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,

        -- ** 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,

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

        -- * 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

    -- -----------------------------------------------------------------------------
    -- 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

    -- -----------------------------------------------------------------------------
    -- 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

    -- -----------------------------------------------------------------------------
    -- 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