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Re: Issue 163, was: Meaning of invalid but well-formed dates

From: Julian Reschke <julian.reschke@gmx.de>
Date: Sun, 17 May 2009 13:56:48 +0200
Message-ID: <4A0FFB80.1040800@gmx.de>
To: "Martin J. Dürst" <duerst@it.aoyama.ac.jp>
CC: Brian Smith <brian@briansmith.org>, 'Geoffrey Sneddon' <foolistbar@googlemail.com>, 'HTTP Working Group' <ietf-http-wg@w3.org>
Julian Reschke wrote:
> Martin J. Dürst wrote:
>> That seems to be backward. Wouldn't the comments be helpful in the 
>> collected ABNF, too?
> 
> The collected ABNF is produced by an ABNF parser (Bill Fenner's), by 
> serializing the rule objects it generates. Thus, it doesn't have the 
> comments anymore.
 > ...

In the meantime I noticed that BAP (Bill Fenner's ABNF Parser) can 
automatically generate comments for printable byte sequences; with that 
feature turned on the generated ABNF is readable enough without the 
extra productions.

See <http://trac.tools.ietf.org/wg/httpbis/trac/changeset/582>. The 
section now reads:

-- snip --
3.2.  Date/Time Formats: Full Date

    HTTP applications have historically allowed three different formats
    for the representation of date/time stamps:

      Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
      Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
      Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format

    The first format is preferred as an Internet standard and represents
    a fixed-length subset of that defined by [RFC1123].  The other
    formats are described here only for compatibility with obsolete
    implementations.  HTTP/1.1 clients and servers that parse the date
    value MUST accept all three formats (for compatibility with
    HTTP/1.0), though they MUST only generate the RFC 1123 format for
    representing HTTP-date values in header fields.  See Appendix A for
    further information.

    All HTTP date/time stamps MUST be represented in Greenwich Mean Time
    (GMT), without exception.  For the purposes of HTTP, GMT is exactly
    equal to UTC (Coordinated Universal Time).  This is indicated in the
    first two formats by the inclusion of "GMT" as the three-letter
    abbreviation for time zone, and MUST be assumed when reading the
    asctime format.  HTTP-date is case sensitive and MUST NOT include
    additional whitespace beyond that specifically included as SP in the
    grammar.

      HTTP-date    = rfc1123-date / obs-date

    Preferred format:

      rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT

      day-name     = %x4D.6F.6E ; "Mon", case-sensitive
                   / %x54.75.65 ; "Tue", case-sensitive
                   / %x57.65.64 ; "Wed", case-sensitive
                   / %x54.68.75 ; "Thu", case-sensitive
                   / %x46.72.69 ; "Fri", case-sensitive
                   / %x53.61.74 ; "Sat", case-sensitive
                   / %x53.75.6E ; "Sun", case-sensitive

      date1        = day SP month SP year
                   ; e.g., 02 Jun 1982

      day          = 2DIGIT
      month        = %x4A.61.6E ; "Jan", case-sensitive
                   / %x46.65.62 ; "Feb", case-sensitive
                   / %x4D.61.72 ; "Mar", case-sensitive
                   / %x41.70.72 ; "Apr", case-sensitive
                   / %x4D.61.79 ; "May", case-sensitive
                   / %x4A.75.6E ; "Jun", case-sensitive
                   / %x4A.75.6C ; "Jul", case-sensitive
                   / %x41.75.67 ; "Aug", case-sensitive
                   / %x53.65.70 ; "Sep", case-sensitive
                   / %x4F.63.74 ; "Oct", case-sensitive
                   / %x4E.6F.76 ; "Nov", case-sensitive
                   / %x44.65.63 ; "Dec", case-sensitive
      year         = 4DIGIT

      GMT   = %x47.4D.54 ; "GMT", case-sensitive

      time-of-day  = hour ":" minute ":" second
                     ; 00:00:00 - 23:59:59

      hour         = 2DIGIT
      minute       = 2DIGIT
      second       = 2DIGIT

    The semantics of day-name, day, month, year, and time-of-day are the
    same as those defined in the RFC 5322 constructs with the
    corresponding name ([RFC5322], Section 3.3).

    Obsolete formats:

      obs-date     = rfc850-date / asctime-date

      rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
      date2        = day "-" month "-" 2DIGIT
                     ; day-month-year (e.g., 02-Jun-82)

      day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
             / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
             / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
             / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
             / %x46.72.69.64.61.79 ; "Friday", case-sensitive
             / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
             / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive


      asctime-date = day-name SP date3 SP time-of-day SP year
      date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
                     ; month day (e.g., Jun  2)

       Note: Recipients of date values are encouraged to be robust in
       accepting date values that may have been sent by non-HTTP
       applications, as is sometimes the case when retrieving or posting
       messages via proxies/gateways to SMTP or NNTP.

       Note: HTTP requirements for the date/time stamp format apply only
       to their usage within the protocol stream.  Clients and servers
       are not required to use these formats for user presentation,
       request logging, etc.
-- snip --

BR, Julian
Received on Sunday, 17 May 2009 11:57:45 GMT

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