[Bug libc/2099] Support for SRV records in getaddrinfo

["psimerda at redhat dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=2099

Pavel Šimerda <psimerda at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |psimerda at redhat dot com

--- Comment #8 from Pavel Šimerda <psimerda at redhat dot com> 2012-07-29 22:51:39 UTC ---
I must agree with binki.

> I'm quite sure that when the SRV spec says "domain", it is referring to the
> full domain. Not the domain in the sense of domainname(1). I.e., you would
> search for _someserv._tcp.host1.domain instead of _someserv._tcp.domain. Am I
> misreading the spec here?

Exactly.

You would for example ask for a client XMPP connection, the service is
'xmpp-server' and socktype is SOCK_STREAM (TCP). You are going to connect as
user@example.net, therefore "example.net" is the domain. The getaddrinfo() call
would roughly look like this:

hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_SRVLOOKUP;
code = getaddrinfo("example.net", "xmpp-server", &hints, &result);

This would translate to DNS SRV query for:

_xmpp-server._tcp.example.net

And in absence of such a record, it would fallback to A/AAAA records:

example.net

The way SRV records work is very similar to the way MX records work.

> If the word "domain" in the SRV spec is interpreted properly, this objection
> makes no sense. Sure, it is likely enough that getaddrinfo("domain",
> "someserv", ...) will not tell you to go ahead and connect directly to
> "domain". But getaddrinfo("host1.domain", "someserv", ...) would likely not hit
> any SRV records at all and fall back to the traditional DNS lookups.
> 
> The main objection to this change would be that programs would suddenly break
> if getaddrinfo(node, serv, ...) would suddenly tried to find the appropriate
> host for accessing serv at node. In reality, few domains set SRV records for
> services where there is no program support. So, most programs which would be
> affected by this change would behave no differently if getaddrinfo() started
> actually looking up services instead of just hosts.

That's correct. But still it's probably better to make it optional.

> It would be really nice to get SRV support in applications with no added
> complexity. Maybe the interface provided by ruli
> http://nongnu.org/ruli/tutorial/getaddrinfo.html is a way to get these
> advantages without departing too far from getaddrinfo()...

I've seen this one also.

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