[web-devel] http-enumerator : Any way to get the headers first?

Michael Snoyman michael at snoyman.com
Mon May 16 20:35:57 CEST 2011

On Mon, May 16, 2011 at 11:23 AM, Erik de Castro Lopo
<mle+hs at mega-nerd.com>wrote:

> Hi all,
> I'm continuing work on the HTTP proxy I'm writing. The absolute
> bare basics are working with Warp, Wai and http-enumerator as long
> as the upstream web server doesn't send gzipped or chunked data. For
> these later two cases, httpe-enumerator helpfully gunzips/unchunks
> the data. That however causes a problem.
> If my proxy simply passes the HTTP headers and data it gets from
> http-enumerator and passes then on to the client, the client barfs
> because the headers claim the data is gzipped or chunked and the
> data actually isn't chunked/gzipped.
> There are a number of possible solutions to this:
>  a) Strip the content/transfer-encoding header and add a
>    content-length header instead. I think this is probably
>    possible with the API as it is, but I haven't figured out
>    how yet.
>  b) Rechunk or re-gzip the data. This seems rather wasteful
>    of CPU resources.
>  c) Modify the Network.Http.Enumerator.http function so that
>    de-chunking/gunzipping is optional.
>  d) Expose the iterHeaders function that is internal to the
>    http-enumerator package so that client code can grab the
>    headers before deciding how to handle the body.
> Are there any other options I haven't thought of yet?
> From the options I have, I actually think d) makes the most sense,
> Would a patch exposing iterHeaders be accepted?
> Cheers,
> Erik
Short answer is that I'm fine exposing iterHeaders, as long as we put a big
fat "advanced users only" comment on it. I agree with you that (b) seems
like a bad idea. (a) is definitely possible, if a bit tricky, but it defeats
the whole purpose of chunking and gzipping, so it probably shouldn't be

I would guess that (c) is really the best option, though I'm guessing you
shied away from it because it involved more substantial changes to
http-enumerator. Maybe we should consider adding an extra httpAdvanced
function that takes additional settings, such as whether or not to
automatically de-chunk/de-gzip. I wouldn't be surprised if we come up with
more such cases in the future.

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