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Re: Syntax presentation (was Re: Unofficial Draft of Content Security Policy)

From: Adam Barth <w3c@adambarth.com>
Date: Tue, 8 Mar 2011 16:57:57 -0800
Message-ID: <AANLkTin6Lbt9EhS-WsVvLe48VByGRvt2Ceo+Q0LOYAsY@mail.gmail.com>
To: Brandon Sterne <bsterne@mozilla.com>
Cc: "public-web-security@w3.org" <public-web-security@w3.org>
On Tue, Mar 8, 2011 at 3:20 PM, Brandon Sterne <bsterne@mozilla.com> wrote:
> On 03/08/2011 02:50 PM, Brandon Sterne wrote:
>> On 03/03/2011 01:33 PM, Adam Barth wrote:
>>> For
>>> example, here's a possible grammar for a CSP policy:
>>>
>>> policy          = directive-list
>>> directive-list  = directive *( ";" directive )
>>> directive       = *LWS directive-name [ LWS directive-value ]
>>> directive-name  = 1*<OCTET, except LWS and ";">
>>> directive-value = *<OCTET, except ";">
>>>
>>> (Of course, the above might not be correct---it's just an example.)
>>
>> Hey Adam,
>>
>> Your ABNF example defines directive names and values by sequences of
>> allowed characters, while the Mozilla grammar enumerates the list of
>> "good directives" and makes room for "future directives" using character
>> sequences.
>
> I neglected to quote the following sentence from your message, which is
> important:
>> This approach follows how, for example, HTTP header fields work.
>> There's a general grammar for HTTP header fields in general, and then
>> a more specific grammar for particular header fields.
>
> The "more specific grammar" for the individual directives is where the
> enumeration of known directives will presumably take place.  I withdraw
> my previous question and ask this one instead :-)
>
> How does one link directive-name in your grammar to, say, the grammar
> for the script-src directive?
>
> In the current revision, you can make the substitution <directive> -->
> <src-directive> --> "script-src".  How would this same transition be
> made between generic and specific directive syntaxes using ABNF?
>
> Hope my question is clear.

One approach is to do this the same way we do this in HTTP:

http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-12#section-3.2
defines the general syntax for headers.

http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-12#section-3.4
lists a bunch of headers that are defined in the spec itself.

HTTP also has a registry where folks can define new headers.  For
example, <http://tools.ietf.org/html/draft-ietf-httpstate-cookie-23#section-9>
adds "Cookie" to the list of headers:

http://www.iana.org/assignments/message-headers/perm-headers.html

That page lists all the officially registered headers with links to
the documents that define them.

I'm not sure we need to jump to having a registry right away.  Let's
just start with a list of directives in the spec itself.  If CSP
becomes a popular way of expressing policy, we might want to add a
registry in the future so we don't need to revise the core CSP spec
every time someone invents a new directive.

Adam
Received on Wednesday, 9 March 2011 00:59:01 GMT

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