我试图弄清楚如何CORS
在 Servant 中添加响应标头(基本上,设置响应标头“Access-Control-Allow-Origin:*”)。我在下面写了一个带有函数的小测试用例,addHeader
但它出错了。我将感谢您帮助找出以下错误。
代码:
{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Data.Aeson
import GHC.Generics
import Network.Wai
import Servant
import Network.Wai.Handler.Warp (run)
import Control.Monad.Trans.Either
import Control.Monad.IO.Class (liftIO)
import Control.Monad (when, (<$!>))
import Data.Text as T
import Data.Configurator as C
import Data.Maybe
import System.Exit (exitFailure)
data User = User
{ name :: T.Text
, password :: T.Text
} deriving (Eq, Show, Generic)
instance ToJSON User
instance FromJSON User
type Token = T.Text
type UserAPI = "grant" :> ReqBody '[JSON] User :> Post '[JSON] (Headers '[Header "Access-Control-Allow-Origin" T.Text] Token)
userAPI :: Proxy UserAPI
userAPI = Proxy
authUser :: User -> Bool
authUser u = case (password u) of
"somepass" -> True
_ -> False
server :: Server UserAPI
server = users
where users :: User -> EitherT ServantErr IO Token
users u = case (authUser u) of
True -> return $ addHeader "*" $ ("ok" :: Token)
False -> return $ addHeader "*" $ ("notok" :: Token)
app :: Application
app = serve userAPI server
main :: IO ()
main = run 8081 app
这是我得到的错误:
src/Test.hs:43:10:
Couldn't match type ‘Headers
'[Header "Access-Control-Allow-Origin" Text] Text’
with ‘Text’
Expected type: Server UserAPI
Actual type: User -> EitherT ServantErr IO Token
In the expression: users
In an equation for ‘server’:
server
= users
where
users :: User -> EitherT ServantErr IO Token
users u
= case (authUser u) of {
True -> return $ addHeader "*" $ ("something" :: Token)
False -> return $ addHeader "*" $ ("something" :: Token) }
src/Test.hs:46:28:
Couldn't match type ‘Text’ with ‘Headers '[Header h v0] Text’
In the expression: addHeader "*"
In the second argument of ‘($)’, namely
‘addHeader "*" $ ("something" :: Token)’
In the expression: return $ addHeader "*" $ ("something" :: Token)
src/Test.hs:47:29:
Couldn't match type ‘Text’ with ‘Headers '[Header h1 v1] Text’
In the expression: addHeader "*"
In the second argument of ‘($)’, namely
‘addHeader "*" $ ("something" :: Token)’
In the expression: return $ addHeader "*" $ ("something" :: Token)
我有一个工作版本,它的工作原理更简单(简单GET
)。但是,对于UserAPI
上述类型,它会出错。addHeader
函数类型似乎与我认为的类型签名一致。我肯定在这里遗漏了一些东西,否则它不会像这样出错。