haddock comments

[time-http.git] / Data / Time / HTTP.hs

diff --git a/Data/Time/HTTP.hs b/Data/Time/HTTP.hs
index 3a3dc3e833aeeeb82b16cf11c22f19d0999ff2eb..9f628063938c744d232aa1751303e3e7b6b23817 100644 (file)
--- a/Data/Time/HTTP.hs
+++ b/Data/Time/HTTP.hs
@@ -1,3 +1,41 @@
+-- |This module provides functions to parse and format HTTP\/1.1 date
+-- and time formats.
+--
+-- The HTTP\/1.1 specification (RFC 2616) says that HTTP\/1.1 clients
+-- and servers which parse the date value MUST accept all the
+-- following formats, though they MUST only generate the RFC 1123
+-- format for representing HTTP-date values in header fields:
+--
+-- > 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
+--
+-- It also says that 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    = 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"
+-- > weekday      = "Monday" | "Tuesday" | "Wednesday"
+-- >              | "Thursday" | "Friday" | "Saturday" | "Sunday"
+-- > month        = "Jan" | "Feb" | "Mar" | "Apr"
+-- >              | "May" | "Jun" | "Jul" | "Aug"
+-- >              | "Sep" | "Oct" | "Nov" | "Dec"
 module Data.Time.HTTP
     ( format
     , parse
@@ -10,7 +48,7 @@ import qualified Text.Parsec as P
 import Data.Time
 import Data.Time.HTTP.Parsec
 
-
+-- |Format an 'UTCTime' in RFC 1123 date and time.
 format :: UTCTime -> String
 format utcTime
     = let timeZone  = TimeZone 0 False "GMT"
@@ -18,7 +56,15 @@ format utcTime
       in
         RFC1123.format zonedTime
 
-
+-- |Parse a date and time string in any of RFC 822, RFC 1123, RFC 850
+-- and ANSI C's asctime() formats. When the string can't be parsed, it
+-- returns 'Nothing'.
+--
+-- This function is even more permissive than what HTTP\/1.1
+-- specifies. That is, it accepts 2-digit years in RFC 822, omitted
+-- separator symbols in RFC 850, omitted sec fields, and non-GMT time
+-- zones. I believe this behavior will not cause a problem but you
+-- should know this.
 parse :: String -> Maybe UTCTime
 parse src = case P.parse p "" src of
               Right ut -> Just ut