IOData.hs

{-# LANGUAGE GADTs #-}
{-# LANGUAGE RankNTypes #-}
-- | @since 2.2.0
module Distribution.Utils.IOData
    ( -- * 'IOData' & 'IODataMode' type
      IOData (..)
    , IODataMode (..)
    , KnownIODataMode (..)
    , withIOData
    , null
    , hPutContents
    ) where

import qualified Data.ByteString.Lazy as LBS
import           Distribution.Compat.Prelude hiding (null)
import qualified Prelude
import qualified System.IO

-- | Represents either textual or binary data passed via I/O functions
-- which support binary/text mode
--
-- @since 2.2
data IOData
    = IODataText String
    -- ^ How Text gets encoded is usually locale-dependent.
    | IODataBinary LBS.ByteString
    -- ^ Raw binary which gets read/written in binary mode.

withIOData :: IOData -> (forall mode. IODataMode mode -> mode -> r) -> r
withIOData (IODataText str) k   = k IODataModeText str
withIOData (IODataBinary lbs) k = k IODataModeBinary lbs

-- | Test whether 'IOData' is empty
null :: IOData -> Bool
null (IODataText s)   = Prelude.null s
null (IODataBinary b) = LBS.null b

instance NFData IOData where
    rnf (IODataText s)     = rnf s
    rnf (IODataBinary lbs) = rnf lbs

-- | @since 2.2
class NFData mode => KnownIODataMode mode where
    -- | 'IOData' Wrapper for 'System.IO.hGetContents'
    --
    -- __Note__: This operation uses lazy I/O. Use 'NFData' to force all
    -- data to be read and consequently the internal file handle to be
    -- closed.
    --
    hGetIODataContents :: System.IO.Handle -> Prelude.IO mode

    toIOData   :: mode -> IOData
    iodataMode :: IODataMode mode

-- | @since 3.2
data IODataMode mode where
    IODataModeText   :: IODataMode String
    IODataModeBinary :: IODataMode LBS.ByteString

instance a ~ Char => KnownIODataMode [a] where
    hGetIODataContents h = do
        System.IO.hSetBinaryMode h False
        System.IO.hGetContents h

    toIOData = IODataText
    iodataMode = IODataModeText

instance KnownIODataMode LBS.ByteString where
    hGetIODataContents h = do
        System.IO.hSetBinaryMode h True
        LBS.hGetContents h

    toIOData = IODataBinary
    iodataMode = IODataModeBinary

-- | 'IOData' Wrapper for 'System.IO.hPutStr' and 'System.IO.hClose'
--
-- This is the dual operation ot 'hGetIODataContents',
-- and consequently the handle is closed with `hClose`.
--
-- /Note:/ this performs lazy-IO.
--
-- @since 2.2
hPutContents :: System.IO.Handle -> IOData -> Prelude.IO ()
hPutContents h (IODataText c) = do
    System.IO.hSetBinaryMode h False
    System.IO.hPutStr h c
    System.IO.hClose h
hPutContents h (IODataBinary c) = do
    System.IO.hSetBinaryMode h True
    LBS.hPutStr h c
    System.IO.hClose h