[Winpcap-users] pcap_next and timeval

[Gianluca Varenni]

----- Original Message ----- 
From: "Tom Brown" <brown at esteem.com>
To: <winpcap-users at winpcap.org>
Sent: Monday, March 16, 2009 2:49 PM
Subject: [Winpcap-users] pcap_next and timeval


> Hi,
>
> I'm writing a C extension to python that makes use of winpcap. The
> existing extensions do not do everything I need.
>
> I'm sending raw ethernet packets to several wireless devices. I am
> trying to determine the time it takes for the devices to respond the to
> the packets I'm sending out. I send to one device at a time and wait for
> it to reply. The device with the wired connection will respond with the
> fastest time.
>
> The network looks like this:
>
> pc---switch---d1***d2***d3***d4***d5
>        |
>        |
>        |
>     company
>     netowrk
>
> I'm using gettimeofday() in my C extension before I call pcap_send().
> When I capture the response with pcap_next(), the timeval is sometimes
> less than the value given by the call to gettimeofday(). I'm using
> gettimeofday() because I'm using mingw32 to compile the extension.
>
> I found this post:
> http://www.winpcap.org/pipermail/winpcap-users/2006-September/001394.html
>
> I also looked in packetNtx\driver\time_calls.h. So, to get the time the
> same way winpcap does, I'd have to call KeQueryPerformanceCounter() and
> KeQuerySystemTime(). However, I won't be able to do that from a user
> application.
>

The corresponding user level API for KeQueryPerforamnceCounter is 
QueryPerformanceCounter (i.e. without Ke).

http://msdn.microsoft.com/en-us/library/ms644904.aspx

Have a nice day
GV

> Is there another way of getting the time that would be more accurate
> than gettimeofday()?
>
> Thanks,
> Tom
>
> PS: Here's my extension function.
>
> static PyObject *Packet32_time(Packet32Object *self, PyObject *args)
> {
> pcap_t *pcap;
> u_char *buf;
> int length;
> PyObject *pyBuf;
> struct pcap_pkthdr header;
> const u_char *pkt_data;
> const u_char *ret;
> PyObject *t;
> struct timeval tv1;
> struct timeval tv2;
> struct timeval tvres;
> int timeout;
>
> if (!PyArg_ParseTuple(args, "Oi:time", &pyBuf, &timeout))
> return NULL;
>
> t = PyTuple_New(3);
>
> pcap = (pcap_t *)PyInt_AS_LONG(self->pcap);
> PyString_AsStringAndSize(pyBuf, (char **)&buf, &length);
>
> if (gettimeofday(&tv1, NULL) == -1) {
> PyTuple_SET_ITEM(t, 0, Py_BuildValue("i", 2));
> PyTuple_SET_ITEM(t, 1, Py_BuildValue("i", 0));
> PyTuple_SET_ITEM(t, 2, Py_BuildValue("i", 0));
> return t;
> }
>
> if (pcap_sendpacket(pcap, buf, length) != 0) {
> PyTuple_SET_ITEM(t, 0, Py_BuildValue("i", 3));
> PyTuple_SET_ITEM(t, 1, Py_BuildValue("i", 0));
> PyTuple_SET_ITEM(t, 2, Py_BuildValue("i", 0));
> return t;
> }
>
> do {
> ret = pcap_next(pcap, &header);
> if (gettimeofday(&tv2, NULL) == -1) {
> PyTuple_SET_ITEM(t, 0, Py_BuildValue("i", 2));
> PyTuple_SET_ITEM(t, 1, Py_BuildValue("i", 0));
> PyTuple_SET_ITEM(t, 2, Py_BuildValue("i", 0));
> return t;
> }
> timersub(&tv2, &tv1, &tvres);
> } while ((ret == NULL) && (tvres.tv_usec < timeout));
>
>
> if (ret != NULL) {
> timersub(&header.ts, &tv1, &tvres);
> PyTuple_SET_ITEM(t, 0, Py_BuildValue("i", 1));
> PyTuple_SET_ITEM(t, 1, Py_BuildValue("i",
> tvres.tv_usec));
> PyTuple_SET_ITEM(t, 2, Py_BuildValue("i",
> tvres.tv_sec));
> } else {
> PyTuple_SET_ITEM(t, 0, Py_BuildValue("i", 0));
> PyTuple_SET_ITEM(t, 1, Py_BuildValue("i", 0));
> PyTuple_SET_ITEM(t, 2, Py_BuildValue("i", 0));
> }
> return t;
> }
>
>
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