[web-devel] Conduit/Wai proxy, HOWTO?

[Jason Dusek]

Please find below my signature a sketch of a WAI proxy server,
which always redirects every request to the same URL.

In the sketch, the function `magic' takes care of translating
from a Network.HTTP.Conduit.Response body to
Network.Wai.ResponseSource body. However, I am a at a loss as to
how to write `magic' safely. The body of a
Network.HTTP.Conduit.Response is a ResumableSource but the body
of Network.Wai.ResponseSource is a plain source and the
conversion from one to the other would seem to involve one of:

  * Connecting the ResumableSource to a Sink, thus regrettably
    forcing it all into memory,

  * Unwrapping the resumable source and trying to figure out
    what to do with the finalizer.

I was originally attracted to Wai/Warp/Conduit by the prospect
of building a high quality proxy server. I am building an web
service that talks to AWS and, for some tasks, must proxy
results back to the user.

I would be very grateful if someone could explain to me how best
to put together a simple, efficient proxy server with Wai and
Conduit.

--
Jason Dusek
pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B


> {-# LANGUAGE OverloadedStrings
>            , RecordWildCards
>   #-}
>
> import           Control.Applicative
> import           Control.Monad
> import           Data.ByteString (ByteString)
> import qualified Data.ByteString.Char8 as Bytes
>
> import qualified Blaze.ByteString.Builder as Blaze
> import qualified Blaze.ByteString.Builder.Char.Utf8 as Blaze
> import           Control.Monad.Trans
> import qualified Data.Conduit as Conduit
> import qualified Data.Conduit.List as Conduit
> import qualified Network.Wai as Wai
> import qualified Network.HTTP.Conduit as Conduit
> import qualified Network.HTTP.Types as HTTP
>
> wai :: String -> Wai.Application
> wai s req at Wai.Request{..} = Conduit.withManager go
>  where
>   magic                         = undefined
>   go manager                    = do
>     request                    <- liftIO $ Conduit.parseUrl s
>     Conduit.Response s _ h src <- Conduit.http request manager
>     return $ Wai.ResponseSource s h (magic src)