Modify the method to generate the 404 page (#240)

lib/inc/drogon/NotFound.h

@@ -15,7 +15,12 @@
  */
 
 #include <drogon/DrTemplate.h>
-
+namespace drogon
+{
+/**
+ * @brief This class is used by the drogon to generate the 404 page. Users don't
+ * use this class directly.
+ */
 class NotFound : public drogon::DrTemplate<NotFound>
 {
   public:
@@ -23,3 +28,4 @@ class NotFound : public drogon::DrTemplate<NotFound>
     virtual ~NotFound(){};
     virtual std::string genText(const drogon::HttpViewData &) override;
 };
+}  // namespace drogon

lib/src/HttpResponseImpl.cc

@@ -78,8 +78,13 @@ HttpResponsePtr HttpResponse::newNotFoundResponse()
         std::call_once(once, []() {
             HttpViewData data;
             data.insert("version", getVersion());
-            notFoundResp = HttpResponse::newHttpViewResponse("NotFound", data);
+            notFoundResp =
+                HttpResponse::newHttpViewResponse("drogon::NotFound", data);
             notFoundResp->setStatusCode(k404NotFound);
+            notFoundResp->setExpiredTime(0);
+            auto str = static_cast<HttpResponseImpl *>(notFoundResp.get())
+                           ->renderToString();
+            LOG_TRACE << *str;
         });
         return notFoundResp;
     }