[ruby-core:63034] [ruby-trunk - Feature #9925] rsock_addrinfo uses DNS family AF_UNSPEC for lookup causing high IPv6 AAAA volume

Issue #9925 has been updated by Nobuyoshi Nakada.

Tracker changed from Bug to Feature
Description updated

It doesn't feel a good idea to change a behavior in a library by an environment variable implicitly.

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Feature #9925: rsock_addrinfo uses DNS family AF_UNSPEC for lookup causing high IPv6 AAAA volume
https://bugs.ruby-lang.org/issues/9925#change-47116

* Author: Aaron Stone
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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In ext/socket/raddrinfo.c, the function `rsock_addrinfo()` always uses `AF_UNSPEC` for DNS queries. This is causing me a very high volume of IPv6 DNS lookups. `rsock_addrinfo()` is used by TCPSocket (and all other Socket base classes, e.g. Socket and UDPSocket), and TCPSocket is used by Net::HTTP.

Remember that DNS does not do negative caching - if a hostname does not have a AAAA record, then DNS will _always_ try to look up that record again!

I propose that the following code should have some way to force IPv4 or IPv6 lookups:

http://rxr.whitequark.org/mri/source/ext/socket/raddrinfo.c

~~~c
378 struct addrinfo*
379 rsock_addrinfo(VALUE host, VALUE port, int socktype, int flags)
380 {
381     struct addrinfo hints;
382 
383     MEMZERO(&hints, struct addrinfo, 1);
384     hints.ai_family = AF_UNSPEC;
385     hints.ai_socktype = socktype;
386     hints.ai_flags = flags;
387     return rsock_getaddrinfo(host, port, &hints, 1);
388 }
~~~

For example, an environment variable named something like `RUBY_GAI` could be set to "INET" or "INET6" to switch the `hints.ai_family` away from `AF_UNSPEC`.



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