RFC 2068                        HTTP/1.1                    January 1997


3.3 Date/Time Formats

3.3.1 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 822, updated by RFC 1123
          Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
          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 RFC 1123  (an update to RFC
   822).  The second format is in common use, but is based on the
   obsolete RFC 850 [12] date format and lacks a four-digit year.
   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.

     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.

   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
   (GMT), without exception. 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    = rfc1123-date | rfc850-date | asctime-date

          rfc1123-date = wkday "," SP date1 SP time SP "GMT"
          rfc850-date  = weekday "," SP date2 SP time SP "GMT"
          asctime-date = wkday SP date3 SP time SP 4DIGIT

          date1        = 2DIGIT SP month SP 4DIGIT
                         ; day month year (e.g., 02 Jun 1982)
          date2        = 2DIGIT "-" month "-" 2DIGIT
                         ; day-month-year (e.g., 02-Jun-82)
          date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
                         ; month day (e.g., Jun  2)

          time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
                         ; 00:00:00 - 23:59:59

          wkday        = "Mon" | "Tue" | "Wed"
                       | "Thu" | "Fri" | "Sat" | "Sun"



Fielding, et. al.           Standards Track                    [Page 21]

RFC 2068                        HTTP/1.1                    January 1997


          weekday      = "Monday" | "Tuesday" | "Wednesday"
                       | "Thursday" | "Friday" | "Saturday" | "Sunday"

          month        = "Jan" | "Feb" | "Mar" | "Apr"
                       | "May" | "Jun" | "Jul" | "Aug"
                       | "Sep" | "Oct" | "Nov" | "Dec"

     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.

3.3.2 Delta Seconds

   Some HTTP header fields allow a time value to be specified as an
   integer number of seconds, represented in decimal, after the time
   that the message was received.

          delta-seconds  = 1*DIGIT

3.4 Character Sets

   HTTP uses the same definition of the term "character set" as that
   described for MIME:

     The term "character set" is used in this document to refer to a
     method used with one or more tables to convert a sequence of octets
     into a sequence of characters. Note that unconditional conversion
     in the other direction is not required, in that not all characters
     may be available in a given character set and a character set may
     provide more than one sequence of octets to represent a particular
     character. This definition is intended to allow various kinds of
     character encodings, from simple single-table mappings such as US-
     ASCII to complex table switching methods such as those that use ISO
     2022's techniques. However, the definition associated with a MIME
     character set name MUST fully specify the mapping to be performed
     from octets to characters. In particular, use of external profiling
     information to determine the exact mapping is not permitted.

     Note: This use of the term "character set" is more commonly
     referred to as a "character encoding." However, since HTTP and MIME
     share the same registry, it is important that the terminology also
     be shared.








Fielding, et. al.           Standards Track                    [Page 22]

RFC 2068                        HTTP/1.1                    January 1997


   HTTP character sets are identified by case-insensitive tokens. The
   complete set of tokens is defined by the IANA Character Set registry
   [19].

          charset = token

   Although HTTP allows an arbitrary token to be used as a charset
   value, any token that has a predefined value within the IANA
   Character Set registry MUST represent the character set defined by
   that registry.  Applications SHOULD limit their use of character sets
   to those defined by the IANA registry.