[Freeswitch-users] Reading custom SIP headers

Dahlberg, David david.dahlberg at fkie.fraunhofer.de
Thu Apr 10 11:45:37 MSD 2014

Am Mittwoch, den 09.04.2014, 18:42 -0500 schrieb Brian West:

> It it does then we need an NDLB flag (for those not in the know NDLB is No Device Left Behind)

Sorry, considering that /any/ header that are not recognised by a
particular software solution and that does not begin with "X-" or
"P-" to be of any use is what IMHO requires a NDLB flag.

X-Headers are a RFC 822 (from 1982!) legacy. By now, considering only 
"X-" headers as potentially meaningful would require FS to implement 
/every possible/ standardized extension to the SIP RFCs, which is 
virtually impossible today. E.g. I am quite certain, that you do /not/ 
implement RFC 4412 ("Resource-Priority") nor was FS able to support a 
custom extension with the necessary data do process it.

For that reason (or more for the problem of migrating a "well known"
X-Header to a "standards" header) the IETF finally deprecated the usage
of "X-" and "P-" prefixes in RFC 6648/BCP 178 and RFC 5727/BCP 67.

Until recently one could write but not read non-X-, non-P- and not known
headers. Fortunately, now there seems to be a patch (FS-6075) in HEAD,
which allows the parsing of arbitrary headers at least for SIP invites.
So please have a look at the most recent git version of FS, Ido.


David Dahlberg     

Fraunhofer FKIE, Dept. Communication Systems (KOM) | Tel: +49-228-9435-845
Fraunhoferstr. 20, 53343 Wachtberg, Germany        | Fax: +49-228-856277

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