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

[Klaus Darilion]

Klaus Darilion schrieb:
> FYI: SipAddHeader() was added to trunk

Of course I meant SIPRemoveHeader() :-)

klaus


> 
> klaus
> 
> Klaus Darilion schrieb:
>> 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
>>
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