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Overview

Drogon is a C++17/20 based HTTP application framework. Drogon can be used to easily build various types of web application server programs using C++. Drogon is the name of a dragon in the American TV series “Game of Thrones” that I really like.

Drogon is a cross-platform framework, It supports Linux, macOS, FreeBSD, OpenBSD, HaikuOS, and Windows. Its main features are as follows:

• Use a non-blocking I/O network lib based on epoll (kqueue under macOS/FreeBSD) to provide high-concurrency, high-performance network IO, please visit the TFB Tests Results for more details;
• Provide a completely asynchronous programming mode;
• Support Http1.0/1.1 (server side and client side);
• Based on template, a simple reflection mechanism is implemented to completely decouple the main program framework, controllers and views.
• Support cookies and built-in sessions;
• Support back-end rendering, the controller generates the data to the view to generate the Html page. Views are described by CSP template files, C++ codes are embedded into Html pages through CSP tags. And the drogon command-line tool automatically generates the C++ code files for compilation;
• Support view page dynamic loading (dynamic compilation and loading at runtime);
• Provide a convenient and flexible routing solution from the path to the controller handler;
• Support filter chains to facilitate the execution of unified logic (such as login verification, Http Method constraint verification, etc.) before handling HTTP requests;
• Support https (based on OpenSSL);
• Support WebSocket (server side and client side);
• Support JSON format request and response, very friendly to the Restful API application development;
• Support file download and upload;
• Support gzip, brotli compression transmission;
• Support pipelining;
• Provide a lightweight command line tool, drogon_ctl, to simplify the creation of various classes in Drogon and the generation of view code;
• Support non-blocking I/O based asynchronously reading and writing database (PostgreSQL and MySQL(MariaDB) database);
• Support asynchronously reading and writing sqlite3 database based on thread pool;
• Support Redis with asynchronous reading and writing;
• Support ARM Architecture;
• Provide a convenient lightweight ORM implementation that supports for regular object-to-database bidirectional mapping;
• Support plugins which can be installed by the configuration file at load time;
• Support AOP with built-in joinpoints.
• Support C++ coroutines

A very simple example

Unlike most C++ frameworks, the main program of the drogon application can be kept clean and simple. Drogon uses a few tricks to decouple controllers from the main program. The routing settings of controllers can be done through macros or configuration file.

Below is the main program of a typical drogon application:

#include <drogon/drogon.h>
using namespace drogon;
int main()
{
    app().setLogPath("./")
         .setLogLevel(trantor::Logger::kWarn)
         .addListener("0.0.0.0", 80)
         .setThreadNum(16)
         .enableRunAsDaemon()
         .run();
}

It can be further simplified by using configuration file as follows:

#include <drogon/drogon.h>
using namespace drogon;
int main()
{
    app().loadConfigFile("./config.json").run();
}

Drogon provides some interfaces for adding controller logic directly in the main() function, for example, user can register a handler like this in Drogon:

app().registerHandler("/test?username={name}",
                    [](const HttpRequestPtr& req,
                       std::function<void (const HttpResponsePtr &)> &&callback,
                       const std::string &name)
                    {
                        Json::Value json;
                        json["result"]="ok";
                        json["message"]=std::string("hello,")+name;
                        auto resp=HttpResponse::newHttpJsonResponse(json);
                        callback(resp);
                    },
                    {Get,"LoginFilter"});

While such interfaces look intuitive, they are not suitable for complex business logic scenarios. Assuming there are tens or even hundreds of handlers that need to be registered in the framework, isn’t it a better practice to implement them separately in their respective classes? So unless your logic is very simple, we don’t recommend using above interfaces. Instead, we can create an HttpSimpleController as follows:

```c++ /// The TestCtrl.h file #pragma once #include <drogon/HttpSimpleController.h> using namespace drogon; class TestCtrl:public drogon::HttpSimpleController { public: void asyncHandleHttpRequest(const HttpRequestPtr& req, std::function<void (const HttpResponsePtr &)> &&callback) override; PATH_LIST_BEGIN PATH_ADD("/test",Get);

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