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Building RESTful Web Service Using C++, Swagger UI And Auto-Documented Endpoints

by LeonidAugust 5th, 2020

Too Long; Didn't Read

This is a 5 minutes tutorial how-to-use Oat++ (AKA oatpp) web framework to build your own C++ performant web-service and integrate it with Swagger-UI. It is a zero-dependency framework, so NO additional installations are required. We are able to build services using Oatpp, a zero dependency-free web service, using C++, Swagger UI and Auto-Documented Endpoints. For Windows: Git, CMake, MSVC. For Mac/Linux : Git, build-essentials, C.Make, make-up, C-Make, and make-down.

featured image - Building RESTful Web Service Using C++, Swagger UI And Auto-Documented Endpoints

This is a 5 minutes tutorial how-to-use Oat++ (AKA oatpp) 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/

On Mac/Linux:

$ mkdir build && cd build/
$ cmake ..
$ make install

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

On Windows:

$ MD build
$ cd build/
$ cmake ..
$ cmake --build . --target INSTALL

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/

Build “oatpp-starter” on Mac/Linux

$ mkdir build && cd build/
$ cmake ..
$ make

Build “oatpp-starter” on Windows

$ MD build
$ cd build/
$ cmake ..
$ cmake --build .

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!"}

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

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/

Linux/Mac:

$ mkdir build && cd build/
$ cmake ..
$ make install

Windows:

$ MD build
$ cd build/
$ cmake ..
$ cmake --build . --target INSTALL

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

...

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
    );
  }());

};

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);

  ...

}

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);
}

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);
}

Build and run… Refresh…