[Haskell-cafe] Wai and http-enumerator not as lazy as I'd like

[Erik de Castro Lopo]

Antoine Latter wrote:

> None of the "lbs" functions in http-enumerator can operate in constant
> space - they are all built on top of the utility function "lbsIter"
> which provides a warning:
> 
> > Convert the HTTP response into a Response value.
> >
> > Even though a Response contains a lazy bytestring, this function does not utilize lazy
> > I/O, and therefore the entire response body will live in memory. If you want constant >
> > memory usage, you'll need to write your own iteratee and use http or httpRedirect
> > directly.

Thanks Antoine. I know I read the documention a number of times
but still managed to fall into that trap. I think it was because
I tired using httpDirect, couldn't figure it out and then fell
back to using the non-lazy lbs version.

Basically I need a serveRequest function with a signature:

    import qualified Network.HTTP.Enumerator     as HE
    import qualified Network.Wai                 as Wai

     serveRequest :: (MonadControlIO m, Failure HE.HttpException m) =>
                        HE.Request m -> m Wai.Response

that calls httpRedirect to do a lazy download of the specified data and
returns it as a Wai.Response using the ResponseEnumerator constructor.

Unfortunately, I've tried a bunch if stuff and nothing I've come up with
even comes close t type checking.

Has anyone done anything like this and care to shed some light?

Cheers,
Erik
-- 
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Erik de Castro Lopo
http://www.mega-nerd.com/