[Users] haze about the REGISTER method

[Andreas Granig]

Weiter Leiter wrote:
>     2) What is the harm of calling fix_nated_contact() in addition
>     to fix_nated_register() in a REGISTER message ?  The configuration
>     file [1] carefully avoids doing this.
> 
> The harm is the same as above: if you do fix_nated_contact(), an AVP
> (with the originating address of the REGISTER, the one that SER sees in
> the networking layer, not the SIP layer) is set, instructing the
> registrar to disregard the body of Contact HF and consider only this AVP
> as true Contact.

More importantly, fix_nated_contact() modifies the URI of the Contact-HF
of the 200-OK, whereas fix_nated_register() only appends parameters to
the URI.

I'm not entirely sure if modifying the Contact URI of responses to
REGISTERs violates RFC3261, because I don't know exactly how to
interpret paragraph 10.3, number 8, but there are at least UACs which
don't accept a 200-OK with modified Contact-URI.

Andy