portable encoding/decoding without going via a handle

Ganesh Sittampalam ganesh at earth.li
Wed Nov 28 08:28:54 CET 2012

Hi Judah,

On 25/11/2012 17:19, Judah Jacobson wrote:

> I think some way to use BufferCodecs without going through the
> filesystem would be very useful.  One other approach would be
> Bytestring-backed Handles; there was talk of them in the past, but I
> don't know of any actual packages for it yet.  That might be a simpler
> approach than manipulating BufferCodecs directly, since you could just
> use the functions from Data.Text.IO <http://Data.Text.IO> and all of the
> buffering and error recovery would get taken care of automatically.
> This 2009 email from Simon Marlow references bytestring-backed handles
> and has a code sample for memory-mapped files that might be helpful:
> http://www.haskell.org/pipermail/glasgow-haskell-users/2009-December/018124.html
> He also mentions bytestring-backed Handles in this talk:
> http://community.haskell.org/~simonmar/GHC-IO.pdf
> That code's probably bitrotted a little, but seems like a good place to
> start.

Thanks for the pointers!

Do you have any thoughts on what the API for creating a
bytestring-backed handle should be? I'm particularly thinking of the
case where we are writing to the bytestring - the type could be
something like

    makeWritableByteStringHandle :: IO (Handle, ByteString)

but then would we end up with a ByteString value that could be being
mutated in parallel with being used. It might be nicer to have it in two
phases, e.g.

    makeWritableByteStringHandle :: IO Handle
    finishByteStringHandle :: Handle -> IO ByteString

but since Handle is a single type rather than a type class, that's not
imlpementable. Perhaps:

    makeWritableByteStringHandle :: IO (Handle, IO ByteString)

where the embedded IO action is only valid after the Handle has been



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