gameServer/Codec/Binary/Base64.hs
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-- |
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-- Module    : Codec.Binary.Base64
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-- Copyright : (c) 2007 Magnus Therning
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-- License   : BSD3
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--
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-- Implemented as specified in RFC 4648
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-- (<http://tools.ietf.org/html/rfc4648>).
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--
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-- Further documentation and information can be found at
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-- <http://www.haskell.org/haskellwiki/Library/Data_encoding>.
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module Codec.Binary.Base64
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    ( encode
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    , decode
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    , decode'
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    , chop
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    , unchop
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    ) where
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import Control.Monad
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import Data.Array
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import Data.Bits
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import Data.Maybe
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import Data.Word
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import qualified Data.Map as M
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-- {{{1 enc/dec map
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_encMap =
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    [ (0, 'A'), (1, 'B'), (2, 'C'), (3, 'D'), (4, 'E')
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    , (5, 'F') , (6, 'G'), (7, 'H'), (8, 'I'), (9, 'J')
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    , (10, 'K'), (11, 'L'), (12, 'M'), (13, 'N'), (14, 'O')
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    , (15, 'P'), (16, 'Q'), (17, 'R'), (18, 'S'), (19, 'T')
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    , (20, 'U'), (21, 'V'), (22, 'W'), (23, 'X'), (24, 'Y')
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    , (25, 'Z'), (26, 'a'), (27, 'b'), (28, 'c'), (29, 'd')
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    , (30, 'e'), (31, 'f'), (32, 'g'), (33, 'h'), (34, 'i')
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    , (35, 'j'), (36, 'k'), (37, 'l'), (38, 'm'), (39, 'n')
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    , (40, 'o'), (41, 'p'), (42, 'q'), (43, 'r'), (44, 's')
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    , (45, 't'), (46, 'u'), (47, 'v'), (48, 'w'), (49, 'x')
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    , (50, 'y'), (51, 'z'), (52, '0'), (53, '1'), (54, '2')
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    , (55, '3'), (56, '4'), (57, '5'), (58, '6'), (59, '7')
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    , (60, '8'), (61, '9'), (62, '+'), (63, '/') ]
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-- {{{1 encodeArray
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encodeArray :: Array Word8 Char
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encodeArray = array (0, 64) _encMap
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-- {{{1 decodeMap
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decodeMap :: M.Map Char Word8
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decodeMap  = M.fromList [(snd i, fst i) | i <- _encMap]
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-- {{{1 encode
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-- | Encode data.
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encode :: [Word8]
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    -> String
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encode = let
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        pad n = take n $ repeat 0
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        enc [] = ""
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        enc l@[o] = (++ "==") . take 2 .enc $ l ++ pad 2
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        enc l@[o1, o2] = (++ "=") . take 3 . enc $ l ++ pad 1
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        enc (o1:o2:o3:os) = let
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                i1 = o1 `shiftR` 2
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                i2 = (o1 `shiftL` 4 .|. o2 `shiftR` 4) .&. 0x3f
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                i3 = (o2 `shiftL` 2 .|. o3 `shiftR` 6) .&. 0x3f
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                i4 = o3 .&. 0x3f
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            in (foldr (\ i s -> (encodeArray ! i) : s) "" [i1, i2, i3, i4]) ++ enc os
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    in enc
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-- {{{1 decode
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-- | Decode data (lazy).
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decode' :: String
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    -> [Maybe Word8]
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decode' = let
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        pad n = take n $ repeat $ Just 0
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        dec [] = []
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        dec l@[Just eo1, Just eo2] = take 1 . dec $ l ++ pad 2
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        dec l@[Just eo1, Just eo2, Just eo3] = take 2 . dec $ l ++ pad 1
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        dec (Just eo1:Just eo2:Just eo3:Just eo4:eos) = let
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                o1 = eo1 `shiftL` 2 .|. eo2 `shiftR` 4
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                o2 = eo2 `shiftL` 4 .|. eo3 `shiftR` 2
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                o3 = eo3 `shiftL` 6 .|. eo4
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            in Just o1:Just o2:Just o3:(dec eos)
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        dec _ = [Nothing]
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    in
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        dec . map (flip M.lookup decodeMap) . takeWhile (/= '=')
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-- | Decode data (strict).
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decode :: String
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    -> Maybe [Word8]
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decode = sequence . decode'
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-- {{{1 chop
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-- | Chop up a string in parts.
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--
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--   The length given is rounded down to the nearest multiple of 4.
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--
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--   /Notes:/
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--
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--   * PEM requires lines that are 64 characters long.
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--
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--   * MIME requires lines that are at most 76 characters long.
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chop :: Int     -- ^ length of individual lines
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    -> String
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    -> [String]
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chop n "" = []
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chop n s = let
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        enc_len | n < 4 = 4
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                | otherwise = n `div` 4 * 4
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    in (take enc_len s) : chop n (drop enc_len s)
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-- {{{1 unchop
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-- | Concatenate the strings into one long string.
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unchop :: [String]
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    -> String
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unchop = foldr (++) ""