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|
--------------------------------------------------------------------
-- |
-- Module : Codec.MIME.QuotedPrintable
-- Copyright : (c) Galois, Inc. 2008
-- License : BSD3
--
-- Maintainer:
-- Stability : provisional
-- Portability:
--
--------------------------------------------------------------------
module Codec.MIME.QuotedPrintable
( decode -- :: String -> String
, encode -- :: String -> String
) where
import Data.Char
-- | 'decode' incoming quoted-printable content, stripping
-- out soft line breaks and
decode :: String -> String
decode "" = ""
decode ('=':'\r':'\n':xs) = decode xs -- soft line break.
decode ('=':x1:x2:xs)
| isHexDigit x1 && isHexDigit x2 =
chr (digitToInt x1 * 16 + digitToInt x2) : decode xs
decode ('=':xs) = '=':decode xs
-- make it explicit that we propagate other '=' occurrences.
decode (x1:xs) = x1:decode xs
-- | 'encode' converts a sequence of characeter _octets_ into
-- quoted-printable form; suitable for transmission in MIME
-- payloads. Note the stress on _octets_; it is assumed that
-- you have already converted Unicode into a <=8-bit encoding
-- (UTF-8, most likely.)
encode :: String -> String
encode xs = encodeLength 0 xs
encodeLength :: Int -> String -> String
encodeLength _ "" = ""
encodeLength n ('=':xs)
| n <= 72 = '=':'3':'D':encodeLength (n+3) xs
| otherwise = '=':'\r':'\n': encodeLength 0 ('=':xs)
encodeLength n (x:xs)
| n >= 75 = '=':'\r':'\n':encodeLength 0 (x:xs)
| ox >= 0x21 && ox <= 0x7e = x : encodeLength (n+1) xs
| (ox == 0x09 || ox == 0x20) && n < 74 = x : encodeLength (n+1) xs
| ox >= 0x100 = error ("QuotedPrintable.encode: encountered > 8 bit character: " ++ show (x,ox))
| n <= 72 = '=':showH (ox `div` 16) : showH (ox `mod` 16) : encodeLength (n+3) xs
| otherwise = '=':'\r':'\n':encodeLength 0 (x:xs)
where
ox = ord x
showH v
| v < 10 = chr (ord_0 + v)
| otherwise = chr (ord_A + (v-10))
ord_0 = ord '0'
ord_A = ord 'A'
|
