{- Copyright © 2007 Magnus Therning
-
- This file is part of dataenc.
-
- Dataenc is free software: you can redistribute it and/or modify it under
- the terms of the GNU Lesser General Public License as published by the
- Free Software Foundation, either version 3 of the License, or (at your
- option) any later version.
-
- Dataenc is distributed in the hope that it will be useful, but WITHOUT
- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with dataenc. If not, see
-}
-- | Uuencoding module.
--
-- Uuencoding is notoriously badly specified. This implementation is
-- compatible with the GNU Sharutils
-- ().
module Codec.Binary.Uu
( encode
, decode
, decode'
, chop
, unchop
) where
import Control.Monad
import Data.Array
import Data.Bits
import Data.Maybe
import Data.Word
import qualified Data.Map as M
-- {{{1 enc/dec map
_encMap =
[ (0, '`'), (1, '!'), (2, '"'), (3, '#'), (4, '$')
, (5, '%'), (6, '&'), (7, '\''), (8, '('), (9, ')')
, (10, '*'), (11, '+'), (12, ','), (13, '-'), (14, '.')
, (15, '/'), (16, '0'), (17, '1'), (18, '2'), (19, '3')
, (20, '4'), (21, '5'), (22, '6'), (23, '7'), (24, '8')
, (25, '9'), (26, ':'), (27, ';'), (28, '<'), (29, '=')
, (30, '>'), (31, '?'), (32, '@'), (33, 'A'), (34, 'B')
, (35, 'C'), (36, 'D'), (37, 'E'), (38, 'F'), (39, 'G')
, (40, 'H'), (41, 'I'), (42, 'J'), (43, 'K'), (44, 'L')
, (45, 'M'), (46, 'N'), (47, 'O'), (48, 'P'), (49, 'Q')
, (50, 'R'), (51, 'S'), (52, 'T'), (53, 'U') ,(54, 'V')
, (55, 'W'), (56, 'X'), (57, 'Y'), (58, 'Z'), (59, '[')
, (60, '\\'), (61, ']'), (62, '^'), (63, '_') ]
-- {{{1 encodeArray
encodeArray :: Array Word8 Char
encodeArray = array (0, 64) _encMap
-- {{{1 decodeMap
decodeMap :: M.Map Char Word8
decodeMap = M.fromList [(snd i, fst i) | i <- _encMap]
-- {{{1 encode
-- | Encode data.
encode :: [Word8]
-> String
encode = let
pad n = take n $ repeat 0
enc [] = ""
enc l@[o] = take 2 . enc $ l ++ pad 2
enc l@[o1, o2] = take 3 . enc $ l ++ pad 1
enc (o1:o2:o3:os) = let
i1 = o1 `shiftR` 2
i2 = (o1 `shiftL` 4 .|. o2 `shiftR` 4) .&. 0x3f
i3 = (o2 `shiftL` 2 .|. o3 `shiftR` 6) .&. 0x3f
i4 = o3 .&. 0x3f
in (foldr (\ i s -> (encodeArray ! i) : s) "" [i1, i2, i3, i4]) ++ enc os
in enc
-- {{{1 decode
-- | Decode data (lazy).
decode' :: String
-> [Maybe Word8]
decode' = let
pad n = take n . repeat $ Just 0
dec [] = []
dec l@[Just eo1, Just eo2] = take 1 . dec $ l ++ pad 2
dec l@[Just eo1, Just eo2, Just eo3] = take 2 . dec $ l ++ pad 1
dec (Just eo1:Just eo2:Just eo3:Just eo4:eos) = let
o1 = eo1 `shiftL` 2 .|. eo2 `shiftR` 4
o2 = eo2 `shiftL` 4 .|. eo3 `shiftR` 2
o3 = eo3 `shiftL` 6 .|. eo4
in Just o1:Just o2:Just o3:(dec eos)
dec _ = [Nothing]
in
dec . map (flip M.lookup decodeMap)
-- | Decode data (strict).
decode :: String
-> Maybe [Word8]
decode = sequence . decode'
-- {{{1 chop
-- | Chop up a string in parts. Each string in the resulting list is prepended
-- with the length according to the uuencode \"specificiation\".
--
-- /Notes:/
--
-- * The length of the strings in the result will be @(n -1) `div` 4 * 4@.
-- The @-1@ comes from the need to prepend the length. Keeping it to a
-- multiple of 4 means that strings returned from 'encode' can be chopped
-- without requiring any changes.
--
-- * The length of lines in GNU's sharutils is 61.
chop :: Int -- ^ length (@1 < n <= 65@, not checked)
-> String
-> [String]
chop n "" = []
chop n s = let
enc_len | n < 5 = 4
| otherwise = (n - 1) `div` 4 * 4
enc_line = take enc_len s
act_len = fromIntegral $ case (length enc_line `divMod` 4) of
(l, 0) -> l * 3
(l, 2) -> l * 3 + 1
(l, 3) -> l * 3 + 2
len = (encodeArray ! act_len)
in (len : enc_line) : chop n (drop enc_len s)
-- {{{1 unchop
-- | Concatenate the strings into one long string. Each string is assumed to
-- be prepended with the length according to the uuencode specification.
unchop :: [String]
-> String
unchop ss = let
singleUnchop (l:cs) = let
act_len = fromIntegral $ decodeMap M.! l
enc_len = case (act_len `divMod` 3) of
(n, 0) -> n * 4
(n, 1) -> n * 4 + 2
(n, 2) -> n * 4 + 3
in take enc_len cs
in foldr (\ s res -> (singleUnchop s) ++ res) "" ss