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/*
* Mausezahn - A fast versatile traffic generator
* Copyright (C) 2008-2010 Herbert Haas
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License version 2 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, see http://www.gnu.org/licenses/gpl-2.0.html
*
*/
#include "mz.h"
#include "mops.h"
// -- TOC: --
//
// u_int16_t mops_sum16 (u_int16_t len, u_int8_t buff[])
// int mops_get_transport_sum (struct mops *mp)
//////////////////////////////////////////////////////////////////////////////////
//
// See also:
//
// RFC1071 - Computing the Internet checksum
//
//////////////////////////////////////////////////////////////////////////////////
// Generic 16-bit checksum code as required for IP and other headers.
// The checksum is calculated over buff[] which is of length len.
//
// RETURN VALUE: The checksum! (Validated - correct!!!)
//
// Example: t16 = mops_sum16 (20, &mp->frame[fp]);
//
u_int16_t mops_sum16 (u_int16_t len, u_int8_t buff[])
{
u_int16_t word16;
u_int32_t sum=0;
u_int16_t i;
// make 16 bit words out of every two adjacent 8 bit words in the packet and add them up
for (i=0; i<len; i=i+2)
{
word16 =((buff[i]<<8)&0xFF00)+buff[i+1];
sum = sum + (u_int32_t) word16;
}
// take only 16 bits out of the 32 bit sum and add up the carries
while (sum>>16)
sum = (sum & 0xFFFF)+(sum >> 16);
// one's complement the result
sum = ~sum;
return ((u_int16_t) sum);
}
// sets UDP or TCP checksum within mp[]->frame
// TODO: copying the whole segment is ugly and slow;
// make it more efficient and realize it in-place.
//
int mops_get_transport_sum(struct mops *mp)
{
u_int8_t buf[MAX_PAYLOAD_SIZE];
u_int16_t len;
int udp_used;
u_int16_t sum;
udp_used = mp->use_UDP; // 0 or 1, 0 means TCP
// IP Pseudoheader (12 Bytes)
mops_hton4(&mp->ip_src, &buf[0]);
mops_hton4(&mp->ip_dst, &buf[4]);
buf[9]=0x00;
// Copy segment
if (udp_used)
{
buf[10]=0x11; // proto UDP (17 dec)
len = mp->udp_len;
mops_hton2(&len, &buf[11]);
memcpy(&buf[13], &mp->frame[mp->begin_UDP], len);
// reset checksum to zero
buf[19] = 0x00;
buf[20] = 0x00;
sum = mops_sum16(len+12, buf);
// insert checksum in UDP header (in frame)
mops_hton2 (&sum, &mp->frame[(mp->begin_UDP)+7]);
}
else
{
buf[10]=0x06; // proto TCP
len = mp->ip_len - mp->ip_IHL;
mops_hton2((u_int16_t*)&len, &buf[11]);
memcpy(&buf[13], &mp->frame[mp->begin_TCP], len);
// reset checksum to zero
buf[29] = 0x00;
buf[30] = 0x00;
sum = mops_sum16(len+12, buf);
// insert checksum in TCP header (in frame)
mops_hton2 (&sum, &mp->frame[(mp->begin_TCP)+17]);
}
return 0;
}
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