Scotty Haskell

{-# LANGUAGE OverloadedStrings #-}

import qualified Data.ByteString.Base64 as Base64
import qualified Data.ByteString.Lazy as BL
import Web.Scotty

-- A top-level constant: decoded once, on first use.
gif :: BL.ByteString
gif = BL.fromStrict (Base64.decodeLenient "R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==")

main :: IO ()
main = scotty 8080 $
  get "/pixel.gif" $ do
    setHeader "Content-Type" "image/gif"
    setHeader "Cache-Control" "no-store"
    raw gif