/*
 *   This program is is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License, version 2 of the
 *   License as published by the Free Software Foundation.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

/**
 * $Id$
 * @file net.c
 * @brief Functions to parse raw packets.
 *
 * @author Arran Cudbard-Bell <a.cudbardb@freeradius.org>
 * @copyright 2014-2015 Arran Cudbard-Bell <a.cudbardb@freeradius.org>
 */
 #include <freeradius-devel/libradius.h>
 #include <freeradius-devel/net.h>

/** Calculate UDP checksum
 *
 * Zero out UDP checksum in UDP header before calling fr_udp_checksum to get 'expected' checksum.
 *
 * @param data Pointer to the start of the UDP header
 * @param len value of udp length field in host byte order. Must be validated to make
 *	  sure it won't overrun data buffer.
 * @param checksum current checksum, leave as 0 to just enable validation.
 * @param src_addr in network byte order.
 * @param dst_addr in network byte order.
 * @return 0 if the checksum is correct, else another number.
 */
uint16_t fr_udp_checksum(uint8_t const *data, uint16_t len, uint16_t checksum,
			 struct in_addr const src_addr, struct in_addr const dst_addr)
{
	uint64_t sum = 0;	/* using 64bits avoids overflow check */
	uint16_t const *p = (uint16_t const *)data;

	uint16_t const *ip_src = (void const *) &src_addr.s_addr;
	uint16_t const *ip_dst = (void const *) &dst_addr.s_addr;
	uint16_t i;

	sum += *(ip_src++);
	sum += *ip_src;
	sum += *(ip_dst++);
	sum += *ip_dst;

	sum += htons(IPPROTO_UDP);
	sum += htons(len);

	for (i = len; i > 1; i -= 2) {
		sum += *p++;
	}

	if (i) {
		sum += (0xff & *(uint8_t const *)p) << 8;
	}

	sum -= checksum;

	while (sum >> 16) {
		sum = (sum & 0xffff) + (sum >> 16);
	}

	return ((uint16_t) ~sum);
}

/** Calculate IP header checksum.
 *
 * Zero out IP header checksum in IP header before calling fr_iph_checksum to get 'expected' checksum.
 *
 * @param data Pointer to the start of the IP header
 * @param ihl value of ip header length field (number of 32 bit words)
 */
uint16_t fr_iph_checksum(uint8_t const *data, uint8_t ihl)
{
	uint64_t sum = 0;
	uint16_t const *p = (uint16_t const *)data;

	uint8_t nwords = (ihl << 1); /* number of 16-bit words */

	for (sum = 0; nwords > 0; nwords--) {
		sum += *p++;
	}
	sum = (sum >> 16) + (sum & 0xffff);
	sum += (sum >> 16);
	return ((uint16_t) ~sum);
}