Generate AAAA and PTR DNS fields for reverses of an IPv6 range.

reverses.c

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

const char *reverse_root = "ip.vpn.xomg.net.";
unsigned short ip6_range[8] = {0x2001, 0x41d0, 0x8, 0x144d, 0xcc, 0, 0, 0};
const char  ip6_netmask  = 7;
const char  ip6_ignore_subs = 0;

const char *zone_file = "db.zone";
const char *reverse_file = "db.reverse";

const char *zone_header = 
"$TTL 60\n" \
"@ IN SOA whiterun.xomg.net. dns-admin+vpn.xomg.net. (%s 10800 3600 2419200 604800)\n" \
"@ IN NS whiterun.xomg.net.\n" \
"\n";

const char *reverse_header =
"$TTL 60\n" \
"@ IN SOA whiterun.xomg.net. dns-admin+vpn.xomg.net. (%s 10800 3600 2419200 604800)\n" \
"@ IN NS whiterun.xomg.net.\n" \
"\n";


FILE *zone_fh, *reverse_fh;
char *zone_format;

char *fqdn = NULL;
char *iprhd = NULL;
char *iphex = NULL;

void write_address(unsigned short *ip) {
    int pos = 0;
    for (char n=(7-ip6_ignore_subs); n >= ip6_netmask; n--) {
        pos += sprintf(fqdn+pos, "%x.", ip[n]);
    }
    strcpy(fqdn+pos, reverse_root);
    
    fprintf(zone_fh, "%s IN AAAA %x:%x:%x:%x:%x:%x:%x:%x\n", fqdn,
        ip[0],ip[1],ip[2],ip[3],ip[4],ip[5],ip[6],ip[7]);
    
    // xxxxxxxxxxxx... // no . or :, only hex.
    sprintf(iphex, "%04x%04x%04x%04x%04x%04x%04x%04x",
        ip[0],ip[1],ip[2],ip[3],ip[4],ip[5],ip[6],ip[7]);
    for (int i=31, j=0; i >= 0; i--, j+=2) {
        iprhd[j] = iphex[i];
        iprhd[j+1] = '.';
    }
    iprhd[64] = 0;

    fprintf(reverse_fh, "%sip6.arpa. IN PTR %s\n", iprhd, fqdn);
}

int loop(int netmask, unsigned short *ip) {
    // init to NET:0:0...
    for (short n=netmask; n < 8; n++) {
        ip[netmask] = 0;
    }
    for (; ip[netmask] < 0xffff; ip[netmask]++) {
        if (netmask == 7-ip6_ignore_subs) {
            write_address(ip);
        } else {
            printf("%x:%x:%x:%x:%x:%x:%x:%x/%d\n",
                ip[0],ip[1],ip[2],ip[3],ip[4],ip[5],ip[6],ip[7],
                netmask*16);
            loop(netmask+1, ip);
        }
    }
}

int main() {
    // That should not really be here, but...
    fqdn = (char*) malloc(sizeof(char)*(8-ip6_netmask)*4 + 2 + strlen(reverse_root));
    iprhd = (char*) malloc(sizeof(char) * 65);
    iphex = (char*) malloc(sizeof(char) * 33);
    
    
    zone_fh = fopen(zone_file, "wb");
    reverse_fh = fopen(reverse_file, "wb");
    
    // Write headers
    char date[32];
    time_t rawtime;
    time (&rawtime);
    struct tm * timeinfo = localtime (&rawtime);
    strftime((char*)&date, 32, "%Y%m%d%S", timeinfo);
    fprintf(zone_fh, zone_header, date);
    fprintf(reverse_fh, reverse_header, date);


    // Start loop
    loop(ip6_netmask, ip6_range);
    
    fclose(zone_fh);
    fclose(reverse_fh);
    
    free(fqdn);
    free(iprhd);
    free(iphex);
    
    return 0;
}