How to get DateTime from the internet?

How to get current date and time from internet or server using C#? I am trying to get time as follows:

public static DateTime GetNetworkTime (string ntpServer)
{
    IPAddress[] address = Dns.GetHostEntry(ntpServer).AddressList;

    if (address == null || address.Length == 0)
        throw new ArgumentException("Could not resolve ip address from '" + ntpServer + "'.", "ntpServer");

    IPEndPoint ep = new IPEndPoint(address[0], 123);
    return GetNetworkTime(ep);
}

I am passing server IP address as netServer, but it does not work properly.

For environments where port 13 is blocked, time from NIST can be web scraped as below,

public static DateTime GetNistTime()
{
    DateTime dateTime = DateTime.MinValue;

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://nist.time.gov/actualtime.cgi?lzbc=siqm9b");
    request.Method = "GET";
    request.Accept = "text/html, application/xhtml+xml, */*";
    request.UserAgent = "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)";
    request.ContentType = "application/x-www-form-urlencoded";
    request.CachePolicy = new RequestCachePolicy(RequestCacheLevel.NoCacheNoStore); //No caching
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    if (response.StatusCode == HttpStatusCode.OK)
    {
        StreamReader stream = new StreamReader(response.GetResponseStream());
        string html = stream.ReadToEnd();//<timestamp time=\"1395772696469995\" delay=\"1395772696469995\"/>
        string time = Regex.Match(html, @"(?<=\btime="")[^""]*").Value;
        double milliseconds = Convert.ToInt64(time) / 1000.0;
        dateTime = new DateTime(1970, 1, 1).AddMilliseconds(milliseconds).ToLocalTime();
    }

    return dateTime;
}

Here is code sample that you can use to retrieve time from NIST Internet Time Service

var client = new TcpClient("time.nist.gov", 13);
using (var streamReader = new StreamReader(client.GetStream()))
{
    var response = streamReader.ReadToEnd();
    var utcDateTimeString = response.Substring(7, 17);
    var localDateTime = DateTime.ParseExact(utcDateTimeString, "yy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal);
}

Here is a quick code to get the time from the header, works without the need of port 13

public static DateTime GetNistTime()
{
    var myHttpWebRequest = (HttpWebRequest)WebRequest.Create("http://www.microsoft.com");
    var response = myHttpWebRequest.GetResponse();
    string todaysDates = response.Headers["date"];
    return DateTime.ParseExact(todaysDates, 
                               "ddd, dd MMM yyyy HH:mm:ss 'GMT'", 
                               CultureInfo.InvariantCulture.DateTimeFormat, 
                               DateTimeStyles.AssumeUniversal);
}

Things could go wrong. All implements of the code founded above are prone to errors. Sometimes, it works and sometimes it trows a WebExpection error message.

A better implementation:

        try{
            using (var response = 
              WebRequest.Create("http://www.google.com").GetResponse())
                //string todaysDates =  response.Headers["date"];
                return DateTime.ParseExact(response.Headers["date"],
                    "ddd, dd MMM yyyy HH:mm:ss 'GMT'",
                    CultureInfo.InvariantCulture.DateTimeFormat,
                    DateTimeStyles.AssumeUniversal);
        }
        catch (WebException)
        {
            return DateTime.Now; //In case something goes wrong. 
        }

Conclusion:

Having your web app depend on a service that provides accurate date information is critical. I have used one of the code founded here in my app and it really mess things up.

One more version of the same idea:

public static class InternetTime
{
    public static DateTimeOffset? GetCurrentTime()
    {
        using (var client = new HttpClient())
        {
            try
            {
                var result = client.GetAsync("https://google.com", 
                      HttpCompletionOption.ResponseHeadersRead).Result;
                return result.Headers.Date;
            }
            catch
            {
                return null;
            }
        }
    }
}

Here HttpCompletionOption.ResponseHeadersRead is used to prevent loading of the rest of the response, as we need only HTTP headers.

Use InternetTime.GetCurrentTime().Value.ToLocalTime() to get current local time.

Important: first check the avaible servers on NIST Internet Time Servers.

public static DateTime GetServerTime()
{
    var result = DateTime.Now;

    // Initialize the list of NIST time servers
    // http://tf.nist.gov/tf-cgi/servers.cgi
    string[] servers = new string[] {
        "time-c.nist.gov",
        "time-d.nist.gov",
        "nist1-macon.macon.ga.us",
        "wolfnisttime.com",
        "nist.netservicesgroup.com",
        "nisttime.carsoncity.k12.mi.us",
        "nist1-lnk.binary.net",
        "wwv.nist.gov",
        "time.nist.gov",
        "utcnist.colorado.edu",
        "utcnist2.colorado.edu",
        "nist-time-server.eoni.com",
        "nist-time-server.eoni.com"
    };
    
    Random rnd = new Random();
    
    foreach (string server in servers.OrderBy(x => rnd.NextDouble()).Take(9))
    {                
        try
        {
            // Connect to the server (at port 13) and get the response. Timeout max 1second
            string serverResponse = string.Empty;
            var tcpClient = new TcpClient(); 
            
            if (tcpClient.ConnectAsync(server, 13).Wait(1000))
            {
                using (var reader = new StreamReader(tcpClient.GetStream()))
                {
                    serverResponse = reader.ReadToEnd();
                }
            }         
            
            // If a response was received
            if (!string.IsNullOrEmpty(serverResponse))
            {
                // Split the response string ("55596 11-02-14 13:54:11 00 0 0 478.1 UTC(NIST) *")
                string[] tokens = serverResponse.Split(' ');

                // Check the number of tokens
                if (tokens.Length >= 6)
                {
                    // Check the health status
                    string health = tokens[5];
                    if (health == "0")
                    {
                        // Get date and time parts from the server response
                        string[] dateParts = tokens[1].Split('-');
                        string[] timeParts = tokens[2].Split(':');

                        // Create a DateTime instance
                        DateTime utcDateTime = new DateTime(
                            Convert.ToInt32(dateParts[0]) + 2000,
                            Convert.ToInt32(dateParts[1]), Convert.ToInt32(dateParts[2]),
                            Convert.ToInt32(timeParts[0]), Convert.ToInt32(timeParts[1]),
                            Convert.ToInt32(timeParts[2]));

                        // Convert received (UTC) DateTime value to the local timezone
                        result = utcDateTime.ToLocalTime();

                        return result;
                        // Response successfully received; exit the loop
                    }
                }
            }
        }
        catch
        {
            // Ignore exception and try the next server
        }
    }
    return result;
}

    public static Nullable<DateTime> GetDateTime()
    {
        Nullable<DateTime> dateTime = null;
        System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)System.Net.WebRequest.Create("http://www.microsoft.com");
        request.Method = "GET";
        request.Accept = "text/html, application/xhtml+xml, */*";
        request.UserAgent = "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)";
        request.ContentType = "application/x-www-form-urlencoded";
        request.CachePolicy = new System.Net.Cache.RequestCachePolicy(System.Net.Cache.RequestCacheLevel.NoCacheNoStore);
        try
        {
            System.Net.HttpWebResponse response = (System.Net.HttpWebResponse)request.GetResponse();
            if (response.StatusCode == System.Net.HttpStatusCode.OK)
            {
                string todaysDates = response.Headers["date"];

                dateTime = DateTime.ParseExact(todaysDates, "ddd, dd MMM yyyy HH:mm:ss 'GMT'",
                    System.Globalization.CultureInfo.InvariantCulture.DateTimeFormat, System.Globalization.DateTimeStyles.AssumeUniversal);
            }
        }
        catch
        {
            dateTime = null;
        }
        return dateTime;
    }