wm: dnsparser

ref: 13738d2aa200eeb5859525225ec1d7bec7e8134e
dir: /tcp.c/

#include <stdio.h>
#include <stdint.h>
#include "common.h"

int
parseTcp(const u_char *pkt, Tcp *tcp)
{
	tcp->start = pos;
	
	get(pkt, TCP_SRCPORT, &tcp->src);
	get(pkt, TCP_DSTPORT, &tcp->dst);
	get(pkt, TCP_SEQNUM, &tcp->seq);
	get(pkt, TCP_ACKNUM, &tcp->ack);
	
	/* offsets are multiplies of 4 (32-bit) values */
	get(pkt, TCP_OFFSET, &tcp->offset);
	/* some(?) compilers may do logical shift */
	tcp->offset = (tcp->offset >> 4) & 0xf;
	tcp->offset *= 4;
	
	get(pkt, TCP_FLAGS, &tcp->flags);
	get(pkt, TCP_WINSIZE, &tcp->winsize);
	get(pkt, TCP_SUM, &tcp->sum);
	get(pkt, TCP_URGPTR, &tcp->urgentptr);
	
	/*
	 * we dont parse tcp options yet, 
	 * offset alone shows size of tcp packet (options + headers)
	 * there is no need to add length of headers to pos twice.
	 *
	 * x--------x------------------------x------------x
	 * ^ pkt[0] ^ pkt[tcp.start]         ^ pkt[pos]   ^ pkt[tcp.offset]
	 *
	 * tcp.start < pos ≤ tcp.offset
	 */
	 
	pos += tcp->offset - (pos - tcp->start);
	return 1;
}

void
printTcp(Tcp tcp)
{
		printf("tcp pkt:\n"
		"\tsrc port: %d\tdst port: %d\n"
		"\tseq num: %u\tack num: %u\n"
		"\toffset: %d\tflags: %b (%x)\n"
		"\twinsize: %d (%x)\tsum: %d\n",
		
		tcp.src, tcp.dst,
		tcp.seq, tcp.ack,
		tcp.offset, tcp.flags, tcp.flags,
		tcp.winsize, tcp.winsize, tcp.sum);
}

Parser tcpParser = {
	.name = "tcp",
	.parse = parseTcp,
	.print = printTcp,
};