[Serusers] [Serdev] loose_route behaviour, detecting single Route with myself

[Nils Ohlmeier]

On Thursday 12 July 2007 09:03:39 Klaus Darilion wrote:
> Martin Hoffmann wrote:
> > In most cases this is what you want, because the presence of Routes
> > indicates an in-dialog message which you want to treat differently (In
>
> Here we see the root problem of the loose_route function: it's naming
> and it's usage.
>
> To identify in-dialog messages the only thing to worry about is the
> to-tag. Nothing more, nothing less.

This was the assumption of the old, and it is unfortunately totaly wrong! See 
below for more details.

> > practice, most UAs just forward the message to the outgoing proxy
> > without adding a Route header, which is perfectly legal as well). The
> > proper test for this, of course, is to check for the presence of a To
> > tag. But it seems to be common to all SER configs I have seen to misuse
> > loose_route() in this way.
>
> Yes.
>
> > Changing the behaviour of loose_route() yet again would mess up a lot of
> > configs as the earlier change messed up a lot of configs (it certainly
> > cost me a couple of hours debugging). Having another function would
> > probably be a better approach. Especially, since loose_route() is
> > actually the wrong name. The function does both loose and static record
> > routing.
>
> I totally agree with you, e.g:
>
> if (in_dialog()) { # probably an alias to has_totag()

No. The To-tag is not enough as criteria for in-dialog. And unfortunately the 
presence of Route isn't as well.

You can basically have these type of ACKs (ACKs illustrate the worst case):
- the UAC uses an outbound proxy without a Route header
  - the in-dialog ACK will have a To-tag and a Route header
  - the out-of-dialog ACK will have a To-tag and no Route header
- the UAC uses a Route header for its outbound proxy
  - then in-dialog ACK will have a To-tag and a Route header (same as above)
  - the out-of-dialog ACK will have a To-tag and a Route header (and this is 
the problematic case!)

The only thing which distinguishes the in-dialog ACKs from the last 
out-of-dialog ACK might be the length of the Route header. If the Route 
header has the length one it might be an out-of-dialog ACK. But in the worst 
case this is equal to an in-dialog ACK with only one Route header. In this 
case the only difference will be the RURI.

>    process_routes(); # may have different return values
>                      # -1: no routes found
>                      # -2: only a single route pointing to "myself"
>                      # 1: loose routing done
>                      # 2: strict routing done
>    ... NAT traversal, security checks, ....
>    t_relay();
>    exit;
> }
>
> process_routes();
> # here proceed according to policy, e.g.
> # -1, -2: handle now incoming request
> # 1, 2: reject out-of-dialog loose/strict-route request
> ...

Ok, what would be the difference then between this new process_routes() 
function and adding more different return values to the existing 
loose_route() function?

  Nils