Add QHttpServer::afterRequest

This function allows to register a function to be run after each request.

Task-number: QTBUG-77090
Change-Id: I40dd4c1e9a447fbe034149ffc1923c7c814cf0e9
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@gmail.com>

10 files changed, 468 insertions, 232 deletions

diff --git a/src/httpserver/CMakeLists.txt b/src/httpserver/CMakeLists.txt
index b3586eb..efcce0d 100644
--- a/src/httpserver/CMakeLists.txt
+++ b/src/httpserver/CMakeLists.txt
@@ -16,6 +16,8 @@ qt_add_module(HttpServer
         qhttpserverrouter.cpp qhttpserverrouter.h qhttpserverrouter_p.h
         qhttpserverrouterrule.cpp qhttpserverrouterrule.h qhttpserverrouterrule_p.h
         qhttpserverrouterviewtraits.h
+        qhttpserverviewtraits.h
+        qhttpserverviewtraits_impl.h
         qthttpserverglobal.h
     INCLUDE_DIRECTORIES
         .
@@ -45,10 +47,3 @@ qt_extend_target(HttpServer CONDITION QT_FEATURE_ssl
     PUBLIC_LIBRARIES
         Qt::SslServer
 )
-
-qt_extend_target(HttpServer CONDITION TARGET Qt::Concurrent
-    SOURCES
-        qhttpserverfutureresponse.cpp qhttpserverfutureresponse.h
-    PUBLIC_LIBRARIES
-        Qt::Concurrent
-)
diff --git a/src/httpserver/httpserver.pro b/src/httpserver/httpserver.pro
index 20f567f..fd1a231 100644
--- a/src/httpserver/httpserver.pro
+++ b/src/httpserver/httpserver.pro
@@ -23,7 +23,9 @@ HEADERS += \
     qhttpserverrouter_p.h \
     qhttpserverrouterrule.h \
     qhttpserverrouterrule_p.h \
-    qhttpserverrouterviewtraits.h
+    qhttpserverrouterviewtraits.h \
+    qhttpserverviewtraits.h \
+    qhttpserverviewtraits_impl.h
 
 SOURCES += \
     qabstracthttpserver.cpp \
diff --git a/src/httpserver/qhttpserver.cpp b/src/httpserver/qhttpserver.cpp
index 413e3c3..fb0b67b 100644
--- a/src/httpserver/qhttpserver.cpp
+++ b/src/httpserver/qhttpserver.cpp
@@ -66,8 +66,7 @@ QHttpServer::QHttpServer(QObject *parent)
     connect(this, &QAbstractHttpServer::missingHandler, this,
             [=] (const QHttpServerRequest &request, QTcpSocket *socket) {
         qCDebug(lcHS) << tr("missing handler:") << request.url().path();
-        sendResponse(
-                QHttpServerResponse(QHttpServerResponder::StatusCode::NotFound), request, socket);
+        sendResponse(QHttpServerResponder::StatusCode::NotFound, request, socket);
     });
 }
 
@@ -103,6 +102,40 @@ QHttpServer::QHttpServer(QObject *parent)
     \sa QHttpServerRouter::addRule
 */
 
+/*! \fn template<typename ViewHandler> void afterRequest(ViewHandler &&viewHandler)
+    Register a function to be run after each request.
+
+    \c ViewHandler can only be a lambda. The lambda definition can take two
+    arguments: \c {QHttpServerResponse &&} and \c {const QHttpServerRequest&} (optional).
+
+    Examples:
+
+    \code
+
+    QHttpServer server;
+
+    // Valid:
+    server.afterRequest([] (QHttpServerResponse &&resp, const QHttpServerRequest &request) {
+        return std::move(resp);
+    }
+    server.afterRequest([] (const QHttpServerRequest &request, QHttpServerResponse &&resp) {
+        return std::move(resp);
+    }
+    server.afterRequest([] (QHttpServerResponse &&resp) { return std::move(resp); }
+
+    // Invalid (compile time error):
+    // resp must be passed by universal reference
+    server.afterRequest([] (QHttpServerResponse &resp, const QHttpServerRequest &request) {
+        return std::move(resp);
+    }
+    // request must be passed by const reference
+    server.afterRequest([] (QHttpServerResponse &&resp, QHttpServerRequest &request) {
+        return std::move(resp);
+    }
+
+    \endcode
+*/
+
 /*!
     Destroys a QHttpServer.
 */
@@ -119,13 +152,22 @@ QHttpServerRouter *QHttpServer::router()
     return &d->router;
 }
 
+void QHttpServer::afterRequestImpl(AfterRequestHandler &&afterRequestHandler)
+{
+    Q_D(QHttpServer);
+    d->afterRequestHandlers.push_back(std::move(afterRequestHandler));
+}
+
 /*!
     \internal
 */
-void QHttpServer::sendResponse(const QHttpServerResponse &response,
+void QHttpServer::sendResponse(QHttpServerResponse &&response,
                                const QHttpServerRequest &request,
                                QTcpSocket *socket)
 {
+    Q_D(QHttpServer);
+    for (auto afterRequestHandler : d->afterRequestHandlers)
+        response = std::move(afterRequestHandler(std::move(response), request));
     response.write(makeResponder(request, socket));
 }
 
diff --git a/src/httpserver/qhttpserver.h b/src/httpserver/qhttpserver.h
index 6d754b1..97c5bc5 100644
--- a/src/httpserver/qhttpserver.h
+++ b/src/httpserver/qhttpserver.h
@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2020 Mikhail Svetkin <mikhail.svetkin@gmail.com>
 ** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -35,6 +36,7 @@
 #include <QtHttpServer/qhttpserverrouterrule.h>
 #include <QtHttpServer/qhttpserverresponse.h>
 #include <QtHttpServer/qhttpserverrouterviewtraits.h>
+#include <QtHttpServer/qhttpserverviewtraits.h>
 
 #include <tuple>
 
@@ -75,6 +77,57 @@ public:
                 std::forward<Args>(args)...);
     }
 
+    template<typename ViewHandler>
+    void afterRequest(ViewHandler &&viewHandler)
+    {
+        using ViewTraits = QHttpServerAfterRequestViewTraits<ViewHandler>;
+        static_assert(ViewTraits::Arguments::StaticAssert,
+                      "ViewHandler arguments are in the wrong order or not supported");
+        afterRequestHelper<ViewTraits, ViewHandler>(std::move(viewHandler));
+    }
+
+    using AfterRequestHandler =
+        std::function<QHttpServerResponse(QHttpServerResponse &&response,
+                      const QHttpServerRequest &request)>;
+private:
+    template<typename ViewTraits, typename ViewHandler>
+    typename std::enable_if<ViewTraits::Arguments::Last::IsRequest::Value &&
+                            ViewTraits::Arguments::Count == 2, void>::type
+            afterRequestHelper(ViewHandler &&viewHandler) {
+        auto handler = [viewHandler](QHttpServerResponse &&resp,
+                                     const QHttpServerRequest &request) {
+            return std::move(viewHandler(std::move(resp), request));
+        };
+
+        afterRequestImpl(std::move(handler));
+    }
+
+    template<typename ViewTraits, typename ViewHandler>
+    typename std::enable_if<ViewTraits::Arguments::Last::IsResponse::Value &&
+                            ViewTraits::Arguments::Count == 1, void>::type
+            afterRequestHelper(ViewHandler &&viewHandler) {
+        auto handler = [viewHandler](QHttpServerResponse &&resp,
+                                     const QHttpServerRequest &) {
+            return std::move(viewHandler(std::move(resp)));
+        };
+
+        afterRequestImpl(std::move(handler));
+    }
+
+    template<typename ViewTraits, typename ViewHandler>
+    typename std::enable_if<ViewTraits::Arguments::Last::IsResponse::Value &&
+                            ViewTraits::Arguments::Count == 2, void>::type
+            afterRequestHelper(ViewHandler &&viewHandler) {
+        auto handler = [viewHandler](QHttpServerResponse &&resp,
+                                     const QHttpServerRequest &request) {
+            return std::move(viewHandler(request, std::move(resp)));
+        };
+
+        afterRequestImpl(std::move(handler));
+    }
+
+    void afterRequestImpl(AfterRequestHandler &&afterRequestHandler);
+
 private:
     template<typename Rule, typename ViewHandler, typename ViewTraits, int ... I, typename ... Args>
     bool routeHelper(QtPrivate::IndexesList<I...>, Args &&... args)
@@ -107,8 +160,8 @@ private:
                          const QHttpServerRequest &request,
                          QTcpSocket *socket)
     {
-        const QHttpServerResponse response(boundViewHandler());
-        sendResponse(response, request, socket);
+        QHttpServerResponse response(boundViewHandler());
+        sendResponse(std::move(response), request, socket);
     }
 
     template<typename ViewTraits, typename T>
@@ -124,8 +177,8 @@ private:
                             ViewTraits::Arguments::PlaceholdersCount == 1, void>::type
             responseImpl(T &boundViewHandler, const QHttpServerRequest &request, QTcpSocket *socket)
     {
-        const QHttpServerResponse response(boundViewHandler(request));
-        sendResponse(response, request, socket);
+        QHttpServerResponse response(boundViewHandler(request));
+        sendResponse(std::move(response), request, socket);
     }
 
     template<typename ViewTraits, typename T>
@@ -150,7 +203,7 @@ private:
 
     bool handleRequest(const QHttpServerRequest &request, QTcpSocket *socket) override final;
 
-    void sendResponse(const QHttpServerResponse &response,
+    void sendResponse(QHttpServerResponse &&response,
                       const QHttpServerRequest &request,
                       QTcpSocket *socket);
 };
diff --git a/src/httpserver/qhttpserver_p.h b/src/httpserver/qhttpserver_p.h
index 649c41f..eb39a9e 100644
--- a/src/httpserver/qhttpserver_p.h
+++ b/src/httpserver/qhttpserver_p.h
@@ -49,6 +49,8 @@
 
 #include <QtCore/qglobal.h>
 
+#include <list>
+
 QT_BEGIN_NAMESPACE
 
 class QHttpServerPrivate: public QAbstractHttpServerPrivate
@@ -59,6 +61,7 @@ public:
     QHttpServerPrivate() = default;
 
     QHttpServerRouter router;
+    std::list<QHttpServer::AfterRequestHandler> afterRequestHandlers;
 };
 
 QT_END_NAMESPACE
diff --git a/src/httpserver/qhttpserverresponse.cpp b/src/httpserver/qhttpserverresponse.cpp
index 9cedeb9..5ed230e 100644
--- a/src/httpserver/qhttpserverresponse.cpp
+++ b/src/httpserver/qhttpserverresponse.cpp
@@ -40,11 +40,20 @@
 
 QT_BEGIN_NAMESPACE
 
-QHttpServerResponse::QHttpServerResponse(QHttpServerResponse &&other)
+QHttpServerResponse::QHttpServerResponse(QHttpServerResponse &&other) noexcept
     : d_ptr(other.d_ptr.take())
 {
 }
 
+QHttpServerResponse& QHttpServerResponse::operator=(QHttpServerResponse &&other) noexcept
+{
+    if (this == &other)
+        return *this;
+
+    qSwap(d_ptr, other.d_ptr);
+    return *this;
+}
+
 QHttpServerResponse::QHttpServerResponse(
         const QHttpServerResponse::StatusCode statusCode)
     : QHttpServerResponse(QHttpServerLiterals::contentTypeXEmpty(),
diff --git a/src/httpserver/qhttpserverresponse.h b/src/httpserver/qhttpserverresponse.h
index 3fef112..df748cb 100644
--- a/src/httpserver/qhttpserverresponse.h
+++ b/src/httpserver/qhttpserverresponse.h
@@ -50,8 +50,8 @@ public:
     QHttpServerResponse(const QHttpServerResponse &other) = delete;
     QHttpServerResponse& operator=(const QHttpServerResponse &other) = delete;
 
-    QHttpServerResponse(QHttpServerResponse &&other);
-    QHttpServerResponse& operator=(QHttpServerResponse &&other) = delete;
+    QHttpServerResponse(QHttpServerResponse &&other) noexcept;
+    QHttpServerResponse& operator=(QHttpServerResponse &&other) noexcept;
 
     QHttpServerResponse(const StatusCode statusCode);
 
diff --git a/src/httpserver/qhttpserverrouterviewtraits.h b/src/httpserver/qhttpserverrouterviewtraits.h
index 94fd5cc..2e812a5 100644
--- a/src/httpserver/qhttpserverrouterviewtraits.h
+++ b/src/httpserver/qhttpserverrouterviewtraits.h
@@ -1,5 +1,6 @@
 /****************************************************************************
 **
+** Copyright (C) 2020 Mikhail Svetkin <mikhail.svetkin@gmail.com>
 ** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -30,14 +31,7 @@
 #ifndef QHTTPSERVERROUTERVIEWTRAITS_H
 #define QHTTPSERVERROUTERVIEWTRAITS_H
 
-#include <QtCore/qglobal.h>
-#include <QtCore/qmetatype.h>
-#include <QtCore/qnamespace.h>
-#include <QtCore/qobjectdefs.h>
-
-#include <functional>
-#include <tuple>
-#include <type_traits>
+#include <QtHttpServer/qhttpserverviewtraits_impl.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -46,220 +40,53 @@ class QHttpServerResponder;
 
 namespace QtPrivate {
 
-template<typename T>
-struct RemoveCVRef
-{
-    using Type = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
-};
-
-
-template<bool classMember, typename ReturnT, typename ... Args>
-struct FunctionTraitsHelper
-{
-    static constexpr const int ArgumentCount = sizeof ... (Args);
-    static constexpr const int ArgumentIndexMax = ArgumentCount - 1;
-    static constexpr const bool IsClassMember = classMember;
-    using ReturnType = ReturnT;
-
-    template <int I>
-    struct Arg {
-        using Type = typename std::tuple_element<I, std::tuple<Args...>>::type;
-
-        using CleanType = typename QtPrivate::RemoveCVRef<Type>::Type;
-
-        static constexpr bool Defined = QMetaTypeId2<CleanType>::Defined;
-    };
-};
-
-template<bool classMember, typename ReturnT>
-struct FunctionTraitsHelper<classMember, ReturnT>
-{
-    static constexpr const int ArgumentCount = 0;
-    static constexpr const int ArgumentIndexMax = -1;
-    static constexpr const bool IsClassMember = classMember;
-    using ReturnType = ReturnT;
-
-    template <int I>
-    struct Arg {
-        using Type = std::false_type;
-        using CleanType = Type;
-        static constexpr bool Defined = QMetaTypeId2<CleanType>::Defined;
-    };
-};
-
-template<typename T>
-struct FunctionTraits;
-
-template<typename T>
-struct FunctionTraits : public FunctionTraits<decltype(&T::operator())>{};
-
-template<typename ReturnT, typename ... Args>
-struct FunctionTraits<ReturnT (*)(Args...)>
-    : public FunctionTraitsHelper<false, ReturnT, Args...>
-{
-};
-
-template<class ReturnT, class ClassT, class ...Args>
-struct FunctionTraits<ReturnT (ClassT::*)(Args...) const>
-    : public FunctionTraitsHelper<true, ReturnT, Args...>
-{
-    using classType = ClassT;
-};
-
 template<typename ViewHandler, bool DisableStaticAssert>
-struct ViewTraitsHelper {
-    using FunctionTraits = typename QtPrivate::FunctionTraits<ViewHandler>;
-    using ArgumentIndexes = typename QtPrivate::Indexes<FunctionTraits::ArgumentCount>::Value;
-
-    struct StaticMath {
-        template <template<typename> class Predicate, bool defaultValue>
-        struct Loop {
-            static constexpr bool eval() noexcept {
-                return defaultValue;
-            }
+struct RouterViewTraitsHelper : ViewTraits<ViewHandler, DisableStaticAssert> {
+    using VTraits = ViewTraits<ViewHandler, DisableStaticAssert>;
+    using FunctionTraits = typename VTraits::FTraits;
+
+    template<int I>
+    struct ArgumentChecker : FunctionTraits::template Arg<I> {
+        using IsRequest = typename VTraits::template Special<I, const QHttpServerRequest &>;
+        static_assert(IsRequest::AssertCondition,
+                      "ViewHandler arguments error: "
+                      "QHttpServerRequest can only be passed as a const reference");
+
+        using IsResponder = typename VTraits::template Special<I, QHttpServerResponder &&>;
+        static_assert(IsResponder::AssertCondition,
+                      "ViewHandler arguments error: "
+                      "QHttpServerResponder can only be passed as a universal reference");
+
+        using IsSpecial = CheckAny<IsRequest, IsResponder>;
+
+        struct IsSimple {
+            static constexpr bool Value = !IsSpecial::Value &&
+                                           I < FunctionTraits::ArgumentCount &&
+                                           FunctionTraits::ArgumentIndexMax != -1;
+            static constexpr bool Valid = FunctionTraits::template Arg<I>::Defined;
 
-            template<typename T, typename ... N>
-            static constexpr T eval(const T it, N ...n) noexcept {
-                return Predicate<T>::eval(it, eval(n...));
-            }
-        };
+            static constexpr bool StaticAssert =
+                DisableStaticAssert || !Value || Valid;
 
-        template<typename T>
-        struct SumPredicate {
-            static constexpr T eval(const T rs, const T ls) noexcept
-            {
-                return rs + ls;
-            }
-        };
 
-        template<typename T>
-        struct AndPredicate {
-            static constexpr T eval(const T rs, const T ls) noexcept
-            {
-                return rs && ls;
-            }
+            static_assert(StaticAssert,
+                          "ViewHandler arguments error: "
+                          "Type is not registered, please use the Q_DECLARE_METATYPE macro "
+                          "to make it known to Qt's meta-object system");
         };
 
-        using Sum = Loop<SumPredicate, false>;
-        using And = Loop<AndPredicate, true>;
-        using Or = Sum;
-    };
-
-    struct Arguments {
-        template<int I>
-        struct StaticCheck {
-            using Arg = typename FunctionTraits::template Arg<I>;
-            using CleanType = typename Arg::CleanType;
+        using CheckOk = CheckAny<IsSimple, IsSpecial>;
 
-            template<typename T, bool Clean = false>
-            static constexpr bool isType() noexcept
-            {
-                using SelectedType =
-                    typename std::conditional<
-                        Clean,
-                        CleanType,
-                        typename Arg::Type
-                    >::type;
-                return std::is_same<SelectedType, T>::value;
-            }
+        static constexpr bool Valid = CheckOk::Valid;
+        static constexpr bool StaticAssert = CheckOk::StaticAssert;
+    };
 
-            template<typename T>
-            struct SpecialHelper {
-                using CleanTypeT = typename QtPrivate::RemoveCVRef<T>::Type;
-
-                static constexpr bool TypeMatched = isType<CleanTypeT, true>();
-                static constexpr bool TypeCVRefMatched = isType<T>();
-
-                static constexpr bool ValidPosition =
-                    (I == FunctionTraits::ArgumentIndexMax ||
-                     I == FunctionTraits::ArgumentIndexMax - 1);
-                static constexpr bool ValidAll = TypeCVRefMatched && ValidPosition;
-
-                static constexpr bool assertCondition =
-                    DisableStaticAssert || !TypeMatched || TypeCVRefMatched;
-
-                static constexpr bool assertConditionOrder =
-                    DisableStaticAssert || !TypeMatched || ValidPosition;
-
-                static constexpr bool staticAssert() noexcept
-                {
-                    static_assert(assertConditionOrder,
-                                  "ViewHandler arguments error: "
-                                  "QHttpServerRequest or QHttpServerResponder"
-                                  " can only be the last argument");
-                    return true;
-                }
-            };
-
-            template<typename ... T>
-            struct CheckAny {
-                static constexpr bool Value = StaticMath::Or::eval(T::Value...);
-                static constexpr bool Valid = StaticMath::Or::eval(T::Valid...);
-                static constexpr bool staticAssert() noexcept
-                {
-                    return StaticMath::Or::eval(T::staticAssert()...);
-                }
-            };
-
-            struct IsRequest {
-                using Helper = SpecialHelper<const QHttpServerRequest &>;
-                static constexpr bool Value = Helper::TypeMatched;
-                static constexpr bool Valid = Helper::ValidAll;
-
-                static constexpr bool staticAssert() noexcept
-                {
-                    static_assert(Helper::assertCondition,
-                                  "ViewHandler arguments error: "
-                                  "QHttpServerRequest can only be passed as a const reference");
-                    return Helper::staticAssert();
-                }
-            };
-
-            struct IsResponder {
-                using Helper = SpecialHelper<QHttpServerResponder &&>;
-                static constexpr bool Value = Helper::TypeMatched;
-                static constexpr bool Valid = Helper::ValidAll;
-
-                static constexpr bool staticAssert() noexcept
-                {
-                    static_assert(Helper::assertCondition,
-                                  "ViewHandler arguments error: "
-                                  "QHttpServerResponder can only be passed as a universal reference");
-                    return Helper::staticAssert();
-                }
-            };
-
-            using IsSpecial = CheckAny<IsRequest, IsResponder>;
-
-            struct IsSimple {
-                static constexpr bool Value = !IsSpecial::Value &&
-                                               I < FunctionTraits::ArgumentCount &&
-                                               FunctionTraits::ArgumentIndexMax != -1;
-                static constexpr bool Valid = Arg::Defined;
-
-                static constexpr bool assertCondition =
-                    DisableStaticAssert || !Value || Valid;
-
-                static constexpr bool staticAssert() noexcept
-                {
-                    static_assert(assertCondition,
-                                  "ViewHandler arguments error: "
-                                  "Type is not registered, please use the Q_DECLARE_METATYPE macro "
-                                  "to make it known to Qt's meta-object system");
-                    return true;
-                }
-            };
-
-            using CheckOk = CheckAny<IsSimple, IsSpecial>;
-
-            static constexpr bool Valid = CheckOk::Valid;
-            static constexpr bool StaticAssert = CheckOk::staticAssert();
-        };
 
+    struct Arguments {
         template<int ... I>
         struct ArgumentsReturn {
             template<int Idx>
-            using Arg = StaticCheck<Idx>;
+            using Arg = ArgumentChecker<Idx>;
 
             template<int Idx>
             static constexpr int metaTypeId() noexcept
@@ -279,9 +106,9 @@ struct ViewTraitsHelper {
                     static_cast<std::size_t>(FunctionTraits::template Arg<I>::Defined)...);
             static constexpr std::size_t PlaceholdersCount = Count - CapturableCount;
 
-            static constexpr bool Valid = StaticMath::And::eval(StaticCheck<I>::Valid...);
+            static constexpr bool Valid = StaticMath::And::eval(Arg<I>::Valid...);
             static constexpr bool StaticAssert =
-                StaticMath::And::eval(StaticCheck<I>::StaticAssert...);
+                StaticMath::And::eval(Arg<I>::StaticAssert...);
 
             using Indexes = typename QtPrivate::IndexesList<I...>;
 
@@ -317,18 +144,20 @@ struct ViewTraitsHelper {
     };
 };
 
+
 } // namespace QtPrivate
 
 template <typename ViewHandler, bool DisableStaticAssert = false>
 struct QHttpServerRouterViewTraits
 {
-    using Helpers = typename QtPrivate::ViewTraitsHelper<ViewHandler, DisableStaticAssert>;
+    using Helpers = typename QtPrivate::RouterViewTraitsHelper<ViewHandler, DisableStaticAssert>;
     using Arguments = decltype(Helpers::Arguments::eval(typename Helpers::ArgumentIndexes{}));
     using BindableType = decltype(
             Helpers::template BindType<Arguments::CapturableCount>::eval(
                 typename Arguments::PlaceholdersIndexes{}));
 };
 
+
 QT_END_NAMESPACE
 
 #endif  // QHTTPSERVERROUTERVIEWTRAITS_H
diff --git a/src/httpserver/qhttpserverviewtraits.h b/src/httpserver/qhttpserverviewtraits.h
new file mode 100644
index 0000000..0469ffb
--- /dev/null
+++ b/src/httpserver/qhttpserverviewtraits.h
@@ -0,0 +1,109 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Mikhail Svetkin <mikhail.svetkin@gmail.com>
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtHttpServer module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 or (at your option) any later version
+** approved by the KDE Free Qt Foundation. The licenses are as published by
+** the Free Software Foundation and appearing in the file LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QHTTPSERVERVIEWTRAITS_H
+#define QHTTPSERVERVIEWTRAITS_H
+
+#include <QtHttpServer/qhttpserverviewtraits_impl.h>
+
+QT_BEGIN_NAMESPACE
+
+class QHttpServerRequest;
+class QHttpServerResponse;
+
+namespace QtPrivate {
+
+template <typename ViewHandler, bool DisableStaticAssert>
+struct AfterRequestViewTraitsHelper : ViewTraits<ViewHandler, DisableStaticAssert> {
+    using VTraits = ViewTraits<ViewHandler, DisableStaticAssert>;
+    using FunctionTraits = typename VTraits::FTraits;
+
+    static_assert(DisableStaticAssert ||
+                  FunctionTraits::ArgumentCount == 2 ||
+                  FunctionTraits::ArgumentCount == 1,
+                  "ViewHandler arguments error: "
+                  "afterRequest can only accept QHttpServerResponse and QHttpServerRequest");
+
+    static_assert(DisableStaticAssert ||
+                  std::is_same<typename FunctionTraits::ReturnType,
+                               QHttpServerResponse>::value,
+                  "ViewHandler return type error: "
+                  "Return type can only be QHttpServerResponse");
+
+    template<int I>
+    struct ArgumentChecker {
+        using IsRequest = typename VTraits::template Special<I, const QHttpServerRequest &>;
+        static_assert(IsRequest::AssertCondition,
+                      "ViewHandler arguments error: "
+                      "QHttpServerRequest can only be passed as a const reference");
+
+        using IsResponse = typename VTraits::template Special<I, QHttpServerResponse &&>;
+        static_assert(IsResponse::AssertCondition,
+                      "ViewHandler arguments error: "
+                      "QHttpServerResponse can only be passed as a universal reference");
+
+        using IsSpecial = CheckAny<IsRequest, IsResponse>;
+
+        static constexpr bool Valid = IsSpecial::Valid;
+        static constexpr bool StaticAssert = IsSpecial::StaticAssert;
+    };
+
+    struct Arguments {
+        template<int ... I>
+        struct ArgumentsReturn {
+            template<int Idx>
+            using Arg = ArgumentChecker<Idx>;
+            static constexpr bool Valid = QtPrivate::StaticMath::And::eval(Arg<I>::Valid...);
+            static constexpr bool StaticAssert = QtPrivate::StaticMath::And::eval(
+                    Arg<I>::StaticAssert...);
+            using Last = Arg<FunctionTraits::ArgumentIndexMax>;
+            static constexpr std::size_t Count = FunctionTraits::ArgumentCount;
+        };
+
+        template<int ... I>
+        static constexpr ArgumentsReturn<I...> eval(QtPrivate::IndexesList<I...>) noexcept
+        {
+            return ArgumentsReturn<I...>{};
+        }
+    };
+};
+
+} // namespace QtPrivate
+
+template <typename ViewHandler, bool DisableStaticAssert = false>
+struct QHttpServerAfterRequestViewTraits
+{
+    using Helpers = typename QtPrivate::AfterRequestViewTraitsHelper<ViewHandler, DisableStaticAssert>;
+    using Arguments = decltype(Helpers::Arguments::eval(typename Helpers::ArgumentIndexes{}));
+};
+
+QT_END_NAMESPACE
+
+#endif  // QHTTPSERVERVIEWTRAITS_H
diff --git a/src/httpserver/qhttpserverviewtraits_impl.h b/src/httpserver/qhttpserverviewtraits_impl.h
new file mode 100644
index 0000000..45c46d7
--- /dev/null
+++ b/src/httpserver/qhttpserverviewtraits_impl.h
@@ -0,0 +1,194 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Mikhail Svetkin <mikhail.svetkin@gmail.com>
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtHttpServer module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 or (at your option) any later version
+** approved by the KDE Free Qt Foundation. The licenses are as published by
+** the Free Software Foundation and appearing in the file LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QHTTPSERVERVIEWTRAITS_IMPL_H
+#define QHTTPSERVERVIEWTRAITS_IMPL_H
+
+#include <QtCore/qglobal.h>
+#include <QtCore/qmetatype.h>
+#include <QtCore/qnamespace.h>
+#include <QtCore/qobjectdefs.h>
+
+#include <functional>
+#include <tuple>
+#include <type_traits>
+
+QT_BEGIN_NAMESPACE
+
+namespace QtPrivate {
+
+template<typename T>
+struct RemoveCVRef
+{
+    using Type = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
+};
+
+
+template<bool classMember, typename ReturnT, typename ... Args>
+struct FunctionTraitsHelper
+{
+    static constexpr const int ArgumentCount = sizeof ... (Args);
+    static constexpr const int ArgumentIndexMax = ArgumentCount - 1;
+    static constexpr const bool IsClassMember = classMember;
+    using ReturnType = ReturnT;
+
+    template <int I>
+    struct Arg {
+        using Type = typename std::tuple_element<I, std::tuple<Args...>>::type;
+
+        using CleanType = typename QtPrivate::RemoveCVRef<Type>::Type;
+
+        static constexpr bool Defined = QMetaTypeId2<CleanType>::Defined;
+    };
+};
+
+template<bool classMember, typename ReturnT>
+struct FunctionTraitsHelper<classMember, ReturnT>
+{
+    static constexpr const int ArgumentCount = 0;
+    static constexpr const int ArgumentIndexMax = -1;
+    static constexpr const bool IsClassMember = classMember;
+    using ReturnType = ReturnT;
+
+    template <int I>
+    struct Arg {
+        using Type = std::false_type;
+        using CleanType = Type;
+        static constexpr bool Defined = QMetaTypeId2<CleanType>::Defined;
+    };
+};
+
+template<typename T>
+struct FunctionTraits;
+
+template<typename T>
+struct FunctionTraits : public FunctionTraits<decltype(&T::operator())>{};
+
+template<typename ReturnT, typename ... Args>
+struct FunctionTraits<ReturnT (*)(Args...)>
+    : public FunctionTraitsHelper<false, ReturnT, Args...>
+{
+};
+
+template<class ReturnT, class ClassT, class ...Args>
+struct FunctionTraits<ReturnT (ClassT::*)(Args...) const>
+    : public FunctionTraitsHelper<true, ReturnT, Args...>
+{
+    using classType = ClassT;
+};
+
+struct StaticMath {
+    template <template<typename> class Predicate, bool defaultValue>
+    struct Loop {
+        static constexpr bool eval() noexcept {
+            return defaultValue;
+        }
+
+        template<typename T, typename ... N>
+        static constexpr T eval(const T it, N ...n) noexcept {
+            return Predicate<T>::eval(it, eval(n...));
+        }
+    };
+
+    template<typename T>
+    struct SumPredicate {
+        static constexpr T eval(const T rs, const T ls) noexcept
+        {
+            return rs + ls;
+        }
+    };
+
+    template<typename T>
+    struct AndPredicate {
+        static constexpr T eval(const T rs, const T ls) noexcept
+        {
+            return rs && ls;
+        }
+    };
+
+    using Sum = Loop<SumPredicate, false>;
+    using And = Loop<AndPredicate, true>;
+    using Or = Sum;
+};
+
+template<typename ... T>
+struct CheckAny {
+    static constexpr bool Value = StaticMath::Or::eval(T::Value...);
+    static constexpr bool Valid = StaticMath::Or::eval(T::Valid...);
+    static constexpr bool StaticAssert = StaticMath::Or::eval(T::StaticAssert...);
+};
+
+template<typename ViewHandler, bool DisableStaticAssert>
+struct ViewTraits {
+    using FTraits = FunctionTraits<ViewHandler>;
+    using ArgumentIndexes = typename Indexes<FTraits::ArgumentCount>::Value;
+
+    template<int I, typename Special>
+    struct SpecialHelper {
+        using Arg = typename FTraits::template Arg<I>;
+        using CleanSpecialT = typename RemoveCVRef<Special>::Type;
+
+        static constexpr bool TypeMatched = std::is_same<typename Arg::CleanType, CleanSpecialT>::value;
+        static constexpr bool TypeCVRefMatched = std::is_same<typename Arg::Type, Special>::value;
+
+        static constexpr bool ValidPosition =
+            (I == FTraits::ArgumentIndexMax ||
+             I == FTraits::ArgumentIndexMax - 1);
+        static constexpr bool ValidAll = TypeCVRefMatched && ValidPosition;
+
+        static constexpr bool AssertCondition =
+            DisableStaticAssert || !TypeMatched || TypeCVRefMatched;
+
+        static constexpr bool AssertConditionOrder =
+            DisableStaticAssert || !TypeMatched || ValidPosition;
+
+        static constexpr bool StaticAssert = AssertCondition && AssertConditionOrder;
+
+        static_assert(AssertConditionOrder,
+                      "ViewHandler arguments error: "
+                      "QHttpServerRequest or QHttpServerResponder"
+                      " can only be the last argument");
+    };
+
+    template<int I, typename T>
+    struct Special {
+        using Helper = SpecialHelper<I, T>;
+        static constexpr bool Value = Helper::TypeMatched;
+        static constexpr bool Valid = Helper::ValidAll;
+        static constexpr bool StaticAssert = Helper::StaticAssert;
+        static constexpr bool AssertCondition = Helper::AssertCondition;
+    };
+};
+
+} // namespace QtPrivate
+
+QT_END_NAMESPACE
+
+#endif  // QHTTPSERVERVIEWTRAITS_IMPL_H