[FEATURE] mid-registrar: Add the "reply_expires_mode"

[liviuchircu]

Is your feature request related to a problem? Please describe.

There are plenty of SIP UAs out there (both open-source and commercial) which get confused when presented with a 200 OK containing both "Expires" and Contact ";expires=" URI params. In the end, they incorrectly choose the "Expires" header value, clearly breaking RFC 3261. The issue is somewhat tied to mid-registrar, in modes such as 1 or 2, where it always presents Contacts with ;expires= parameters to the upstream UA, but most often will also leave the "Expires" header untouched, taken right from the downstream 200 OK reply.

Describe the solution you'd like

A new mid-registrar modparam, reply_expires_mode, which would default to "strip", obviously removing the "Expires" header from upstream-forwarded 200 OK replies. This will make mid-registrar's SIP traffic more visually appealing, eliminating all "Expires vs. ;expires=" confusions of shaky SIP stacks. Other modes can be:

• "none" ("don't touch the Expires at all", the default if backporting this to 3.1, 3.2)
• "min-expires" (set the Expires to the minimum expiration across all upstream-presented Contacts)

Implementation

• Component:
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Describe alternatives you've considered

Additional context

[volga629-1]

@liviuchircu I know you really busy with upcoming event and release, but is possible to set higher priority on this feature.
It really really needs it to resolve upstream PBX's bogus Contact headers expire params on REGISTER reply.
Is this feature will be possible to set expire param and remove Expire ?
I provided full details in support ticket.