9df13e73ae
This lets readonly repos be used. If a repo is readonly, we can ignore the keys database, because nothing that we can do will change the state of the repo anyway.
103 lines
3.1 KiB
Haskell
103 lines
3.1 KiB
Haskell
{- Simple IO exception handling (and some more)
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-
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- Copyright 2011-2015 Joey Hess <id@joeyh.name>
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-
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- License: BSD-2-clause
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-}
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{-# LANGUAGE ScopedTypeVariables #-}
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{-# OPTIONS_GHC -fno-warn-tabs #-}
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module Utility.Exception (
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module X,
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catchBoolIO,
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catchMaybeIO,
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catchDefaultIO,
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catchMsgIO,
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catchIO,
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tryIO,
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bracketIO,
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catchNonAsync,
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tryNonAsync,
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tryWhenExists,
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catchIOErrorType,
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IOErrorType(..),
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catchPermissionDenied,
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) where
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import Control.Monad.Catch as X hiding (Handler)
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import qualified Control.Monad.Catch as M
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import Control.Exception (IOException, AsyncException)
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import Control.Monad
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import Control.Monad.IO.Class (liftIO, MonadIO)
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import System.IO.Error (isDoesNotExistError, ioeGetErrorType)
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import GHC.IO.Exception (IOErrorType(..))
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import Utility.Data
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{- Catches IO errors and returns a Bool -}
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catchBoolIO :: MonadCatch m => m Bool -> m Bool
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catchBoolIO = catchDefaultIO False
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{- Catches IO errors and returns a Maybe -}
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catchMaybeIO :: MonadCatch m => m a -> m (Maybe a)
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catchMaybeIO a = catchDefaultIO Nothing $ a >>= (return . Just)
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{- Catches IO errors and returns a default value. -}
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catchDefaultIO :: MonadCatch m => a -> m a -> m a
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catchDefaultIO def a = catchIO a (const $ return def)
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{- Catches IO errors and returns the error message. -}
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catchMsgIO :: MonadCatch m => m a -> m (Either String a)
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catchMsgIO a = do
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v <- tryIO a
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return $ either (Left . show) Right v
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{- catch specialized for IO errors only -}
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catchIO :: MonadCatch m => m a -> (IOException -> m a) -> m a
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catchIO = M.catch
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{- try specialized for IO errors only -}
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tryIO :: MonadCatch m => m a -> m (Either IOException a)
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tryIO = M.try
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{- bracket with setup and cleanup actions lifted to IO.
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-
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- Note that unlike catchIO and tryIO, this catches all exceptions. -}
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bracketIO :: (MonadMask m, MonadIO m) => IO v -> (v -> IO b) -> (v -> m a) -> m a
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bracketIO setup cleanup = bracket (liftIO setup) (liftIO . cleanup)
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{- Catches all exceptions except for async exceptions.
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- This is often better to use than catching them all, so that
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- ThreadKilled and UserInterrupt get through.
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-}
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catchNonAsync :: MonadCatch m => m a -> (SomeException -> m a) -> m a
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catchNonAsync a onerr = a `catches`
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[ M.Handler (\ (e :: AsyncException) -> throwM e)
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, M.Handler (\ (e :: SomeException) -> onerr e)
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]
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tryNonAsync :: MonadCatch m => m a -> m (Either SomeException a)
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tryNonAsync a = go `catchNonAsync` (return . Left)
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where
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go = do
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v <- a
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return (Right v)
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{- Catches only DoesNotExist exceptions, and lets all others through. -}
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tryWhenExists :: MonadCatch m => m a -> m (Maybe a)
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tryWhenExists a = do
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v <- tryJust (guard . isDoesNotExistError) a
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return (eitherToMaybe v)
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{- Catches only IO exceptions of a particular type.
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- Ie, use HardwareFault to catch disk IO errors. -}
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catchIOErrorType :: MonadCatch m => IOErrorType -> (IOException -> m a) -> m a -> m a
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catchIOErrorType errtype onmatchingerr a = catchIO a onlymatching
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where
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onlymatching e
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| ioeGetErrorType e == errtype = onmatchingerr e
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| otherwise = throwM e
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catchPermissionDenied :: MonadCatch m => (IOException -> m a) -> m a -> m a
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catchPermissionDenied = catchIOErrorType PermissionDenied
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