send and delete a file with Yesod

sendTempFile.hs

{-# LANGUAGE TemplateHaskell
           , QuasiQuotes
           , OverloadedStrings
           , TypeFamilies
 #-}

import Yesod
import Yesod.Handler

import Data.Maybe
import System.IO
import System.Directory
import System.Process
import Text.Printf

import Network.Wai

-- http://github.com/softmechanics/wai/commit/2cb5ea47ca458f4b91a73e01a1dd0a29e84e001e
import Network.Wai.Enumerator (fromTempFile)

type Handler = GHandler SendTempFile SendTempFile

data SendTempFile = SendTempFile
mkYesod "SendTempFile" [$parseRoutes|
/ RootR GET
|]
instance Yesod SendTempFile where approot _ = ""

tempFileChooseRep :: ContentType -> FilePath -> ChooseRep
tempFileChooseRep ct fp = const $ return (ct, ResponseEnumerator $ fromTempFile fp)

sendTempFile :: ContentType -> FilePath -> GHandler sub master a
sendTempFile ct fp = sendResponse $ tempFileChooseRep ct fp

genGraph :: IO FilePath
genGraph = do
  (f,h) <- openTempFile "/tmp" "tmp.txt"
  hPutStrLn h f
  hClose h
  return f

getRootR :: Handler ()
getRootR = do
  liftIO genGraph >>= sendTempFile typePlain

main = do
  basicHandler 3000 SendTempFile