On 6 October 2011 14:58, Simon Marlow <marlo...@gmail.com> wrote:
> ... What you can do is make a withHandleFD:
>
> withHandleFD :: Handle -> (FD -> IO a) -> IO a
>
> it's still quite dodgy, depending on what you do with the FD. Perhaps it
> should be called unsafeWithHandleFD.
>
> Anyway, patches gratefully accepted...
Maybe something like this together with a big warning message
explaining the danger:
{-# LANGUAGE NamedFieldPuns #-}
module System.Posix.IO where
import Control.Concurrent.MVar (MVar)
unsafeWithHandleFd :: Handle -> (Fd -> IO a) -> IO a
unsafeWithHandleFd h@(FileHandle _ m) f = unsafeWithHandleFd' h m f
unsafeWithHandleFd h@(DuplexHandle _ _ w) f = unsafeWithHandleFd' h w f
unsafeWithHandleFd' :: Handle -> MVar Handle__ -> (Fd -> IO a) -> IO a
unsafeWithHandleFd' h m f =
withHandle' "unsafeWithHandleFd" h m $ \h_@Handle__{haDevice} ->
case cast haDevice of
Nothing -> ioError (ioeSetErrorString (mkIOError IllegalOperation
"unsafeWithHandleFd"
(Just h) Nothing)
"handle is not a file descriptor")
Just fd -> do
x <- f (Fd (FD.fdFD fd))
return (h_, x)
I'm not sure about the DuplexHandle case. I mimicked handleToFd by
only converting the write side but I have no idea why that is correct.
Bas
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