c++ - boost 异步 tcp 客户端

Question

我刚刚开始使用 boost。我正在使用异步套接字编写 TCP 客户端-服务器。

任务如下:

1. 客户端向服务器发送一个数字
2. 客户端可以在收到服务器的回答之前发送另一个数字。
3. 服务器收到一个数字，用它做一些计算并将结果发送回客户端。
4. 多个客户端可以连接到服务器。

现在可以执行以下操作

• 从客户端发送一个数字到服务器
• 服务器在当前线程中接收到一个数字并在 OnReceive 处理程序中进行计算(我知道这很糟糕......但是我应该如何启动一个新线程来并行计算)
• 服务器返回应答但客户端已经断开连接

如何让客户端在键盘输入数字的同时等待服务器的响应？

为什么我的客户端不等待服务器的响应？

客户端代码:

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

class TCPClient
{
    public:
        TCPClient(boost::asio::io_service& IO_Service, tcp::resolver::iterator EndPointIter);
        void Close();

    private:
        boost::asio::io_service& m_IOService;
        tcp::socket m_Socket;

        string m_SendBuffer;
        static const size_t m_BufLen = 100;
        char m_RecieveBuffer[m_BufLen*2];

        void OnConnect(const boost::system::error_code& ErrorCode, tcp::resolver::iterator EndPointIter);
        void OnReceive(const boost::system::error_code& ErrorCode);
        void OnSend(const boost::system::error_code& ErrorCode);
        void DoClose();
};

TCPClient::TCPClient(boost::asio::io_service& IO_Service, tcp::resolver::iterator EndPointIter)
: m_IOService(IO_Service), m_Socket(IO_Service), m_SendBuffer("")
{
    tcp::endpoint EndPoint = *EndPointIter;

    m_Socket.async_connect(EndPoint,
        boost::bind(&TCPClient::OnConnect, this, boost::asio::placeholders::error, ++EndPointIter));
}

void TCPClient::Close()
{
    m_IOService.post(
        boost::bind(&TCPClient::DoClose, this));
}
void TCPClient::OnConnect(const boost::system::error_code& ErrorCode, tcp::resolver::iterator EndPointIter)
{
    cout << "OnConnect..." << endl;
    if (ErrorCode == 0)
    {
        cin >> m_SendBuffer;
        cout << "Entered: " << m_SendBuffer << endl;
        m_SendBuffer += "\0";

        m_Socket.async_send(boost::asio::buffer(m_SendBuffer.c_str(),m_SendBuffer.length()+1),
            boost::bind(&TCPClient::OnSend, this,
            boost::asio::placeholders::error));
    } 
    else if (EndPointIter != tcp::resolver::iterator())
    {
        m_Socket.close();
        tcp::endpoint EndPoint = *EndPointIter;

        m_Socket.async_connect(EndPoint, 
            boost::bind(&TCPClient::OnConnect, this, boost::asio::placeholders::error, ++EndPointIter));
    }
}

void TCPClient::OnReceive(const boost::system::error_code& ErrorCode)
{
    cout << "receiving..." << endl;
    if (ErrorCode == 0)
    {
        cout << m_RecieveBuffer << endl;

        m_Socket.async_receive(boost::asio::buffer(m_RecieveBuffer, m_BufLen),
            boost::bind(&TCPClient::OnReceive, this, boost::asio::placeholders::error));
    } 
    else 
    {
        cout << "ERROR! OnReceive..." << endl;
        DoClose();
    }
}

void TCPClient::OnSend(const boost::system::error_code& ErrorCode)
{
    cout << "sending..." << endl;
    if (!ErrorCode)
    {
        cout << "\""<< m_SendBuffer <<"\" has been sent" << endl;
        m_SendBuffer = "";

        m_Socket.async_receive(boost::asio::buffer(m_RecieveBuffer, m_BufLen),
            boost::bind(&TCPClient::OnReceive, this, boost::asio::placeholders::error));
    }
    else
    {
        cout << "OnSend closing" << endl;
        DoClose();
    }

}

void TCPClient::DoClose()
{
    m_Socket.close();
}

int main()
{
    try 
    {
        cout << "Client is starting..." << endl;
        boost::asio::io_service IO_Service;

        tcp::resolver Resolver(IO_Service);

        string port = "13";
        tcp::resolver::query Query("127.0.0.1", port);

        tcp::resolver::iterator EndPointIterator = Resolver.resolve(Query);

        TCPClient Client(IO_Service, EndPointIterator);

        cout << "Client is started!" << endl;

        cout << "Enter a query string " << endl;

        boost::thread ClientThread(boost::bind(&boost::asio::io_service::run, &IO_Service));

        Client.Close();
        ClientThread.join();
    } 
    catch (exception& e)
    {
        cerr << e.what() << endl;
    }

    cout << "\nClosing";
    getch();
}

这是控制台的输出

Client is starting...
Client is started!
OnConnect...
12
Entered: 12
sending...
"12" has been sent
receiving...
ERROR! OnReceive...

Closing

服务器部分

class Session
{
    public:
        Session(boost::asio::io_service& io_service)
            : socket_(io_service)
        {
            dataRx[0] = '\0';
            dataTx[0] = '\0';
        }

        tcp::socket& socket()
        {
            return socket_;
        }

        void start()
        {
            socket_.async_read_some(boost::asio::buffer(dataRx, max_length),
                boost::bind(&Session::handle_read, this,
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred));
        }

        void handle_read(const boost::system::error_code& error, size_t bytes_transferred)
        {
            cout << "reading..." << endl;
            cout << "Data: " << dataRx << endl;

            if (!error)
            {
                if (!isValidData())
                {
                    cout << "Bad data!" << endl;
                    sprintf(dataTx, "Bad data!\0");
                    dataRx[0] = '\0';
                }
                else
                {
                    sprintf(dataTx, getFactorization().c_str());
                    dataRx[0] = '\0';
                }

                boost::asio::async_write(socket_,
                    boost::asio::buffer(dataTx, max_length*2),
                    boost::bind(&Session::handle_write, this,
                    boost::asio::placeholders::error));
            }
            else
            {
                delete this;
            }
        }

        void handle_write(const boost::system::error_code& error)
        {
            cout << "writing..." << endl;
            if (!error)
            {
                cout << "dataTx sent: " << dataTx << endl;
                dataTx[0] = '\0';

                socket_.async_read_some(boost::asio::buffer(dataRx, max_length),
                    boost::bind(&Session::handle_read, this,
                    boost::asio::placeholders::error,
                    boost::asio::placeholders::bytes_transferred));
            }
            else
            {
                delete this;
            }
        }

        string getFactorization() const
        {
            //Do something
        }

        bool isValidData()
        {
            locale loc; 
            for (int i = 0; i < strlen(dataRx); i++)
                if (!isdigit(dataRx[i],loc))
                    return false;

            return true;
        }

    private:
        tcp::socket socket_;
        static const size_t max_length = 100;
        char dataRx[max_length];
        char dataTx[max_length*2];
};

class Server
{
    public:
        Server(boost::asio::io_service& io_service, short port)
            : io_service_(io_service),
            acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
        {
            Session* new_session = new Session(io_service_);
            acceptor_.async_accept(new_session->socket(),
                boost::bind(&Server::handle_accept, this, new_session,
                boost::asio::placeholders::error));
        }

        void handle_accept(Session* new_session, const boost::system::error_code& error)
        {
            if (!error)
            {
                new_session->start();
                new_session = new Session(io_service_);
                acceptor_.async_accept(new_session->socket(),
                    boost::bind(&Server::handle_accept, this, new_session,
                    boost::asio::placeholders::error));
            }
            else
            {
                delete new_session;
            }
        }

    private:
        boost::asio::io_service& io_service_;
        tcp::acceptor acceptor_;
};

int main(int argc, char* argv[])
{
    cout << "Server is runing..." << endl;
    try
    {
        boost::asio::io_service io_service;

        int port = 13;
        Server s(io_service, port);
        cout << "Server is run!" << endl;
        io_service.run();
    }
    catch (boost::system::error_code& e)
    {
        std::cerr << e << "\n";
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}

服务器的输出

Server is runing...
Server is run!
reading...
Data: 12
writing...
dataTx sent: 13    //just send back received ++number
reading...
Data:

非常感谢您的帮助

========

已添加

好的，我明白了。但是检查 ErrorCode == boost::asio::error::eof 不起作用...我做错了什么？

else if (ErrorCode == boost::asio::error::eof)
{
    cout << "boost::asio::error::eof in OnReceive!" << endl;
}
else 
{
    cout << "ERROR! OnReceive..." << ErrorCode << endl;
    DoClose();
}

打印出来的是ERROR! OnReceive...system:10009 好像是我比较的不对

========

已添加

我找到了根本原因。我已经声明使用 async_receive(而不是 async_read_some)并将 main 中的行交换为

ClientThread.join();
Client.Close();

现在可以正常使用了!

现在我正在尝试同时从套接字读取数据和向套接字写入数据(因为客户端应该能够在收到服务器的响应之前发送额外的请求。

在 OnConnect 函数中我创建了 boost 线程:

boost::thread addMsgThread(boost::bind(&TCPClient::addMsgLoop, this));
boost::thread receivingThread(boost::bind(&TCPClient::startReceiving, this));
boost::thread sendingThread(boost::bind(&TCPClient::startSending, this));

实现

void TCPClient::startReceiving()
{
    cout << "receiving..." << endl;
    m_RecieveBuffer[0] = '\0';
    m_Socket.async_receive(boost::asio::buffer(m_RecieveBuffer, m_BufLen),
        boost::bind(&TCPClient::receivingLoop, this, boost::asio::placeholders::error)); //runtime error here
    cout << "m_RecieveBuffer = " << m_RecieveBuffer << endl;
}

void TCPClient::receivingLoop(const boost::system::error_code& ErrorCode)
{
    cout << "receiving..." << endl;
    if (ErrorCode == 0)
    {
        cout << "m_RecieveBuffer = " << m_RecieveBuffer << endl;

        m_Socket.async_receive(boost::asio::buffer(m_RecieveBuffer, m_BufLen),
            boost::bind(&TCPClient::receivingLoop, this, boost::asio::placeholders::error));
    }
    else 
    {
        cout << "ERROR! receivingLoop..." << ErrorCode << endl;
        DoClose();
    }
}

void TCPClient::addMsgLoop()
{
    while (true)
    {
        string tmp;
        cin >> tmp;

        cout << "Entered: " << tmp << endl;
        tmp += "\0";

        try
        {
            msgQueue.push(tmp);
        }
        catch(exception &e)
        {
            cerr << "Canno add msg to send queue... " << e.what() << endl;
        }
    }
}

receive 和 send 线程的问题相同:运行时错误(在 boost 库中的某处写入访问冲突)。

void TCPClient::startReceiving()
{
     ...
     m_Socket.async_receive(); //runtime error here
}

在后续版本中一切正常(但我不知道如何在回答前实现多次发送)。谁能告诉我如何解决这个问题或如何通过其他方式实现这个问题？可能合并会有所帮助，但我现在确信这是个好方法。

Answer 1

boost::asio::ip::tcp::socket::async_read_some顾名思义就是不保证读取完整的数据。当客户端完成写入时，它将 error 对象设置为 boost::asio::error::eof。

你得到的错误是因为:

服务器部分

        if (!error)
        {
            ...
        }
        else
        {
            delete this;
        }

在 else block 中，您假设这是一个错误情况并关闭连接。这并非总是如此。在 else 之前，您需要检查 error == boost::asio::error::eof。

除此之外，在读取处理程序中，您应该继续收集缓冲区中读取的任何内容，直到您遇到 error == boost::asio::error::eof。只有这样，您才应该验证读取的数据并写回客户端。

查看 HTTP 服务器 1 , 2 , 3在 examples 中实现部分。

更新:更新问题的答案

更新后的代码存在线程同步问题。

1. msgQueue 被两个或多个线程同时访问，没有任何锁。
2. 可以同时调用同一个套接字上的读写。

如果我正确理解你的问题，你想:

1. 获取用户输入并将其发送到服务器。
2. 保持同时接收服务器的响应。

您可以使用两个 boost::asio::io_service::strands对于这两个任务。使用 Asio 时，链是同步任务的方式。 Asio 确保发布在链中的任务同步执行。

1. 在 strand1 中发布一个 send 任务，如下所示:read_user_input -> send_to_server -> handle_send -> read_user_input

2. 在 strand2 中发布一个 read 任务，如下所示:read_some -> handle_read -> read_some

   <

这将确保 msgQueue 不会被两个线程同时访问。使用两个套接字对服务器进行读取和写入，以确保不会在同一个套接字上同时调用读取和写入。