Add registerMiddleware (drogonframework#2052)

lib/inc/drogon/HttpAppFramework.h

@@ -691,6 +691,24 @@ class DROGON_EXPORT HttpAppFramework : public trantor::NonCopyable
         return *this;
     }
 
+    /// Register middleware objects created and initialized by the user
+    /**
+     * This method is similar to the above method.
+     */
+    template <typename T>
+    HttpAppFramework &registerMiddleware(
+        const std::shared_ptr<T> &middlewarePtr)
+    {
+        static_assert(std::is_base_of<HttpMiddlewareBase, T>::value,
+                      "Error! Only middleware objects can be registered here");
+        static_assert(!T::isAutoCreation,
+                      "Middleware created and initialized "
+                      "automatically by drogon cannot be "
+                      "registered here");
+        DrClassMap::setSingleInstance(middlewarePtr);
+        return *this;
+    }
+
     /// Register a default handler into the framework when no handler matches
     /// the request. If set, it is executed if the static file router does
     /// not find any file corresponding to the request. Thus it replaces

lib/tests/integration_test/client/main.cc

@@ -1053,7 +1053,7 @@ void doTest(const HttpClientPtr &client, std::shared_ptr<test::Case> TEST_CTX)
                         [TEST_CTX, req](ReqResult r,
                                         const HttpResponsePtr &resp) {
                             REQUIRE(r == ReqResult::Ok);
-                            CHECK(resp->body() == "123test321");
+                            CHECK(resp->body() == "1234test4321");
                         });
 
     req = HttpRequest::newHttpRequest();

lib/tests/integration_test/server/MiddlewareTest.cc

@@ -132,7 +132,8 @@ class MiddlewareTest : public drogon::HttpController<MiddlewareTest>
                   Get,
                   "Middleware1",
                   "Middleware2",
-                  "Middleware3");
+                  "Middleware3",
+                  "Middleware4");
     ADD_METHOD_TO(MiddlewareTest::handleRequest,
                   "/test-middleware-block",
                   Get,

lib/tests/integration_test/server/main.cc

@@ -154,6 +154,30 @@ std::string_view fromRequest(const HttpRequest &req)
 }
 }  // namespace drogon
 
+class Middleware4 : public drogon::HttpMiddleware<Middleware4, false>
+{
+  public:
+    Middleware4()
+    {
+        LOG_DEBUG << "Middleware4\n";
+    };
+
+    void invoke(const HttpRequestPtr &req,
+                MiddlewareNextCallback &&nextCb,
+                MiddlewareCallback &&mcb) override
+    {
+        auto ptr = req->attributes()->get<std::shared_ptr<std::string>>(
+            "test-middleware");
+        ptr->append("4");
+
+        nextCb([req, ptr, mcb = std::move(mcb)](const HttpResponsePtr &resp) {
+            ptr->append("4");
+            resp->setBody(*ptr);
+            mcb(resp);
+        });
+    }
+};
+
 /// Some examples in the main function show some common functions of drogon. In
 /// practice, we don't need such a lengthy main function.
 int main()
@@ -268,6 +292,10 @@ int main()
     app().registerFilter(filterPtr);
     app().setIdleConnectionTimeout(30s);
 
+    // Install custom Middleware
+    auto middlewarePtr = std::make_shared<Middleware4>();
+    app().registerMiddleware(middlewarePtr);
+
     // AOP example
     app().registerBeginningAdvice(
         []() { LOG_DEBUG << "Event loop is running!"; });