Ntp client does not work! urgent!

[kknd]

for example i got print
1
18446744072894420334
18446744071623573120
fr 9. apr 23:06:54 2010
3
18446744073709551521
18446744071623573120
to 7. feb 07:26:41 2036

one correct, one wrong, just in 2 seconds after i clicked connect time server button. here is the wrong time i got(or calculated after i got the udp packet)

No.     Time        Source                Destination           Protocol Info
   1725 860.103066  207.46.232.182        192.168.1.104         NTP      NTP server
 
Frame 1725 (90 bytes on wire, 90 bytes captured)
Ethernet II, Src: Arcadyan_98:a7:bc (00:1a:2a:98:a7:bc), Dst: CompalCo_66:ef:cb (00:16:d4:66:ef:cb)
Internet Protocol, Src: 207.46.232.182 (207.46.232.182), Dst: 192.168.1.104 (192.168.1.104)
User Datagram Protocol, Src Port: ntp (123), Dst Port: 19277 (19277)
Network Time Protocol
    Flags: 0x1c
        00.. .... = Leap Indicator: no warning (0)
        ..01 1... = Version number: NTP Version 3 (3)
        .... .100 = Mode: server (4)
    Peer Clock Stratum: secondary reference (3)
    Peer Polling Interval: invalid (0)
    Peer Clock Precision: 0,015625 sec
    Root Delay:    0,0716 sec
    Root Dispersion:    0,0804 sec
    Reference Clock ID: 69.36.241.112
    Reference Clock Update Time: Apr  9, 2010 21:07:27,5338 UTC
    Originate Time Stamp: NULL
    Receive Time Stamp: Apr  9, 2010 21:11:45,3768 UTC
    Transmit Time Stamp: Apr  9, 2010 21:11:45,3768 UTC
 
0000  00 16 d4 66 ef cb 00 1a 2a 98 a7 bc 08 00 45 00   ...f....*.....E.
0010  00 4c c3 71 00 00 76 11 07 3a cf 2e e8 b6 c0 a8   .L.q..v..:......
0020  01 68 00 7b 4b 4d 00 38 13 4f 1c 03 00 fa 00 00   .h.{KM.8.O......
0030  12 56 00 00 14 92 45 24 f1 70 cf 6a 15 8f 88 a4   .V....E$.p.j....
0040  aa 6e 00 00 00 00 00 00 00 00 cf 6a 16 91 60 73   .n.........j..`s
0050  83 85 cf 6a 16 91 60 73 83 85                     ...j..`s..

No.     Time        Source                Destination           Protocol Info
   1725 860.103066  207.46.232.182        192.168.1.104         NTP      NTP server

Frame 1725 (90 bytes on wire, 90 bytes captured)
Ethernet II, Src: Arcadyan_98:a7:bc (00:1a:2a:98:a7:bc), Dst: CompalCo_66:ef:cb (00:16:d4:66:ef:cb)
Internet Protocol, Src: 207.46.232.182 (207.46.232.182), Dst: 192.168.1.104 (192.168.1.104)
User Datagram Protocol, Src Port: ntp (123), Dst Port: 19277 (19277)
Network Time Protocol
    Flags: 0x1c
        00.. .... = Leap Indicator: no warning (0)
        ..01 1... = Version number: NTP Version 3 (3)
        .... .100 = Mode: server (4)
    Peer Clock Stratum: secondary reference (3)
    Peer Polling Interval: invalid (0)
    Peer Clock Precision: 0,015625 sec
    Root Delay:    0,0716 sec
    Root Dispersion:    0,0804 sec
    Reference Clock ID: 69.36.241.112
    Reference Clock Update Time: Apr  9, 2010 21:07:27,5338 UTC
    Originate Time Stamp: NULL
    Receive Time Stamp: Apr  9, 2010 21:11:45,3768 UTC
    Transmit Time Stamp: Apr  9, 2010 21:11:45,3768 UTC

0000  00 16 d4 66 ef cb 00 1a 2a 98 a7 bc 08 00 45 00   ...f....*.....E.
0010  00 4c c3 71 00 00 76 11 07 3a cf 2e e8 b6 c0 a8   .L.q..v..:......
0020  01 68 00 7b 4b 4d 00 38 13 4f 1c 03 00 fa 00 00   .h.{KM.8.O......
0030  12 56 00 00 14 92 45 24 f1 70 cf 6a 15 8f 88 a4   .V....E$.p.j....
0040  aa 6e 00 00 00 00 00 00 00 00 cf 6a 16 91 60 73   .n.........j..`s
0050  83 85 cf 6a 16 91 60 73 83 85                     ...j..`s..

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[squidge]

Yes, that's because your readPendingDatagrams method is incorrect. You should read into a buffer and then take the last 8 bytes of that buffer. Currently you are just overwriting the same buffer until you run out of bytes to read, so the buffer can be invalid unless it is segmented right by the tcp protocol. So it will work sometimes and not at all at others.

[kknd]

I see, but how to code that, any idea? could not code more then that.. i can not still get the correct time but sometimes..

while (udpSocket->hasPendingDatagrams()) {
    QByteArray byteArray;
    byteArray = udpSocket->read(48);
    ui->textEdit->append(QString::number(byteArray.size()));
 
    QByteArray lastbyteArray(byteArray.right(8));
 
    quint64 seconds = 0;
    for (int i=0; i<=3; ++i)
    {
         seconds = (seconds << 8) | lastbyteArray[i];
    }
 
    ui->textEdit->append(QString::number(seconds, 10));

while (udpSocket->hasPendingDatagrams()) {
    QByteArray byteArray;
    byteArray = udpSocket->read(48);
    ui->textEdit->append(QString::number(byteArray.size()));

    QByteArray lastbyteArray(byteArray.right(8));

    quint64 seconds = 0;
    for (int i=0; i<=3; ++i)
    {
         seconds = (seconds << 8) | lastbyteArray[i];
    }

    ui->textEdit->append(QString::number(seconds, 10));

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[squidge]

Each time you call udpSocket->read you need to append onto the end of your buffer. I don't think I need to describe how to do that

Secondly, there's a chance that readyRead occurs more than once, as you may not receive all the data in a single call, so your method needs to know how much data to expect, and only parse the data when it has received a full & valid packet.