System/IO/Error.hs

{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}

-----------------------------------------------------------------------------
-- |
-- Module : System.IO.Error
-- Copyright : (c) The University of Glasgow 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : portable
--
-- Standard IO Errors.
--
-----------------------------------------------------------------------------

module System.IO.Error (

 -- * I\/O errors
 IOError,

 userError,

 mkIOError,

 annotateIOError,

 -- ** Classifying I\/O errors
 isAlreadyExistsError,
 isDoesNotExistError,
 isAlreadyInUseError,
 isFullError,
 isEOFError,
 isIllegalOperation,
 isPermissionError,
 isUserError,
 isResourceVanishedError,

 -- ** Attributes of I\/O errors
 ioeGetErrorType,
 ioeGetLocation,
 ioeGetErrorString,
 ioeGetHandle,
 ioeGetFileName,

 ioeSetErrorType,
 ioeSetErrorString,
 ioeSetLocation,
 ioeSetHandle,
 ioeSetFileName,

 -- * Types of I\/O error
 IOErrorType, -- abstract

 alreadyExistsErrorType,
 doesNotExistErrorType,
 alreadyInUseErrorType,
 fullErrorType,
 eofErrorType,
 illegalOperationErrorType,
 permissionErrorType,
 userErrorType,
 resourceVanishedErrorType,

 -- ** 'IOErrorType' predicates
 isAlreadyExistsErrorType,
 isDoesNotExistErrorType,
 isAlreadyInUseErrorType,
 isFullErrorType,
 isEOFErrorType,
 isIllegalOperationErrorType,
 isPermissionErrorType,
 isUserErrorType,
 isResourceVanishedErrorType,

 -- * Throwing and catching I\/O errors

 ioError,

 catchIOError,
 tryIOError,

 modifyIOError,
 ) where

import Control.Exception.Base

import Data.Either
import Data.Maybe

import GHC.Base
import GHC.IO
import GHC.IO.Exception
import GHC.IO.Handle.Types
import Text.Show

-- | The construct 'tryIOError' @comp@ exposes IO errors which occur within a
-- computation, and which are not fully handled.
--
-- Non-I\/O exceptions are not caught by this variant; to catch all
-- exceptions, use 'Control.Exception.try' from "Control.Exception".
--
-- @since 4.4.0.0
tryIOError :: IO a -> IO (Either IOError a)
tryIOError f = catch (do r <- f
 return (Right r))
 (return . Left)

-- -----------------------------------------------------------------------------
-- Constructing an IOError

-- | Construct an 'IOError' of the given type where the second argument
-- describes the error location and the third and fourth argument
-- contain the file handle and file path of the file involved in the
-- error if applicable.
mkIOError :: IOErrorType -> String -> Maybe Handle -> Maybe FilePath -> IOError
mkIOError t location maybe_hdl maybe_filename =
 IOError{ ioe_type = t,
 ioe_location = location,
 ioe_description = "",
 ioe_errno = Nothing,
 ioe_handle = maybe_hdl,
 ioe_filename = maybe_filename
 }

-- -----------------------------------------------------------------------------
-- IOErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments already exists.
isAlreadyExistsError :: IOError -> Bool
isAlreadyExistsError = isAlreadyExistsErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments does not exist.
isDoesNotExistError :: IOError -> Bool
isDoesNotExistError = isDoesNotExistErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- one of its arguments is a single-use resource, which is already
-- being used (for example, opening the same file twice for writing
-- might give this error).
isAlreadyInUseError :: IOError -> Bool
isAlreadyInUseError = isAlreadyInUseErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the device is full.
isFullError :: IOError -> Bool
isFullError = isFullErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the end of file has been reached.
isEOFError :: IOError -> Bool
isEOFError = isEOFErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the operation was not possible.
-- Any computation which returns an 'IO' result may fail with
-- 'isIllegalOperation'. In some cases, an implementation will not be
-- able to distinguish between the possible error causes. In this case
-- it should fail with 'isIllegalOperation'.
isIllegalOperation :: IOError -> Bool
isIllegalOperation = isIllegalOperationErrorType . ioeGetErrorType

-- | An error indicating that an 'IO' operation failed because
-- the user does not have sufficient operating system privilege
-- to perform that operation.
isPermissionError :: IOError -> Bool
isPermissionError = isPermissionErrorType . ioeGetErrorType

-- | A programmer-defined error value constructed using 'userError'.
isUserError :: IOError -> Bool
isUserError = isUserErrorType . ioeGetErrorType

-- | An error indicating that the operation failed because the
-- resource vanished. See 'resourceVanishedErrorType'.
--
-- @since 4.14.0.0
isResourceVanishedError :: IOError -> Bool
isResourceVanishedError = isResourceVanishedErrorType . ioeGetErrorType

-- -----------------------------------------------------------------------------
-- IOErrorTypes

-- | I\/O error where the operation failed because one of its arguments
-- already exists.
alreadyExistsErrorType :: IOErrorType
alreadyExistsErrorType = AlreadyExists

-- | I\/O error where the operation failed because one of its arguments
-- does not exist.
doesNotExistErrorType :: IOErrorType
doesNotExistErrorType = NoSuchThing

-- | I\/O error where the operation failed because one of its arguments
-- is a single-use resource, which is already being used.
alreadyInUseErrorType :: IOErrorType
alreadyInUseErrorType = ResourceBusy

-- | I\/O error where the operation failed because the device is full.
fullErrorType :: IOErrorType
fullErrorType = ResourceExhausted

-- | I\/O error where the operation failed because the end of file has
-- been reached.
eofErrorType :: IOErrorType
eofErrorType = EOF

-- | I\/O error where the operation is not possible.
illegalOperationErrorType :: IOErrorType
illegalOperationErrorType = IllegalOperation

-- | I\/O error where the operation failed because the user does not
-- have sufficient operating system privilege to perform that operation.
permissionErrorType :: IOErrorType
permissionErrorType = PermissionDenied

-- | I\/O error that is programmer-defined.
userErrorType :: IOErrorType
userErrorType = UserError

-- | I\/O error where the operation failed because the resource vanished.
-- This happens when, for example, attempting to write to a closed
-- socket or attempting to write to a named pipe that was deleted.
--
-- @since 4.14.0.0
resourceVanishedErrorType :: IOErrorType
resourceVanishedErrorType = ResourceVanished

-- -----------------------------------------------------------------------------
-- IOErrorType predicates

-- | I\/O error where the operation failed because one of its arguments
-- already exists.
isAlreadyExistsErrorType :: IOErrorType -> Bool
isAlreadyExistsErrorType AlreadyExists = True
isAlreadyExistsErrorType _ = False

-- | I\/O error where the operation failed because one of its arguments
-- does not exist.
isDoesNotExistErrorType :: IOErrorType -> Bool
isDoesNotExistErrorType NoSuchThing = True
isDoesNotExistErrorType _ = False

-- | I\/O error where the operation failed because one of its arguments
-- is a single-use resource, which is already being used.
isAlreadyInUseErrorType :: IOErrorType -> Bool
isAlreadyInUseErrorType ResourceBusy = True
isAlreadyInUseErrorType _ = False

-- | I\/O error where the operation failed because the device is full.
isFullErrorType :: IOErrorType -> Bool
isFullErrorType ResourceExhausted = True
isFullErrorType _ = False

-- | I\/O error where the operation failed because the end of file has
-- been reached.
isEOFErrorType :: IOErrorType -> Bool
isEOFErrorType EOF = True
isEOFErrorType _ = False

-- | I\/O error where the operation is not possible.
isIllegalOperationErrorType :: IOErrorType -> Bool
isIllegalOperationErrorType IllegalOperation = True
isIllegalOperationErrorType _ = False

-- | I\/O error where the operation failed because the user does not
-- have sufficient operating system privilege to perform that operation.
isPermissionErrorType :: IOErrorType -> Bool
isPermissionErrorType PermissionDenied = True
isPermissionErrorType _ = False

-- | I\/O error that is programmer-defined.
isUserErrorType :: IOErrorType -> Bool
isUserErrorType UserError = True
isUserErrorType _ = False

-- | I\/O error where the operation failed because the resource vanished.
-- See 'resourceVanishedErrorType'.
--
-- @since 4.14.0.0
isResourceVanishedErrorType :: IOErrorType -> Bool
isResourceVanishedErrorType ResourceVanished = True
isResourceVanishedErrorType _ = False

-- -----------------------------------------------------------------------------
-- Miscellaneous

ioeGetErrorType :: IOError -> IOErrorType
ioeGetErrorString :: IOError -> String
ioeGetLocation :: IOError -> String
ioeGetHandle :: IOError -> Maybe Handle
ioeGetFileName :: IOError -> Maybe FilePath

ioeGetErrorType ioe = ioe_type ioe

ioeGetErrorString ioe
 | isUserErrorType (ioe_type ioe) = ioe_description ioe
 | otherwise = show (ioe_type ioe)

ioeGetLocation ioe = ioe_location ioe

ioeGetHandle ioe = ioe_handle ioe

ioeGetFileName ioe = ioe_filename ioe

ioeSetErrorType :: IOError -> IOErrorType -> IOError
ioeSetErrorString :: IOError -> String -> IOError
ioeSetLocation :: IOError -> String -> IOError
ioeSetHandle :: IOError -> Handle -> IOError
ioeSetFileName :: IOError -> FilePath -> IOError

ioeSetErrorType ioe errtype = ioe{ ioe_type = errtype }
ioeSetErrorString ioe str = ioe{ ioe_description = str }
ioeSetLocation ioe str = ioe{ ioe_location = str }
ioeSetHandle ioe hdl = ioe{ ioe_handle = Just hdl }
ioeSetFileName ioe filename = ioe{ ioe_filename = Just filename }

-- | Catch any 'IOError' that occurs in the computation and throw a
-- modified version.
modifyIOError :: (IOError -> IOError) -> IO a -> IO a
modifyIOError f io = catch io (\e -> ioError (f e))

-- -----------------------------------------------------------------------------
-- annotating an IOError

-- | Adds a location description and maybe a file path and file handle
-- to an 'IOError'. If any of the file handle or file path is not given
-- the corresponding value in the 'IOError' remains unaltered.
annotateIOError :: IOError
 -> String
 -> Maybe Handle
 -> Maybe FilePath
 -> IOError
annotateIOError ioe loc hdl path =
 ioe{ ioe_handle = hdl `mplus` ioe_handle ioe,
 ioe_location = loc, ioe_filename = path `mplus` ioe_filename ioe }

-- | The 'catchIOError' function establishes a handler that receives any
-- 'IOError' raised in the action protected by 'catchIOError'.
-- An 'IOError' is caught by
-- the most recent handler established by one of the exception handling
-- functions. These handlers are
-- not selective: all 'IOError's are caught. Exception propagation
-- must be explicitly provided in a handler by re-raising any unwanted
-- exceptions. For example, in
--
-- > f = catchIOError g (\e -> if IO.isEOFError e then return [] else ioError e)
--
-- the function @f@ returns @[]@ when an end-of-file exception
-- (cf. 'System.IO.Error.isEOFError') occurs in @g@; otherwise, the
-- exception is propagated to the next outer handler.
--
-- When an exception propagates outside the main program, the Haskell
-- system prints the associated 'IOError' value and exits the program.
--
-- Non-I\/O exceptions are not caught by this variant; to catch all
-- exceptions, use 'Control.Exception.catch' from "Control.Exception".
--
-- @since 4.4.0.0
catchIOError :: IO a -> (IOError -> IO a) -> IO a
catchIOError = catch