-- Copyright 2020 United States Government as represented by the Administrator
-- of the National Aeronautics and Space Administration. All Rights Reserved.
--
-- Disclaimers
--
-- Licensed under the Apache License, Version 2.0 (the "License"); you may
-- not use this file except in compliance with the License. You may obtain a
-- copy of the License at
--
--      https://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-- License for the specific language governing permissions and limitations
-- under the License.
--
-- | Auxiliary functions for working with values of type 'ByteString'.
module Data.ByteString.Extra where

import           Control.Exception    ( catch )
import qualified Data.ByteString.Lazy as B
import           System.IO.Error      ( isDoesNotExistError )

-- * Safe I/O

-- | Safely read a file into a lazy 'ByteString', returning a 'Left' error
-- message if the file cannot be opened.
safeReadFile :: FilePath -> IO (Either String B.ByteString)
safeReadFile :: String -> IO (Either String ByteString)
safeReadFile String
fp =
  IO (Either String ByteString)
-> (IOError -> IO (Either String ByteString))
-> IO (Either String ByteString)
forall e a. Exception e => IO a -> (e -> IO a) -> IO a
catch (ByteString -> Either String ByteString
forall a. a -> Either String a
forall (m :: * -> *) a. Monad m => a -> m a
return (ByteString -> Either String ByteString)
-> IO ByteString -> IO (Either String ByteString)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> String -> IO ByteString
B.readFile String
fp) ((IOError -> IO (Either String ByteString))
 -> IO (Either String ByteString))
-> (IOError -> IO (Either String ByteString))
-> IO (Either String ByteString)
forall a b. (a -> b) -> a -> b
$ \IOError
e ->
    if IOError -> Bool
isDoesNotExistError IOError
e
      then Either String ByteString -> IO (Either String ByteString)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return (Either String ByteString -> IO (Either String ByteString))
-> Either String ByteString -> IO (Either String ByteString)
forall a b. (a -> b) -> a -> b
$ String -> Either String ByteString
forall a b. a -> Either a b
Left (String -> Either String ByteString)
-> String -> Either String ByteString
forall a b. (a -> b) -> a -> b
$ String -> String
strByteStringFileNotFound String
fp
      else Either String ByteString -> IO (Either String ByteString)
forall a. a -> IO a
forall (m :: * -> *) a. Monad m => a -> m a
return (Either String ByteString -> IO (Either String ByteString))
-> Either String ByteString -> IO (Either String ByteString)
forall a b. (a -> b) -> a -> b
$ String -> Either String ByteString
forall a b. a -> Either a b
Left (String -> Either String ByteString)
-> String -> Either String ByteString
forall a b. (a -> b) -> a -> b
$ String -> String
strByteStringCannotOpenFile String
fp

-- ** Error messages

-- | File-not-found message.
strByteStringFileNotFound :: FilePath -> String
strByteStringFileNotFound :: String -> String
strByteStringFileNotFound String
fp = String
"File not found: " String -> String -> String
forall a. [a] -> [a] -> [a]
++ String
fp

-- | Cannot-open-file message.
strByteStringCannotOpenFile :: FilePath -> String
strByteStringCannotOpenFile :: String -> String
strByteStringCannotOpenFile String
fp = String
"Error opening file " String -> String -> String
forall a. [a] -> [a] -> [a]
++ String
fp