allow IO

servant-server/src/Servant/Server/Utils/CustomCombinators.hs

@@ -18,6 +18,7 @@ module Servant.Server.Utils.CustomCombinators (
   RouteResult(..),
 ) where
 
+import           Control.Monad.IO.Class
 import           Data.ByteString
 import           Data.Proxy
 import           Data.Text
@@ -50,32 +51,32 @@ makeCaptureCombinator ::
   forall api combinator arg context .
   (HasServer api context,
    WithArg arg (ServerT api Handler) ~ (arg -> ServerT api Handler)) =>
-  (Text -> RouteResult arg)
+  (Text -> IO (RouteResult arg))
   -> CombinatorImplementation combinator arg api context
 makeCaptureCombinator getArg = CI $ \ Proxy context delayed ->
   CaptureRouter $
   route (Proxy :: Proxy api) context $ addCapture delayed $ \ captured ->
-  (liftRouteResult (getArg captured))
+  (liftRouteResult =<< liftIO (getArg captured))
 
 makeRequestCheckCombinator ::
   forall api combinator context .
   (HasServer api context,
    WithArg () (ServerT api Handler) ~ ServerT api Handler) =>
-  (Request -> RouteResult ())
+  (Request -> IO (RouteResult ()))
   -> CombinatorImplementation combinator () api context
 makeRequestCheckCombinator check = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addMethodCheck delayed $
-  withRequest $ \ request -> liftRouteResult $ check request
+  withRequest $ \ request -> liftRouteResult =<< liftIO (check request)
 
 makeAuthCombinator ::
   forall api combinator arg context .
   (HasServer api context,
    WithArg arg (ServerT api Handler) ~ (arg -> ServerT api Handler)) =>
-  (Request -> RouteResult arg)
+  (Request -> IO (RouteResult arg))
   -> CombinatorImplementation combinator arg api context
 makeAuthCombinator authCheck = CI $ \ Proxy context delayed ->
   route (Proxy :: Proxy api) context $ addAuthCheck delayed $
-  withRequest $ \ request -> liftRouteResult $ authCheck request
+  withRequest $ \ request -> liftRouteResult =<< liftIO (authCheck request)
 
 makeReqBodyCombinator ::
   forall api combinator arg context .
@@ -94,9 +95,9 @@ makeCombinator ::
   (ServerT (combinator :> api) Handler ~ (arg -> ServerT api Handler),
    WithArg arg (ServerT api Handler) ~ (arg -> ServerT api Handler),
    HasServer api context) =>
-  (Request -> RouteResult arg)
+  (Request -> IO (RouteResult arg))
   -> CombinatorImplementation combinator arg api context
 makeCombinator getArg = CI $ \ Proxy context delayed ->
-  route (Proxy :: Proxy api) context $ addBodyCheck delayed -- fixme: shouldn't be body
+  route (Proxy :: Proxy api) context $ addBodyCheck delayed
   (return ())
-  (\ () -> withRequest $ \ request -> liftRouteResult $ getArg request)
+  (\ () -> withRequest $ \ request -> liftRouteResult =<< liftIO (getArg request))

servant-server/test/Servant/Server/Utils/CustomCombinatorsSpec.hs

@@ -152,9 +152,6 @@ spec = do
     response <- runApp app request
     responseStatus response `shouldBe` status418
 
-  it "allows to write a combinator using IO" $ do
-    pending
-
   it "allows to pick the request check phase" $ do
     pending
 
@@ -178,8 +175,8 @@ instance HasServer api context => HasServer (StringCapture :> api) context where
   type ServerT (StringCapture :> api) m = String -> ServerT api m
   route = runCI $ makeCaptureCombinator getCapture
 
-getCapture :: Text -> RouteResult String
-getCapture = \case
+getCapture :: Text -> IO (RouteResult String)
+getCapture snippet = return $ case snippet of
   "error" -> FailFatal $ ServantErr 418 "I'm a teapot" "" []
   text -> Route $ cs text
 
@@ -189,8 +186,9 @@ instance HasServer api context => HasServer (CheckFooHeader :> api) context wher
   type ServerT (CheckFooHeader :> api) m = ServerT api m
   route = runCI $ makeRequestCheckCombinator checkFooHeader
 
-checkFooHeader :: Request -> RouteResult ()
-checkFooHeader request = case lookup "Foo" (requestHeaders request) of
+checkFooHeader :: Request -> IO (RouteResult ())
+checkFooHeader request = return $
+  case lookup "Foo" (requestHeaders request) of
     Just _ -> Route ()
     Nothing -> FailFatal err400
 
@@ -203,8 +201,8 @@ instance HasServer api context => HasServer (AuthCombinator :> api) context wher
   type ServerT (AuthCombinator :> api) m = User -> ServerT api m
   route = runCI $ makeAuthCombinator checkAuth
 
-checkAuth :: Request -> RouteResult User
-checkAuth request = case lookup "Auth" (requestHeaders request) of
+checkAuth :: Request -> IO (RouteResult User)
+checkAuth request = return $ case lookup "Auth" (requestHeaders request) of
   Just "secret" -> Route $ User "Alice"
   Just _ -> FailFatal err401
   Nothing -> FailFatal err400
@@ -215,8 +213,8 @@ instance HasServer api context => HasServer (FooHeader :> api) context where
   type ServerT (FooHeader :> api) m = String -> ServerT api m
   route = runCI $ makeCombinator getCustom
 
-getCustom :: Request -> RouteResult String
-getCustom request = case lookup "Foo" (requestHeaders request) of
+getCustom :: Request -> IO (RouteResult String)
+getCustom request = return $ case lookup "Foo" (requestHeaders request) of
   Nothing -> FailFatal err400
   Just l -> Route $ cs l