Incorrect handling of DNS SRV and DNS NAPTR records

[Roger James]

Linphone on ubuntu is patched to use the libexosip2 library rather than libbellesip. The current libexosip2 package does not appear to handle the lookup of voip DNS SRV records correctly. The causes the handling of sip uris when not using an outbound proxy to be broken.

For example here in the Uk the Andres and Arnold voip service tells it's users to use sip urls in the the form "sip:<number>@aa.org.uk"

The domain aa.org.uk does not contain any NAPTR records but does contain SRV records pointing at the correct server.

roger@dragon:~$ host -t NAPTR aa.org.uk
aa.org.uk has no NAPTR record
roger@dragon:~$ host -t SRV _sip._udp.aa.org.uk
_sip._udp.aa.org.uk has SRV record 1 0 5060 voiceless.aa.org.uk.

Linphone using libexosip2 first queries aa.net.uk for a NAPTR. When this fails it queries aa.net.uk again for an address record. This returns the address of a server associated with aa.org.uk (I believe this is a web server).

The correct behavior should be to prefix the domain with "_sip._udp." and look for a SRV record, then resolve the address from there.

Ubuntu release 17.04