servant无法流式传输JSON

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE OverloadedStrings #-}

import Servant
import qualified Data.Aeson.Streaming as AS
import qualified Data.ByteString.Lazy as BL
import qualified Data.Conduit as C
import qualified Network.HTTP.Media as M
import qualified Network.Wai as Wai

data StreamedJSON = StreamedJSON deriving (Generic)

instance ToJSON StreamedJSON
instance FromJSON StreamedJSON

type API = "stream" :> Get '[M.JSON] (C.Source IO BL.ByteString)

server :: Server API
server = return $ C.sourceList [BL.pack "some json data"]

main :: IO ()
main = Wai.run 8080 (serve api server)
  where
    api = Proxy :: Proxy API

import Network.Wai
import Network.HTTP.Types
import qualified Data.Conduit as C
import qualified Data.ByteString.Lazy as BL
import qualified Data.Aeson.Streaming as AS

streamingMiddleware :: Middleware
streamingMiddleware app request respond = do
  case requestMethod request of
    "POST" -> do
      let sink = AS.decodeJson C.sinkLbs
      result <- C.runConduit $ requestBodySource request C.$$ sink
      -- 处理 result
      respond $ responseLBS ok200 [] "JSON processed"
    _ -> app request respond

import Servant
import qualified Network.Streaming as NS

type StreamingAPI = "stream" :> Get '[JSON] (NS.Source IO BL.ByteString)

streamingServer :: Server StreamingAPI
streamingServer = return $ NS.sourceList [BL.pack "some json data"]

main :: IO ()
main = run 8080 (serve api streamingServer)
  where
    api = Proxy :: Proxy StreamingAPI