This problem is terrible it accepts some version of ipv6 that's not correct it should be changed to accept valid ipv4 addresses and valid ipv6 addresses as according to man 3 inet_pton.
AF_INET src points to a character string containing an IPv4 network address in dotted-decimal format, "ddd.ddd.ddd.ddd", where ddd is a decimal number of up to three digits in the range 0 to 255. The address is converted to a struct in_addr and copied to dst, which must be sizeof(struct in_addr) (4) bytes (32 bits) long. AF_INET6 src points to a character string containing an IPv6 network address. The address is converted to a struct in6_addr and copied to dst, which must be sizeof(struct in6_addr) (16) bytes (128 bits) long. The allowed formats for IPv6 addresses follow these rules: 1. The preferred format is x:x:x:x:x:x:x:x. This form consists of eight hexadecimal numbers, each of which expresses a 16-bit value (i.e., each x can be up to 4 hex digits). 2. A series of contiguous zero values in the preferred format can be abbreviated to ::. Only one instance of :: can occur in an address. For example, the loopback address 0:0:0:0:0:0:0:1 can be abbreviated as ::1. The wildcard address, consisting of all zeros, can be written as ::. 3. An alternate format is useful for expressing IPv4-mapped IPv6 addresses. This form is written as x:x:x:x:x:x:d.d.d.d, where the six leading xs are hexadecimal values that define the six most-significant 16-bit pieces of the address (i.e., 96 bits), and the ds express a value in dotted-decimal notation that defines the least significant 32 bits of the address. An example of such an address is ::FFFF:18.104.22.168. See RFC 2373 for further details on the representation of IPv6 addresses.