dhcp.c

/*
Copyright (c) 2014, Pierre-Henri Symoneaux
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

* Neither the name of LightDhcpClient nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
#include "dhcp.h"

#include <stdlib.h>
#include <string.h>

int build_dhcp_discover(struct dhcp_pkt* pkt, unsigned char* src_mac, int mac_len)
{
    memset(pkt, 0, sizeof(struct dhcp_pkt));
    pkt->op      = OP_BOOT_REQUEST;
    pkt->htype   = HW_TYPE_ETHERNET;
    pkt->hlen    = HW_LENGTH_ETHERNET;
    pkt->hops    = 0x00;
    pkt->xid     = 0x3903f326; //TODO: Random transaction ID
    pkt->secs    = 0x0000;
    pkt->flags   = 0x0000;
    pkt->ci_addr = 0x00000000;
    pkt->yi_addr = 0x00000000;
    pkt->si_addr = 0x00000000;
    pkt->gi_addr = 0x00000000;

    // memcpy(pkt->cm_addr, src_mac, mac_len); // LINK problem
	int i;
	for(i = 0; i < mac_len; i++)
		pkt->cm_addr[i] = src_mac[i];

    pkt->magic = DHCP_MAGIC;

    //Add DHCP options
    pkt->opt[0] = OPTION_DHCP_MESSAGE_TYPE;
    pkt->opt[1] = 0x01;
    pkt->opt[2] = VALUE_MESSAGE_DISCOVER;

    pkt->opt[3] = OPTION_PARAMETER_REQUEST_LIST;
    pkt->opt[4] = 0x03;
    pkt->opt[5] = OPTION_ROUTER; // Ask for gateway address
    pkt->opt[6] = OPTION_SUBNET_MASK; // Ask for the netmask
    pkt->opt[7] = OPTION_DNS; // ASK for DNS address

    pkt->opt[8] = DHCP_END;


    //TODO : Use the same procedure to write options, than the one used to read options
//    pkt->opt[0].id = 53;
//    pkt->opt[0].len = 0x01;
//    pkt->opt[0].values[0] = 0x01;
//
//    pkt->opt[1].id = DHCP_END;

    return sizeof(struct dhcp_pkt);
}

int is_dhcp(struct dhcp_pkt* pkt)
{
	// It's a DHCP packet if dhcp magic number is good
	//TODO: check the packet length ?
    return pkt->magic == DHCP_MAGIC;
}

struct dhcp_opt* get_dhcp_option(struct dhcp_pkt *pkt, int *offset)
{
    if(pkt->opt[*offset] == 0x00 || pkt->opt[*offset] == DHCP_END)
        return NULL;
	// If the opt != end or != empty, cast the memory zone into a option struct, and return it
	struct dhcp_opt* opt = (struct dhcp_opt*)&(pkt->opt[*offset]);
	*offset += sizeof(struct dhcp_opt) + opt->len;
    return opt;
}

unsigned int char_to_ip(unsigned char* ip)
{
	return htonl(ip[0] << 24 | ip[1] << 16 | ip[2] << 8 | ip[3]);
}