[Haskell-cafe] cannot catch exception

[Michael Snoyman]

Another approach would be to use the Data.Text.IO.hGetContents function on
a file handle that explicitly sets its character encoding to UTF-8. This is
what we do in rio:

https://www.stackage.org/haddock/lts-13.10/rio-0.1.8.0/src/RIO.Prelude.IO.html#readFileUtf8

On Mon, Mar 4, 2019 at 3:36 PM David Fox <dsf at seereason.com> wrote:

> This fixes it by forcing the evaluation of the decode where it can be
> caught:
>
> return $ Right $! TE.decodeUtf8 bufferStrict
>
> or
>
> Right <$> evaluate (TE.decodeUtf8 bufferStrict)
>
>
>
> On Mon, Mar 4, 2019 at 3:50 AM Kees Bleijenberg <
> K.Bleijenberg at lijbrandt.nl> wrote:
>
>> Hi all,
>>
>>
>>
>> The program reads lots of small Text files. readCDFile handles the
>> encoding. Below is the simplest version of readCDFile.
>>
>> If I call readCDFile "/home/kees/freeDB/inputError/" "blah" (the file
>> blah does not exist) I get:
>>
>> Left "MyError: /home/kees/freeDB/inputError/blah: openBinaryFile: does
>> not exist (No such file or directory)". The exception is caught by
>> exceptionHandler
>>
>> If I call readCDFile "/home/kees/freeDB/inputError/" "67129209" I get
>> freeDB: Cannot decode byte '\xa0': Data.Text.Internal.Encoding.decodeUtf8:
>> Invalid UTF-8 stream. The exception is not caught by exceptionHandler (No
>> “MyError: ” in front). The file 67129209 is indeed bad encoded.
>>
>> I’am using SomeException. Still, this ‘bad encoding exception’ is not
>> caught. Why?
>>
>>
>>
>> Kees
>>
>>
>>
>> import qualified Data.Text as T
>>
>> import System.FilePath.Posix
>>
>> import qualified Data.Text.Encoding as TE
>>
>> import qualified Data.ByteString.Lazy as B
>>
>> import Prelude hiding (catch)
>>
>> import Control.Exception
>>
>>
>>
>> main :: IO ()
>>
>> main = do
>>
>>           res <- readCDFile "/home/kees/freeDB/inputError/" "67129209"
>>
>>           print res
>>
>>
>>
>> readCDFile :: FilePath -> FilePath -> IO (Either String T.Text)
>>
>> readCDFile baseDir fn = do
>>
>>   catch ( do
>>
>>             buffer <- B.readFile (combine baseDir fn)
>>
>>             let bufferStrict = B.toStrict buffer
>>
>>             return $ Right $ TE.decodeUtf8 bufferStrict
>>
>>          ) exceptionHandler
>>
>>
>>
>> exceptionHandler :: SomeException -> IO (Either String T.Text)
>>
>> exceptionHandler e = do let err = show e
>>
>>                         return $ Left $ "MyError: " ++ err
>>
>>
>>
>>
>>
>>
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> Virusvrij.
>> www.avast.com
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>> <#m_152412307694788344_m_4240515626836095125_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
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