{-# LANGUAGE ScopedTypeVariables #-} ----------------------------------------------------------------------------- -- | -- Module : Data.Aeson.Extra.Stream -- Copyright : (C) 2015-2016 Oleg Grenrus -- License : BSD3 -- Maintainer : Oleg Grenrus -- module Data.Aeson.Extra.Stream ( streamDecode, ) where import Prelude () import Prelude.Compat import Control.Applicative (many, (<|>)) import Data.Aeson (FromJSON, Result (..), Value, fromJSON) import Data.Aeson.Parser (value) import qualified Data.Attoparsec.ByteString.Char8 as A8 import qualified Data.Attoparsec.ByteString.Lazy as A import qualified Data.ByteString.Lazy as LBS streamParse :: LBS.ByteString -> ([Value], Maybe String) streamParse = start where start bs = case A.parse (lexemeChar '[') bs of A.Done bs' _ -> first bs' A.Fail _ _ err -> ([], Just err) first bs = case A.parse (lexemeChar ']') bs of A.Done {} -> ([], Nothing) A.Fail {} -> go bs go bs = case A.parse valueEnd bs of A.Done _ (r, False) -> ([r], Nothing) A.Done bs' (r, True) -> case go bs' of ~(rs, end) -> (r:rs, end) A.Fail _ _ err -> ([], Just err) valueEnd = do v <- value c <- True <$ lexemeChar ',' <|> False <$ lexemeChar ']' return (v, c) lexemeChar c = many A8.space *> A8.char c <* many A8.space -- | Lazyly parse 'LBS.ByteString' with top-level JSON array. -- -- /Note:/ inspecting result's second field will force the list! -- -- @ -- let ~(values, err) = 'streamDecode' bs -- traverse_ processValue values -- maybe (pure ()) printError err -- @ -- -- @since 0.3.2.0 streamDecode :: forall a. FromJSON a => LBS.ByteString -> ([a], Maybe String) streamDecode bs = go values where (values, err) = streamParse bs go :: [Value] -> ([a], Maybe String) go [] = ([], err) go (v:vs) = case fromJSON v of Error err' -> ([], Just err') Success x -> case go vs of ~(xs, err') -> (x:xs, err')