Merge pull request #457 from kosmikus/fix-router-sharing

Fix router sharing

servant-server/CHANGELOG.md

@@ -1,10 +1,11 @@
 0.7
 ---
 
-* The `Router` type has been changed. There are now more situations where
+* The `Router` type has been changed. Static router tables should now
-  servers will make use of static lookups to efficiently route the request
+  be properly shared between requests, drastically increasing the
-  to the correct endpoint. Functions `layout` and `layoutWithContext` have
+  number of situations where servers will be able to route requests
-  been added to visualize the router layout for debugging purposes. Test
+  efficiently. Functions `layout` and `layoutWithContext` have been
+  added to visualize the router layout for debugging purposes. Test
   cases for expected router layouts have been added.
 * Export `throwError` from module `Servant`
 * Add `Handler` type synonym

servant-server/src/Servant/Server.hs

@@ -132,21 +132,13 @@ serve p = serveWithContext p EmptyContext
 
 serveWithContext :: (HasServer layout context)
     => Proxy layout -> Context context -> Server layout -> Application
-serveWithContext p context server = toApplication (runRouter (route p context d))
+serveWithContext p context server =
-  where
+  toApplication (runRouter (route p context (emptyDelayed (Route server))))
-    d = Delayed r r r r (\ _ _ _ -> Route server)
-    r = return (Route ())
 
 -- | The function 'layout' produces a textual description of the internal
 -- router layout for debugging purposes. Note that the router layout is
 -- determined just by the API, not by the handlers.
 --
--- This function makes certain assumptions about the well-behavedness of
--- the 'HasServer' instances of the combinators which should be ok for the
--- core servant constructions, but might not be satisfied for some other
--- combinators provided elsewhere. It is possible that the function may
--- crash for these.
---
 -- Example:
 --
 -- For the following API
@@ -168,7 +160,7 @@ serveWithContext p context server = toApplication (runRouter (route p context d)
 -- > │  └─ e/
 -- > │     └─•
 -- > ├─ b/
--- > │  └─ <dyn>/
+-- > │  └─ <capture>/
 -- > │     ├─•
 -- > │     ┆
 -- > │     └─•
@@ -185,7 +177,7 @@ serveWithContext p context server = toApplication (runRouter (route p context d)
 --
 -- [@─•@] Leaves reflect endpoints.
 --
--- [@\<dyn\>/@] This is a delayed capture of a path component.
+-- [@\<capture\>/@] This is a delayed capture of a path component.
 --
 -- [@\<raw\>@] This is a part of the API we do not know anything about.
 --
@@ -200,10 +192,8 @@ layout p = layoutWithContext p EmptyContext
 -- | Variant of 'layout' that takes an additional 'Context'.
 layoutWithContext :: (HasServer layout context)
     => Proxy layout -> Context context -> Text
-layoutWithContext p context = routerLayout (route p context d)
+layoutWithContext p context =
-  where
+  routerLayout (route p context (emptyDelayed (FailFatal err501)))
-    d = Delayed r r r r (\ _ _ _ -> FailFatal err501)
-    r = return (Route ())
 
 -- Documentation
 

servant-server/src/Servant/Server/Experimental/Auth.hs

@@ -12,6 +12,7 @@
 
 module Servant.Server.Experimental.Auth where
 
+import           Control.Monad.Trans                        (liftIO)
 import           Control.Monad.Trans.Except                 (runExceptT)
 import           Data.Proxy                                 (Proxy (Proxy))
 import           Data.Typeable                              (Typeable)
@@ -24,10 +25,11 @@ import           Servant.Server.Internal                    (HasContextEntry,
                                                              HasServer, ServerT,
                                                              getContextEntry,
                                                              route)
-import           Servant.Server.Internal.Router             (Router' (WithRequest))
+import           Servant.Server.Internal.RoutingApplication (addAuthCheck,
-import           Servant.Server.Internal.RoutingApplication (RouteResult (FailFatal, Route),
+                                                             delayedFailFatal,
-                                                             addAuthCheck)
+                                                             DelayedIO,
-import           Servant.Server.Internal.ServantErr         (ServantErr, Handler)
+                                                             withRequest)
+import           Servant.Server.Internal.ServantErr         (Handler)
 
 -- * General Auth
 
@@ -57,8 +59,10 @@ instance ( HasServer api context
   type ServerT (AuthProtect tag :> api) m =
     AuthServerData (AuthProtect tag) -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (subserver `addAuthCheck` authCheck request)
+    route (Proxy :: Proxy api) context (subserver `addAuthCheck` withRequest authCheck)
       where
+        authHandler :: Request -> Handler (AuthServerData (AuthProtect tag))
         authHandler = unAuthHandler (getContextEntry context)
-        authCheck = fmap (either FailFatal Route) . runExceptT . authHandler
+        authCheck :: Request -> DelayedIO (AuthServerData (AuthProtect tag))
+        authCheck = (>>= either delayedFailFatal return) . liftIO . runExceptT . authHandler

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

@@ -22,6 +22,7 @@ module Servant.Server.Internal
   , module Servant.Server.Internal.ServantErr
   ) where
 
+import           Control.Monad.Trans        (liftIO)
 import qualified Data.ByteString            as B
 import qualified Data.ByteString.Char8      as BC8
 import qualified Data.ByteString.Lazy       as BL
@@ -70,7 +71,11 @@ import           Servant.Server.Internal.ServantErr
 class HasServer layout context where
   type ServerT layout (m :: * -> *) :: *
 
-  route :: Proxy layout -> Context context -> Delayed (Server layout) -> Router
+  route ::
+       Proxy layout
+    -> Context context
+    -> Delayed env (Server layout)
+    -> Router env
 
 type Server layout = ServerT layout Handler
 
@@ -120,12 +125,12 @@ instance (KnownSymbol capture, FromHttpApiData a, HasServer sublayout context)
      a -> ServerT sublayout m
 
   route Proxy context d =
-    DynamicRouter $ \ first ->
+    CaptureRouter $
         route (Proxy :: Proxy sublayout)
               context
-              (addCapture d $ case parseUrlPieceMaybe first :: Maybe a of
+              (addCapture d $ \ txt -> case parseUrlPieceMaybe txt :: Maybe a of
-                 Nothing -> return $ Fail err400
+                 Nothing -> delayedFail err400
-                 Just v  -> return $ Route v
+                 Just v  -> return v
               )
 
 allowedMethodHead :: Method -> Request -> Bool
@@ -144,41 +149,41 @@ processMethodRouter handleA status method headers request = case handleA of
       bdy = if allowedMethodHead method request then "" else body
       hdrs = (hContentType, cs contentT) : (fromMaybe [] headers)
 
-methodCheck :: Method -> Request -> IO (RouteResult ())
+methodCheck :: Method -> Request -> DelayedIO ()
 methodCheck method request
-  | allowedMethod method request = return $ Route ()
+  | allowedMethod method request = return ()
-  | otherwise                    = return $ Fail err405
+  | otherwise                    = delayedFail err405
 
-acceptCheck :: (AllMime list) => Proxy list -> B.ByteString -> IO (RouteResult ())
+acceptCheck :: (AllMime list) => Proxy list -> B.ByteString -> DelayedIO ()
 acceptCheck proxy accH
-  | canHandleAcceptH proxy (AcceptHeader accH) = return $ Route ()
+  | canHandleAcceptH proxy (AcceptHeader accH) = return ()
-  | otherwise                                  = return $ FailFatal err406
+  | otherwise                                  = delayedFailFatal err406
 
 methodRouter :: (AllCTRender ctypes a)
              => Method -> Proxy ctypes -> Status
-             -> Delayed (Handler a)
+             -> Delayed env (Handler a)
-             -> Router
+             -> Router env
 methodRouter method proxy status action = leafRouter route'
   where
-    route' request respond =
+    route' env request respond =
           let accH = fromMaybe ct_wildcard $ lookup hAccept $ requestHeaders request
           in runAction (action `addMethodCheck` methodCheck method request
                                `addAcceptCheck` acceptCheck proxy accH
-                       ) respond $ \ output -> do
+                       ) env request respond $ \ output -> do
                let handleA = handleAcceptH proxy (AcceptHeader accH) output
                processMethodRouter handleA status method Nothing request
 
 methodRouterHeaders :: (GetHeaders (Headers h v), AllCTRender ctypes v)
                     => Method -> Proxy ctypes -> Status
-                    -> Delayed (Handler (Headers h v))
+                    -> Delayed env (Handler (Headers h v))
-                    -> Router
+                    -> Router env
 methodRouterHeaders method proxy status action = leafRouter route'
   where
-    route' request respond =
+    route' env request respond =
           let accH    = fromMaybe ct_wildcard $ lookup hAccept $ requestHeaders request
           in runAction (action `addMethodCheck` methodCheck method request
                                `addAcceptCheck` acceptCheck proxy accH
-                       ) respond $ \ output -> do
+                       ) env request respond $ \ output -> do
                 let headers = getHeaders output
                     handleA = handleAcceptH proxy (AcceptHeader accH) (getResponse output)
                 processMethodRouter handleA status method (Just headers) request
@@ -230,8 +235,8 @@ instance (KnownSymbol sym, FromHttpApiData a, HasServer sublayout context)
   type ServerT (Header sym a :> sublayout) m =
     Maybe a -> ServerT sublayout m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    let mheader = parseHeaderMaybe =<< lookup str (requestHeaders request)
+    let mheader req = parseHeaderMaybe =<< lookup str (requestHeaders req)
     in  route (Proxy :: Proxy sublayout) context (passToServer subserver mheader)
     where str = fromString $ symbolVal (Proxy :: Proxy sym)
 
@@ -262,10 +267,10 @@ instance (KnownSymbol sym, FromHttpApiData a, HasServer sublayout context)
   type ServerT (QueryParam sym a :> sublayout) m =
     Maybe a -> ServerT sublayout m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    let querytext = parseQueryText $ rawQueryString request
+    let querytext r = parseQueryText $ rawQueryString r
-        param =
+        param r =
-          case lookup paramname querytext of
+          case lookup paramname (querytext r) of
             Nothing       -> Nothing -- param absent from the query string
             Just Nothing  -> Nothing -- param present with no value -> Nothing
             Just (Just v) -> parseQueryParamMaybe v -- if present, we try to convert to
@@ -298,13 +303,13 @@ instance (KnownSymbol sym, FromHttpApiData a, HasServer sublayout context)
   type ServerT (QueryParams sym a :> sublayout) m =
     [a] -> ServerT sublayout m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    let querytext = parseQueryText $ rawQueryString request
+    let querytext r = parseQueryText $ rawQueryString r
         -- if sym is "foo", we look for query string parameters
         -- named "foo" or "foo[]" and call parseQueryParam on the
         -- corresponding values
-        parameters = filter looksLikeParam querytext
+        parameters r = filter looksLikeParam (querytext r)
-        values = mapMaybe (convert . snd) parameters
+        values r = mapMaybe (convert . snd) (parameters r)
     in  route (Proxy :: Proxy sublayout) context (passToServer subserver values)
     where paramname = cs $ symbolVal (Proxy :: Proxy sym)
           looksLikeParam (name, _) = name == paramname || name == (paramname <> "[]")
@@ -329,9 +334,9 @@ instance (KnownSymbol sym, HasServer sublayout context)
   type ServerT (QueryFlag sym :> sublayout) m =
     Bool -> ServerT sublayout m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    let querytext = parseQueryText $ rawQueryString request
+    let querytext r = parseQueryText $ rawQueryString r
-        param = case lookup paramname querytext of
+        param r = case lookup paramname (querytext r) of
           Just Nothing  -> True  -- param is there, with no value
           Just (Just v) -> examine v -- param with a value
           Nothing       -> False -- param not in the query string
@@ -352,8 +357,8 @@ instance HasServer Raw context where
 
   type ServerT Raw m = Application
 
-  route Proxy _ rawApplication = RawRouter $ \ request respond -> do
+  route Proxy _ rawApplication = RawRouter $ \ env request respond -> do
-    r <- runDelayed rawApplication
+    r <- runDelayed rawApplication env request
     case r of
       Route app   -> app request (respond . Route)
       Fail a      -> respond $ Fail a
@@ -386,10 +391,10 @@ instance ( AllCTUnrender list a, HasServer sublayout context
   type ServerT (ReqBody list a :> sublayout) m =
     a -> ServerT sublayout m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy sublayout) context (addBodyCheck subserver (bodyCheck request))
+    route (Proxy :: Proxy sublayout) context (addBodyCheck subserver bodyCheck)
     where
-      bodyCheck request = do
+      bodyCheck = withRequest $ \ request -> do
         -- See HTTP RFC 2616, section 7.2.1
         -- http://www.w3.org/Protocols/rfc2616/rfc2616-sec7.html#sec7.2.1
         -- See also "W3C Internet Media Type registration, consistency of use"
@@ -397,11 +402,11 @@ instance ( AllCTUnrender list a, HasServer sublayout context
         let contentTypeH = fromMaybe "application/octet-stream"
                          $ lookup hContentType $ requestHeaders request
         mrqbody <- handleCTypeH (Proxy :: Proxy list) (cs contentTypeH)
-               <$> lazyRequestBody request
+               <$> liftIO (lazyRequestBody request)
         case mrqbody of
-          Nothing        -> return $ FailFatal err415
+          Nothing        -> delayedFailFatal err415
-          Just (Left e)  -> return $ FailFatal err400 { errBody = cs e }
+          Just (Left e)  -> delayedFailFatal err400 { errBody = cs e }
-          Just (Right v) -> return $ Route v
+          Just (Right v) -> return v
 
 -- | Make sure the incoming request starts with @"/path"@, strip it and
 -- pass the rest of the request path to @sublayout@.
@@ -418,28 +423,28 @@ instance (KnownSymbol path, HasServer sublayout context) => HasServer (path :> s
 instance HasServer api context => HasServer (RemoteHost :> api) context where
   type ServerT (RemoteHost :> api) m = SockAddr -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \req ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (passToServer subserver $ remoteHost req)
+    route (Proxy :: Proxy api) context (passToServer subserver remoteHost)
 
 instance HasServer api context => HasServer (IsSecure :> api) context where
   type ServerT (IsSecure :> api) m = IsSecure -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \req ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (passToServer subserver $ secure req)
+    route (Proxy :: Proxy api) context (passToServer subserver secure)
 
     where secure req = if isSecure req then Secure else NotSecure
 
 instance HasServer api context => HasServer (Vault :> api) context where
   type ServerT (Vault :> api) m = Vault -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \req ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (passToServer subserver $ vault req)
+    route (Proxy :: Proxy api) context (passToServer subserver vault)
 
 instance HasServer api context => HasServer (HttpVersion :> api) context where
   type ServerT (HttpVersion :> api) m = HttpVersion -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \req ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (passToServer subserver $ httpVersion req)
+    route (Proxy :: Proxy api) context (passToServer subserver httpVersion)
 
 -- | Basic Authentication
 instance ( KnownSymbol realm
@@ -450,12 +455,12 @@ instance ( KnownSymbol realm
 
   type ServerT (BasicAuth realm usr :> api) m = usr -> ServerT api m
 
-  route Proxy context subserver = WithRequest $ \ request ->
+  route Proxy context subserver =
-    route (Proxy :: Proxy api) context (subserver `addAuthCheck` authCheck request)
+    route (Proxy :: Proxy api) context (subserver `addAuthCheck` authCheck)
     where
        realm = BC8.pack $ symbolVal (Proxy :: Proxy realm)
        basicAuthContext = getContextEntry context
-       authCheck req = runBasicAuth req realm basicAuthContext
+       authCheck = withRequest $ \ req -> runBasicAuth req realm basicAuthContext
 
 -- * helpers
 

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

@@ -6,6 +6,7 @@
 module Servant.Server.Internal.BasicAuth where
 
 import           Control.Monad          (guard)
+import           Control.Monad.Trans    (liftIO)
 import qualified Data.ByteString        as BS
 import           Data.ByteString.Base64 (decodeLenient)
 import           Data.Monoid            ((<>))
@@ -57,13 +58,13 @@ decodeBAHdr req = do
 
 -- | Run and check basic authentication, returning the appropriate http error per
 -- the spec.
-runBasicAuth :: Request -> BS.ByteString -> BasicAuthCheck usr -> IO (RouteResult usr)
+runBasicAuth :: Request -> BS.ByteString -> BasicAuthCheck usr -> DelayedIO usr
 runBasicAuth req realm (BasicAuthCheck ba) =
   case decodeBAHdr req of
      Nothing -> plzAuthenticate
-     Just e  -> ba e >>= \res -> case res of
+     Just e  -> liftIO (ba e) >>= \res -> case res of
        BadPassword    -> plzAuthenticate
        NoSuchUser     -> plzAuthenticate
-       Unauthorized   -> return $ FailFatal err403
+       Unauthorized   -> delayedFailFatal err403
-       Authorized usr -> return $ Route usr
+       Authorized usr -> return usr
-  where plzAuthenticate = return $ FailFatal err401 { errHeaders = [mkBAChallengerHdr realm] }
+  where plzAuthenticate = delayedFailFatal err401 { errHeaders = [mkBAChallengerHdr realm] }

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

@@ -1,5 +1,7 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE OverloadedStrings #-}
 module Servant.Server.Internal.Router where
 
@@ -8,36 +10,41 @@ import qualified Data.Map                                   as M
 import           Data.Monoid
 import           Data.Text                                  (Text)
 import qualified Data.Text                                  as T
-import           Network.Wai                                (Request, Response, pathInfo)
+import           Network.Wai                                (Response, pathInfo)
 import           Servant.Server.Internal.RoutingApplication
 import           Servant.Server.Internal.ServantErr
 
-type Router = Router' RoutingApplication
+type Router env = Router' env RoutingApplication
 
 -- | Internal representation of a router.
-data Router' a =
+--
-    WithRequest   (Request -> Router' a)
+-- The first argument describes an environment type that is
-      -- ^ current request is passed to the router
+-- expected as extra input by the routers at the leaves. The
-  | StaticRouter  (Map Text (Router' a)) [a]
+-- environment is filled while running the router, with path
+-- components that can be used to process captures.
+--
+data Router' env a =
+    StaticRouter  (Map Text (Router' env a)) [env -> a]
       -- ^ the map contains routers for subpaths (first path component used
       --   for lookup and removed afterwards), the list contains handlers
       --   for the empty path, to be tried in order
-  | DynamicRouter (Text -> Router' a)
+  | CaptureRouter (Router' (Text, env) a)
-      -- ^ first path component passed to the function and removed afterwards
+      -- ^ first path component is passed to the child router in its
-  | RawRouter     a
+      --   environment and removed afterwards
+  | RawRouter     (env -> a)
       -- ^ to be used for routes we do not know anything about
-  | Choice        (Router' a) (Router' a)
+  | Choice        (Router' env a) (Router' env a)
       -- ^ left-biased choice between two routers
   deriving Functor
 
 -- | Smart constructor for a single static path component.
-pathRouter :: Text -> Router' a -> Router' a
+pathRouter :: Text -> Router' env a -> Router' env a
 pathRouter t r = StaticRouter (M.singleton t r) []
 
 -- | Smart constructor for a leaf, i.e., a router that expects
 -- the empty path.
 --
-leafRouter :: a -> Router' a
+leafRouter :: (env -> a) -> Router' env a
 leafRouter l = StaticRouter M.empty [l]
 
 -- | Smart constructor for the choice between routers.
@@ -46,40 +53,27 @@ leafRouter l = StaticRouter M.empty [l]
 --   * Two static routers can be joined by joining their maps
 --     and concatenating their leaf-lists.
 --   * Two dynamic routers can be joined by joining their codomains.
---   * Two 'WithRequest' routers can be joined by passing them
---     the same request and joining their codomains.
---   * A 'WithRequest' router can be joined with anything else by
---     passing the same request to both but ignoring it in the
---     component that does not need it.
 --   * Choice nodes can be reordered.
 --
-choice :: Router -> Router -> Router
+choice :: Router' env a -> Router' env a -> Router' env a
 choice (StaticRouter table1 ls1) (StaticRouter table2 ls2) =
   StaticRouter (M.unionWith choice table1 table2) (ls1 ++ ls2)
-choice (DynamicRouter fun1)  (DynamicRouter fun2)  =
+choice (CaptureRouter router1)   (CaptureRouter router2)   =
-  DynamicRouter (\ first -> choice (fun1 first) (fun2 first))
+  CaptureRouter (choice router1 router2)
-choice (WithRequest router1) (WithRequest router2) =
-  WithRequest (\ request -> choice (router1 request) (router2 request))
-choice (WithRequest router1) router2 =
-  WithRequest (\ request -> choice (router1 request) router2)
-choice router1 (WithRequest router2) =
-  WithRequest (\ request -> choice router1 (router2 request))
 choice router1 (Choice router2 router3) = Choice (choice router1 router2) router3
 choice router1 router2 = Choice router1 router2
 
 -- | Datatype used for representing and debugging the
--- structure of a router. Abstracts from the functions
+-- structure of a router. Abstracts from the handlers
--- being used in the actual router and the handlers at
+-- at the leaves.
--- the leaves.
 --
 -- Two 'Router's can be structurally compared by computing
 -- their 'RouterStructure' using 'routerStructure' and
 -- then testing for equality, see 'sameStructure'.
 --
 data RouterStructure =
-    WithRequestStructure   RouterStructure
+    StaticRouterStructure  (Map Text RouterStructure) Int
-  | StaticRouterStructure  (Map Text RouterStructure) Int
+  | CaptureRouterStructure RouterStructure
-  | DynamicRouterStructure RouterStructure
   | RawRouterStructure
   | ChoiceStructure        RouterStructure RouterStructure
   deriving (Eq, Show)
@@ -87,18 +81,15 @@ data RouterStructure =
 -- | Compute the structure of a router.
 --
 -- Assumes that the request or text being passed
--- in 'WithRequest' or 'DynamicRouter' does not
+-- in 'WithRequest' or 'CaptureRouter' does not
 -- affect the structure of the underlying tree.
 --
-routerStructure :: Router' a -> RouterStructure
+routerStructure :: Router' env a -> RouterStructure
-routerStructure (WithRequest f) =
-  WithRequestStructure $
-    routerStructure (f (error "routerStructure: dummy request"))
 routerStructure (StaticRouter m ls) =
   StaticRouterStructure (fmap routerStructure m) (length ls)
-routerStructure (DynamicRouter f) =
+routerStructure (CaptureRouter router) =
-  DynamicRouterStructure $
+  CaptureRouterStructure $
-    routerStructure (f (error "routerStructure: dummy text"))
+    routerStructure router
 routerStructure (RawRouter _) =
   RawRouterStructure
 routerStructure (Choice r1 r2) =
@@ -108,21 +99,20 @@ routerStructure (Choice r1 r2) =
 
 -- | Compare the structure of two routers.
 --
-sameStructure :: Router' a -> Router' b -> Bool
+sameStructure :: Router' env a -> Router' env b -> Bool
 sameStructure r1 r2 =
   routerStructure r1 == routerStructure r2
 
 -- | Provide a textual representation of the
 -- structure of a router.
 --
-routerLayout :: Router' a -> Text
+routerLayout :: Router' env a -> Text
 routerLayout router =
   T.unlines (["/"] ++ mkRouterLayout False (routerStructure router))
   where
     mkRouterLayout :: Bool -> RouterStructure -> [Text]
-    mkRouterLayout c (WithRequestStructure r)    = mkRouterLayout c r
     mkRouterLayout c (StaticRouterStructure m n) = mkSubTrees c (M.toList m) n
-    mkRouterLayout c (DynamicRouterStructure r)  = mkSubTree c "<dyn>" (mkRouterLayout False r)
+    mkRouterLayout c (CaptureRouterStructure r)  = mkSubTree c "<capture>" (mkRouterLayout False r)
     mkRouterLayout c  RawRouterStructure         =
       if c then ["├─ <raw>"] else ["└─ <raw>"]
     mkRouterLayout c (ChoiceStructure r1 r2)     =
@@ -146,45 +136,52 @@ routerLayout router =
     mkSubTree False path children = ("└─ " <> path <> "/") : map ("   " <>) children
 
 -- | Apply a transformation to the response of a `Router`.
-tweakResponse :: (RouteResult Response -> RouteResult Response) -> Router -> Router
+tweakResponse :: (RouteResult Response -> RouteResult Response) -> Router env -> Router env
 tweakResponse f = fmap (\a -> \req cont -> a req (cont . f))
 
 -- | Interpret a router as an application.
-runRouter :: Router -> RoutingApplication
+runRouter :: Router () -> RoutingApplication
-runRouter (WithRequest router) request respond =
+runRouter r = runRouterEnv r ()
-  runRouter (router request) request respond
+
-runRouter (StaticRouter table ls) request respond =
+runRouterEnv :: Router env -> env -> RoutingApplication
+runRouterEnv router env request respond =
+  case router of
+    StaticRouter table ls ->
       case pathInfo request of
-    []   -> runChoice ls request respond
+        []   -> runChoice ls env request respond
         -- This case is to handle trailing slashes.
-    [""] -> runChoice ls request respond
+        [""] -> runChoice ls env request respond
-    first : rest | Just router <- M.lookup first table
+        first : rest | Just router' <- M.lookup first table
           -> let request' = request { pathInfo = rest }
-         in  runRouter router request' respond
+             in  runRouterEnv router' env request' respond
         _ -> respond $ Fail err404
-runRouter (DynamicRouter fun)  request respond =
+    CaptureRouter router' ->
       case pathInfo request of
         []   -> respond $ Fail err404
         -- This case is to handle trailing slashes.
         [""] -> respond $ Fail err404
         first : rest
           -> let request' = request { pathInfo = rest }
-         in  runRouter (fun first) request' respond
+             in  runRouterEnv router' (first, env) request' respond
-runRouter (RawRouter app)      request respond = app request respond
+    RawRouter app ->
-runRouter (Choice r1 r2)       request respond =
+      app env request respond
-  runChoice [runRouter r1, runRouter r2] request respond
+    Choice r1 r2 ->
+      runChoice [runRouterEnv r1, runRouterEnv r2] env request respond
 
 -- | Try a list of routing applications in order.
 -- We stop as soon as one fails fatally or succeeds.
 -- If all fail normally, we pick the "best" error.
 --
-runChoice :: [RoutingApplication] -> RoutingApplication
+runChoice :: [env -> RoutingApplication] -> env -> RoutingApplication
-runChoice []       _request respond = respond (Fail err404)
+runChoice ls =
-runChoice [r]       request respond = r request respond
+  case ls of
-runChoice (r : rs)  request respond =
+    []       -> \ _ _ respond -> respond (Fail err404)
-  r request $ \ response1 ->
+    [r]      -> r
+    (r : rs) ->
+      \ env request respond ->
+      r env request $ \ response1 ->
       case response1 of
-    Fail _ -> runChoice rs request $ \ response2 ->
+        Fail _ -> runChoice rs env request $ \ response2 ->
           respond $ highestPri response1 response2
         _      -> respond response1
   where

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

@@ -8,7 +8,10 @@
 {-# LANGUAGE StandaloneDeriving         #-}
 module Servant.Server.Internal.RoutingApplication where
 
+import           Control.Monad                      (ap, liftM)
+import           Control.Monad.Trans                (MonadIO(..))
 import           Control.Monad.Trans.Except         (runExceptT)
+import           Data.Text                          (Text)
 import           Network.Wai                        (Application, Request,
                                                      Response, ResponseReceived)
 import           Prelude                            ()
@@ -95,69 +98,108 @@ toApplication ra request respond = ra request routingRespond
 -- The accept header check can be performed as the final
 -- computation in this block. It can cause a 406.
 --
-data Delayed c where
+data Delayed env c where
-  Delayed :: { capturesD :: IO (RouteResult captures)
+  Delayed :: { capturesD :: env -> DelayedIO captures
-             , methodD   :: IO (RouteResult ())
+             , methodD   :: DelayedIO ()
-             , authD     :: IO (RouteResult auth)
+             , authD     :: DelayedIO auth
-             , bodyD     :: IO (RouteResult body)
+             , bodyD     :: DelayedIO body
-             , serverD   :: (captures -> auth -> body -> RouteResult c)
+             , serverD   :: captures -> auth -> body -> Request -> RouteResult c
-             } -> Delayed c
+             } -> Delayed env c
 
-instance Functor Delayed where
+instance Functor (Delayed env) where
-   fmap f Delayed{..}
+  fmap f Delayed{..} =
-    = Delayed { capturesD = capturesD
+    Delayed
-              , methodD   = methodD
+      { serverD = \ c a b req -> f <$> serverD c a b req
-              , authD     = authD
+      , ..
-              , bodyD     = bodyD
-              , serverD   = (fmap.fmap.fmap.fmap) f serverD
       } -- Note [Existential Record Update]
 
+-- | Computations used in a 'Delayed' can depend on the
+-- incoming 'Request', may perform 'IO, and result in a
+-- 'RouteResult, meaning they can either suceed, fail
+-- (with the possibility to recover), or fail fatally.
+--
+newtype DelayedIO a = DelayedIO { runDelayedIO :: Request -> IO (RouteResult a) }
+
+instance Functor DelayedIO where
+  fmap = liftM
+
+instance Applicative DelayedIO where
+  pure = return
+  (<*>) = ap
+
+instance Monad DelayedIO where
+  return x = DelayedIO (const $ return (Route x))
+  DelayedIO m >>= f =
+    DelayedIO $ \ req -> do
+      r <- m req
+      case r of
+        Fail      e -> return $ Fail e
+        FailFatal e -> return $ FailFatal e
+        Route     a -> runDelayedIO (f a) req
+
+instance MonadIO DelayedIO where
+  liftIO m = DelayedIO (const $ Route <$> m)
+
+-- | A 'Delayed' without any stored checks.
+emptyDelayed :: RouteResult a -> Delayed env a
+emptyDelayed result =
+  Delayed (const r) r r r (\ _ _ _ _ -> result)
+  where
+    r = return ()
+
+-- | Fail with the option to recover.
+delayedFail :: ServantErr -> DelayedIO a
+delayedFail err = DelayedIO (const $ return $ Fail err)
+
+-- | Fail fatally, i.e., without any option to recover.
+delayedFailFatal :: ServantErr -> DelayedIO a
+delayedFailFatal err = DelayedIO (const $ return $ FailFatal err)
+
+-- | Gain access to the incoming request.
+withRequest :: (Request -> DelayedIO a) -> DelayedIO a
+withRequest f = DelayedIO (\ req -> runDelayedIO (f req) req)
+
 -- | Add a capture to the end of the capture block.
-addCapture :: Delayed (a -> b)
+addCapture :: Delayed env (a -> b)
-           -> IO (RouteResult a)
+           -> (Text -> DelayedIO a)
-           -> Delayed b
+           -> Delayed (Text, env) b
-addCapture Delayed{..} new
+addCapture Delayed{..} new =
-    = Delayed { capturesD = combineRouteResults (,) capturesD new
+  Delayed
-              , methodD   = methodD
+    { capturesD = \ (txt, env) -> (,) <$> capturesD env <*> new txt
-              , authD     = authD
+    , serverD   = \ (x, v) a b req -> ($ v) <$> serverD x a b req
-              , bodyD     = bodyD
+    , ..
-              , serverD   = \ (x, v) y z -> ($ v) <$> serverD x y z
     } -- Note [Existential Record Update]
 
 -- | Add a method check to the end of the method block.
-addMethodCheck :: Delayed a
+addMethodCheck :: Delayed env a
-               -> IO (RouteResult ())
+               -> DelayedIO ()
-               -> Delayed a
+               -> Delayed env a
-addMethodCheck Delayed{..} new
+addMethodCheck Delayed{..} new =
-    = Delayed { capturesD = capturesD
+  Delayed
-              , methodD   = combineRouteResults const methodD new
+    { methodD = methodD <* new
-              , authD     = authD
+    , ..
-              , bodyD     = bodyD
-              , serverD   = serverD
     } -- Note [Existential Record Update]
 
 -- | Add an auth check to the end of the auth block.
-addAuthCheck :: Delayed (a -> b)
+addAuthCheck :: Delayed env (a -> b)
-             -> IO (RouteResult a)
+             -> DelayedIO a
-             -> Delayed b
+             -> Delayed env b
-addAuthCheck Delayed{..} new
+addAuthCheck Delayed{..} new =
-    = Delayed { capturesD = capturesD
+  Delayed
-              , methodD   = methodD
+    { authD   = (,) <$> authD <*> new
-              , authD     = combineRouteResults (,) authD new
+    , serverD = \ c (y, v) b req -> ($ v) <$> serverD c y b req
-              , bodyD     = bodyD
+    , ..
-              , serverD   = \ x (y, v) z -> ($ v) <$> serverD x y z
     } -- Note [Existential Record Update]
 
 -- | Add a body check to the end of the body block.
-addBodyCheck :: Delayed (a -> b)
+addBodyCheck :: Delayed env (a -> b)
-             -> IO (RouteResult a)
+             -> DelayedIO a
-             -> Delayed b
+             -> Delayed env b
-addBodyCheck Delayed{..} new
+addBodyCheck Delayed{..} new =
-    = Delayed { capturesD = capturesD
+  Delayed
-              , methodD   = methodD
+    { bodyD   = (,) <$> bodyD <*> new
-              , authD     = authD
+    , serverD = \ c a (z, v) req -> ($ v) <$> serverD c a z req
-              , bodyD     = combineRouteResults (,) bodyD new
+    , ..
-              , serverD   = \ x y (z, v) -> ($ v) <$> serverD x y z
     } -- Note [Existential Record Update]
 
 
@@ -165,43 +207,24 @@ addBodyCheck Delayed{..} new
 -- The accept header check should occur after the body check,
 -- but this will be the case, because the accept header check
 -- is only scheduled by the method combinators.
-addAcceptCheck :: Delayed a
+addAcceptCheck :: Delayed env a
-                -> IO (RouteResult ())
+               -> DelayedIO ()
-                -> Delayed a
+               -> Delayed env a
-addAcceptCheck Delayed{..} new
+addAcceptCheck Delayed{..} new =
-    = Delayed { capturesD = capturesD
+  Delayed
-              , methodD   = methodD
+    { bodyD = bodyD <* new
-              , authD     = authD
+    , ..
-              , bodyD     = combineRouteResults const bodyD new
-              , serverD   = serverD
     } -- Note [Existential Record Update]
 
 -- | Many combinators extract information that is passed to
 -- the handler without the possibility of failure. In such a
 -- case, 'passToServer' can be used.
-passToServer :: Delayed (a -> b) -> a -> Delayed b
+passToServer :: Delayed env (a -> b) -> (Request -> a) -> Delayed env b
-passToServer d x = ($ x) <$> d
+passToServer Delayed{..} x =
-
+  Delayed
--- | The combination 'IO . RouteResult' is a monad, but we
+    { serverD = \ c a b req -> ($ x req) <$> serverD c a b req
--- don't explicitly wrap it in a newtype in order to make it
+    , ..
--- an instance. This is the '>>=' of that monad.
+    } -- Note [Existential Record Update]
---
--- We stop on the first error.
-bindRouteResults :: IO (RouteResult a) -> (a -> IO (RouteResult b)) -> IO (RouteResult b)
-bindRouteResults m f = do
-  r <- m
-  case r of
-    Fail      e -> return $ Fail e
-    FailFatal e -> return $ FailFatal e
-    Route     a -> f a
-
--- | Common special case of 'bindRouteResults', corresponding
--- to 'liftM2'.
-combineRouteResults :: (a -> b -> c) -> IO (RouteResult a) -> IO (RouteResult b) -> IO (RouteResult c)
-combineRouteResults f m1 m2 =
-  m1 `bindRouteResults` \ a ->
-  m2 `bindRouteResults` \ b ->
-  return (Route (f a b))
 
 -- | Run a delayed server. Performs all scheduled operations
 -- in order, and passes the results from the capture and body
@@ -209,24 +232,29 @@ combineRouteResults f m1 m2 =
 --
 -- This should only be called once per request; otherwise the guarantees about
 -- effect and HTTP error ordering break down.
-runDelayed :: Delayed a
+runDelayed :: Delayed env a
+           -> env
+           -> Request
            -> IO (RouteResult a)
-runDelayed Delayed{..} =
+runDelayed Delayed{..} env = runDelayedIO $ do
-  capturesD `bindRouteResults` \ c ->
+  c <- capturesD env
-  methodD   `bindRouteResults` \ _ ->
+  methodD
-  authD     `bindRouteResults` \ a ->
+  a <- authD
-  bodyD     `bindRouteResults` \ b ->
+  b <- bodyD
-  return (serverD c a b)
+  DelayedIO (\ req -> return $ serverD c a b req)
 
 -- | Runs a delayed server and the resulting action.
 -- Takes a continuation that lets us send a response.
 -- Also takes a continuation for how to turn the
 -- result of the delayed server into a response.
-runAction :: Delayed (Handler a)
+runAction :: Delayed env (Handler a)
+          -> env
+          -> Request
           -> (RouteResult Response -> IO r)
           -> (a -> RouteResult Response)
           -> IO r
-runAction action respond k = runDelayed action >>= go >>= respond
+runAction action env req respond k =
+  runDelayed action env req >>= go >>= respond
   where
     go (Fail e)      = return $ Fail e
     go (FailFatal e) = return $ FailFatal e

servant-server/test/Servant/Server/RouterSpec.hs

@@ -25,9 +25,9 @@ routerSpec = do
   let app' :: Application
       app' = toApplication $ runRouter router'
 
-      router', router :: Router
+      router', router :: Router ()
       router' = tweakResponse (fmap twk) router
-      router = leafRouter $ \_ cont -> cont (Route $ responseBuilder (Status 201 "") [] "")
+      router = leafRouter $ \_ _ cont -> cont (Route $ responseBuilder (Status 201 "") [] "")
 
       twk :: Response -> Response
       twk (ResponseBuilder (Status i s) hs b) = ResponseBuilder (Status (i + 1) s) hs b
@@ -69,11 +69,9 @@ shouldHaveSameStructureAs p1 p2 =
   unless (sameStructure (makeTrivialRouter p1) (makeTrivialRouter p2)) $
     expectationFailure ("expected:\n" ++ unpack (layout p2) ++ "\nbut got:\n" ++ unpack (layout p1))
 
-makeTrivialRouter :: (HasServer layout '[]) => Proxy layout -> Router
+makeTrivialRouter :: (HasServer layout '[]) => Proxy layout -> Router ()
-makeTrivialRouter p = route p EmptyContext d
+makeTrivialRouter p =
-  where
+  route p EmptyContext (emptyDelayed (FailFatal err501))
-    d = Delayed r r r r (\ _ _ _ -> FailFatal err501)
-    r = return (Route ())
 
 type End = Get '[JSON] ()
 

servant-server/test/Servant/Server/UsingContextSpec/TestCombinators.hs

@@ -20,7 +20,6 @@ module Servant.Server.UsingContextSpec.TestCombinators where
 import           GHC.TypeLits
 
 import           Servant
-import           Servant.Server.Internal.RoutingApplication
 
 data ExtractFromContext
 
@@ -31,7 +30,7 @@ instance (HasContextEntry context String, HasServer subApi context) =>
     String -> ServerT subApi m
 
   route Proxy context delayed =
-    route subProxy context (fmap (inject context) delayed :: Delayed (Server subApi))
+    route subProxy context (fmap (inject context) delayed)
     where
       subProxy :: Proxy subApi
       subProxy = Proxy

servant-server/test/Servant/ServerSpec.hs

@@ -48,7 +48,7 @@ import           Servant.API                ((:<|>) (..), (:>), AuthProtect,
                                              Raw, RemoteHost, ReqBody,
                                              StdMethod (..), Verb, addHeader)
 import           Servant.API.Internal.Test.ComprehensiveAPI
-import           Servant.Server             (ServantErr (..), Server, Handler, err401, err403,
+import           Servant.Server             (Server, Handler, err401, err403,
                                              err404, serve, serveWithContext,
                                              Context((:.), EmptyContext))
 import           Test.Hspec                 (Spec, context, describe, it,