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Make parseEscape errors more informative #37

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Make parseEscape errors more informative #37

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9128326
Make parseEscape errors more informative
lierdakil Dec 9, 2021
0d6b81d
Add some tests for parseEscape
lierdakil Jan 20, 2022
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18 changes: 15 additions & 3 deletions crypto-sodium/lib/Crypto/Sodium/Salt/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,10 @@ module Crypto.Sodium.Salt.Internal
( parseEscapes
) where

import Control.Monad (liftM2)
import Data.Char (isSpace)
import Data.Maybe (listToMaybe)
import Text.ParserCombinators.ReadP (eof, readP_to_S, many)
import Text.ParserCombinators.ReadP (ReadP, readP_to_S, (<++))
import Text.Read.Lex (lexChar)

-- | Parse a Haskell string literal with escapes.
Expand All @@ -19,6 +21,16 @@ import Text.Read.Lex (lexChar)
--
-- This function can fail if there are invalid escape sequences.
parseEscapes :: MonadFail m => String -> m String
parseEscapes str = case listToMaybe (readP_to_S (many lexChar <* eof) str) of
parseEscapes str = case listToMaybe (readP_to_S (many' lexChar) str) of
Just (result, "") -> pure result
_ -> fail $ "Failed to parse raw bytes (no parse): " <> str
Just (_, rest) -> fail $ case rest of
'\\':rest' -> "Failed to parse character escape '\\"
<> takeWhile (\c -> not (isSpace c) && c /= '\\') rest' <> "'"
-- the next case shouldn't happen since 'lexChar' can only fail on escapes
_ -> "Failed to parse string with escapes"
<> " at input position " <> show (length str - length rest)
-- the last case shouldn't happen since parser will happily parse zero characters
_ -> fail $ "Failed to parse string with escapes: " <> str

many' :: ReadP a -> ReadP [a]
many' p = liftM2 (:) p (many' p) <++ pure []