请用C++ 的 boost.asio 库实现一个简单示例

以下是一个简单的示例，使用boost.asio库实现了一个基于TCP协议的echo服务器和客户端。当客户端向服务器发送消息时，服务器将原封不动地返回该消息。

服务器端代码：

#include <iostream>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

int main()
{
    try
    {
        boost::asio::io_service io_service;

        //监听端口号为1234
        tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 1234));

        while (true)
        {
            tcp::socket socket(io_service);

            //等待客户端连接
            acceptor.accept(socket);

            boost::system::error_code error;

            //读取客户端发送的消息
            boost::asio::streambuf buffer;
            boost::asio::read_until(socket, buffer, "\n", error);
            if (error)
                std::cerr << "Error reading: " << error.message() << std::endl;
            else
            {
                std::string message = boost::asio::buffer_cast<const char*>(buffer.data());
                std::cout << "Received message: " << message;

                //将消息原封不动地返回
                boost::asio::write(socket, boost::asio::buffer(message), error);
                if (error)
                    std::cerr << "Error writing: " << error.message() << std::endl;
            }
        }
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << std::endl;
    }

    return 0;
}

客户端代码：

#include <iostream>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

int main()
{
    try
    {
        boost::asio::io_service io_service;

        //连接服务器端口号为1234
        tcp::resolver resolver(io_service);
        tcp::resolver::query query("localhost", "1234");
        tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
        tcp::socket socket(io_service);
        boost::asio::connect(socket, endpoint_iterator);

        std::string message;
        std::cout << "Enter message: ";
        std::getline(std::cin, message);

        //向服务器发送消息
        boost::asio::write(socket, boost::asio::buffer(message + "\n"));

        //读取服务器返回的消息
        boost::asio::streambuf buffer;
        boost::asio::read_until(socket, buffer, "\n");
        std::string response = boost::asio::buffer_cast<const char*>(buffer.data());
        std::cout << "Received response: " << response;
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << std::endl;
    }

    return 0;
}