Getting TCP timestamp

[g.katsarov]

Hello, 

I want to get the timestamp of a tcp packet, I had a look in the tcp.cpp file but my limited programming knowledge I am not able to get it right. I would be very grateful if somebody could help me whit this, thank you in advance.

[Matias Fontanini]

You can get the timestamp from a Packet object. Something like:

Sniffer sniffer = ...;

while (Packet pkt = sniffer.next_packet()) {

    Timestamp ts = pkt.timestamp();

}

See the documentation in case you are in doubt:

http://libtins.github.io/docs/latest/d9/d36/classTins_1_1Timestamp.html

http://libtins.github.io/docs/latest/da/da0/classTins_1_1Packet.html

[g.katsarov]

Thank you Matias, I will try it on Monday because I am writing it in the University.

[g.katsarov]

I am trying to do it for Sniffer::sniff_loop in the callback function. That seems to work but haven't checked it properly yet.
         
            while (Packet pkt = pdu.rfind_pdu<RawPDU>()) {
                Timestamp ts = pkt.timestamp();
                std::cout << "Ts: " << pkt.timestamp().seconds()<< std::endl;

            }

On Saturday, 17 January 2015 00:53:17 UTC+1, Matias Fontanini wrote:

[Matias Fontanini]

You can't get a timestamp on the sniff_loop callback function. If you want a timestamp, you need to use Sniffer::next_packet.

[g.katsarov]

It is giving some possible output but I haven't checked it properly, so I guess you are right. So what can I do? This is basically the structure:

#include "Psnifferlibtins.h"

using namespace Tins;

using namespace std;

int CBHandler::sniffer(char* device)

{

Sniffer sniffer(device);

sniffer.sniff_loop(std::bind(

&CBHandler::sniffer_callback,

            this,

            std::placeholders::_1)

);

return 0;

}

bool CBHandler::sniffer_callback(const PDU &pdu)

{

        const RawPDU &raw = pdu.rfind_pdu<RawPDU>();      

const IP &ip = pdu.rfind_pdu<IP>();

const TCP &tcp = pdu.rfind_pdu<TCP>();

        //a lot of things that are not important here

return true;
}

[Matias Fontanini]

Just translate it so you use Packet:

int CBHandler::sniffer(char* device)

{

Sniffer sniffer(device);

while (Packet pkt = sniffer.next_packet()) {

             sniffer_callback(pkt);

        }

return 0;

}

bool CBHandler::sniffer_callback(const Packet &pkt)

{

     const auto timestamp = pkt.timestamp();

     const PDU& pdu = *pkt.packet();

     const RawPDU &raw = pdu.rfind_pdu<RawPDU>();

// same as before

[g.katsarov]

But in this case do I need the CBHandler struct(that's why I am doing the bind with the placeholders like one of your examples), I used in order to keep the values of some of the variables that I didn't want to get changed with every packet entering the loop. Or now with the next_packet I won't have this problem. There are few examples with the next_packet and I really don't understand, I am sorry. 

[Matias Fontanini]

That code is the exact equivalent of your previous code, except now you have the timestamp.

[g.katsarov]

Thank you for the prompt response, I will think on it and try it tomorrow in the university because it is 01:07 AM in Germany. 

[g.katsarov]

Shouldn't it be const PDU& pdu = *pkt.pdu(); instead of const PDU& pdu = *pkt.packet(); in order to get the pdu?

On Tuesday, 20 January 2015 00:58:51 UTC+1, Matias Fontanini wrote:

[g.katsarov]

If i have const PDU& pdu = *pkt.packet(); I get the following errors:
'const class Tins::Packet' has no member named 'packet'
Method 'packet' could not be resolved

If I have const PDU& pdu = *pkt.Packet(); I get the following error:
error: invalid use of 'Tins::Packet::Packet'

If I have const PDU& pdu = *pkt.pdu(); I get the following output:
terminate called after throwing an instance of 'Tins::pdu_not_found'
  what():  PDU not found
Aborted (core dumped)

[Matias Fontanini]

It is the last choice, pdu(). You get that exception since you lookeed for a PDU which is not in that packet. Catch the exception and go on

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[g.katsarov]

Ok, so my question is how to declare "raw" out of the try function because afterwards it is not recognized and the only lame solution I am capable of is to put the rest in the try function.

    const auto timestamp = pkt.timestamp().seconds();                                        
    cout << "ts: " << timestamp;

    const PDU &pdu = *pkt.pdu();

    try
    {

        const RawPDU &raw = pdu.rfind_pdu<RawPDU>();
    }

    catch (Tins::pdu_not_found e)
    {
        cout << "An exception occurred. Exception Nr.'\n'";
        return true;

[Matias Fontanini]

Although I'd like to help you, this question falls outside of the scope of the library, it's more like a basic programming question. Please use other resources to solve this, like stackoverflow, etc.

[g.katsarov]

Ok, thank you, I just don't have enough knowledge in C++.

[Georgi Katsarov]

Everything is working perfectly, thank you for all your assistance.