;

            // Thanks to Jim Hollenhorst <hollenho@attbi.com>
            DateTime trts = DateTime.Now.AddMilliseconds(LocalClockOffset);

            st.year = (short)trts.Year;
            st.month = (short)trts.Month;
            st.dayOfWeek = (short)trts.DayOfWeek;
            st.day = (short)trts.Day;
            st.hour = (short)trts.Hour;
            st.minute = (short)trts.Minute;
            st.second = (short)trts.Second;
            st.milliseconds = (short)trts.Millisecond;

            SetLocalTime(ref st);
        }

        // The URL of the time server we're connecting to
        private string TimeServer;
    }
}

Answer 2

Use a time server or a time server. This will allow you to affirmatively know that all callers to the server are synchronized with a high degree of accuracy.

It is best to use this in scenarios where relying on the servers synchronization service is not adequate. Azure for example is a case that comes to mind...