added encoder + recognize soft line breaks on the decoding side

1 files changed, 37 insertions, 1 deletions

diff --git a/Codec/MIME/QuotedPrintable.hs b/Codec/MIME/QuotedPrintable.hs
index d6c058e..72fbaa6 100644
--- a/Codec/MIME/QuotedPrintable.hs
+++ b/Codec/MIME/QuotedPrintable.hs
@@ -11,15 +11,51 @@
 --------------------------------------------------------------------
 
 
-module Codec.MIME.QuotedPrintable where
+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'