Iterate range of addresses between two IPV6 addresses - c

Question

I need some way to iterate over the range of addresses between two IPv6 addresses. i.e. if the first IP is 2a03:6300:1:103:219:5bff:fe31:13e1 and the second one is 2a03:6300:1:103:219:5bff:fe31:13f4, I would like to visit the 19 addresses in that range.
With IPv4 I just do inet_aton for string representation and get htonl of s_addr in the resulting struct, but how can I do that for IPv6?
For simplify:
struct in6_addr sn,en;
long i;
s="2a03:6300:1:103:219:5bff:fe31:13e1";
e="2a03:6300:1:103:219:5bff:fe31:13f4";
inet_pton(AF_INET6,s,&sn);
inet_pton(AF_INET6,e,&en);
[..]
for (i = _first_ipv6_representation; i<=_second_ipv6_representation; i++){
/* stuck here */
}

Answer 1

Old answer stricken per your comments, updated to iterate a range of addresses:
char output[64];
struct in6_addr sn, en;
int octet;
s="2a03:6300:1:103:219:5bff:fe31:13e1";
e="2a03:6300:1:103:219:5bff:fe31:13f4";
inet_pton(AF_INET6,s,&sn);
inet_pton(AF_INET6,e,&en);
for ( ; ; ) {
/* print the address */
if (!inet_ntop(AF_INET6, &sn, output, sizeof(output))) {
perror("inet_ntop");
break;
}
printf("%s\n", output);
/* break if we hit the last address or (sn > en) */
if (memcmp(sn.s6_addr, en.s6_addr, 16) >= 0) break;
/* increment sn, and move towards en */
for (octet = 15; octet >= 0; --octet) {
if (sn.s6_addr[octet] < 255) {
sn.s6_addr[octet]++;
break;
} else sn.s6_addr[octet] = 0;
}
if (octet < 0) break; /* top of logical address range */
}

Answer 2

It's tricky indeed (I like this question). Basically you need to increment and compare integers that are stored like this: uint8_t s6_addr[16].
Find a cool way to convert those arrays to 128b integers and work from that
Define two functions inc_s6 and cmp_s6 that increment / compare such arrays
Here is an attempt at inc_s6:
void inc_s6(uint8_t *addr)
{
int i = 0;
for (i = 15; i >= 0; i--) {
if (++addr[i])
break;
}
}
The compare function is a lot easier.

Answer 3

For clarification:
I'm using that for some proxy-server that have a lot of binded IPv6 and to delegate new IP for each request.
My increment function with some additional explanation:
const char *s="2a03:6300:2:200:0:0:0:1"; // first ip in range
struct in6_addr sn;
inet_pton(AF_INET6,s,&sn);
static struct in6_addr cn = sn; //current ip in6_addr struct
unsigned int skipBits=126;
unsigned __int128 icn,skip; // works only with gcc
if (skipBits!=0){ // now we need to skip netmask bits to get next ip
skip=pow(2,(128-skipBits))-2;
u_int32_t swap;
swap=ntohl(cn.s6_addr32[3]);
cn.s6_addr32[3]=ntohl(cn.s6_addr32[0]);
cn.s6_addr32[0]=swap;
swap=ntohl(cn.s6_addr32[2]);
cn.s6_addr32[2]=ntohl(cn.s6_addr32[1]);
cn.s6_addr32[1]=swap;
memcpy(&icn,&cn,sizeof icn);
// increment, works very fast because gcc will compile it into sse2 intrinsic (double int64 operations)
icn+=skip;
memcpy(&cn,&icn,sizeof icn);
swap=ntohl(cn.s6_addr32[3]);
cn.s6_addr32[3]=ntohl(cn.s6_addr32[0]);
cn.s6_addr32[0]=swap;
swap=ntohl(cn.s6_addr32[2]);
cn.s6_addr32[2]=ntohl(cn.s6_addr32[1]);
cn.s6_addr32[1]=swap;
}
I don't show compare function because #sixlettervariables solution works good enough.

Answer 4

Python3:
import ipaddress
st_add=int(ips.ip_address(st_add).packed.hex(),16)
end_add=int(ips.ip_address(end_add).packed.hex(),16)
Ips=set(ips.ip_address(ip).compressed for ip in range(st_add,end_add))