Add MonadCatch and MonadMask instances to RouteResultT and DelayedIO

changelog.d/issue-1829

@@ -0,0 +1,4 @@
+synopsis: Add MonadCatch and MonadMask instances to RouteResultT and DelayedIO
+packages: servant-server
+prs: #1830
+issues: #1829

servant-server/src/Servant/Server/Internal/DelayedIO.hs

@@ -5,7 +5,7 @@
 module Servant.Server.Internal.DelayedIO where
 
 import Control.Monad.Base (MonadBase (..))
-import Control.Monad.Catch (MonadThrow (..))
+import Control.Monad.Catch (MonadCatch (..), MonadMask, MonadThrow (..))
 import Control.Monad.Reader (MonadReader (..), ReaderT (..), runReaderT)
 import Control.Monad.Trans (MonadIO (..), MonadTrans (..))
 import Control.Monad.Trans.Control (MonadBaseControl (..))
@@ -30,7 +30,9 @@ newtype DelayedIO a = DelayedIO {runDelayedIO' :: ReaderT Request (ResourceT (Ro
     ( Applicative
     , Functor
     , Monad
+    , MonadCatch
     , MonadIO
+    , MonadMask
     , MonadReader Request
     , MonadResource
     , MonadThrow

servant-server/src/Servant/Server/Internal/RouteResult.hs

@@ -6,9 +6,9 @@
 
 module Servant.Server.Internal.RouteResult where
 
-import Control.Monad (ap, liftM)
+import Control.Monad (ap)
 import Control.Monad.Base (MonadBase (..))
-import Control.Monad.Catch (MonadThrow (..))
+import Control.Monad.Catch (ExitCase (..), MonadCatch (..), MonadMask (..), MonadThrow (..))
 import Control.Monad.Trans (MonadIO (..), MonadTrans (..))
 import Control.Monad.Trans.Control
   ( ComposeSt
@@ -72,8 +72,48 @@ instance MonadBaseControl b m => MonadBaseControl b (RouteResultT m) where
 
 instance MonadTransControl RouteResultT where
   type StT RouteResultT a = RouteResult a
-  liftWith f = RouteResultT $ liftM return $ f runRouteResultT
+  liftWith f = RouteResultT (return <$> f runRouteResultT)
   restoreT = RouteResultT
 
 instance MonadThrow m => MonadThrow (RouteResultT m) where
   throwM = lift . throwM
+
+instance MonadCatch m => MonadCatch (RouteResultT m) where
+  catch (RouteResultT m) f = RouteResultT $ catch m (runRouteResultT . f)
+
+instance MonadMask m => MonadMask (RouteResultT m) where
+  mask f = RouteResultT $ mask $ \u -> runRouteResultT $ f (q u)
+    where
+      q
+        :: (m (RouteResult a) -> m (RouteResult a))
+        -> RouteResultT m a
+        -> RouteResultT m a
+      q u (RouteResultT b) = RouteResultT (u b)
+  uninterruptibleMask f = RouteResultT $ uninterruptibleMask $ \u -> runRouteResultT $ f (q u)
+    where
+      q
+        :: (m (RouteResult a) -> m (RouteResult a))
+        -> RouteResultT m a
+        -> RouteResultT m a
+      q u (RouteResultT b) = RouteResultT (u b)
+
+  generalBracket acquire release use = RouteResultT $ do
+    (eb, ec) <-
+      generalBracket
+        (runRouteResultT acquire)
+        ( \resourceRoute exitCase -> case resourceRoute of
+            Fail e -> pure $ Fail e -- nothing to release, acquire didn't succeed
+            FailFatal e -> pure $ FailFatal e
+            Route resource -> case exitCase of
+              ExitCaseSuccess (Route b) -> runRouteResultT (release resource (ExitCaseSuccess b))
+              ExitCaseException e -> runRouteResultT (release resource (ExitCaseException e))
+              _ -> runRouteResultT (release resource ExitCaseAbort)
+        )
+        ( \case
+            Fail e -> pure $ Fail e -- nothing to release, acquire didn't succeed
+            FailFatal e -> pure $ FailFatal e
+            Route resource -> runRouteResultT (use resource)
+        )
+    -- The order in which we perform those two effects doesn't matter,
+    -- since the error message is the same regardless.
+    return ((,) <$> eb <*> ec)