Safe JSON response helper

[singpolyma]

I currently use:

safeJSONresponse :: (Aeson.FromJSON a) => Response -> InputStream ByteString - > IO (Either Error (Response, a))
safeJSONresponse resp i = runUnexceptionalIO $ runEitherT $ do
   v <- fmapLT (\e -> handle e (fromException e)) $ fromIO $
      parseFromStream Aeson.json' i
   case Aeson.fromJSON v of
      Aeson.Success a -> return (resp, a)
      Aeson.Error _ -> throwT parseError
   where
   parseError = Error Unavailable (T.pack "JSON parse error")
   handle _ (Just (ParseException _)) = parseError
   handle e _ = Error Unavailable (T.pack $ "Exception: " ++ show e)

For something generic to go into the library, this would probably be simplified to use Maybe and only catch the parse error -- other exceptions would still go through.

[istathar]

So you obviously know about jsonHandler. Is the problem that exceptions come out of it?

AfC

[singpolyma]

@afcowie my specific issue is that parse errors are exceptions with it (because parseFromStream can throw a ParseException separately from aeson returning Error)