PHP: gethostbyname bug

Question

I am using gethostbyname() to get the ip address of domains in an application.

In some cases invalid addresses like '50.9.49' are checked also.

echo gethostbyname('50.9.49'); // returns 50.9.0.49

In this cases gethostbyname should return false or the unmodified invalid ip address. however the functions returns the modified IP address 50.9.0.49.

Looks like a bug in php. The quick fix seems to be to check for invalid numerical addresses before, are there any other suggestions?

Answer 1

PHP's gethostbyname actually uses the results of the underlying OS's gethostbyname, e.g., from Linux's netdb.h or Windows' Winsock2.h. It's those functions that actually produce the return value, not PHP.

/* {{{ php_gethostbyname */
static char *php_gethostbyname(char *name)
{
    struct hostent *hp;
    struct in_addr in;

    hp = gethostbyname(name);

    if (!hp || !*(hp->h_addr_list)) {
        return estrdup(name);
    }

    memcpy(&in.s_addr, *(hp->h_addr_list), sizeof(in.s_addr));

    return estrdup(inet_ntoa(in));
}
/* }}} */

Answer 2

It seems like this is an undocumented feature for how IPs works. As mentioned in the comments for your question, ping 50.9.49 in Windows actually pings 50.9.0.49. If you enter an adress as a.b.d, it automatically inserts a zero as c: a.b.0.d. If you just enter a.d, two zeroes are inserted: a.0.0.d.

This has been tested with both Windows 7 and Debian Linux.