如何使用 Boost ASIO 创建到服务器的多个连接

Question

我使用 Boost Asio 作为 TCP 网络解决方案。

这是我的服务器代码：

Server.h ：

#ifndef VIBRANIUM_CORE_SERVER_H
#define VIBRANIUM_CORE_SERVER_H
#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
#include <boost/asio.hpp>
#include <deque>
#include "Logger.h"
#include "Client.h"

using boost::asio::ip::tcp;
namespace Vibranium {
    class Server {
    public:
        Server(boost::asio::io_service &io_service, short port)
                : acceptor_(io_service, tcp::endpoint(tcp::v4(), port)),
                  socket_(io_service) {
            do_accept();
            Logger::Log("Server Started! Listening on Port("+std::to_string(port)+")", Logger::Success, true);
        }
        static std::deque<std::shared_ptr<Client>> Clients;

    private:
        void do_accept();
        int incrementor;
        tcp::acceptor acceptor_;
        tcp::socket socket_;
    };

}


#endif //VIBRANIUM_CORE_SERVER_H

Server.cpp ：

#include "Server.h"
#include "Client.h"

using namespace Vibranium;
std::deque<std::shared_ptr<Client>> Server::Clients;
void Server::do_accept()
{
    acceptor_.async_accept(socket_,
   [this](boost::system::error_code ec)
   {
       if (!ec)
       {
           incrementor++;
           Logger::Log("New Connection (ID: " + std::to_string(incrementor) + ")",Logger::Success);
           std::shared_ptr<Client> c = std::make_shared<Client>(std::move(socket_));
           c->start();
           c->connectionId = incrementor;
           Server::Clients.push_back(c);
       }

       do_accept();
   });
}

Client.h ：

#ifndef VIBRANIUM_CORE_CLIENT_H
#define VIBRANIUM_CORE_CLIENT_H

#include <cstdlib>
#include <iostream>
#include <memory>
#include <utility>
#include <boost/asio.hpp>

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

namespace Vibranium{
    class Client: public std::enable_shared_from_this<Client>
    {
    public:
        Client(tcp::socket socket)
        : socket_(std::move(socket))
        {
        }
        void start();
        int connectionId;
    private:
        void do_read();
        void do_write(std::size_t length);
        tcp::socket socket_;
        enum { max_length = 1024 };
        char data_[max_length];
    };
}
#endif //VIBRANIUM_CORE_CLIENT_H

Client.cpp ：

#include "Client.h"
#include "Server.h"

void Vibranium::Client::start() {
    do_read();
}

void Vibranium::Client::do_read() {
    auto self(shared_from_this());
    socket_.async_read_some(boost::asio::buffer(data_, max_length),
    [this, self](boost::system::error_code ec, std::size_t length)
    {
        if ((boost::asio::error::eof == ec) || (boost::asio::error::connection_reset == ec))
        {
            Logger::Log("Disconnected ID: " + std::to_string(connectionId),Logger::Error, true);
            for (int i = 0; i < Server::Clients.size(); ++i) {
                if(Server::Clients[i]->connectionId == connectionId)
                    Server::Clients.erase(Server::Clients.begin()+i);
            }
        }
        else
        {
            std::cout.write(data_, length);
            std::cout << "\n";
            do_write(length);
        }
    });
}

void Vibranium::Client::do_write(std::size_t length) {
    auto self(shared_from_this());
    boost::asio::async_write(socket_, boost::asio::buffer(data_, length),
     [this, self](boost::system::error_code ec, std::size_t /*length*/)
     {
         if (!ec)
         {
             do_read();
         }
     });
}

这是我启动服务器的方式：

#include "Config.h"
#include "Database/MySQLConnection.h"
#include "Implementation/LoginDatabase.h"
#include "Banner.h"
#include "Server/Server.h"
#include <boost/asio.hpp>

using boost::asio::ip::tcp;
using namespace std;
using namespace Vibranium;

int main() {
    //Don't mind Logger::FatalError it's just for coloring!
    Banner::Show(Logger::Error,"AuthServer");
    Config config("AuthServer");
    std::string defaultPort = "8080";
    MySQLConnectionInfo mySqlConnectionInfo(config, "LoginDatabaseInfo");
    LoginDatabaseConnection loginDatabaseConnection(mySqlConnectionInfo);
    loginDatabaseConnection.LoadDatabase();

    try
    {
        boost::asio::io_service io_service;
        Server s(io_service, std::stoi(config.GetConfigValue("AuthServerPort", defaultPort)));
        io_service.run();
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}

以下是我尝试同时建立多个连接并使它们保持活动状态的方法：

Config config("AuthServer");
std::string defaultIP   = "127.0.0.1";
std::string defaultPort = "8080";
int connectionsNumber   = CommandQuestion<int>::AskQuestion("How many connections do you want established?");
std::cout << "Initializing " << std::to_string(connectionsNumber) << " connection/s." << std::endl;

std::cout << "Trying to connect to  " <<  defaultIP << " on port: " << config.GetConfigValue("AuthServerPort", defaultPort)  << std::endl;
for (int i = 0; i < connectionsNumber; ++i) {
   try
    {
        boost::asio::io_context io_context;
        tcp::socket s(io_context);
        tcp::resolver resolver(io_context);
        boost::asio::connect(s, resolver.resolve( defaultIP,config.GetConfigValue("AuthServerPort", defaultPort)));

        std::string message = "I am testing here!!!";
        size_t request_length = std::strlen(message.c_str());
        boost::asio::write(s, boost::asio::buffer(message, request_length));

        char reply[max_length];
        size_t reply_length = boost::asio::read(s,boost::asio::buffer(reply, request_length));
        Logger::Log(std::to_string(i) + " Connected!",Logger::Success);
        /*        std::cout << "Reply is: ";
                std::cout.write(reply, reply_length);
                std::cout << "\n";*/
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

}

我能够建立成功的连接，但是在创建并传输示例回显消息后，它们被直接删除。

当我尝试初始化例如 3 个连接时，我在服务器上看到以下输出：

Server Started! Listening on Port(8085)
New Connection (ID: 1)
I am testing here!!!
Disconnected ID: 1
New Connection (ID: 2)
I am testing here!!!
Disconnected ID: 2
New Connection (ID: 3)
I am testing here!!!
Disconnected ID: 3

我正在从同一台 PC 但从另一个 C++ 目标可执行文件初始化到服务器的连接。 因此，我启动并运行了服务器可执行文件和另一个试图创建多个连接并同时保持它们的可执行文件。

如何使我的连接在创建后持续存在而不是直接断开？ 我的错误在哪里，我该如何解决？

Answer 1

当tcp::socket超出范围（ 参考）时，它会关闭它的连接。 如果要保持连接打开，则必须使对象保持活动状态。

您可以通过将io_context移出客户端示例中的循环并保留一些用于保存套接字的列表来实现此目的：

  boost::asio::io_context io_context;
  std::vector<tcp::socket> sockets{};

  for (int i = 0; i < connectionsNumber; ++i) {

    try {
      sockets.emplace_back(io_context);
      tcp::socket& s{sockets.back()};

      // initialize socket as before ...

客户端循环完成后，服务器输出将显示断开连接消息：

New Connection (ID: 2)
Hello, world!
New Connection (ID: 3)
Hello, world!
New Connection (ID: 4)
Hello, world!
Disconnected ID: 2
Disconnected ID: 3
Disconnected ID: 4

附加说明：您没有显示do_write的内容，但我假设您对该函数的实现以某种方式再次调用do_read ，以便它可以处理最终的 EOF 或连接重置。