OpenWrt – Rev 4

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/*
 * Utility used to calculate the 6rd subnet.
 *
 * Copyright 2012, Stéphan Kochen <stephan@kochen.nl>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/errno.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define INET_PREFIXSTRLEN (INET_ADDRSTRLEN+3)
#define INET6_PREFIXSTRLEN (INET6_ADDRSTRLEN+4)

static void print_usage()
{
        fprintf(stderr, "Usage: 6rdcalc <v6 prefix>/<mask> <v4 address>/<mask>\n");
        exit(1);
}

static void print_error()
{
        fprintf(stderr, "%s", strerror(errno));
        exit(1);
}

static void parse_str(int af, char *str, void *addr, unsigned long *mask)
{
        int ret;
        char *slash;

        /* Split the address at the slash. */
        if ((slash = strchr(str, '/')) == NULL)
                print_usage();
        *slash = '\0';

        /* Parse the address. */
        if ((ret = inet_pton(af, str, addr)) != 1) {
                if (ret == 0)
                        print_usage();
                else
                        print_error();
        }

        /* Parse the mask. */
        *mask = strtoul(slash+1, NULL, 10);
        if ((af == AF_INET  && *mask >  32) ||
                (af == AF_INET6 && *mask > 128))
                print_usage();
}

int main(int argc, const char **argv)
{
        char v6str[INET6_PREFIXSTRLEN], v4str[INET_PREFIXSTRLEN];
        struct in6_addr v6;
        struct in_addr v4;
        unsigned long v6it, v4it, mask;
        unsigned char *byte4, *byte6;
        unsigned char bit4, bit6;

        /* Check parameters. */
        if (argc != 3)
                print_usage();

        /* Parse the v6 address. */
        strncpy(v6str, argv[1], INET6_PREFIXSTRLEN);
        v6str[INET6_PREFIXSTRLEN-1] = '\0';
        parse_str(AF_INET6, v6str, &v6, &v6it);

        /* Parse the v4 address */
        strncpy(v4str, argv[2], INET_PREFIXSTRLEN);
        v6str[INET_PREFIXSTRLEN-1] = '\0';
        parse_str(AF_INET, v4str, &v4, &v4it);

        /* Check if the combined mask is within bounds. */
        mask = (32 - v4it) + v6it;
        if (mask > 128)
                print_usage();

        /* Combine the addresses. */
        while (v4it < 32) {
                byte6 = (unsigned char *)(&v6.s6_addr) + (v6it >> 3);
                byte4 = (unsigned char *)(&v4.s_addr)  + (v4it >> 3);
                bit6 = 128 >> (v6it & 0x07);
                bit4 = 128 >> (v4it & 0x07);

                if (*byte4 & bit4)
                        *byte6 |= bit6;
                else
                        *byte6 &= ~bit6;

                v4it++; v6it++;
        }

        /* Clear remaining bits. */
        while (v6it < 128) {
                byte6 = (unsigned char *)(&v6.s6_addr) + (v6it >> 3);
                bit6 = 128 >> (v6it & 0x07);

                *byte6 &= ~bit6;

                v6it++;
        }

        /* Print the subnet prefix. */
        if (inet_ntop(AF_INET6, &v6, v6str, sizeof(v6str)) == NULL)
                print_error();
        printf("%s/%lu\n", v6str, mask);
        return 0;
}