std::net lacks reverse DNS lookup

[murarth]

std::old_io::net::addrinfo::get_address_name accepts an IpAddr and attempts to resolve it to a hostname String. No such functionality exists (as far as I can tell) in the new std::net module.

I know that the std::net module is incomplete and, perhaps, this was already a planned addition. I'm just hoping to make sure that it's not forgotten.

[murarth]

So, it turns out that the default behavior of getnameinfo is to return the given IP address as a string when it can't resolve to a hostname. This seems undesirable to me. There's a flag NI_NAMEREQD that will cause it to return an error instead, but the value of this flag differs by platform.

So, I'm wondering whether I should accept the default behavior and document it or collect values of NI_NAMEREQD on all supported platforms. I have these so far:

Platform	Value	Source
Linux	8	/usr/include/netdb.h on my system
Windows	4	header provided by wine-dev
Mac OS X	4	here

[murarth]

I had another idea: Attempt to parse the result of getnameinfo as an IpAddr to identify this case. Not the ugliest workaround, I think.