ApiClient Example

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Example project how-to use oatpp ApiClient and how it works

About ApiClient

Oatpp ApiClient is a mechanism which enables you to generate Web Api Clients in declarative manner. Under the hood it uses provided RequestExecutor to perform http requests. Thus you are abstracted from the low-level http-client library implementation and can substitute any other http-client library at any time with zero code changes. Roughly you may treat oatpp ApiClient as Java Retrofit for C++.

In this example you can configure to use such RequestExecutors:

Example overview

In this example you will find:

  • ApiClient built for http://httpbin.org/ web service.
  • Simple (Synchronous) API calls example.
  • Async API calls example processed with oatpp::async::Executor. See Oatpp Coroutines.

Project layout

|- CMakeLists.txt                          // projects CMakeLists.txt
|- src/
|   |- DemoApiClient.hpp                   // ApiClient built for http://httpbin.org/ web service
|   |- DemoApiModels.hpp                   // DTOs objects for DemoApiClient
|   |- SimpleExample.hpp                   // Simple (Synchronous) API calls example
|   |- AsyncExample.hpp                    // Async API calls example
|   |- App.cpp                             // main is here
|- test/                                   // test folder
|- utility/install-oatpp-modules.sh        // utility script to install required oatpp-modules.

Build and Run

Using CMake


  • Curl installed. You may refer to this sh script - how to install curl - install-curl.sh.
    Or try something like $ apk add curl-dev

  • oatpp and oatpp-curl modules installed. You may run utility/install-oatpp-modules.sh script to install required oatpp modules.

$ mkdir build && cd build
$ cmake ..
$ make 
$ ./example-api-client-exe      # - run application.

In Docker

$ docker build -t example-api-client .
$ docker run -t example-api-client

ApiClient declaration overview

Use API_CALL for simple (synchronous) calls.
Use API_CALL_ASYNC for non-blocking Async calls.

class DemoApiClient : public oatpp::web::client::ApiClient {
#include OATPP_CODEGEN_BEGIN(ApiClient)
  API_CALL("GET", "get", doGet)
  API_CALL("POST", "post", doPost, BODY_STRING(String, body))
  API_CALL_ASYNC("GET", "get", doGetAsync)
  API_CALL_ASYNC("POST", "post", doPostAsync, BODY_STRING(String, body))

#include OATPP_CODEGEN_END(ApiClient)

Example calls overview


  auto data = client->doGet()->readBodyToString();
  OATPP_LOGD(TAG, "[doGet] data='%s'", data->c_str());

  auto data = client->doPost("Some data passed to POST")->readBodyToString();
  OATPP_LOGD(TAG, "[doPost] data='%s'", data->c_str());


class SendCoroutine : public oatpp::async::Coroutine<SendCoroutine> {
  std::shared_ptr<DemoApiClient> m_client;

  SendCoroutine(const std::shared_ptr<DemoApiClient> client) : m_client(client) {}

  Action act() override {
    return m_client->doPostAsync("<POST-DATA-HERE>").callbackTo(&SendDtoCoroutine::onResponse);

  Action onResponse(const std::shared_ptr<Response>& response) {
    return response->readBodyToStringAsync().callbackTo(&SendDtoCoroutine::onBody);

  Action onBody(const oatpp::String& body) {
    OATPP_LOGD(TAG, "[SendCoroutine. doPostAsync] data='%s'", body->c_str());
    return finish();


Request executor configuration

In App.cpp method run. Try to substitute different RequestExecutors by switching from Curl to oatpp built-in request executor.

void run(){
  /* Create ObjectMapper for serialization of DTOs  */
  auto objectMapper = oatpp::parser::json::mapping::ObjectMapper::createShared();
  /* Create RequestExecutor which will execute ApiClient's requests */
  //auto requestExecutor = createOatppExecutor();  // <-- Uncomment this
  auto requestExecutor = createCurlExecutor();     // <-- Comment this
  /* DemoApiClient uses DemoRequestExecutor and json::mapping::ObjectMapper */
  /* ObjectMapper passed here is used for serialization of outgoing DTOs */
  auto client = DemoApiClient::createShared(requestExecutor, objectMapper);