The inet_ntop() function returns an IPv6 string for the string "April Fool's Day"

[MisterVector]

Description

The following code:

<?php
    $ip = "April Fool's Day";
    
    echo inet_ntop($ip) !== false ? "Valid IP!" : "Invalid IP!";

Resulted in this output:

Valid IP!

But I expected this output instead:

Invalid IP!

The length of the $ip variable is 16 characters, which would equal a packed IPv6 address, however it is an invalid address given that some characters are not in the hexadecimal range.

PHP Version

Tested using PHP 8.3.21, 8.4.10, 8.2.29 and 8.1.33 from https://onlinephp.io/

Operating System

No response

[devnexen]

AFAIK seems to me this PHP inet_ntop is not entirely correct. see the following basic C

#include <stdio.h>
#include <arpa/inet.h>

int main(void)
{
	char buffer[40];
	const char *p = inet_ntop(AF_INET6, "April Fool's Day", buffer, 16);
	fprintf(stderr, "%s\n", p);
	p = inet_ntop(AF_INET6, "April Fool's Day", buffer, **sizeof(buffer)**);
	fprintf(stderr, "%s\n", p);
	return 0;
}

(null)
4170:7269:6c20:466f:6f6c:2773:2044:6179

hint: address_len is not used.

nvm in fact inet_ntop PHP is correct and is a straight wrapper around the C call, it does not check the validity of the input. Thus the fact it works with "non sense" inputs is expected as the C call takes a(ny) pointer.

[jdarwood007]

This seems to be any string that is 16 characters in length

var_dump(inet_ntop("Enthusiastically"));
var_dump(inet_ntop("Well-thought-out"));
var_dump(inet_ntop("Secondhand Store"));
var_dump(inet_ntop("Klingon Warbird"));

[nielsdos]

This is not a bug. inet_ntop converts a binary representation of an IP address into a string representation.
April Fool's Day is a binary input, if you look at the bytes this could represent an IP address.
So yes, there exists IP addresses that spell out April Fool's Day when you interpret the binary bytes as text.