{-# LANGUAGE FlexibleInstances #-}
-- |
-- Module : Data.Serialize.RLP
-- License : LGPL-3 (see LICENSE)
--
-- Maintainer : Javier Sagredo
-- Stability : stable
--
-- An implementation of the Recursive Length Prefix method
-- as described in the Yellow Paper .
--
-- To actually use this module, the type that is going to
-- be encoded has to be instance of RLPSerialize defining
-- 'toRLP' and 'fromRLP'.
--------------------------------------------------------------------------------
module Data.Serialize.RLP (
-- * The RLP Type
RLPT(..),
-- ** Subtleties
-- $subtleties
-- * Helper Int functions
toBigEndian,
toBigEndianS,
fromBigEndian,
fromBigEndianS,
-- * Helper String functions
toByteString,
toByteStringS,
fromByteString,
fromByteStringS,
-- * The RLPSerialize class
RLPSerialize(..)
-- * Example
-- $example
-- * Errors and special cases
-- $failexample
) where
import Data.Serialize.RLP.Internal
import qualified Data.ByteString as DBS
import qualified Data.ByteString.Lazy as DBSL
import qualified Data.ByteString.Char8 as DBSC
--------------------------------------------------------------------------------
-- $subtleties
-- The idea of transforming a custom type into RLPT is to
-- preserve the original structure as far as possible. For example,
-- suppose we have a data structure:
--
-- > data Name = (String, String) -- represents the first and last name of a Person
-- > data Person = Person Name Int -- represents the whole name of a Person and its age
--
-- Then the desired output of the transformation of a Person value to RLPT should be (pseudocode):
--
-- > RLPL [ RLPL [ RLPB, RLPB ], RLPB ]
--
-- This way the structure is clearly preserved. Eventhough this does not have
-- to be true as the transformation to RLPL is defined by the user and a custom
-- process can be implemented, it is advised to follow this guideline for better
-- understanding of the generated code.
--
-- It is important to remark that although it can't be imposed, it doesn't make sense to try
-- to transform to RLP types with more than one constructor that don't difer in structure.
-- The transformation should encode
-- a way to find out which of the constructors belongs to the data so not only data is being
-- encoded in the result, also information about the structure futher than the actual length
-- prefixes. That's why it only makes sense to transform to RLP types with just one constructor.
-- On the other hand, it's perfectly viable to encode types with more than one constructor if
-- the structure of each of them is different as it can be adjusted via pattern matching
-- strategies.
--------------------------------------------------------------------------------
-- | The 'RLPSerialize' class provides functions for transforming values to RLPT structures.
-- For encoding and decoding values with the RLP protocol, 'toRLP' and 'fromRLP' have to
-- be implemented.
--
-- Instances of RLPSerialize are expected to satisfy the following property:
--
-- > fromRLP . toRLP == id
--
-- In such case, it can be assured with the default definition that:
--
-- > rlpDecode . rlpEncode == id
--
-- RLPSerialize makes use of the Get and Put classes together with a set of
-- custom serializations for encoding and decoding RLPT data.
class RLPSerialize a where
-- | Transform a value to the 'RLPT' structure that best fits its internal structure
toRLP :: a -> RLPT
-- | Transform an 'RLPT' structure back into the value it represents.
-- Its return type is 'Maybe a' because it can fail
fromRLP :: RLPT -> Maybe a
-- | Transform a value to an 'RLPT' structure and then encode it following the
-- RLP standard.
rlpEncode :: a -> DBSL.ByteString
rlpEncode = rlpEncodeI . toRLP
-- | Transform a ByteString to an 'RLPT' structure following the RLP standard and
-- then transform it to the original type. It returns 'Left s' when failing on the
-- decoding of the transforming from RLPT into the required type, and 'Right v' on
-- success.
rlpDecode :: DBSL.ByteString -> Either String a
rlpDecode x = case rlpDecodeI x :: Either String RLPT of
Left m -> Left m
Right v -> case fromRLP v of
Nothing -> Left "RLPT value couldn't ve transformed into the required type"
Just v' -> Right v'
{-# MINIMAL toRLP, fromRLP #-}
-- RLPT values don't have to be transformed as they already are RLPT
instance RLPSerialize RLPT where
toRLP = id
fromRLP = Just . id
-- ByteStrings just have to be encapsulated
-- Also, it only makes sense to disencapsulate from a ByteString
instance RLPSerialize DBS.ByteString where
toRLP = RLPB
fromRLP (RLPB b) = Just b
fromRLP _ = Nothing
-- Ints have to be transformed into its Big-endian form
-- and then they are treated as ByteStrings.
-- The same applies for the inverse transformation. They
-- are treated as ByteStrings and then interpreted as a
-- Big-endian encoded Int.
instance RLPSerialize Int where
toRLP = toRLP . toBigEndianS
fromRLP = maybe Nothing (\s -> if DBSC.head s == '\NUL'
then Nothing
else case fromBigEndianS s of
Left _ -> Nothing
Right v -> Just v ) .
(fromRLP :: RLPT -> Maybe DBS.ByteString)
-- Serializing lists implies making a list with the serialization
-- of each element
instance {-# OVERLAPPABLE #-} RLPSerialize a => RLPSerialize [a] where
toRLP = RLPL . map toRLP
fromRLP (RLPL x) = if any (\a -> case a of
Nothing -> True
_ -> False) r
then Nothing
else Just $ map unJust r
where r = map fromRLP x
fromRLP _ = Nothing
-- Bools are serialized as [0] or [1] in a ByteArray
-- THIS IS AN ASUMPTION considering Bool equivalent to
-- integers in the range 0..1
instance RLPSerialize Bool where
toRLP True = RLPB $ toByteStringS "\SOH"
toRLP False = RLPB $ toByteStringS "\NUL"
fromRLP x
| x == toRLP True = Just True
| x == toRLP False = Just False
| otherwise = Nothing
-- Strings are serialized as ByteStrings
instance {-# OVERLAPPING #-} RLPSerialize String where
toRLP = RLPB . toByteStringS
fromRLP (RLPB x) = Just $ fromByteStringS x
fromRLP _ = Nothing
-- Chars are just length-one strings
instance RLPSerialize Char where
toRLP = RLPB . toByteStringS . (: [])
fromRLP (RLPB x) = Just $ head $ fromByteStringS x
fromRLP _ = Nothing
-- Tuples are transformed into Lists
instance (RLPSerialize a, RLPSerialize b) => RLPSerialize (a, b) where
toRLP (x, y) = RLPL [toRLP x, toRLP y]
fromRLP (RLPL [x, y]) =
maybe Nothing
(\x' -> maybe Nothing
(\y' -> Just (x', y'))
(fromRLP y))
(fromRLP x)
fromRLP _ = Nothing
instance (RLPSerialize a, RLPSerialize b, RLPSerialize c) => RLPSerialize (a, b, c) where
toRLP (x, y, z) = RLPL [toRLP x, toRLP y, toRLP z]
fromRLP (RLPL [x, y, z]) =
maybe Nothing
(\x' -> maybe Nothing
(\y' -> maybe Nothing
(\z' -> Just (x', y', z'))
(fromRLP z))
(fromRLP y))
(fromRLP x)
fromRLP _ = Nothing
instance (RLPSerialize a, RLPSerialize b, RLPSerialize c, RLPSerialize d) => RLPSerialize (a, b, c, d) where
toRLP (a1, a2, a3, a4) = RLPL [toRLP a1, toRLP a2, toRLP a3, toRLP a4]
fromRLP (RLPL [a1, a2, a3, a4]) =
maybe Nothing
(\a1' -> maybe Nothing
(\a2' -> maybe Nothing
(\a3' -> maybe Nothing
(\a4' -> Just (a1', a2', a3', a4'))
(fromRLP a4))
(fromRLP a3))
(fromRLP a2))
(fromRLP a1)
fromRLP _ = Nothing
instance (RLPSerialize a, RLPSerialize b, RLPSerialize c, RLPSerialize d, RLPSerialize e) => RLPSerialize (a, b, c, d, e) where
toRLP (a1, a2, a3, a4, a5) = RLPL [toRLP a1, toRLP a2, toRLP a3, toRLP a4, toRLP a5]
fromRLP (RLPL [a1, a2, a3, a4, a5]) =
maybe Nothing
(\a1' -> maybe Nothing
(\a2' -> maybe Nothing
(\a3' -> maybe Nothing
(\a4' -> maybe Nothing
(\a5' -> Just (a1', a2', a3', a4', a5'))
(fromRLP a5))
(fromRLP a4))
(fromRLP a3))
(fromRLP a2))
(fromRLP a1)
fromRLP _ = Nothing
instance (RLPSerialize a, RLPSerialize b, RLPSerialize c, RLPSerialize d, RLPSerialize e, RLPSerialize f) => RLPSerialize (a, b, c, d, e, f) where
toRLP (a1, a2, a3, a4, a5, a6) = RLPL [toRLP a1, toRLP a2, toRLP a3, toRLP a4, toRLP a5, toRLP a6]
fromRLP (RLPL [a1, a2, a3, a4, a5, a6]) =
maybe Nothing
(\a1' -> maybe Nothing
(\a2' -> maybe Nothing
(\a3' -> maybe Nothing
(\a4' -> maybe Nothing
(\a5' -> maybe Nothing
(\a6' -> Just (a1', a2', a3', a4', a5', a6'))
(fromRLP a6))
(fromRLP a5))
(fromRLP a4))
(fromRLP a3))
(fromRLP a2))
(fromRLP a1)
fromRLP _ = Nothing
--------------------------------------------------------------------------------
-- $example
-- For a full example, we reproduce the implementation of the Person type as in the
-- subtleties section.
--
-- First of all, we define the type:
--
-- > type Name = (String, String)
-- > data Person = Person {
-- > name :: Name,
-- > age :: Int
-- > } deriving (Show)
--
-- Then we have to make it an instance of RLPSerialize:
--
-- >instance RLPSerialize Person where
-- > toRLP p = RLPL [
-- > RLPL [
-- > toRLP . toByteStringS . fst . name $ p,
-- > toRLP . toByteStringS . snd . name $ p
-- > ],
-- > toRLP . age $ p]
-- >
-- > fromRLP (RLPL [ RLPL [ RLPB a, RLPB b ], RLPB c ]) =
-- > case fromBigEndianS c of
-- > Right v -> Just $ Person (fromByteStringS a, fromByteStringS b) v
-- > _ -> Nothing
-- > fromRLP _ = Nothing
--
-- This way, if the decoding gives rise to other structure than the expected, a the
-- resulting value would be 'Nothing'. We can now use our decoder and encoder
-- with our custom type:
--
-- > p = Person ("John", "Snow") 33
-- > e = rlpEncode p
-- > -- "\204\202\132John\132Snow!" ~ [204,202,132,74,111,104,110,132,83,110,111,119,33]
-- > rlpDecode e :: Maybe Person
-- > -- Right (Person {name = ("John","Snow"), age = 33})
--
--------------------------------------------------------------------------------
-- $failexample
-- In case we run into an error situation, depending whether the RLPT structure is not well
-- formed or the generated structure couldn't be transformed into the expected type, an error
-- is returned in the form of a 'Left' value.
--
-- Just to see this as an example, if we chop the resulting ByteString, there's no way to
-- generate a correct RLPT structure so an error is thrown:
--
-- > rlpDecode $ DBSL.take 6 $ rlpEncode $ RLPL [ RLPB $ toByteStringS "John", RLPB $ toByteStringS "Snow" ] :: Either String RLPT
-- > -- Left "not enough bytes"
--
-- On the other hand, if we try to transform an incorrect value from the decoded RLPT we
-- generate a new error:
--
-- > rlpDecode $ rlpEncode $ RLPB $ toByteStringS "\STX" :: Either String Bool
-- > -- Left "RLPT value couldn't ve transformed into the required type"
--
-- If a ByteString is the result of the concatenation of more than one serialized RLPT structure,
-- only the first one would be decoded. This isn't quite specified in the Yellow Paper although it is possible that an error should be thrown when finding trailing bytes:
--
-- > a = rlpEncode $ RLPL [ RLPB $ toByteStringS "John", RLPB $ toByteStringS "Snow" ]
-- > b = DBSL.append a a
-- > -- "\202\132John\132Snow\202\132John\132Snow"
-- > rlpDecode b :: Either String RLPT
-- > -- Right (RLPL [RLPB "John",RLPB "Snow"])