Subject: [Simple] MSRP-07 and charsets

From: Pekka Pessi <[email-masked]>
Date: Mon, 09 Aug 2004 16:41:27 +0300

Hello all,

There is no mention about charsets in MSRP except for the SDP
attributes used by session setup. I think the MSRP spec was
supposed to declare UTF-8 as the default charset. A message
without a charset parameter in Content-Type would default to
UTF-8, and all the endpoints should accept messages using UTF-8.

However, I'm afraid it will take some time before UTF-8 will be
universally available, so it might be worthwhile to negotiate the
charsets for the MSRP session.

HTTP uses Accept-Charset header for that purpose. We could define
a accept-charset attribute. Here is a proposal based on
cut'n'paste from RFC 2616.

--Pekka

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X.X.X The accept-charset attribute

The accept-charset attribute can be used to indicate what
character sets are acceptable for the endpoint. The attribute
allows endpoints capable of understanding more special-purpose
character sets to announce their capabilities.

accept-charset = accept-charset-label ":" charset-list
accept-charset-label = "accept-charset"
charset-list = chatset-entry *( SP charset-entry)
chatset-entry = token | "*"

Character set values are described in [17]. 

An example is

   a=accept-charset:iso-8859-15,iso-8859-1,utf-8

The special value "*", if present in the accept-charset attribute,
matches every character set. Even if no "*" is present
in an accept-charset attribute, the endpoint is required to accept
UTF-8 encoded text.

   OPEN ISSUE: is this reasonable requirement? Unicode fonts may
   be an overkill for very simple devices with text-only display.

If no accept-charset attribute is present in SDP sent by the
endpoint, the default is that any character set is acceptable. If
an accept-charset attribute is present, and if the other endpoint
cannot send messages which are acceptable according to the
accept-charset attribute, then the endpoint may reject the
session. Alternatively, if the endpoint accepts the session and if
the session is set up with SIP, the endpoint may issue Warning
code 305.

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15.3.5 Accept Charsets

   Attribute-name:  accept-charsets
   Long-form  Attribute Name:  MSRP Charsets
   Type:  Media level
   Subject to Charset Attribute:  No
   Purpose and Appropriate Values:  See Section X.X.X

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From: Rohan Mahy <[email-masked]>
Date: Fri, 13 Aug 2004 18:44:33 -0700

Hi,

SIP uses the UTF-8 charset exclusively.  Since all expected usages of 
MSRP in the foreseeable future will be signaled via SIP, I don't see 
requiring UTF-8 for MSRP to be a hardship.

thanks,
-rohan