----------------------------------------------------------------------------- -- | -- Module : Codec.Binary.Base64 -- Copyright : (c) Dominic Steinitz 2005, Warrick Gray 2002 -- License : BSD-style (see the file ReadMe.tex) -- -- Maintainer : dominic.steinitz@blueyonder.co.uk -- Stability : experimental -- Portability : portable -- -- Base64 encoding and decoding functions provided by Warwick Gray. -- See <http://homepages.paradise.net.nz/warrickg/haskell/http/#base64> -- and <http://www.faqs.org/rfcs/rfc2045.html>. -- ----------------------------------------------------------------------------- module Network.HTTP.Base64 ( encode , decode , chop72 , Octet ) where {------------------------------------------------------------------------ This is what RFC2045 had to say: 6.8. Base64 Content-Transfer-Encoding The Base64 Content-Transfer-Encoding is designed to represent arbitrary sequences of octets in a form that need not be humanly readable. The encoding and decoding algorithms are simple, but the encoded data are consistently only about 33 percent larger than the unencoded data. This encoding is virtually identical to the one used in Privacy Enhanced Mail (PEM) applications, as defined in RFC 1421. A 65-character subset of US-ASCII is used, enabling 6 bits to be represented per printable character. (The extra 65th character, "=", is used to signify a special processing function.) NOTE: This subset has the important property that it is represented identically in all versions of ISO 646, including US-ASCII, and all characters in the subset are also represented identically in all versions of EBCDIC. Other popular encodings, such as the encoding used by the uuencode utility, Macintosh binhex 4.0 [RFC-1741], and the base85 encoding specified as part of Level 2 PostScript, do not share these properties, and thus do not fulfill the portability requirements a binary transport encoding for mail must meet. The encoding process represents 24-bit groups of input bits as output strings of 4 encoded characters. Proceeding from left to right, a 24-bit input group is formed by concatenating 3 8bit input groups. These 24 bits are then treated as 4 concatenated 6-bit groups, each of which is translated into a single digit in the base64 alphabet. When encoding a bit stream via the base64 encoding, the bit stream must be presumed to be ordered with the most-significant-bit first. That is, the first bit in the stream will be the high-order bit in the first 8bit byte, and the eighth bit will be the low-order bit in the first 8bit byte, and so on. Each 6-bit group is used as an index into an array of 64 printable characters. The character referenced by the index is placed in the output string. These characters, identified in Table 1, below, are selected so as to be universally representable, and the set excludes characters with particular significance to SMTP (e.g., ".", CR, LF) and to the multipart boundary delimiters defined in RFC 2046 (e.g., "-"). Table 1: The Base64 Alphabet Value Encoding Value Encoding Value Encoding Value Encoding 0 A 17 R 34 i 51 z 1 B 18 S 35 j 52 0 2 C 19 T 36 k 53 1 3 D 20 U 37 l 54 2 4 E 21 V 38 m 55 3 5 F 22 W 39 n 56 4 6 G 23 X 40 o 57 5 7 H 24 Y 41 p 58 6 8 I 25 Z 42 q 59 7 9 J 26 a 43 r 60 8 10 K 27 b 44 s 61 9 11 L 28 c 45 t 62 + 12 M 29 d 46 u 63 / 13 N 30 e 47 v 14 O 31 f 48 w (pad) = 15 P 32 g 49 x 16 Q 33 h 50 y The encoded output stream must be represented in lines of no more than 76 characters each. All line breaks or other characters not found in Table 1 must be ignored by decoding software. In base64 data, characters other than those in Table 1, line breaks, and other white space probably indicate a transmission error, about which a warning message or even a message rejection might be appropriate under some circumstances. Special processing is performed if fewer than 24 bits are available at the end of the data being encoded. A full encoding quantum is always completed at the end of a body. When fewer than 24 input bits are available in an input group, zero bits are added (on the right) to form an integral number of 6-bit groups. Padding at the end of the data is performed using the "=" character. Since all base64 input is an integral number of octets, only the following cases can arise: (1) the final quantum of encoding input is an integral multiple of 24 bits; here, the final unit of encoded output will be an integral multiple of 4 characters with no "=" padding, (2) the final quantum of encoding input is exactly 8 bits; here, the final unit of encoded output will be two characters followed by two "=" padding characters, or (3) the final quantum of encoding input is exactly 16 bits; here, the final unit of encoded output will be three characters followed by one "=" padding character. Because it is used only for padding at the end of the data, the occurrence of any "=" characters may be taken as evidence that the end of the data has been reached (without truncation in transit). No such assurance is possible, however, when the number of octets transmitted was a multiple of three and no "=" characters are present. Any characters outside of the base64 alphabet are to be ignored in base64-encoded data. Care must be taken to use the proper octets for line breaks if base64 encoding is applied directly to text material that has not been converted to canonical form. In particular, text line breaks must be converted into CRLF sequences prior to base64 encoding. The important thing to note is that this may be done directly by the encoder rather than in a prior canonicalization step in some implementations. NOTE: There is no need to worry about quoting potential boundary delimiters within base64-encoded bodies within multipart entities because no hyphen characters are used in the base64 encoding. ----------------------------------------------------------------------------} {- The following properties should hold: decode . encode = id decode . chop72 . encode = id I.E. Both "encode" and "chop72 . encode" are valid methods of encoding input, the second variation corresponds better with the RFC above, but outside of MIME applications might be undesireable. But: The Haskell98 Char type is at least 16bits (and often 32), these implementations assume only 8 significant bits, which is more than enough for US-ASCII. -} import Data.Array (Array, array, (!)) import Data.Bits (shiftL, shiftR, (.&.), (.|.)) import Data.Char (chr, ord) import Data.Word (Word8) type Octet = Word8 encodeArray :: Array Int Char encodeArray = array (0,64) [ (0,'A'), (1,'B'), (2,'C'), (3,'D'), (4,'E'), (5,'F') , (6,'G'), (7,'H'), (8,'I'), (9,'J'), (10,'K'), (11,'L') , (12,'M'), (13,'N'), (14,'O'), (15,'P'), (16,'Q'), (17,'R') , (18,'S'), (19,'T'), (20,'U'), (21,'V'), (22,'W'), (23,'X') , (24,'Y'), (25,'Z'), (26,'a'), (27,'b'), (28,'c'), (29,'d') , (30,'e'), (31,'f'), (32,'g'), (33,'h'), (34,'i'), (35,'j') , (36,'k'), (37,'l'), (38,'m'), (39,'n'), (40,'o'), (41,'p') , (42,'q'), (43,'r'), (44,'s'), (45,'t'), (46,'u'), (47,'v') , (48,'w'), (49,'x'), (50,'y'), (51,'z'), (52,'0'), (53,'1') , (54,'2'), (55,'3'), (56,'4'), (57,'5'), (58,'6'), (59,'7') , (60,'8'), (61,'9'), (62,'+'), (63,'/') ] -- Convert between 4 base64 (6bits ea) integers and 1 ordinary integer (32 bits) -- clearly the upmost/leftmost 8 bits of the answer are 0. -- Hack Alert: In the last entry of the answer, the upper 8 bits encode -- the integer number of 6bit groups encoded in that integer, ie 1, 2, 3. -- 0 represents a 4 :( int4_char3 :: [Int] -> [Char] int4_char3 (a:b:c:d:t) = let n = (a `shiftL` 18 .|. b `shiftL` 12 .|. c `shiftL` 6 .|. d) in (chr (n `shiftR` 16 .&. 0xff)) : (chr (n `shiftR` 8 .&. 0xff)) : (chr (n .&. 0xff)) : int4_char3 t int4_char3 [a,b,c] = let n = (a `shiftL` 18 .|. b `shiftL` 12 .|. c `shiftL` 6) in [ (chr (n `shiftR` 16 .&. 0xff)) , (chr (n `shiftR` 8 .&. 0xff)) ] int4_char3 [a,b] = let n = (a `shiftL` 18 .|. b `shiftL` 12) in [ (chr (n `shiftR` 16 .&. 0xff)) ] int4_char3 [_] = error "Network.HTTP.Base64.int4_char3: impossible number of Ints." int4_char3 [] = [] -- Convert triplets of characters to -- 4 base64 integers. The last entries -- in the list may not produce 4 integers, -- a trailing 2 character group gives 3 integers, -- while a trailing single character gives 2 integers. char3_int4 :: [Char] -> [Int] char3_int4 (a:b:c:t) = let n = (ord a `shiftL` 16 .|. ord b `shiftL` 8 .|. ord c) in (n `shiftR` 18 .&. 0x3f) : (n `shiftR` 12 .&. 0x3f) : (n `shiftR` 6 .&. 0x3f) : (n .&. 0x3f) : char3_int4 t char3_int4 [a,b] = let n = (ord a `shiftL` 16 .|. ord b `shiftL` 8) in [ (n `shiftR` 18 .&. 0x3f) , (n `shiftR` 12 .&. 0x3f) , (n `shiftR` 6 .&. 0x3f) ] char3_int4 [a] = let n = (ord a `shiftL` 16) in [(n `shiftR` 18 .&. 0x3f),(n `shiftR` 12 .&. 0x3f)] char3_int4 [] = [] -- Retrieve base64 char, given an array index integer in the range [0..63] enc1 :: Int -> Char enc1 ch = encodeArray!ch -- | Cut up a string into 72 char lines, each line terminated by CRLF. chop72 :: String -> String chop72 str = let (bgn,end) = splitAt 70 str in if null end then bgn else "\r\n" ++ chop72 end -- Pads a base64 code to a multiple of 4 characters, using the special -- '=' character. quadruplets :: [Char] -> [Char] quadruplets (a:b:c:d:t) = a:b:c:d:quadruplets t quadruplets [a,b,c] = [a,b,c,'='] -- 16bit tail unit quadruplets [a,b] = [a,b,'=','='] -- 8bit tail unit quadruplets [_] = error "Network.HTTP.Base64.quadruplets: impossible number of characters." quadruplets [] = [] -- 24bit tail unit enc :: [Int] -> [Char] enc = quadruplets . map enc1 dcd :: String -> [Int] dcd [] = [] dcd (h:t) | h <= 'Z' && h >= 'A' = ord h - ord 'A' : dcd t | h >= '0' && h <= '9' = ord h - ord '0' + 52 : dcd t | h >= 'a' && h <= 'z' = ord h - ord 'a' + 26 : dcd t | h == '+' = 62 : dcd t | h == '/' = 63 : dcd t | h == '=' = [] -- terminate data stream | otherwise = dcd t -- Principal encoding and decoding functions. encode :: [Octet] -> String encode = enc . char3_int4 . (map (chr .fromIntegral)) {- prop_base64 os = os == (f . g . h) os where types = (os :: [Word8]) f = map (fromIntegral. ord) g = decode . encode h = map (chr . fromIntegral) -} decode :: String -> [Octet] decode = (map (fromIntegral . ord)) . int4_char3 . dcd