From e60714c0b2e5ea4656916a5b658a8d5eada98a3a Mon Sep 17 00:00:00 2001
From: Vladislav Oleshko <vladislav.oleshko@gmail.com>
Date: Tue, 1 Feb 2022 16:31:05 +0300
Subject: [PATCH] Separate middleware for handlers

---
 examples/example_middleware.cpp   |  55 ++++++
 include/crow.h                    |   1 +
 include/crow/app.h                |   3 +-
 include/crow/http_connection.h    | 151 +--------------
 include/crow/http_request.h       |   1 +
 include/crow/middleware.h         | 308 ++++++++++++++++++++++++++++++
 include/crow/middleware_context.h |  15 +-
 include/crow/routing.h            | 128 ++++---------
 include/crow/utility.h            |  31 +++
 tests/unittest.cpp                |  55 +++++-
 10 files changed, 494 insertions(+), 254 deletions(-)
 create mode 100644 examples/example_middleware.cpp
 create mode 100644 include/crow/middleware.h

diff --git a/examples/example_middleware.cpp b/examples/example_middleware.cpp
new file mode 100644
index 000000000..f04264e1d
--- /dev/null
+++ b/examples/example_middleware.cpp
@@ -0,0 +1,55 @@
+#include "crow.h"
+
+struct RequestLogger
+{
+    struct context
+    {};
+
+    void before_handle(crow::request& req, crow::response& /*res*/, context& /*ctx*/)
+    {
+        CROW_LOG_INFO << "Request to:" + req.url;
+    }
+
+    void after_handle(crow::request& /*req*/, crow::response& /*res*/, context& /*ctx*/)
+    {}
+};
+
+// Per handler middleware has to extend ILocalMiddleware
+// It is called only if enabled
+struct SecretContentGuard : crow::ILocalMiddleware
+{
+    struct context
+    {};
+
+    void before_handle(crow::request& /*req*/, crow::response& res, context& /*ctx*/)
+    {
+        res.write("SECRET!");
+        res.code = 403;
+        res.end();
+    }
+
+    void after_handle(crow::request& /*req*/, crow::response& /*res*/, context& /*ctx*/)
+    {}
+};
+
+int main()
+{
+    // ALL middleware (including per handler) is listed
+    crow::App<RequestLogger, SecretContentGuard> app;
+
+    CROW_ROUTE(app, "/")
+    ([]() {
+        return "Hello, world!";
+    });
+
+    CROW_ROUTE(app, "/secret")
+    // Enable SecretContentGuard for this handler
+    .middlewares<decltype(app), SecretContentGuard>()
+    ([]() {
+        return "";
+    });
+
+    app.port(18080).run();
+
+    return 0;
+}
diff --git a/include/crow.h b/include/crow.h
index 1687f9647..25c136ad6 100644
--- a/include/crow.h
+++ b/include/crow.h
@@ -17,6 +17,7 @@
 #include "crow/http_response.h"
 #include "crow/multipart.h"
 #include "crow/routing.h"
+#include "crow/middleware.h"
 #include "crow/middleware_context.h"
 #include "crow/compression.h"
 #include "crow/http_connection.h"
diff --git a/include/crow/app.h b/include/crow/app.h
index ec1b27e93..f88a3bdc9 100644
--- a/include/crow/app.h
+++ b/include/crow/app.h
@@ -68,7 +68,7 @@ namespace crow
         }
 
         /// Process the request and generate a response for it
-        void handle(const request& req, response& res)
+        void handle(request& req, response& res)
         {
             router_.handle(req, res);
         }
@@ -394,6 +394,7 @@ namespace crow
 
         // middleware
         using context_t = detail::context<Middlewares...>;
+        using mw_container_t = std::tuple<Middlewares...>;
         template<typename T>
         typename T::context& get_context(const request& req)
         {
diff --git a/include/crow/http_connection.h b/include/crow/http_connection.h
index d370d3fa0..22a0f879f 100644
--- a/include/crow/http_connection.h
+++ b/include/crow/http_connection.h
@@ -15,6 +15,7 @@
 #include "crow/settings.h"
 #include "crow/task_timer.h"
 #include "crow/middleware_context.h"
+#include "crow/middleware.h"
 #include "crow/socket_adaptors.h"
 #include "crow/compression.h"
 
@@ -23,150 +24,6 @@ namespace crow
     using namespace boost;
     using tcp = asio::ip::tcp;
 
-    namespace detail
-    {
-        template<typename MW>
-        struct check_before_handle_arity_3_const
-        {
-            template<typename T, void (T::*)(request&, response&, typename MW::context&) const = &T::before_handle>
-            struct get
-            {};
-        };
-
-        template<typename MW>
-        struct check_before_handle_arity_3
-        {
-            template<typename T, void (T::*)(request&, response&, typename MW::context&) = &T::before_handle>
-            struct get
-            {};
-        };
-
-        template<typename MW>
-        struct check_after_handle_arity_3_const
-        {
-            template<typename T, void (T::*)(request&, response&, typename MW::context&) const = &T::after_handle>
-            struct get
-            {};
-        };
-
-        template<typename MW>
-        struct check_after_handle_arity_3
-        {
-            template<typename T, void (T::*)(request&, response&, typename MW::context&) = &T::after_handle>
-            struct get
-            {};
-        };
-
-        template<typename T>
-        struct is_before_handle_arity_3_impl
-        {
-            template<typename C>
-            static std::true_type f(typename check_before_handle_arity_3_const<T>::template get<C>*);
-
-            template<typename C>
-            static std::true_type f(typename check_before_handle_arity_3<T>::template get<C>*);
-
-            template<typename C>
-            static std::false_type f(...);
-
-        public:
-            static const bool value = decltype(f<T>(nullptr))::value;
-        };
-
-        template<typename T>
-        struct is_after_handle_arity_3_impl
-        {
-            template<typename C>
-            static std::true_type f(typename check_after_handle_arity_3_const<T>::template get<C>*);
-
-            template<typename C>
-            static std::true_type f(typename check_after_handle_arity_3<T>::template get<C>*);
-
-            template<typename C>
-            static std::false_type f(...);
-
-        public:
-            static const bool value = decltype(f<T>(nullptr))::value;
-        };
-
-        template<typename MW, typename Context, typename ParentContext>
-        typename std::enable_if<!is_before_handle_arity_3_impl<MW>::value>::type
-          before_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
-        {
-            mw.before_handle(req, res, ctx.template get<MW>(), ctx);
-        }
-
-        template<typename MW, typename Context, typename ParentContext>
-        typename std::enable_if<is_before_handle_arity_3_impl<MW>::value>::type
-          before_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
-        {
-            mw.before_handle(req, res, ctx.template get<MW>());
-        }
-
-        template<typename MW, typename Context, typename ParentContext>
-        typename std::enable_if<!is_after_handle_arity_3_impl<MW>::value>::type
-          after_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
-        {
-            mw.after_handle(req, res, ctx.template get<MW>(), ctx);
-        }
-
-        template<typename MW, typename Context, typename ParentContext>
-        typename std::enable_if<is_after_handle_arity_3_impl<MW>::value>::type
-          after_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
-        {
-            mw.after_handle(req, res, ctx.template get<MW>());
-        }
-
-        template<int N, typename Context, typename Container, typename CurrentMW, typename... Middlewares>
-        bool middleware_call_helper(Container& middlewares, request& req, response& res, Context& ctx)
-        {
-            using parent_context_t = typename Context::template partial<N - 1>;
-            before_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
-
-            if (res.is_completed())
-            {
-                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
-                return true;
-            }
-
-            if (middleware_call_helper<N + 1, Context, Container, Middlewares...>(middlewares, req, res, ctx))
-            {
-                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
-                return true;
-            }
-
-            return false;
-        }
-
-        template<int N, typename Context, typename Container>
-        bool middleware_call_helper(Container& /*middlewares*/, request& /*req*/, response& /*res*/, Context& /*ctx*/)
-        {
-            return false;
-        }
-
-        template<int N, typename Context, typename Container>
-        typename std::enable_if<(N < 0)>::type
-          after_handlers_call_helper(Container& /*middlewares*/, Context& /*context*/, request& /*req*/, response& /*res*/)
-        {
-        }
-
-        template<int N, typename Context, typename Container>
-        typename std::enable_if<(N == 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res)
-        {
-            using parent_context_t = typename Context::template partial<N - 1>;
-            using CurrentMW = typename std::tuple_element<N, typename std::remove_reference<Container>::type>::type;
-            after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
-        }
-
-        template<int N, typename Context, typename Container>
-        typename std::enable_if<(N > 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res)
-        {
-            using parent_context_t = typename Context::template partial<N - 1>;
-            using CurrentMW = typename std::tuple_element<N, typename std::remove_reference<Container>::type>::type;
-            after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
-            after_handlers_call_helper<N - 1, Context, Container>(middlewares, ctx, req, res);
-        }
-    } // namespace detail
 
 #ifdef CROW_ENABLE_DEBUG
     static std::atomic<int> connectionCount;
@@ -316,8 +173,11 @@ namespace crow
 
                 ctx_ = detail::context<Middlewares...>();
                 req.middleware_context = static_cast<void*>(&ctx_);
+                req.middleware_container = static_cast<void*>(middlewares_);
                 req.io_service = &adaptor_.get_io_service();
-                detail::middleware_call_helper<0, decltype(ctx_), decltype(*middlewares_), Middlewares...>(*middlewares_, req, res, ctx_);
+
+                detail::middleware_call_helper<detail::middleware_call_criteria_only_global,
+                    0, decltype(ctx_), decltype(*middlewares_)>(*middlewares_, req, res, ctx_);
 
                 if (!res.completed_)
                 {
@@ -351,6 +211,7 @@ namespace crow
 
                 // call all after_handler of middlewares
                 detail::after_handlers_call_helper<
+                  detail::middleware_call_criteria_only_global,
                   (static_cast<int>(sizeof...(Middlewares)) - 1),
                   decltype(ctx_),
                   decltype(*middlewares_)>(*middlewares_, ctx_, req_, res);
diff --git a/include/crow/http_request.h b/include/crow/http_request.h
index 809f5edfe..c27778005 100644
--- a/include/crow/http_request.h
+++ b/include/crow/http_request.h
@@ -34,6 +34,7 @@ namespace crow
         std::string remote_ip_address; ///< The IP address from which the request was sent.
 
         void* middleware_context{};
+        void* middleware_container{};
         boost::asio::io_service* io_service{};
 
         /// Construct an empty request. (sets the method to `GET`)
diff --git a/include/crow/middleware.h b/include/crow/middleware.h
new file mode 100644
index 000000000..d527845f7
--- /dev/null
+++ b/include/crow/middleware.h
@@ -0,0 +1,308 @@
+#pragma once
+
+#include "crow/http_request.h"
+#include "crow/http_response.h"
+#include "crow/utility.h"
+
+#include <tuple>
+#include <type_traits>
+#include <iostream>
+#include <utility>
+
+namespace crow {
+
+    /// Local middleware should extend ILocalMiddleware 
+    struct ILocalMiddleware {
+        using call_global = std::false_type;
+    };
+
+    namespace detail
+    {
+        template<typename MW>
+        struct check_before_handle_arity_3_const
+        {
+            template<typename T, void (T::*)(request&, response&, typename MW::context&) const = &T::before_handle>
+            struct get
+            {};
+        };
+
+        template<typename MW>
+        struct check_before_handle_arity_3
+        {
+            template<typename T, void (T::*)(request&, response&, typename MW::context&) = &T::before_handle>
+            struct get
+            {};
+        };
+
+        template<typename MW>
+        struct check_after_handle_arity_3_const
+        {
+            template<typename T, void (T::*)(request&, response&, typename MW::context&) const = &T::after_handle>
+            struct get
+            {};
+        };
+
+        template<typename MW>
+        struct check_after_handle_arity_3
+        {
+            template<typename T, void (T::*)(request&, response&, typename MW::context&) = &T::after_handle>
+            struct get
+            {};
+        };
+
+        template<typename MW>
+        struct check_global_call_false {
+            template<typename T, typename std::enable_if<T::call_global::value == false, bool>::type = true>
+            struct get
+            {};
+        };
+
+        template<typename T>
+        struct is_before_handle_arity_3_impl
+        {
+            template<typename C>
+            static std::true_type f(typename check_before_handle_arity_3_const<T>::template get<C>*);
+
+            template<typename C>
+            static std::true_type f(typename check_before_handle_arity_3<T>::template get<C>*);
+
+            template<typename C>
+            static std::false_type f(...);
+
+        public:
+            static const bool value = decltype(f<T>(nullptr))::value;
+        };
+
+        template<typename T>
+        struct is_after_handle_arity_3_impl
+        {
+            template<typename C>
+            static std::true_type f(typename check_after_handle_arity_3_const<T>::template get<C>*);
+
+            template<typename C>
+            static std::true_type f(typename check_after_handle_arity_3<T>::template get<C>*);
+
+            template<typename C>
+            static std::false_type f(...);
+
+        public:
+            static constexpr bool value = decltype(f<T>(nullptr))::value;
+        };
+
+        template<typename MW, typename Context, typename ParentContext>
+        typename std::enable_if<!is_before_handle_arity_3_impl<MW>::value>::type
+          before_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
+        {
+            mw.before_handle(req, res, ctx.template get<MW>(), ctx);
+        }
+
+        template<typename MW, typename Context, typename ParentContext>
+        typename std::enable_if<is_before_handle_arity_3_impl<MW>::value>::type
+          before_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
+        {
+            mw.before_handle(req, res, ctx.template get<MW>());
+        }
+
+        template<typename MW, typename Context, typename ParentContext>
+        typename std::enable_if<!is_after_handle_arity_3_impl<MW>::value>::type
+          after_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
+        {
+            mw.after_handle(req, res, ctx.template get<MW>(), ctx);
+        }
+
+        template<typename MW, typename Context, typename ParentContext>
+        typename std::enable_if<is_after_handle_arity_3_impl<MW>::value>::type
+          after_handler_call(MW& mw, request& req, response& res, Context& ctx, ParentContext& /*parent_ctx*/)
+        {
+            mw.after_handle(req, res, ctx.template get<MW>());
+        }
+
+        
+        template<template<typename QueryMW> class CallCriteria, // Checks if QueryMW should be called in this context 
+            int N, typename Context, typename Container>
+        typename std::enable_if<(N < std::tuple_size<typename std::remove_reference<Container>::type>::value), bool>::type
+          middleware_call_helper(Container& middlewares, request& req, response& res, Context& ctx)
+        {
+
+            using CurrentMW = typename std::tuple_element<N, typename std::remove_reference<Container>::type>::type;
+
+            if (!CallCriteria<CurrentMW>::value) {
+                return middleware_call_helper<CallCriteria, N + 1, Context, Container>(middlewares, req, res, ctx);
+            }
+
+            using parent_context_t = typename Context::template partial<N - 1>;
+            before_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
+            if (res.is_completed())
+            {
+                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
+                return true;
+            }
+
+            if (middleware_call_helper<CallCriteria, N + 1, Context, Container>(middlewares, req, res, ctx))
+            {
+                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
+                return true;
+            }
+
+            return false;
+        }
+
+        template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
+        typename std::enable_if<(N >= std::tuple_size<typename std::remove_reference<Container>::type>::value), bool>::type
+          middleware_call_helper(Container& /*middlewares*/, request& /*req*/, response& /*res*/, Context& /*ctx*/)
+        {
+            return false;
+        }
+
+        template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
+        typename std::enable_if<(N < 0)>::type
+          after_handlers_call_helper(Container& /*middlewares*/, Context& /*context*/, request& /*req*/, response& /*res*/)
+        {
+        }
+
+        template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
+        typename std::enable_if<(N == 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res)
+        {
+            using parent_context_t = typename Context::template partial<N - 1>;
+            using CurrentMW = typename std::tuple_element<N, typename std::remove_reference<Container>::type>::type;
+            if (CallCriteria<CurrentMW>::value) {
+                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
+            }
+        }
+
+        template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
+        typename std::enable_if<(N > 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res)
+        {
+            using parent_context_t = typename Context::template partial<N - 1>;
+            using CurrentMW = typename std::tuple_element<N, typename std::remove_reference<Container>::type>::type;
+            if (CallCriteria<CurrentMW>::value) {
+                after_handler_call<CurrentMW, Context, parent_context_t>(std::get<N>(middlewares), req, res, ctx, static_cast<parent_context_t&>(ctx));
+            }
+            after_handlers_call_helper<CallCriteria, N - 1, Context, Container>(middlewares, ctx, req, res);
+        }
+
+        // A CallCriteria that accepts only global middleware
+        template<typename MW>
+        struct middleware_call_criteria_only_global
+        {
+            template<typename C>
+            static std::false_type f(typename check_global_call_false<MW>::template get<C>*);
+
+            template<typename C>
+            static std::true_type f(...);
+
+            static const bool value = decltype(f<MW>(nullptr))::value;
+        };
+
+        // wrapped_handler_call transparently wraps a handler call behind (req, res, args...)
+        template<typename F, typename... Args>
+        typename std::enable_if<black_magic::is_callable<F, const crow::request, crow::response&, Args...>::value>::type
+          wrapped_handler_call(crow::request& req, crow::response& res, const F& f, Args&&... args)
+        {
+            static_assert(std::is_same<void, decltype(f(std::declval<crow::request>(), std::declval<crow::response&>(), std::declval<Args>()...))>::value,
+                          "Handler function with response argument should have void return type");
+
+            f(req, res, std::forward<Args>(args)...);
+        }
+
+        template<typename F, typename... Args>
+        typename std::enable_if<black_magic::is_callable<F, crow::request&, crow::response&, Args...>::value
+            && !black_magic::is_callable<F, const crow::request, crow::response&, Args...>::value
+        >::type
+          wrapped_handler_call(crow::request& req, crow::response& res, const F& f, Args&&... args)
+        {
+            static_assert(std::is_same<void, decltype(f(std::declval<crow::request&>(), std::declval<crow::response&>(), std::declval<Args>()...))>::value,
+                          "Handler function with response argument should have void return type");
+
+            f(req, res, std::forward<Args>(args)...);
+        }
+
+        template<typename F, typename... Args>
+        typename std::enable_if<black_magic::is_callable<F, crow::response&, Args...>::value>::type
+          wrapped_handler_call(crow::request& /*req*/, crow::response& res, const F& f, Args&&... args)
+        {
+            static_assert(std::is_same<void, decltype(f(std::declval<crow::response&>(), std::declval<Args>()...))>::value,
+                          "Handler function with response argument should have void return type");
+
+            f(res, std::forward<Args>(args)...);
+        }
+
+        template<typename F, typename... Args>
+        typename std::enable_if<black_magic::is_callable<F, crow::request, Args...>::value>::type
+          wrapped_handler_call(crow::request& req, crow::response& res, const F& f, Args&&... args)
+        {
+            static_assert(!std::is_same<void, decltype(f(std::declval<crow::request>(), std::declval<Args>()...))>::value,
+                          "Handler function cannot have void return type; valid return types: string, int, crow::response, crow::returnable");
+
+            res = crow::response(f(req, std::forward<Args>(args)...));
+            res.end();
+        }
+
+        template<typename F, typename... Args>
+        typename std::enable_if<black_magic::is_callable<F, Args...>::value>::type
+          wrapped_handler_call(crow::request& /*req*/, crow::response& res, const F& f, Args&&... args)
+        {
+            static_assert(!std::is_same<void, decltype(f(std::declval<Args>()...))>::value,
+                          "Handler function cannot have void return type; valid return types: string, int, crow::response, crow::returnable");
+
+            res = crow::response(f(std::forward<Args>(args)...));
+            res.end();
+        }
+
+        template<typename F, typename App, typename... Middlewares>
+        struct handler_middleware_wrapper
+        {
+            // CallCriteria bound to the current Middlewares pack
+            template<typename MW>
+            struct middleware_call_criteria
+            {
+                static constexpr bool value = black_magic::has_type<MW, std::tuple<Middlewares...>>::value;
+            };
+
+            template<typename... Args>
+            void operator()(crow::request& req, crow::response& res, Args&&... args) const
+            {
+                auto& ctx = *reinterpret_cast<typename App::context_t*>(req.middleware_context);
+                auto& container = *reinterpret_cast<typename App::mw_container_t*>(req.middleware_container);
+
+                bool completed = middleware_call_helper<middleware_call_criteria,
+                    0, typename App::context_t, typename App::mw_container_t>(container, req, res, ctx);
+
+                if (completed) return;
+
+                wrapped_handler_call(req, res, f, std::forward<Args>(args)...);
+
+                after_handlers_call_helper<
+                  middleware_call_criteria,
+                  std::tuple_size<typename App::mw_container_t>::value - 1,
+                  typename App::context_t,
+                  typename App::mw_container_t>(container, ctx, req, res);
+            }
+
+            F f;
+        };
+
+        template<typename Route, typename App, typename... Middlewares>
+        struct handler_call_bridge
+        {   
+            template<typename MW>
+            using check_app_contains = typename black_magic::has_type<MW, typename App::mw_container_t>;
+
+            static_assert(black_magic::all_true<(std::is_base_of<crow::ILocalMiddleware, Middlewares>::value)...>::value,
+              "Local middleware has to inherit crow::ILocalMiddleware");
+
+            static_assert(black_magic::all_true<(check_app_contains<Middlewares>::value)...>::value,
+              "Local middleware has to be listed in app middleware");
+
+            template<typename F>
+            void operator()(F&& f) const
+            {
+                auto wrapped = handler_middleware_wrapper<F, App, Middlewares...> {std::forward<F>(f)};
+                tptr->operator()(std::move(wrapped));
+            }
+
+            Route* tptr;
+        };
+
+    } // namespace detail
+} // namespace crow
diff --git a/include/crow/middleware_context.h b/include/crow/middleware_context.h
index 3ac5b488b..6d9c3b122 100644
--- a/include/crow/middleware_context.h
+++ b/include/crow/middleware_context.h
@@ -34,23 +34,18 @@ namespace crow
         };
 
 
-
-        template<int N, typename Context, typename Container, typename CurrentMW, typename... Middlewares>
-        bool middleware_call_helper(Container& middlewares, request& req, response& res, Context& ctx);
-
-
-
         template<typename... Middlewares>
         struct context : private partial_context<Middlewares...>
         //struct context : private Middlewares::context... // simple but less type-safe
         {
-            template<int N, typename Context, typename Container>
+            template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
             friend typename std::enable_if<(N == 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res);
-            template<int N, typename Context, typename Container>
+            template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
             friend typename std::enable_if<(N > 0)>::type after_handlers_call_helper(Container& middlewares, Context& ctx, request& req, response& res);
 
-            template<int N, typename Context, typename Container, typename CurrentMW, typename... Middlewares2>
-            friend bool middleware_call_helper(Container& middlewares, request& req, response& res, Context& ctx);
+            template<template<typename QueryMW> class CallCriteria, int N, typename Context, typename Container>
+            friend typename std::enable_if<(N < std::tuple_size<typename std::remove_reference<Container>::type>::value), bool>::type
+              middleware_call_helper(Container& middlewares, request& req, response& res, Context& ctx);
 
             template<typename T>
             typename T::context& get()
diff --git a/include/crow/routing.h b/include/crow/routing.h
index d95efc33b..a77894476 100644
--- a/include/crow/routing.h
+++ b/include/crow/routing.h
@@ -15,6 +15,7 @@
 #include "crow/logging.h"
 #include "crow/websocket.h"
 #include "crow/mustache.h"
+#include "crow/middleware.h"
 
 namespace crow
 {
@@ -44,7 +45,7 @@ namespace crow
             return {};
         }
 
-        virtual void handle(const request&, response&, const routing_params&) = 0;
+        virtual void handle(request&, response&, const routing_params&) = 0;
         virtual void handle_upgrade(const request&, response& res, SocketAdaptor&&)
         {
             res = response(404);
@@ -109,7 +110,7 @@ namespace crow
             {
                 H1& handler;
                 const routing_params& params;
-                const request& req;
+                request& req;
                 response& res;
             };
 
@@ -251,7 +252,7 @@ namespace crow
 
                 typename handler_type_helper<ArgsWrapped...>::type handler_;
 
-                void operator()(const request& req, response& res, const routing_params& params)
+                void operator()(request& req, response& res, const routing_params& params)
                 {
                     detail::routing_handler_call_helper::call<
                       detail::routing_handler_call_helper::call_params<
@@ -378,7 +379,7 @@ namespace crow
         void validate() override
         {}
 
-        void handle(const request&, response& res, const routing_params&) override
+        void handle(request&, response& res, const routing_params&) override
         {
             res = response(404);
             res.end();
@@ -490,7 +491,7 @@ namespace crow
             }
         }
 
-        void handle(const request& req, response& res, const routing_params& params) override
+        void handle(request& req, response& res, const routing_params& params) override
         {
             if (!custom_templates_base.empty())
                 mustache::set_base(custom_templates_base);
@@ -518,7 +519,7 @@ namespace crow
 #else
         template<typename Func, unsigned... Indices>
 #endif
-        std::function<void(const request&, response&, const routing_params&)>
+        std::function<void(request&, response&, const routing_params&)>
           wrap(Func f, black_magic::seq<Indices...>)
         {
 #ifdef CROW_MSVC_WORKAROUND
@@ -547,7 +548,7 @@ namespace crow
         }
 
     private:
-        std::function<void(const request&, response&, const routing_params&)> erased_handler_;
+        std::function<void(request&, response&, const routing_params&)> erased_handler_;
     };
 
     /// Default rule created when CROW_ROUTE is called.
@@ -570,94 +571,18 @@ namespace crow
         }
 
         template<typename Func>
-        typename std::enable_if<black_magic::CallHelper<Func, black_magic::S<Args...>>::value, void>::type
-          operator()(Func&& f)
-        {
-            static_assert(black_magic::CallHelper<Func, black_magic::S<Args...>>::value ||
-                            black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value,
-                          "Handler type is mismatched with URL parameters");
-            static_assert(!std::is_same<void, decltype(f(std::declval<Args>()...))>::value,
-                          "Handler function cannot have void return type; valid return types: string, int, crow::response, crow::returnable");
-
+        void operator()(Func&& f) {
             handler_ = (
 #ifdef CROW_CAN_USE_CPP14
               [f = std::move(f)]
 #else
               [f]
 #endif
-              (const request&, response& res, Args... args) {
-                  res = response(f(args...));
-                  res.end();
+              (crow::request& req, crow::response& res, Args... args) {
+                  detail::wrapped_handler_call(req, res, f, std::forward<Args>(args)...);
               });
         }
 
-        template<typename Func>
-        typename std::enable_if<
-          !black_magic::CallHelper<Func, black_magic::S<Args...>>::value &&
-            black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value,
-          void>::type
-          operator()(Func&& f)
-        {
-            static_assert(black_magic::CallHelper<Func, black_magic::S<Args...>>::value ||
-                            black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value,
-                          "Handler type is mismatched with URL parameters");
-            static_assert(!std::is_same<void, decltype(f(std::declval<crow::request>(), std::declval<Args>()...))>::value,
-                          "Handler function cannot have void return type; valid return types: string, int, crow::response, crow::returnable");
-
-            handler_ = (
-#ifdef CROW_CAN_USE_CPP14
-              [f = std::move(f)]
-#else
-              [f]
-#endif
-              (const crow::request& req, crow::response& res, Args... args) {
-                  res = response(f(req, args...));
-                  res.end();
-              });
-        }
-
-        template<typename Func>
-        typename std::enable_if<
-          !black_magic::CallHelper<Func, black_magic::S<Args...>>::value &&
-            !black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value &&
-            black_magic::CallHelper<Func, black_magic::S<crow::response&, Args...>>::value,
-          void>::type
-          operator()(Func&& f)
-        {
-            static_assert(black_magic::CallHelper<Func, black_magic::S<Args...>>::value ||
-                            black_magic::CallHelper<Func, black_magic::S<crow::response&, Args...>>::value,
-                          "Handler type is mismatched with URL parameters");
-            static_assert(std::is_same<void, decltype(f(std::declval<crow::response&>(), std::declval<Args>()...))>::value,
-                          "Handler function with response argument should have void return type");
-            handler_ = (
-#ifdef CROW_CAN_USE_CPP14
-              [f = std::move(f)]
-#else
-              [f]
-#endif
-              (const crow::request&, crow::response& res, Args... args) {
-                  f(res, args...);
-              });
-        }
-
-        template<typename Func>
-        typename std::enable_if<
-          !black_magic::CallHelper<Func, black_magic::S<Args...>>::value &&
-            !black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value &&
-            !black_magic::CallHelper<Func, black_magic::S<crow::response&, Args...>>::value,
-          void>::type
-          operator()(Func&& f)
-        {
-            static_assert(black_magic::CallHelper<Func, black_magic::S<Args...>>::value ||
-                            black_magic::CallHelper<Func, black_magic::S<crow::request, Args...>>::value ||
-                            black_magic::CallHelper<Func, black_magic::S<crow::request, crow::response&, Args...>>::value,
-                          "Handler type is mismatched with URL parameters");
-            static_assert(std::is_same<void, decltype(f(std::declval<crow::request>(), std::declval<crow::response&>(), std::declval<Args>()...))>::value,
-                          "Handler function with response argument should have void return type");
-
-            handler_ = std::move(f);
-        }
-
         template<typename Func>
         void operator()(std::string name, Func&& f)
         {
@@ -665,7 +590,7 @@ namespace crow
             (*this).template operator()<Func>(std::forward(f));
         }
 
-        void handle(const request& req, response& res, const routing_params& params) override
+        void handle(request& req, response& res, const routing_params& params) override
         {
             if (!custom_templates_base.empty())
                 mustache::set_base(custom_templates_base);
@@ -673,17 +598,28 @@ namespace crow
                 mustache::set_base("templates");
 
             detail::routing_handler_call_helper::call<
-              detail::routing_handler_call_helper::call_params<
-                decltype(handler_)>,
-              0, 0, 0, 0,
-              black_magic::S<Args...>,
-              black_magic::S<>>()(
-              detail::routing_handler_call_helper::call_params<
-                decltype(handler_)>{handler_, params, req, res});
+                detail::routing_handler_call_helper::call_params<decltype(handler_)>,
+                0, 0, 0, 0,
+                black_magic::S<Args...>,
+                black_magic::S<>>()
+                (
+                    detail::routing_handler_call_helper::call_params<decltype(handler_)>
+                    {handler_, params, req, res}
+                );
+        }
+
+        /// Enable local middleware for this handler
+        template<typename App, typename... Middlewares>
+        crow::detail::handler_call_bridge<TaggedRule<Args...>, App, Middlewares...>
+          middlewares()
+        {
+            // the handler_call_bridge allows the functor to be placed directly after this function
+            // instead of wrapping it with more parentheses
+            return {this};
         }
 
     private:
-        std::function<void(const crow::request&, crow::response&, Args...)> handler_;
+        std::function<void(crow::request&, crow::response&, Args...)> handler_;
     };
 
     const int RULE_SPECIAL_REDIRECT_SLASH = 1;
@@ -1507,7 +1443,7 @@ namespace crow
             return std::string();
         }
 
-        void handle(const request& req, response& res)
+        void handle(request& req, response& res)
         {
             HTTPMethod method_actual = req.method;
             if (req.method >= HTTPMethod::InternalMethodCount)
diff --git a/include/crow/utility.h b/include/crow/utility.h
index 782804971..9a382f866 100644
--- a/include/crow/utility.h
+++ b/include/crow/utility.h
@@ -237,6 +237,37 @@ namespace crow
             static constexpr bool value = sizeof(__test<F, Args...>(0)) == sizeof(char);
         };
 
+        // Check Tuple contains type T
+        template <typename T, typename Tuple>
+        struct has_type;
+
+        template <typename T>
+        struct has_type<T, std::tuple<>> : std::false_type {};
+
+        template <typename T, typename U, typename... Ts>
+        struct has_type<T, std::tuple<U, Ts...>> : has_type<T, std::tuple<Ts...>> {};
+
+        template <typename T, typename... Ts>
+        struct has_type<T, std::tuple<T, Ts...>> : std::true_type {};
+
+        // Check F is callable with Args
+        template<typename F, typename...Args>
+        struct is_callable
+        {
+            template<typename F2, typename...Args2>
+            static std::true_type __test(decltype(std::declval<F2>()(std::declval<Args2>()...)) *) { return {}; }
+
+            template<typename F2, typename...Args2>
+            static std::false_type __test(...) { return {}; }
+
+            static constexpr bool value = decltype(__test<F, Args...>(nullptr))::value;
+        };
+
+        // Kind of fold expressions in C++11
+        template<bool...>
+        struct bool_pack;
+        template<bool... bs>
+        using all_true = std::is_same<bool_pack<bs..., true>, bool_pack<true, bs...>>;
 
         template<int N>
         struct single_tag_to_type
diff --git a/tests/unittest.cpp b/tests/unittest.cpp
index 10d49ccd1..ed739c266 100644
--- a/tests/unittest.cpp
+++ b/tests/unittest.cpp
@@ -44,10 +44,11 @@ TEST_CASE("Rule")
     r.validate();
 
     response res;
+    request req;
 
     // executing handler
     CHECK(0 == x);
-    r.handle(request(), res, routing_params());
+    r.handle(req, res, routing_params());
     CHECK(1 == x);
 
     // registering handler with request argument
@@ -60,7 +61,7 @@ TEST_CASE("Rule")
 
     // executing handler
     CHECK(1 == x);
-    r.handle(request(), res, routing_params());
+    r.handle(req, res, routing_params());
     CHECK(2 == x);
 } // Rule
 
@@ -1374,6 +1375,56 @@ TEST_CASE("middleware_context")
     app.stop();
 } // middleware_context
 
+struct LocalSecretMiddleware : crow::ILocalMiddleware {
+    struct context
+    {};
+
+    void before_handle(request& /*req*/, response& res, context& /*ctx*/)
+    {
+        res.code = 403;
+        res.end();
+    }
+
+    void after_handle(request& /*req*/, response& /*res*/, context& /*ctx*/)
+    {}
+};
+
+TEST_CASE("local_middleware")
+{
+    App<LocalSecretMiddleware> app;
+
+    CROW_ROUTE(app, "/")
+    ([]() {
+        return "works!";
+    });
+
+    CROW_ROUTE(app, "/secret")
+    .middlewares<decltype(app), LocalSecretMiddleware>()
+    ([]() {
+        return "works!";
+    });
+
+    app.validate();
+
+    // Local middleware is handled at router level, so we don't have to send requests manually
+    {
+        request req;
+        response res;
+        req.url = "/";
+        app.handle(req, res);
+        CHECK(200 == res.code);
+    }
+
+    {
+        request req;
+        response res;
+        req.url = "/secret";
+        app.handle(req, res);
+        CHECK(403 == res.code);
+    }
+
+} // local_middleware
+
 TEST_CASE("middleware_cookieparser")
 {
     static char buf[2048];