Re: [Sip] Open Issue #7: CANCEL for non-INVITE

[Kim Liu <[e-mail]>]

What special check?

if (cancel.method != INVITE) do_error_respose();

You would have to make checks in any case to validate
the CANCEL from an authentication/authorization level,
to see if the method the CANCEL was referring to actually
existed, etc.  There already have to be places in the
message processing where a CANCEL can be rejected due
to various reasons.

Or, inversely, if CANCEL is allowed for non-INVITEs,
then you have to make a special check to see if the
original method was an INVITE, to send back the 487
until receiving an ACK, etc.

Shail Bhatnagar wrote:
> 
> Kim Liu wrote:
> 
> My take is that although CANCEL for non-INVITE is academic,
> it should be allowed. Main reason is to not make special checks
> in the state machine about original method and this CANCEL.
> 
> >
> > Limit CANCEL for INVITE only.  Trying to handle CANCELs
> > for all/arbitrary methods otherwise is going to be prohibitively
> > complex task -- it will end up as a bunch of special
> > cases -- i.e. if CANCEL is allowed for all methods,
> > how do you treat a CANCEL for a CANCEL?  A CANCEL for
> > a BYE?  A CANCEL for an ACK?  That's ridiculous --
> > you automatically end up with more special cases for
> > handling CANCEL to handle CANCELs for methods where
> > CANCEL makes no sense.
> >
> > It's a case of confusing an application specific
> > signal (trying to stop a service/application started
> > by another method) with a generic procotol level
> > signal (CANCEL).  Since only INVITE and BYE can
> > start/change/stop a call, every other method almost
> > has to be an application or service specific
> > invocation, rather than session affecting -- if
> > this assumption is made, then CANCEL, as a session
> > level signal, is not apropriate for halting a
> > service.
> >
> > Kim
> >
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