3 -- import qualified Data.ByteString.Lazy as BL
4 import qualified Data.ByteString.Char8 as BC
5 import qualified Data.Map.Strict as M
6 import qualified Text.Parsec.ByteString as ParsecBS
7 import Text.ParserCombinators.Parsec
8 import Control.Applicative ((<*))
11 data BVal = Bint Integer
15 deriving (Ord, Eq, Show)
17 type InfoDict = M.Map BVal BVal
20 -- >>> import Data.Either
24 -- >>> parse bencStr "Bstr" (BC.pack "4:spam")
26 -- >>> parse bencStr "Bstr" (BC.pack "0:")
28 -- >>> parse bencStr "Bstr" (BC.pack "0:hello")
31 bencStr :: ParsecBS.Parser BC.ByteString
32 bencStr = do _ <- spaces
33 ds <- many1 digit <* char ':'
34 s <- count (read ds) anyChar
39 -- >>> parse bencInt "Bint" (BC.pack "i42e")
41 -- >>> parse bencInt "Bint" (BC.pack "i123e")
43 -- >>> parse bencInt "Bint" (BC.pack "i1e")
45 -- >>> parse bencInt "Bint" (BC.pack "i0e")
47 -- >>> parse bencInt "Bint" (BC.pack "i-1e")
49 -- >>> isLeft $ parse bencInt "Bint" (BC.pack "i01e")
51 -- >>> isLeft $ parse bencInt "Bint" (BC.pack "i00e")
53 -- >>> isLeft $ parse bencInt "Bint" (BC.pack "i002e")
55 bencInt :: ParsecBS.Parser Integer
56 bencInt = do _ <- spaces
57 ds <- between (char 'i') (char 'e') numbers
59 where numbers = do d' <- char '-' <|> digit
62 parseNumber '0' [] = return "0"
63 parseNumber '0' _ = unexpected "numbers cannot be left-padded with zeros"
64 parseNumber '-' [] = unexpected "sign without any digits"
65 parseNumber '-' (d'':_) | d'' == '0' = unexpected "numbers cannot be left-padded with zeros"
66 parseNumber d'' ds'' = return (d'':ds'')
70 -- >>> parse bencList "Blist" (BC.pack "le")
72 -- >>> parse bencList "Blist" (BC.pack "l4:spam4:eggse")
73 -- Right ["spam","eggs"]
74 -- >>> parse bencList "Blist" (BC.pack "l4:spami42ee")
76 -- >>> parse bencList "Blist" (BC.pack "l4:spam4:eggsli42eee")
77 -- Right ["spam","eggs",[42]]
78 bencList :: ParsecBS.Parser [BVal]
79 bencList = do _ <- spaces
80 between (char 'l') (char 'e') (many bencVal)
84 -- >>> parse bencDict "Bdict" (BC.pack "de")
85 -- Right (fromList [])
86 -- >>> parse bencDict "Bdict" (BC.pack "d3:cow3:moo4:spam4:eggse")
87 -- Right (fromList [("cow","moo"),("spam","eggs")])
88 -- >>> parse bencDict "Bdict" (BC.pack "d4:spaml1:a1:bee")
89 -- Right (fromList [("spam",["a","b"])])
90 -- >>> parse bencDict "Bdict" (BC.pack "d9:publisher3:bob17:publisher-webpage15:www.example.com18:publisher.location4:homee")
91 -- Right (fromList [("publisher","bob"),("publisher-webpage","www.example.com"),("publisher.location","home")])
92 bencDict :: ParsecBS.Parser (M.Map BVal BVal)
93 bencDict = between (char 'd') (char 'e') $ M.fromList <$> many kvpair
94 where kvpair = do k <- bencStr
98 bencVal :: ParsecBS.Parser BVal
99 bencVal = Bstr <$> bencStr <|>
101 Blist <$> bencList <|>
104 decode :: BC.ByteString -> Either ParseError BVal
105 decode = parse bencVal "BVal"
107 -- given an input dict or int or string, encode
108 -- it into a bencoded bytestring.
109 -- | encode bencoded-values
111 -- >>> encode (Bstr (BC.pack ""))
113 -- >>> encode (Bstr (BC.pack "spam"))
115 -- >>> encode (Bint 0)
117 -- >>> encode (Bint 42)
119 -- >>> encode (Blist [(Bstr (BC.pack "spam")), (Bstr (BC.pack "eggs"))])
121 -- >>> encode (Blist [])
123 -- >>> encode (Bdict (M.fromList [(Bstr $ BC.pack "spam", Bstr $ BC.pack "eggs")]))
125 encode :: BVal -> String
126 encode (Bstr bs) = let s = BC.unpack bs
127 in show (length s) ++ ":" ++ s
128 encode (Bint i) = "i" ++ show i ++ "e"
129 encode (Blist xs) = "l" ++ encodeList xs ++ "e"
130 where encodeList = foldr ((++) . encode) ""
131 encode (Bdict d) = "d" ++ encodeDict d ++ "e"
132 where encodeDict m = concat [encode k ++ encode (m M.! k) | k <- M.keys m]