Re: [VCARDDAV] [calsify] Escaping dquote in a parameter value

[Cyrus Daboo <[e-mail]>]

Hi Jack,

--On June 20, 2012 7:56:44 AM +0100 Jack <[e-mail]> wrote:

>> I ruled out use of \ because some parsers erroneously eat that, and
>> it would also be tempting to use \" which is definitely not possible
>>  because the dquote cannot appear.
>
> However "\" is already specified in RFC2445 as the escape character in
> TEXT (4.3.11).
>
> That section specifies that a DQUOTE is not to appear in a TEXT; but it
> also specifies that a ";" shall not appear in a TEXT, and then goes on
> to specify that a ";" must be escaped thus: "\;". So I read it as saying
> (as clearly as anything is said in that document) that a DQUOTE should
> be escaped thus: "\"".

First please use RFC5545 as your reference not RFC2445.

Second, the syntax for a parameter value, as opposed to a property value, 
is different. Here is the 5545 syntax:

     param-value   = paramtext / quoted-string

     paramtext     = *SAFE-CHAR

     quoted-string = DQUOTE *QSAFE-CHAR DQUOTE

     QSAFE-CHAR    = WSP / %x21 / %x23-7E / NON-US-ASCII
     ; Any character except CONTROL and DQUOTE

     SAFE-CHAR     = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E
                   / NON-US-ASCII
     ; Any character except CONTROL, DQUOTE, ";", ":", ","

So a DQUOTE is not allowed in either paramtext or quoted-string, and there 
is no affordance for any kind of escape character.

It is also true that CONTROL characters are not allowed. Now that I think 
of it, there have been situations I have come across where line feeds at 
least were needed in a parameter value. That suggest that perhaps my 
proposed ^ escape mechanism should be broadened to allow some specific 
CONTROLs, e.g.:

^n  - LF
^r  - CR
^t  - HTAB



-- 
Cyrus Daboo