[web-devel] Upgrading to warp 2

24 Feb 2014

      Hi all,

So I decided to upgrade one of my programs to Warp 2.x, but I'm getting
stuck on generating the Response from a "sourceFileRange" (from
Data.Conduit.Binary).

Here's a snippet of the relevant code:

    serveFile :: Integer -> [(Maybe Integer, Maybe Integer)] -> IO Response
    serveFile fsz [(l,h)] = do
      let l' = maybe 0 id l
      let h' = maybe (fsz-1) id h
      let n = (h' - l' + 1)
      let src = mapOutput (Chunk . fromByteString) $ sourceFileRange sfp
(Just l') (Just n)
      return $ responseSource partialContent206
                         [ hdrContentLength n
                         , (hContentType, mimeType)
                         , hdrContentRange l' h' fsz
                         , hdrAcceptRangesBytes
                         , hdrConnectionClose
                         ] src

When I try this I get:

  src/Handlers.hs:96:54:
    No instance for (MonadResource IO)
      arising from a use of `sourceFileRange'
    Possible fix: add an instance declaration for (MonadResource IO)
    In the second argument of `($)', namely
      `sourceFileRange sfp (Just l') (Just n)'
    In the expression:
      mapOutput (Chunk . fromByteString)
      $ sourceFileRange sfp (Just l') (Just n)
    In an equation for `src':
        src
          = mapOutput (Chunk . fromByteString)
            $ sourceFileRange sfp (Just l') (Just n)

... which I guess kinda makes sense -- you'd need a ResourceT (or
similar) in the monad stack. I'm just not sure how or where to introduce
the ResourceT to get this working.

If I introduce an explicit type signature for "src",

   src :: forall m . MonadResource m => Source m (Flush Builder)

then that line compiles, but I get the equivalent error at the usage
site of "src" in the third argument to "responseSource" (which again
also makes sense).

Anyone got any pointers?

Regards,

[web-devel] Upgrading to warp 2

Bardur Arantsson