如何在 Servant 中访问 http headers？

Question

我有一个带 rest 的简单 servant 应用程序 api:

type API = "items" :> Get '[JSON] [MyData]

app :: Application
app = serve api server

api :: Proxy API
api = Proxy

server :: Server API
server = getItems

getItems :: ExceptT ServantErr IO [MyData]
getItems = ......

startApp :: IO ()
startApp = run 1234 app

如何根据条件访问 http headers 和 return 特定响应，例如 http403？

Answer 1

使用 Header (servant)

type API = Header "Auth-token" String :> "items" :> Get '[JSON] [MyData]

然后

handler :: Maybe String -> ExceptT ServantErr IO [MyData]
handler (Just "secret-code") = right [mydata]
handler _                    = left $ err403 { errBody = "no access" }