[Haskell-cafe] Web application interface
jeremy at n-heptane.com
Thu Jan 14 10:42:05 EST 2010
Happstack is currently bundled with it's own lazy I/O based HTTP
backend. Ideally, we would like to split that out, and allow happstack
to be used with that backend, hyena, or other options.
A primary using for using hyena would be for the benefits of
predictability and constant space usage that iterators bring. People
do actually running into the issues that come with lazy I/O, such as
running out of file descriptors, etc. So, I feel like I would want to
stick with using iterators the whole way when using hyena, and not
convert back to a lazy ByteString?
Happstack now includes support for sendfile(). This is done by adding
another constructor to the Response type:
Then here on line 197, we match on that case and use sendfile to send
This makes it difficult for use to be compatible with WAI. We can
write a wrapper that converts the sendfile case to use lazy
bytestrings instead, but then we lose the advantages of using sendfile.
I wonder if the 'Response' portion of WAI should support all three
currently used methods:
- lazy I/O
I haven't really thought about how that would work..
hyena currently includes a Network.WAI which uses ByteString:
gotta run, sorry about any typos!
On Jan 13, 2010, at 8:46 AM, Michael Snoyman wrote:
> I recently read (again) the wiki page on a web application
> interface for Haskell. It seems like this basically works out to
> Hack, but using an enumerator instead of lazy bytestring in the
> response type. Is anyone working on implementing this? If not, I
> would like to create the package, though I wouldn't mind some
> community input on some design decisions:
> * Hack has been fairly well-tested in the past year and I think it
> provides the features that people want. Therefore, I would want to
> model the Environment variable for WAI from Hack. I *could* just
> import Hack in WAI and use the exact same Environment data type.
> * If using a different data type for Environment, should I replace
> the String parts with ByteStrings? On the one hand, ByteStrings are
> the "correct" data type since the HTTP protocol does not specify a
> character encoding; on the other hand, Strings are easier to deal
> * It's simple to write a function to convert between a lazy
> bytestring and an enumerator, meaning it would be very easy to write
> conversion functions between Hack and WAI applications. This would
> make it simpler for people to use either backend.
> If someone else is already working on WAI, please let me know, I
> don't want to have duplicate implementations. The idea here is to
> consolidate, not split the community. I have a few Hack handlers
> (simpleserver, cgi, fastcgi) that I would happily convert to WAI
> handlers as well.
>  http://www.haskell.org/haskellwiki/WebApplicationInterface
>  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hack
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