Hi all.
I'm trying to compile the example WAI application, as defined in
http://www.haskell.org/haskellwiki/WebApplicationInterface
However there are several bugs.
1) The example application returns:
return (status, responseHeaders, enumerator)
where status is an integer
2) The CgiAdapter expects:
(status, reason, respHeaders, output) <- application environ
In detail, the type "Application", used in CgiAdapter is never defined.
Manlio Perillo
[Original discussion in haskell-cafe:
http://www.haskell.org/pipermail/haskell-cafe/2009-February/055270.html]
Manlio Perillo:
> Here are the problems:
>
> 1) supported HTTP methods are fixed, since you use a custom data type
(Btw. It is not my proposal, Johan Tibell has written it. I'll mail
him to notify him about this discussion.)
I agree with that. In my own framework prototype i have
data HttpMethod = OPTIONS
| GET
| HEAD
| POST
| PUT
| DELETE
| TRACE
| CONNECT
| Extension String
deriving (Eq, Show)
> 2) no support for other possible CGI variables
> (or simply custom variables: I use the environ dictionary to store
> application configuration, and I think it is a great thing).
A user dictionary / association list could be useful. A Trie is
probably faster than a Map so i am not sure if the Map type should be
used. Could also be implemented by the frameworks themselves.
> 3) No support for optimized file serving, like with WSGI file_wrapper
Would be nice to have provided it is cross-platform.
> 4) No support for keeping "complex" state (like database connection) in
> the environ.
>
> I have read some examples with CGI package, where a custom monad
> transformer is used.
> I'm not sure if this solution is flexible and "scalable".
This should be a task for the framework itself. Using a ReaderT or
StateT transformer is very common in Haskell.
> 5) I can't find documentation about the type of the response.
> It is rather clear that it is
> (ByteString, [(ByteString, ByteString)], Enumerator)
>
> but this should be documented somewhere.
It's a wiki so feel free to change it or add more documentation.
About the enumerator, using it is indeed debatable because it is not
immediately obvious how it works, but i haven't seen anything for
Haskell that works better. Like other haskellers have said lazy
bytestrings with IO is asking for trouble. I have been bitten by it
myself and it is hard to debug. Imho lazy bytestrings are only useful
when the data generator is a pure function.
Regards,
Felix
