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{-# LANGUAGE OverloadedStrings #-}
-- | Minimal JSON / RFC 7159 support
--
-- The API is heavily inspired by @aeson@'s API but puts emphasis on
-- simplicity rather than performance. The 'ToJSON' instances are
-- intended to have an encoding compatible with @aeson@'s encoding.
--
module Haddock.Utils.Json
( Value(..)
, Object, object, Pair, (.=)
, encodeToString
, encodeToBuilder
, ToJSON(toJSON)
)
where
import Data.Char
import Data.Int
import Data.String
import Data.Word
import Data.List
import Data.Monoid
import Data.ByteString.Builder (Builder)
import qualified Data.ByteString.Builder as BB
-- TODO: We may want to replace 'String' with 'Text' or 'ByteString'
-- | A JSON value represented as a Haskell value.
data Value = Object !Object
| Array [Value]
| String String
| Number !Double
| Bool !Bool
| Null
deriving (Eq, Read, Show)
-- | A key\/value pair for an 'Object'
type Pair = (String, Value)
-- | A JSON \"object\" (key/value map).
type Object = [Pair]
infixr 8 .=
-- | A key-value pair for encoding a JSON object.
(.=) :: ToJSON v => String -> v -> Pair
k .= v = (k, toJSON v)
-- | Create a 'Value' from a list of name\/value 'Pair's.
object :: [Pair] -> Value
object = Object
instance IsString Value where
fromString = String
-- | A type that can be converted to JSON.
class ToJSON a where
-- | Convert a Haskell value to a JSON-friendly intermediate type.
toJSON :: a -> Value
instance ToJSON () where
toJSON () = Array []
instance ToJSON Value where
toJSON = id
instance ToJSON Bool where
toJSON = Bool
instance ToJSON a => ToJSON [a] where
toJSON = Array . map toJSON
instance ToJSON a => ToJSON (Maybe a) where
toJSON Nothing = Null
toJSON (Just a) = toJSON a
instance (ToJSON a,ToJSON b) => ToJSON (a,b) where
toJSON (a,b) = Array [toJSON a, toJSON b]
instance (ToJSON a,ToJSON b,ToJSON c) => ToJSON (a,b,c) where
toJSON (a,b,c) = Array [toJSON a, toJSON b, toJSON c]
instance (ToJSON a,ToJSON b,ToJSON c, ToJSON d) => ToJSON (a,b,c,d) where
toJSON (a,b,c,d) = Array [toJSON a, toJSON b, toJSON c, toJSON d]
instance ToJSON Float where
toJSON = Number . realToFrac
instance ToJSON Double where
toJSON = Number
instance ToJSON Int where toJSON = Number . realToFrac
instance ToJSON Int8 where toJSON = Number . realToFrac
instance ToJSON Int16 where toJSON = Number . realToFrac
instance ToJSON Int32 where toJSON = Number . realToFrac
instance ToJSON Word where toJSON = Number . realToFrac
instance ToJSON Word8 where toJSON = Number . realToFrac
instance ToJSON Word16 where toJSON = Number . realToFrac
instance ToJSON Word32 where toJSON = Number . realToFrac
-- | Possibly lossy due to conversion to 'Double'
instance ToJSON Int64 where toJSON = Number . realToFrac
-- | Possibly lossy due to conversion to 'Double'
instance ToJSON Word64 where toJSON = Number . realToFrac
-- | Possibly lossy due to conversion to 'Double'
instance ToJSON Integer where toJSON = Number . fromInteger
------------------------------------------------------------------------------
-- 'BB.Builder'-based encoding
-- | Serialise value as JSON/UTF8-encoded 'Builder'
encodeToBuilder :: ToJSON a => a -> Builder
encodeToBuilder = encodeValueBB . toJSON
encodeValueBB :: Value -> Builder
encodeValueBB jv = case jv of
Bool True -> "true"
Bool False -> "false"
Null -> "null"
Number n
| isNaN n || isInfinite n -> encodeValueBB Null
| Just i <- doubleToInt64 n -> BB.int64Dec i
| otherwise -> BB.doubleDec n
Array a -> encodeArrayBB a
String s -> encodeStringBB s
Object o -> encodeObjectBB o
encodeArrayBB :: [Value] -> Builder
encodeArrayBB [] = "[]"
encodeArrayBB jvs = BB.char8 '[' <> go jvs <> BB.char8 ']'
where
go = Data.Monoid.mconcat . intersperse (BB.char8 ',') . map encodeValueBB
encodeObjectBB :: Object -> Builder
encodeObjectBB [] = "{}"
encodeObjectBB jvs = BB.char8 '{' <> go jvs <> BB.char8 '}'
where
go = Data.Monoid.mconcat . intersperse (BB.char8 ',') . map encPair
encPair (l,x) = encodeStringBB l <> BB.char8 ':' <> encodeValueBB x
encodeStringBB :: String -> Builder
encodeStringBB str = BB.char8 '"' <> go str <> BB.char8 '"'
where
go = BB.stringUtf8 . escapeString
------------------------------------------------------------------------------
-- 'String'-based encoding
-- | Serialise value as JSON-encoded Unicode 'String'
encodeToString :: ToJSON a => a -> String
encodeToString jv = encodeValue (toJSON jv) []
encodeValue :: Value -> ShowS
encodeValue jv = case jv of
Bool b -> showString (if b then "true" else "false")
Null -> showString "null"
Number n
| isNaN n || isInfinite n -> encodeValue Null
| Just i <- doubleToInt64 n -> shows i
| otherwise -> shows n
Array a -> encodeArray a
String s -> encodeString s
Object o -> encodeObject o
encodeArray :: [Value] -> ShowS
encodeArray [] = showString "[]"
encodeArray jvs = ('[':) . go jvs . (']':)
where
go [] = id
go [x] = encodeValue x
go (x:xs) = encodeValue x . (',':) . go xs
encodeObject :: Object -> ShowS
encodeObject [] = showString "{}"
encodeObject jvs = ('{':) . go jvs . ('}':)
where
go [] = id
go [(l,x)] = encodeString l . (':':) . encodeValue x
go ((l,x):lxs) = encodeString l . (':':) . encodeValue x . (',':) . go lxs
encodeString :: String -> ShowS
encodeString str = ('"':) . showString (escapeString str) . ('"':)
------------------------------------------------------------------------------
-- helpers
-- | Try to convert 'Double' into 'Int64', return 'Nothing' if not
-- representable loss-free as integral 'Int64' value.
doubleToInt64 :: Double -> Maybe Int64
doubleToInt64 x
| fromInteger x' == x
, x' <= toInteger (maxBound :: Int64)
, x' >= toInteger (minBound :: Int64)
= Just (fromIntegral x')
| otherwise = Nothing
where
x' = round x
-- | Minimally escape a 'String' in accordance with RFC 7159, "7. Strings"
escapeString :: String -> String
escapeString s
| not (any needsEscape s) = s
| otherwise = escape s
where
escape [] = []
escape (x:xs) = case x of
'\\' -> '\\':'\\':escape xs
'"' -> '\\':'"':escape xs
'\b' -> '\\':'b':escape xs
'\f' -> '\\':'f':escape xs
'\n' -> '\\':'n':escape xs
'\r' -> '\\':'r':escape xs
'\t' -> '\\':'t':escape xs
c | ord c < 0x10 -> '\\':'u':'0':'0':'0':intToDigit (ord c):escape xs
| ord c < 0x20 -> '\\':'u':'0':'0':'1':intToDigit (ord c - 0x10):escape xs
| otherwise -> c : escape xs
-- unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
needsEscape c = ord c < 0x20 || c `elem` ['\\','"']
|
