Hi, let me explain first how things do work, and then we can see how to change
:) - I agree that things may be simpler (for user understanding/usage) and may
be improved.
So, right now the outgoing protocol is determined based on next hop URI and the
set network socket. What @oteren said is correct - the "transport=TCP" does not
have anything to do with the received proto, but it indicates the proto to be
used to reach that URI (so it is not about the inbound proto, but about
outbound proto).
OpenSIPS looks for the "transport" param in target URI to see if there is any
special protocol requested for the next hop URI. This is correlated withe the
protocol from the requested net socket (via force_send_socket) -> if they
conflict, the proto URI has priority; if one in NONE, the other one will win.
No proto explicitly requested -> UDP will be used.
So, the outbound protocol can be right now controlled via the transport URI
param (this actually makes that protocol a must and gives no fallback
posibility) or via the used netowork interface ( you can do
force_send_socket("tcp:.....") - if the URI does not forces another proto, the
socket proto will be used). I would say this force_send_socket() is closest to
what you need (setting a preferred transport proto without messing with the sip
message), but has no fallback to another proto.
Maybe adding a new function like set_preferred_proto(tcp, tls) - this will set
the outbound protocol if none is forced by the target URI (via the transport
param). It will allow you to change the default (which now is hardcoded to UDP)
and to have a fallback. If TCP is not available, TLS will be used (like in your
case when the DNS based proto selection did not return anything usable).
Looking forward for input and comments :)
Regards,
Bogdan
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