Don't default to IPv4 if the host has no IPv4 interface

[ckonstanski]

If usocket is used on an IPv6-only host, and if the endpoint it is trying to reach resolves to both an IPv4 and IPv6 DNS address, usocket will always try the IPv4 address. A smarter decision needs to be made. Perhaps look at the routing table?

Is there a way to tell usocket to use IPv6 only?

[binghe]

Hi,

this is a reasonable requirement (although I've never seen any IPv6-only host). Looking at the routing table is not feasible, as there's no portable API to do that (or root privilege is required). I think it's fine to add a special variable, say *ipv6-only-p* indicating all USOCKET functions will work in IPv6-only mode whenever this variable is non-NIL.

--Chun

[ckonstanski]

This solution would work fine and be much appreciated. For context: I work at a major telecom and we're standing up 75k new ipv6-only hosts in the next three years for one project alone. The lack of ipv4 has been painful on many fronts.

[binghe]

Hi, with 1b712f6 I believe the obvious issues when calling GET-HOST-BY-NAME and GET-RANDOM-HOST-BY-NAME have been resolved:

CL-USER 11 > (usocket:get-host-by-name "localhost")
#(127 0 0 1)

CL-USER 10 > (let ((usocket:*ipv6-only-p* t)) (usocket:get-host-by-name "localhost"))
#(0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1)

I didn't touch any backend-specific code. I don't know if this is already enough, but if you can have a test on latest usocket code that will be more helpful and I will work with you closely fixing whatever more related issues quickly.

--Chun

[ckonstanski]

Thanks for adding this. I'm still waiting for it to land in quicklisp. Once it does, I'll let you know how it goes.