awdad

#include <stdio.h>

#define DATA_OFFSET_POS 12

int main (int argc, char *argv[]) {

	FILE *fp_in;
	FILE *fp_out;

	if (argc != 3) {
		perror("Usage: <input file> <output file>");
		return 1;
	}

	if ((fp_in = fopen(argv[1], "rb")) == 0) {
		perror("Cannot find input file");
		return 2;
	}
	if ((fp_out = fopen(argv[2], "wb")) == 0) {
		perror("Cannot find output file");
		return 3;
	}

	fseek(fp_in, 0L, SEEK_END);
	int filelen = ftell(fp_in);
	rewind(fp_in);

	int fp_count = 0;
	unsigned int IHL;
	unsigned int packet_size;
	unsigned int data_offset;
	unsigned int header_size;
	unsigned int data_length;
	while (fp_count < filelen) {

		fseek(fp_in, fp_count, SEEK_SET);
		printf("Offset : %u\n", fp_count);

		// determine IHL for this packet
		unsigned char bytes[4];
		printf("Offset before read : %i\n", (int) ftell(fp_in));
		fread(bytes, 1, 4, fp_in);
		printf("Offset after read : %i\n", (int) ftell(fp_in));
		IHL = bytes[0] & 0x0F;

		// determine packet_size for this packet
		packet_size = (((int)bytes[2])<<8) | ((int)bytes[3]);
		printf("Therefore, offset of packet_size : %i\n", (int) ftell(fp_in)-2);
		printf("Packet Size : %u\n", packet_size);

		// determine data_offset for this packet
		fseek(fp_in, fp_count + DATA_OFFSET_POS + (IHL*4), SEEK_SET);
		unsigned char bytes2[1];
		fread(bytes2, 1, 1, fp_in);
		data_offset = (bytes2[0] & (15<<4))>>4;

		// determine where to read data from
		header_size = (IHL+data_offset)*4;
		printf("Total Header Size : %u\n", header_size);

		// seek to where we should read from
		fseek(fp_in, fp_count+header_size, SEEK_SET);

		// determine amount of data to read
		data_length = packet_size - header_size;

		// read in the data
		unsigned char data[data_length];
		fread(data, 1, data_length, fp_in);

		// write out the data
		fwrite(data, 1, data_length, fp_out);

		// update file pointer count
		fp_count += packet_size;
		printf("Data Length : %u\n", data_length);
		printf("\n");
	}

}