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Better invalid json message (issue #558) #559

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a827fe0
Show that we're going to try parse valid json
JoeMShanahan Jul 9, 2017
f1be673
Remove "double quotes" parser name
JoeMShanahan Jul 9, 2017
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72 changes: 39 additions & 33 deletions Data/Aeson/Parser/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,7 +39,8 @@ import Prelude.Compat
import Control.Applicative ((<|>))
import Control.Monad (void, when)
import Data.Aeson.Types.Internal (IResult(..), JSONPath, Result(..), Value(..))
import Data.Attoparsec.ByteString.Char8 (Parser, char, decimal, endOfInput, isDigit_w8, signed, string)
import Data.Attoparsec.ByteString.Char8 (Parser, (<?>), char, decimal, endOfInput, isDigit_w8, signed, string)
import Data.List (intercalate)
import Data.Scientific (Scientific)
import Data.Text (Text)
import Data.Vector as Vector (Vector, empty, fromListN, reverse)
Expand Down Expand Up @@ -165,43 +166,47 @@ arrayValues val = do
-- implementations in other languages conform to that same restriction
-- to preserve interoperability and security.
value :: Parser Value
value = do
skipSpace
w <- A.peekWord8'
case w of
DOUBLE_QUOTE -> A.anyWord8 *> (String <$> jstring_)
OPEN_CURLY -> A.anyWord8 *> object_
OPEN_SQUARE -> A.anyWord8 *> array_
C_f -> string "false" *> pure (Bool False)
C_t -> string "true" *> pure (Bool True)
C_n -> string "null" *> pure Null
_ | w >= 48 && w <= 57 || w == 45
-> Number <$> scientific
| otherwise -> fail "not a valid json value"
value = parser <?> "valid json"
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"valid json" is indeed misleading, since the error is that the JSON is in fact invalid, but that's easy to change of course. Another issue is that annotating this recursive parser is going to result in large stacks of duplicated "valid json" strings when parsing nested structures like "[[[[[[[[[[[[[[[[[[[[[[[". Instead, you can insert this error string just in eitherDecodeWith, or perhaps add more descriptive information here, such as the current position, that may become quite heavy. It can be helpful as well, for instance by indicating where the potential mismatched brackets are, but there may also be a more lightweight solution.

where
parser = do
skipSpace
w <- A.peekWord8'
case w of
DOUBLE_QUOTE -> A.anyWord8 *> (String <$> jstring_)
OPEN_CURLY -> A.anyWord8 *> object_
OPEN_SQUARE -> A.anyWord8 *> array_
C_f -> string "false" *> pure (Bool False)
C_t -> string "true" *> pure (Bool True)
C_n -> string "null" *> pure Null
_ | w >= 48 && w <= 57 || w == 45
-> Number <$> scientific
| otherwise -> fail "not a valid json value"

-- | Strict version of 'value'. See also 'json''.
value' :: Parser Value
value' = do
skipSpace
w <- A.peekWord8'
case w of
DOUBLE_QUOTE -> do
!s <- A.anyWord8 *> jstring_
return (String s)
OPEN_CURLY -> A.anyWord8 *> object_'
OPEN_SQUARE -> A.anyWord8 *> array_'
C_f -> string "false" *> pure (Bool False)
C_t -> string "true" *> pure (Bool True)
C_n -> string "null" *> pure Null
_ | w >= 48 && w <= 57 || w == 45
-> do
!n <- scientific
return (Number n)
| otherwise -> fail "not a valid json value"
value' = parser <?> "valid json"
where
parser = do
skipSpace
w <- A.peekWord8'
case w of
DOUBLE_QUOTE -> do
!s <- A.anyWord8 *> jstring_
return (String s)
OPEN_CURLY -> A.anyWord8 *> object_'
OPEN_SQUARE -> A.anyWord8 *> array_'
C_f -> string "false" *> pure (Bool False)
C_t -> string "true" *> pure (Bool True)
C_n -> string "null" *> pure Null
_ | w >= 48 && w <= 57 || w == 45
-> do
!n <- scientific
return (Number n)
| otherwise -> fail "not a valid json value"

-- | Parse a quoted JSON string.
jstring :: Parser Text
jstring = A.word8 DOUBLE_QUOTE *> jstring_
jstring = (A.word8 DOUBLE_QUOTE <?> "double qoutes") *> jstring_

-- | Parse a string without a leading quote.
jstring_ :: Parser Text
Expand Down Expand Up @@ -257,7 +262,8 @@ eitherDecodeWith p to s =
L.Done _ v -> case to v of
ISuccess a -> Right a
IError path msg -> Left (path, msg)
L.Fail _ _ msg -> Left ([], msg)
L.Fail _ namedFailures msg -> Left ([], failMsg)
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Maybe also add the first component of Fail (position?) in the error message.

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👍

where failMsg = intercalate ", " (msg : namedFailures)
{-# INLINE eitherDecodeWith #-}

eitherDecodeStrictWith :: Parser Value -> (Value -> IResult a) -> B.ByteString
Expand Down