a scotty server serving a file from disk and proxying a request (to itself)

scotty.hs

module Main where

import Control.Monad (when, replicateM)
import Control.Monad.IO.Class (liftIO)
import qualified Data.ByteString as BS
import qualified Blaze.ByteString.Builder as B
import qualified Network.HTTP.Client as C
import Web.Scotty

chunkSize = 32 * 1024
totalSize = 1024 * 1024 * 1024
numChunks = totalSize `div` chunkSize
genChunk = BS.concat $ replicate (chunkSize `div` 16) ("01234567" :: BS.ByteString)

main = C.withManager C.defaultManagerSettings $ \manager ->
  scotty 8000 $ do
    get "/file" serveFile
    get "/url" $ proxy manager
    get "/gen" serveGenerated

serveFile = file "file"

proxy manager = do      
  response <- liftIO $ do
    req <- C.parseUrl "http://localhost:8000/file"
    C.responseOpen req manager
  let bodyReader = fmap BS.concat $ replicateM 8 $ C.responseBody response 
  stream $ ioCopy bodyReader $ C.responseClose response

serveGenerated = stream $ \write flush ->
  let step 0 = flush
      step n = write (B.insertByteString genChunk) >> step (n-1)
   in step $ numChunks

ioCopy reader close write flush = step >> flush where
   step = do chunk <- reader
             if (BS.length chunk > 0) 
               then (write $ B.insertByteString chunk) >> step
               else close