Multiple headers with the same name
Curatica
I was curious about the ability to use a header name multiple times in
a message (such as SET-PARAMS which is the only one I tested). The
specification is grammatically incoherent when it refers to this
subject:
"Multiple headers with the same name MAY be present in a message if
and only if the entire value for that header is defined as a
commaseparated
list [i.e., #(values)]".
The way I read it is that multiple headers with the same name CANNOT
be present in a message but the effect can be achieved by specifying
the header once and its multiple values as a comma separated list:
<header-name>:<value-1>,<value-2>,...<value-n>
where the colon, ":" and the commas, "," are to be taken textually.
I tried to use this technique to set multiple values for the parameter
"Vendor-Specific-Parameters". The server that I use for testing did
not tolerate the commas and returned 404 (Illegal Value for Header).
But it accepted a semicolon, ";", instead of a comma. This is the same
separator it uses when it returns multiple values for "Vendor-Specific-
Parameters" in a response to GET-PARAMS.
I wonder if I misread the specification or the server is incorrect in
using ";" instead of ","...
Thanks a lot.
Arsen Chaloyan
On Mon, Dec 28, 2009 at 5:55 AM, Curatica <cura...@gmail.com> wrote:
> Hi Arsen,
>
> I was curious about the ability to use a header name multiple times in
> a message (such as SET-PARAMS which is the only one I tested). The
> specification is grammatically incoherent when it refers to this
> subject:
>
> "Multiple headers with the same name MAY be present in a message if
> and only if the entire value for that header is defined as a
> commaseparated
> list [i.e., #(values)]".
Honestly speaking, I don't fully understand how, when and for what the
same header name should be present in a message.
>
> The way I read it is that multiple headers with the same name CANNOT
> be present in a message but the effect can be achieved by specifying
> the header once and its multiple values as a comma separated list:
>
> <header-name>:<value-1>,<value-2>,...<value-n>
I'm not sure such an option exists.
>
> where the colon, ":" and the commas, "," are to be taken textually.
>
> I tried to use this technique to set multiple values for the parameter
> "Vendor-Specific-Parameters". The server that I use for testing did
> not tolerate the commas and returned 404 (Illegal Value for Header).
> But it accepted a semicolon, ";", instead of a comma. This is the same
> separator it uses when it returns multiple values for "Vendor-Specific-
> Parameters" in a response to GET-PARAMS.
The value of "Vendor-Specific-Parameters" header is a string
consisting of ";" separated name-value pairs. So it's a bit special
case.
>
> I wonder if I misread the specification or the server is incorrect in
> using ";" instead of ","...
Server behaves according to spec to me, as name-value pairs should be
separated by ";"
vendor-specific = "Vendor-Specific-Parameters" ":"
[vendor-specific-av-pair
*(";" vendor-specific-av-pair)] CRLF
>
> Thanks a lot.
You're welcome
>
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--
Arsen Chaloyan
The author of UniMRCP
http://www.unimrcp.org