Exemple #1
0
        public async Task <NtpMessage> SendAsync()
        {
            var timeServerEndPoint = GetIPEndPoint(this.Server, NtpPort);

            NtpMessage responsePacket;
            Timestamp  transmitTimestamp;

            using (var updClient = new UdpClient(this.Port))
            {
                updClient.Connect(timeServerEndPoint);

                transmitTimestamp = new Timestamp(DateTime.UtcNow);
                var ntpPacket         = new NtpMessage(NtpVersion, Mode.Client, transmitTimestamp);
                var ntpRequestPayload = ntpPacket.GetBytes();

                await updClient.SendAsync(ntpRequestPayload, ntpRequestPayload.Length);

                // TODO Add timeout
                var response = await updClient.ReceiveAsync();

                responsePacket = new NtpMessage(response.Buffer, DateTime.UtcNow);
            }

            // Validate the response
            if (!ResponseIsValid(responsePacket, transmitTimestamp))
            {
                throw new InvalidOperationException("The response was not valid.");
            }

            return(responsePacket);
        }
Exemple #2
0
        private static bool ResponseIsValid(NtpMessage response, Timestamp transmitTimestamp)
        {
            if (response.Stratum == Stratum.Unspecified)
            {
                return(false);
            }

            if (response.OriginateTimestamp.Seconds != transmitTimestamp.Seconds)
            {
                return(false);
            }

            /*
             * https://tools.ietf.org/html/rfc4330
             * "4.  The server reply should be discarded if any of the LI, Stratum,
             * or Transmit Timestamp fields is 0 or the Mode field is not 4
             * (unicast) or 5 (broadcast)."
             *
             * LI should not be 3?
             */
            //if (response.LeapIndicator == LeapIndicator.NoWarning)
            //{
            //    return false;
            //}

            if (response.Mode != Mode.Server)
            {
                return(false);
            }

            if (response.TransmitTimestamp.Seconds == 0)
            {
                return(false);
            }

            if (response.RootDelay.Seconds >= 1)
            {
                return(false);
            }

            if (response.RootDispersion.Seconds >= 1)
            {
                return(false);
            }

            return(true);
        }