Re: Using versions instead of XEmacs codenames in User-Agent

["Bjørn Mork" <bmork@dod.no>]

Steve Youngs <steve@youngs.au.com> writes:
> * Bjørn Mork <bmork@dod.no> writes:
>   > Steve Youngs <steve@youngs.au.com> writes:
>   >> 
>   >> Yep, however, IMHO, this...
>   >> 
>   >> SXEmacs/22.1.1 (Aston Martin, berkeley-unix)
>   >> 
>   >> doesn't look anywhere near as nice as...
>   >> 
>   >> SXEmacs/22.1.1 "Aston Martin" (berkeley-unix)
>
>   > Maybe.  But it doesn't really matter since the first version uses a
>   > perfectly legal comment while the second is an invalid User-Agent
>   > field.
>
> OK, now I'm really confused.  Because going by what you quoted about
> tokens and separators, aren't both of them invalid? And if not, why
> not?

Oh, I left that as an exercise :-)

More from RFC 2616:

<quote>
14.43 User-Agent

   The User-Agent request-header field contains information about the
   user agent originating the request. This is for statistical purposes,
   the tracing of protocol violations, and automated recognition of user
   agents for the sake of tailoring responses to avoid particular user
   agent limitations. User agents SHOULD include this field with
   requests. The field can contain multiple product tokens (section 3.8)
   and comments identifying the agent and any subproducts which form a
   significant part of the user agent. By convention, the product tokens
   are listed in order of their significance for identifying the
   application.

       User-Agent     = "User-Agent" ":" 1*( product | comment )

   Example:

       User-Agent: CERN-LineMode/2.15 libwww/2.17b3
</quote>

and

<quote>
   Comments can be included in some HTTP header fields by surrounding
   the comment text with parentheses. Comments are only allowed in
   fields containing "comment" as part of their field value definition.
   In all other fields, parentheses are considered part of the field
   value.

       comment        = "(" *( ctext | quoted-pair | comment ) ")"
       ctext          = <any TEXT excluding "(" and ")">
</quote>


> Also, what the hell does RFC 2616 - "Hypertext Transfer Protocol --
> HTTP/1.1" have to do with email headers?  I honestly don't understand
> that at all?

No, that's not very clear.  I assume it's because that's the RFC where
the User-Agent field is currently specified. RFC 2822 gives these
generic rules for optional header fields:

<quote>
3.6.8. Optional fields

   Fields may appear in messages that are otherwise unspecified in this
   standard.  They MUST conform to the syntax of an optional-field.
   This is a field name, made up of the printable US-ASCII characters
   except SP and colon, followed by a colon, followed by any text which
   conforms to unstructured.

   The field names of any optional-field MUST NOT be identical to any
   field name specified elsewhere in this standard.

optional-field  =       field-name ":" unstructured CRLF

field-name      =       1*ftext

ftext           =       %d33-57 /               ; Any character except
                        %d59-126                ;  controls, SP, and
                                                ;  ":".

   For the purposes of this standard, any optional field is
   uninterpreted.
</quote>

which allows any syntax.  However, when it comes to mail and Usenet
user agents the current USEFOR draft is probably a better reference
than both RFC 2822 and RFC 2616:

http://www.ietf.org/internet-drafts/draft-ietf-usefor-usefor-02.txt

Luckily, it seems to mostly agree with RFC 2616:

<quote>
3.2.12  User-Agent

   The User-Agent header contains information about the user agent
   (typically a newsreader) generating the article, for statistical
   purposes and tracing of standards violations to specific software
   needing correction.  It is intended that this header be suitable for
   use in Email.

   user-agent      =  "User-Agent:" SP 1*product CRLF

   product         =  [CFWS] token [CFWS] [ "/" product-version ]

   product-version =  [CFWS] token [CFWS]

   This header MAY contain multiple product-tokens identifying the agent
   and any subproducts which form a significant part of the posting
   agent, listed in order of their significance for identifying the
   application.
      NOTE: This header supersedes the role performed redundantly by
      experimental headers such as X-Newsreader, X-Mailer,
      X-Posting-Agent, X-Http-User-Agent, and other headers previously
      used on Usenet and in Email for this purpose.  Use of these
      experimental headers SHOULD be discontinued in favor of the
      single, standard User-Agent header.
      NOTE: [RFC2616] describes a similar facility for the HTTP
      protocol.  This specification differs in that "{" and "}" are
      allowed in tokens (<product> and <product-version>) and comments
      are permitted wherever whitespace is allowed. 
</quote>

IMHO, it's best using a syntax that conforms to USEFOR, RFC 2616 and
RFC 2822 unless there are good reasons not to do so.  That means
sticking with the RFC 2616 definition even for mail and news user
agents.  But that's only an opionion.


Bjørn
-- 
Ignoramus!