Posts tagged ‘WinPcap’

How to read a PCap file from Wireshark with C++

In my Computer Security class I am taking as part of my Masters of Computer Science course, we need to parse a Pcap dump file.


It is expected you have Visual Studio 2010 already. It may work the same with Visual C++ 2010.

Step 1 – Install Wireshark

We are going to use Wireshark to get a packet capture. Wireshark is a nice easy tool to get a packet capture.

Make sure to install Wireshark and let Wireshark install WinPcap when it prompts you.

Step 2 – Create a new project in Visual Studio

I already have post on creating a WinPcap project in Visual Studio and getting it to compile, so follow it.

How to compile WinPcap with Visual Studio 2010?

Step 3 – Get a packet capture.

  1. Open Wireshark and start capturing file.
  2. Open your browser or go to a few sites.
  3. Stop the packet capture.
  4. Save the packet capture to a file.
    I named my file smallcapture.pcap.

Step 4 – Add C++ code to read the packet capture

I am going to paste the code for you and put the comments and steps in the code.

* How to read a packet capture file.

* Step 1 - Add includes
#include <string>
#include <iostream>
#include <pcap.h>

using namespace std;

int main(int argc, char *argv[])
	* Step 2 - Get a file name

	string file = "C:\\users\\jared\\testfiles\\smallcapture.pcap";

	* Step 3 - Create an char array to hold the error.

	// Note: errbuf in pcap_open functions is assumed to be able to hold at least PCAP_ERRBUF_SIZE chars
	//       PCAP_ERRBUF_SIZE is defined as 256.
	char errbuff[PCAP_ERRBUF_SIZE];

	* Step 4 - Open the file and store result in pointer to pcap_t

	// Use pcap_open_offline
	pcap_t * pcap = pcap_open_offline(file.c_str(), errbuff);

	* Step 5 - Create a header and a data object

	// Create a header object:
	struct pcap_pkthdr *header;

	// Create a character array using a u_char
	// u_char is defined here:
	// C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Include\WinSock2.h
	// typedef unsigned char   u_char;
	const u_char *data;

	* Step 6 - Loop through packets and print them to screen
	u_int packetCount = 0;
	while (int returnValue = pcap_next_ex(pcap, &header, &data) >= 0)
		// Print using printf. See printf reference:

		// Show the packet number
		printf("Packet # %i\n", ++packetCount);

		// Show the size in bytes of the packet
		printf("Packet size: %d bytes\n", header->len);

		// Show a warning if the length captured is different
		if (header->len != header->caplen)
			printf("Warning! Capture size different than packet size: %ld bytes\n", header->len);

		// Show Epoch Time
		printf("Epoch Time: %d:%d seconds\n", header->ts.tv_sec, header->ts.tv_usec);

		// loop through the packet and print it as hexidecimal representations of octets
		// We also have a function that does this similarly below: PrintData()
		for (u_int i=0; (i < header->caplen ) ; i++)
			// Start printing on the next after every 16 octets
			if ( (i % 16) == 0) printf("\n");

			// Print each octet as hex (x), make sure there is always two characters (.2).
			printf("%.2x ", data[i]);

		// Add two lines between packets

You are now reading packets in C++. Now you can start working on differentiating the packet types.