（1）ASIO

（一）IO服务、IO对象基础介绍

// TestBoost.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//
/*
* 使用 Boost.Asio 进行异步数据处理：
* (1)I/O 服务:抽象了操作系统的接口，允许第一时间进行异步数据处理
* (2)I/O 对象:则用于初始化特定的操作
*/
#include <boost/asio.hpp>
#include <iostream> 

void handler5(const boost::system::error_code& error)
{
    std::cout << "定时器5结束返回！" << std::endl;
}

void handler10(const boost::system::error_code& error)
{
    std::cout << "定时器10结束返回！" << std::endl;
}

int main()
{
    //定义了一个 I/O 服务,所有 I/O 对象通常都需要一个 I/O 服务作为它们的构造函数的第一个参数
    boost::asio::io_service io_service;  
    //定义定时器
    boost::asio::deadline_timer timer5(io_service,boost::posix_time::seconds(5));
    //启动异步操作 在此不阻塞
    timer5.async_wait(handler5);

    boost::asio::deadline_timer timer10(io_service, boost::posix_time::seconds(10));
    timer10.async_wait(handler10);

    //在此阻塞：控制权被操作系统接管定时器结束后调用handler函数
    //如果此处不想被阻塞，可以在一个新的线程内部调用 run()，此时会阻塞那个新的线程
    //一旦特定的 I/O 服务(io_service)的所有异步操作都完成了，控制权就会返回给 run() 方法
    io_service.run();

    //以上两个handler分别在5s 10s后执行，然后才run阻塞结束返回main
    std::cout << "主程序结束" << std::endl;
}

//运行结果
PS C:\Users\dujinwei\source\repos\TestBoost\Debug> .\TestBoost.exe
定时器5结束返回！
定时器10结束返回！
主程序结束

（二）简单异步网络请求

/*
* 网络编程
* 流程 域名解析->返回解析IP地址->创建连接
*/

#include <boost/asio.hpp>
#include <boost/array.hpp>
#include <iostream>
#include <string>
#include <sstream>

boost::asio::io_service io_service;
boost::asio::ip::tcp::resolver resolver(io_service);  //域名解析句柄
boost::asio::ip::tcp::socket socketIp(io_service);      //连接句柄
boost::array<char, 4096> buffer;                      //缓冲区，接收返回数据

//（3）接受请求返回的数据 bytes_transferred 接收一次数据的大小，接收完所有数据后 read_handler 报错不再执行
void read_handler(const boost::system::error_code& error, std::size_t bytes_transferred)
{
    if (!error)
    {
        std::cout << std::string(buffer.data(), bytes_transferred) << std::endl;
        //循环接收数据
        socketIp.async_read_some(boost::asio::buffer(buffer), read_handler);
    }
}

//（2）创建连接
void connect_handler(const boost::system::error_code& error)
{
    if (!error)
    {
        std::string host = "www.baidu.com";
        std::stringstream stream;
        stream << "GET https://" << host << " HTTP/1.0\r\n";
        stream << "Accept: */*\r\n";
        //stream << "Accept-Encoding: gzip, deflate, br\r\n";//不要编码，否则还得多一个解码的步骤
        stream << "Accept-Language: zh-Hans-CN, zh-Hans; q=0.8, en-US; q=0.5, en; q=0.3\r\n";
        stream << "Connection: Keep-Alive\r\n";
        stream << "Host: " << host << "\r\n";
        stream << "User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/17.17134\r\n";
        stream << "\r\n";

        char buff[1024];
        int ret = 0;
        ret = snprintf(buff, sizeof(buff), "%s", stream.str().c_str());

        boost::asio::write(socketIp, boost::asio::buffer(buff));
        socketIp.async_read_some(boost::asio::buffer(buffer), read_handler);
    }
}

//（1）域名解析 返回解析后的IP地址供连接使用
void resolve_handler(const boost::system::error_code& error, boost::asio::ip::tcp::resolver::iterator iIp)
{
    if (!error)
    {
        //创建连接 iIp 为域名解析后返回的IP地址
        socketIp.async_connect(*iIp, connect_handler);
    }
}



int main()
{
    //创建一个查询
    boost::asio::ip::tcp::resolver::query query("www.baidu.com", "80");

    //解析域名 调用resolve_handler
    resolver.async_resolve(query, resolve_handler);

    io_service.run();
}

//运行结果
PS C:\Users\dujinwei\source\repos\TestBoost\Debug> .\TestBoost.exe
HTTP/1.0 200 OK
Accept-Ranges: bytes
Cache-Control: max-age=1
Content-Length: 7382
Content-Type: text/html
Date: Tue, 07 Sep 2021 13:05:51 GMT
Etag: "1cd6-5480030886bc0"
Expires: Tue, 07 Sep 2021 13:05:52 GMT
Last-Modified: Wed, 08 Feb 2017 07:55:35 GMT
P3p: CP=" OTI DSP COR IVA OUR IND COM "
P3p: CP=" OTI DSP COR IVA OUR IND COM "
Server: Apache
Set-Cookie: BAIDUID=1D94402EBAFCE7B5FE67770DDED0C95E:FG=1; expires=Wed, 07-Sep-22 13:05:51 GMT; max-age=31536000; path=/; domain=.baidu.com; version=1
Set-Cookie: BAIDUID=1D94402EBAFCE7B561CD6D4699CFA9D8:FG=1; expires=Wed, 07-Sep-22 13:05:51 GMT; max-age=31536000; path=/; domain=.baidu.com; version=1
Vary: Accept-Encoding,User-Agent

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