ReactiveX 学习笔记（24）使用 RxCpp + C++ REST SDK 调用 REST API

JSON : Placeholder

JSON : Placeholder (https://jsonplaceholder.typicode.com/) 是一个用于测试的 REST API 网站。
以下使用 Task API/Rx.NET + Json.NET 调用该网站的 REST API，获取字符串以及 JSON 数据。

• GET /posts/1
• GET /posts
• POST /posts
• PUT /posts/1
• DELETE /posts/1

所有 GET API 都返回JSON数据，格式（JSON-Schema）如下：

{
  "type":"object",
  "properties": {
    "userId": {"type" : "integer"},
    "id": {"type" : "integer"},
    "title": {"type" : "string"},
    "body": {"type" : "string"}
  }
}

安装 C++ REST SDK

$ brew install cpprestsdk
$ brew install boost
$ brew install libressl

安装 "JSON for Modern C++"

$ brew tap nlohmann/json
$ brew install nlohmann_json

下载 RxCpp

$ git clone --recursive https://github.com/ReactiveX/RxCpp.git

创建工程

打开 Xcode，File / New / Project...
在向导的第1页选 macOS / Command Line Tool
在向导的第2页语言选 C++，Product Name 填上任意名称
在向导的第3页选择任意文件夹，点击 Create 创建工程。

配置工程

将 System Header Search Paths 设置为
/usr/local/Cellar/cpprestsdk/2.10.2/include
/usr/local/Cellar/boost/1.67.0_1/include
/usr/local/Cellar/libressl/2.7.4/include
/usr/local/Cellar/nlohmann_json/3.1.2/include
RxCpp安装文件夹/Rx/v2/src

将 Library Search Paths 设置为
/usr/local/Cellar/cpprestsdk/2.10.2/lib
/usr/local/Cellar/boost/1.67.0_1/lib
/usr/local/Cellar/libressl/2.7.4/lib

将 Other Linker Flags 设置为
-lcpprest -lboost_system -lboost_thread-mt -lboost_chrono-mt -lssl -lcrypto

cpprestsdk: Undefined symbols for architecture x86_64

Post

在工程中添加 post.hpp，内容如下

#ifndef Post_hpp
#define Post_hpp

#include <iostream>
#include <nlohmann/json.hpp>
using nlohmann::json;

struct Post {
    int userId;
    int id;
    std::string title;
    std::string body;
};
void to_json(json& j, const Post& p);
void from_json(const json& j, Post& p);
std::ostream& operator<<(std::ostream& out, const Post& p);

#endif /* Post_hpp */

在工程中添加 post.cpp，内容如下

#include "Post.hpp"
#include <boost/algorithm/string/replace.hpp>
using namespace std;

void to_json(json& j, const Post& p) {
    j = json{{"userId", p.userId}, {"id", p.id}, {"title", p.title}, {"body", p.body}};
}
void from_json(const json& j, Post& p) {
    p.userId = j.at("userId").get<int>();
    p.id = j.at("id").get<int>();
    p.title = j.at("title").get<string>();
    p.body = boost::algorithm::replace_all_copy(j.at("body").get<string>(), "
", "\n");
}
std::ostream& operator<<(std::ostream& out, const Post& p) {
    cout << "Post {userId = " << p.userId
        << ", id = " << p.id
        << ", title = "" << p.title
        << "", body = "" << p.body
        << ""}";
    return out;
}

RestApi

在工程中添加 RestApi.hpp，内容如下

#ifndef RestApi_hpp
#define RestApi_hpp

#include <cpprest/http_client.h>
#include <cpprest/filestream.h>
#include <cpprest/json.h>

using namespace utility;                    // Common utilities like string conversions
//using namespace web;                        // Common features like URIs.
using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features
using namespace concurrency::streams;       // Asynchronous streams

#include "rxcpp/rx.hpp"
namespace Rx {
    using namespace rxcpp;
    using namespace rxcpp::sources;
    using namespace rxcpp::operators;
    using namespace rxcpp::util;
}
using namespace Rx;

#include <nlohmann/json.hpp>
using nlohmann::json;

template<class T>
struct RestApi {
    http_client client;
    
    RestApi(const uri &base_uri) : client(base_uri) {}
    
    observable<string_t> getString(const string_t &path_query_fragment) {
        return observable<>::create<string_t>(
        [&](subscriber<string_t> s){
            client
            .request(methods::GET, path_query_fragment)
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    s.on_next(v);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }
    
    observable<T> getObject(const string_t &path_query_fragment) {
        return observable<>::create<T>(
        [&](subscriber<T> s){
            client
            .request(methods::GET, path_query_fragment)
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    json j = json::parse(v);
                    T t = j;
                    s.on_next(t);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }
    
    observable<T> getArray(const string_t &path_query_fragment) {
        return observable<>::create<T>(
        [&](subscriber<T> s){
            client
            .request(methods::GET, path_query_fragment)
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    json j = json::parse(v);
                    std::vector<T> vec = j;
                    for(const auto& t : vec)
                        s.on_next(t);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }

    observable<string_t> createObject(const string_t& url, const T& obj) {
        return observable<>::create<string_t>(
        [&](subscriber<string_t> s){
            json j = obj;
            client
            .request(methods::POST, url, j.dump(), U("application/json"))
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    s.on_next(v);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }
    
    observable<string_t> updateObject(const string_t& url, const T& obj) {
        return observable<>::create<string_t>(
        [&](subscriber<string_t> s){
            json j = obj;
            client
            .request(methods::PUT, url, j.dump(), U("application/json"))
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    s.on_next(v);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }
    
    observable<string_t> deleteObject(const string_t& url) {
        return observable<>::create<string_t>(
        [&](subscriber<string_t> s){
            client
            .request(methods::DEL, url)
            .then([](http_response response) -> pplx::task<string_t> {
                return response.extract_string();
            })
            .then([&](pplx::task<string_t> previousTask) {
                try {
                    string_t const & v = previousTask.get();
                    s.on_next(v);
                    s.on_completed();
                } catch (http_exception const & e) {
                    s.on_error(std::current_exception());
                }
            })
            .wait();
        });
    }
};

#endif /* RestApi_hpp */

main

将 main.cpp 的内容改为

#include "Post.hpp"
#include "RestApi.hpp"

using namespace std;

int main(int argc, char* argv[])
{
    RestApi<Post> api(U("https://jsonplaceholder.typicode.com/"));
    api.getString(U("posts/1")).subscribe([](const string_t& v){cout << v << endl;});
    api.getObject(U("posts/1")).subscribe([](const Post& v){cout << v << endl;});
    api.getArray(U("posts")).take(2).subscribe([](const Post& v){cout << v << endl;});
    Post o;
    o.id = 0;
    o.userId = 101;
    o.title = U("test title");
    o.body = U("test body");
    api.createObject(U("posts"), o).subscribe([](string_t v){cout << v << endl;});
    api.updateObject(U("posts/1"), o).subscribe([](string_t v){cout << v << endl;});
    api.deleteObject(U("posts/1")).subscribe([](string_t v){cout << v << endl;});

    return 0;
}

输出结果

{
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"
}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 1, title = "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", body = "quia et suscipit
suscipit recusandae consequuntur expedita et cum
reprehenderit molestiae ut ut quas totam
nostrum rerum est autem sunt rem eveniet architecto"}
Post {userId = 1, id = 2, title = "qui est esse", body = "est rerum tempore vitae
sequi sint nihil reprehenderit dolor beatae ea dolores neque
fugiat blanditiis voluptate porro vel nihil molestiae ut reiciendis
qui aperiam non debitis possimus qui neque nisi nulla"}
{
  "body": "test body",
  "id": 101,
  "title": "test title",
  "userId": 101
}
{
  "body": "test body",
  "id": 1,
  "title": "test title",
  "userId": 101
}
{}