DEV Community

Cover image for C++ RESTful web service with Swagger-UI and auto-documented endpoints
Oat++ profile image Leonid Stryzhevskyi
Leonid Stryzhevskyi for Oat++

Posted on • Originally published at Medium

C++ RESTful web service with Swagger-UI and auto-documented endpoints

#webdev #cpp #rest #swagger

This is a 5 minutes tutorial how-to-use Oat++ web framework to build your own C++ performant web-service and integrate it with Swagger-UI.

Pre Requirements

  • For Mac/Linux: Git, build-essentials, CMake.
  • For Windows: Git, CMake, MSVC.

Install Oat++

Clone oatpp repo:

$ git clone https://github.com/oatpp/oatpp
$ cd oatpp/
Enter fullscreen mode Exit fullscreen mode

On Mac/Linux:

$ mkdir build && cd build/
$ cmake ..
$ make install
Enter fullscreen mode Exit fullscreen mode

For more detailed instructions see - installing Oat++ on Unix/Linux.

On Windows:

$ MD build
$ cd build/
$ cmake ..
$ cmake --build . --target INSTALL
Enter fullscreen mode Exit fullscreen mode

For more detailed instructions see - installing Oat++ on Windows.

Now we are able to build services using Oat++. It is a zero-dependency framework, so NO additional installations are required.

Build and Run Starter Project

Clone “oatpp-starter”

$ git clone --depth=1 https://github.com/oatpp/oatpp-starter my-service
$ cd my-service/
Enter fullscreen mode Exit fullscreen mode

Build “oatpp-starter” on Mac/Linux

$ mkdir build && cd build/
$ cmake ..
$ make
Enter fullscreen mode Exit fullscreen mode

Build “oatpp-starter” on Windows

$ MD build
$ cd build/
$ cmake ..
$ cmake --build .
Enter fullscreen mode Exit fullscreen mode

Run compiled executable:

  • Mac/Linux - $ ./my-project-exe
  • Windows - $ .\src\Debug\my-project-exe.exe

Now go to localhost:8000 and make sure that you can see the response from server

{"statusCode": 200, "message": "Hello World!"}
Enter fullscreen mode Exit fullscreen mode

Project Structure 

- src/
   |
   |- controller/              
   |   |
   |   |- MyController.hpp  // Endpoints are declared here
   |
   |- dto/
   |   |
   |   |- DTOs.hpp          // DTOs are here
   |
   |- App.cpp               // main is here
   |- AppComponent.hpp      // Application components configuration
Enter fullscreen mode Exit fullscreen mode

MyController class - contains declared endpoints and their info together with additional Swagger annotations.

MyDto class - resides in DTOs.hpp. Describes the Data-Transfer-Object used in the "Hello World" response mentioned above. In oatpp DTOs are used in ObjectMapping and Serialization/Deserialization.

App.cpp file - this is an applications' entry point. Here Application Components are loaded, Controllers' endpoints are added to the Router, and the server starts.

AppComponent class - basically it is a collection of components that will be loaded on application start. Here we configure things like which ConnectionProvider to use, port to listen to, which ObjectMapper to use.

Integrate Swagger-UI

To integrate Swagger-UI in the project we have to do the following:

  • Clone and install oatpp-swagger module
  • Add oatpp-swagger to CMakeLists.txt
  • Add corresponding code to AppComponent.hpp and App.cpp

Install oatpp-swagger

$ git clone https://github.com/oatpp/oatpp-swagger
$ cd oatpp-swagger/
Enter fullscreen mode Exit fullscreen mode

Linux/Mac:

$ mkdir build && cd build/
$ cmake ..
$ make install
Enter fullscreen mode Exit fullscreen mode

Windows:

$ MD build
$ cd build/
$ cmake ..
$ cmake --build . --target INSTALL
Enter fullscreen mode Exit fullscreen mode

Add oatpp-swagger to CMakeLists.txt

...

## add libs
find_package(oatpp          1.1.0 REQUIRED)
find_package(oatpp-swagger  1.1.0 REQUIRED) # <-- add this

target_link_libraries(${project_name}-lib
        PUBLIC oatpp::oatpp
        PUBLIC oatpp::oatpp-swagger         # <-- add this
)

## define path to swagger-ui res folder
add_definitions( 
  -DOATPP_SWAGGER_RES_PATH="${OATPP_BASE_DIR}/bin/oatpp-swagger/res"
) # <-- add this

...
Enter fullscreen mode Exit fullscreen mode

AppComponent.hpp

Here we add oatpp::swagger::DocumentInfo and oatpp::swagger::Resources components which give general information about our API document and specify a path to Swagger-UI resources:

#include "oatpp-swagger/Model.hpp"
#include "oatpp-swagger/Resources.hpp"

...

class AppComponent {

...

  /**
   *  General API docs info
   */
  OATPP_CREATE_COMPONENT(
    std::shared_ptr<oatpp::swagger::DocumentInfo>, 
    swaggerDocumentInfo
  )([] {

    oatpp::swagger::DocumentInfo::Builder builder;
    builder
     .setTitle("My Demo Service with Swagger-UI")
     .setDescription("C++/oat++ Web Service with Swagger-UI")
     .setVersion("1.0")
     .setContactName("Mr. Developer")
     .setContactUrl("https://oatpp.io/")
     .setLicenseName("Apache License, Version 2.0")
     .setLicenseUrl("http://www.apache.org/licenses/LICENSE-2.0")
     .addServer("http://localhost:8000", "server on localhost");
     return builder.build();
  }());

  /**
   *  Swagger-Ui Resources
   */
  OATPP_CREATE_COMPONENT(
    std::shared_ptr<oatpp::swagger::Resources>, 
    swaggerResources
  )([] {
    return oatpp::swagger::Resources::loadResources(
      OATPP_SWAGGER_RES_PATH
    );
  }());

};
Enter fullscreen mode Exit fullscreen mode

App.cpp

Here we add oatpp::swagger::Controller to Router with the list of endpoints we want to document

#include "oatpp-swagger/Controller.hpp"

...

void run() {

  ...

  auto docEndpoints =
    oatpp::swagger::Controller::Endpoints::createShared();

  docEndpoints->pushBackAll(myController->getEndpoints());

  auto swaggerController =
    oatpp::swagger::Controller::createShared(docEndpoints);

  swaggerController->addEndpointsToRouter(router);

  ...

}
Enter fullscreen mode Exit fullscreen mode

Now if everything is ok, and OATPP_SWAGGER_RES_PATH path is set correctly in the AppComponent.hpp, we should be able to build and run our project and see Swagger-UI at http://localhost:8000/swagger/ui in the browser

Additional Info for Endpoint

Our endpoint is already present in the document with the proper method and path. Oat++ automatically documents most of the endpoints’ info, such as endpoint name, method, path, parameter names, and parameter types. However, there are things that should be specified explicitly.

Annotate endpoint with additional information

In the file MyController.hpp we add ENDPOINT_INFO above the root ENDPOINT with summary and response information:

ENDPOINT_INFO(root) {
  info->summary = "Root endpoint with 'Hello World!!!' message";
  info->addResponse<Object<MyDto>>(
    Status::CODE_200, 
    "application/json"
  );
}
ENDPOINT("GET", "/", root) {
  auto dto = MyDto::createShared();
  dto->statusCode = 200;
  dto->message = "Hello World!";
  return createDtoResponse(Status::CODE_200, dto);
}
Enter fullscreen mode Exit fullscreen mode

Build, Run, and go to http://localhost:8000/swagger/ui in the browser. Refresh

Notice, that summary is added to the endpoint and MyDto schema automatically documented in the Models.

Expand endpoint info and check that response is documented correctly

Basically that’s it 🎉

Now we have Swagger-UI integrated into our project and we can easily add and document endpoints!

Add endpoint

Let’s add one more "echo" endpoint and see how it is documented in the swagger.

In the file MyController.hpp:

ENDPOINT_INFO(echo) {
  info->summary = "Echo endpoint with custom message";
  info->addResponse<Object<MyDto>>(
    Status::CODE_200,
    "application/json"
  );
}
ENDPOINT("POST", "/echo/status/{status}", echo,
         PATH(Int32, status), BODY_STRING(String, message)) {
  auto dto = MyDto::createShared();
  dto->statusCode = status;
  dto->message = message;
  return createDtoResponse(Status::CODE_200, dto);
}
Enter fullscreen mode Exit fullscreen mode

Build and run… Refresh…

Expand echo endpoint info - you can see the "status" and "Request Body" parameters:

Put in some values:

Execute the request and verify that you have a correct response from the server:

That’s it. You may experiment by adding more endpoints, playing with parameters, and DTO-fields to see how it is being documented in Swagger-UI.

Useful Links

‌

Top comments (0)

Read next

marcinjaniak profile image

Authorizing endpoints of external apps in k8s

Marcin Janiak -

dhyfullah_ghalebahmed_d1 profile image

Create new action in Laravel nova for download PDF for all websites pages

Dhyfullah Ghaleb ahmed -

mitchell_cheng profile image

Text compression & Code splitting & Modern image formats - Performance optimization

Mitchell -

mds05 profile image

Understanding the Spring Security Architecture

Md Shahriar -