[asterisk-dev] reset/remove SipAddHeader() headers

[Klaus Darilion]

John Todd schrieb:
> On Jan 14, 2009, at 8:50 AM, Klaus Darilion wrote:
> 
>> Hi!
>>
>> As far as I saw in chan_sip (at least 1.4.22) once SIP headers are  
>> added
>> with SipAddHeader() there is no way to remove them, which is bad if  
>> the
>> request is rerouted to another SIp destination, e.g:
>>
>> user      Asterisk      GW1        GW2
>> ---INVITE-->
>>          add certain
>>          header for GW1:
>>          SipAddHeader(..)
>>
>>               ---INVITE--->
>>               (contains additional
>>               header)
>>
>>
>>               <--500-------
>>
>>          reroute request
>>          to a different GW
>>
>>
>>              ----------INVITE-------->
>>              this request also contains
>>              the added SIP header
>>
>> Headers added with SipAddHeader are added to the incoming channel as
>> global channel variables SIPADDHEADER01, SIPADDHEADER02, ....
>>
>> Then on outgoing requests chan_sip will traverse the channel variables
>> for SIPADDHEADERxx and add them.
>>
>> Thus, it would be useful to reset the channel variables somehow, e.g.
>> with an application SipAddHeaderReset();
>>
>> I could not find any existing solution, thus what do you think about
>> this new application?
>>
>> thanks
>> klaus
> 
> 
> 
> There be dragons.
> 
> I agree that there probably should be some way to do this, but a way  
> to do this properly does not immediately come to mind.  For instance,  
> in the event that GW2 sends a 302 redirect, how does one execute the  
> SipAddHeaderReset() application or function?  That 302 redirect step  
> never breaks out of Dial() - the redirect just magically happens.  The  
> dialplan (or AGI, or whatever) never has a chance to execute any other  
> commands such as adding headers or removing headers or whatever.  I  
> don't have an answer on how this should be handled elegantly.
> 
> Even in the instance where a 500 is received and somehow the dialplan  
> is re-entered, it seems burdensome to remove ALL headers and start  
> from scratch.  Wouldn't you just want to remove the specific header  
> that is causing problems?  This would imply some sort of indexing, or  
> at the minimum, regexp-style string matching so I could say:
> 
>   exten => _X11.,SipRemoveHeader(X-PSAP-ID)
> 
> which would remove both of these headers:
> 
> X-PSAP-ID: 33-MONTCOPA-PRIMARY-9929312311AA
> X-PSAP-ID: 33-MONTCOPA-BACK-99283122833CD
> 
> Lastly, I wouldn't restrict header removal just to headers that have  
> been added by prior steps in the dialplan of Asterisk.  Why not allow  
> deletion of arbitrary headers?  This would permit more control over  
> messaging.  (Though I will admit a glaring memory hole on my part - I  
> assume Asterisk passes through headers unmodified from UA-to-UA... is  
> that correct?  My first memory impression is "Yes" but the more I  
> think about it the less certain I am, and I don't have time to test  
> right now.)
> 
> Or am I missing your concept?

Of course you are right and the SipAddHeader mechanism could be made 
much more generic - my idea was just to start with an easy and doable 
solution.

I submitted a patch which also takes at least some of your ideas - to 
remove selectively too: http://bugs.digium.com/view.php?id=14246


core show application SIPRemoveHeader
gw*CLI>
   -= Info about application 'SIPRemoveHeader' =-

[Synopsis]
Remove SIP headers previously added with SIPAddHeader

[Description]
   SIPRemoveHeader()
SIPRemoveHeader() allows you to remove headers which were previously
added with SIPAddHeader(). If no parameter is supplied, all previously
added headers will be removed. If a parameter is supplied, only the matching
headers will be removed.

For example you have added these 2 headers:
   SIPAddHeader(P-Asserted-Identity: sip:foo at bar);
   SIPAddHeader(P-Preferred-Identity: sip:bar at foo);

   // remove all headers
   SIPRemoveHeader();

   // remove all P- headers
   SIPRemoveHeader(P-);

   // remove one the PAI header (note the : at the end)
   SIPRemoveHeader(P-Asserted-Identity:);



regards
klaus