151129 17:38:09 [Warning] IP address '104.197.125.66' has been resolved to the host name '66.125.197.104.bc.googleusercontent.com', which resembles IPv4-address itself.

Google cloud resolves all its internal addresses like the above, so thousands of warnings are generated in the error log. IMHO the warning is not really useful and the detection is too sensitive in the following function:

static inline bool is_hostname_valid(const char *hostname)
{
/*
A hostname is invalid if it starts with a number followed by a dot
(IPv4 address).
*/

The above affirmation complies to RFC952, but is obsoleted by RFC1123.

RFC1123 specifies the following:

The syntax of a legal Internet host name was specified in RFC-952
[DNS:4]. One aspect of host name syntax is hereby changed: the
restriction on the first character is relaxed to allow either a
letter or a digit. Host software MUST support this more liberal
syntax.

Suggestion: make the above referenced function RFC1123 compliant.