Proposal: add System.Posix.fdReadBuf/fdWriteBuf

[Don Stewart]

marlowsd:
> http://hackage.haskell.org/trac/ghc/ticket/3218
>
> From the ticket:
>
> Functions for reading/writing actual arrays of bytes in memory.  At the  
> moment, `System.Posix` only provides
>
> {{{
> fdRead :: Fd
>        -> ByteCount -- ^How many bytes to read
>        -> IO (String, ByteCount) -- ^The bytes read, how many bytes were 
> read.
>
> fdWrite :: Fd -> String -> IO ByteCount
> }}}
>
> which are not only wrong (`String`?), but too slow for many purposes.
>
> I propose
>
> {{{
> Mon May 11 16:21:02 BST 2009  Simon Marlow <marlowsd at gmail.com>
>   * add fdReadBuf, fdWriteBuf
>
>   -- | Read data from an 'Fd' into memory.  This is exactly equivalent
>   -- to the POSIX @read@ function.
>   fdReadBuf :: Fd
>             -> Ptr Word8    -- ^ Memory in which to put the data
>             -> ByteCount    -- ^ Maximum number of bytes to read
>             -> IO Bytecount -- ^ Number of bytes read (zero for EOF)
>
>   -- | Write data from memory to an 'Fd'.  This is exactly equivalent
>   -- to the POSIX @write@ function.
>   fdWriteBuf :: Fd
>              -> Ptr Word8    -- ^ Memory containing the data to write
>              -> ByteCount    -- ^ Maximum number of bytes to write
>              -> IO ByteCount -- ^ Number of bytes written
> }}}
>
> darcs patches are attached to the ticket.
>
> Discussion: 2 weeks (ends 25 May)

Rocking. Go for it.