[sr-dev] Headers for IMS Extensions

[Daniel-Constantin Mierla]

Hi Jason,

I'm just continuing on a topic discussed few messages back in this thread.

Actually it is recommended to avoid adding new direct header hooks in 
sip_msg_t structure, because it becomes too big compared with what 
actually a SIP message has in terms of headers. Apart of invite which 
can have between 10-20 headers in average, the rest have less number of 
headers. Note that all headers are linked in a list held in 
sip_msg_t->headers.

Getting a header from the list is possible with several functions, 
depending whether you want the first or next header, searched by 
internal ID (if that header has one) or simply by name. The prototypes 
for these functions are in parser/msg_parse.h:

hdr_field_t* get_hdr(sip_msg_t *msg, enum _hdr_types_t ht);
hdr_field_t* next_sibling_hdr(hdr_field_t *hf);
hdr_field_t* get_hdr_by_name(sip_msg_t *msg, char *name, int name_len);
hdr_field_t* next_sibling_hdr_by_name(hdr_field_t *hf);

So getting my X-Header would be like:

parse_headers(msg, HDR_EOH_F, 0);
hdr = get_hdr_by_name(msg, "X-Header", strlen("X-Header"));

Some of them may be even removed from sip_msg_t (like priority or 
subject) which are not common at all.

Cheers,
Daniel

On 11/4/11 6:35 AM, Jason Penton wrote:
> Hey Henning,
>
> Ahh, thanks for that, thats perfect for now!
>
> A pity, those names should have been a little more descriptive ;)
>
> Thanks
> Jason
>
> On Thu, Nov 3, 2011 at 3:27 PM, Henning Westerholt <hw at kamailio.org 
> <mailto:hw at kamailio.org>> wrote:
>
>     On Thursday 03 November 2011, Jason Penton wrote:
>     > For Asserted and preferred identities, we don't need to parse
>     the content,
>     > but in other headers I have not gotten to yet, we may need to.
>
>     Hi Jason,
>
>     do you talk about p-asserted and p-preferred header? This are
>     fairly standard
>     headers, there are even some PVs to access them right now i think.
>
>     > Please help me understand, I would have thought from an architecture
>     > perspective, we would populate the sip_msg structure with all
>     possible sip
>     > headers  as well as the parsers. What is the reason we don't do this
>     > currently? performance?
>
>     I'd guess the reasons is memory efficiency. The structure get
>     bigger and
>     bigger with every pointer. But for p-asserted and p-preffered,
>     they are
>     already included it seems:
>
>            struct hdr_field* pai;
>            struct hdr_field* ppi;
>
>     Best regards,
>
>     Henning
>
>
>
>
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-- 
Daniel-Constantin Mierla -- http://www.asipto.com
Kamailio Advanced Training, Dec 5-8, Berlin: http://asipto.com/u/kat
http://linkedin.com/in/miconda -- http://twitter.com/miconda

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