从异步服务器套接字写 - 但不读

问题描述 投票:0回答:1

好吧,我与插座很新,我试图做多同步客户端异步服务器。问题是,我的服务器无法从客户端读取任何数据,并且也没有给出错误!

这里是我的服务器类:

#define READ_BUF_SIZE 512

struct Connection {
    boost::asio::ip::tcp::socket socket;
    boost::asio::streambuf read_buffer;
    Connection(boost::asio::io_service & io_service) : socket(io_service), read_buffer() { }
    Connection(boost::asio::io_service & io_service, size_t max_buffer_size) : socket(io_service), read_buffer(max_buffer_size) { }
};

class CServer {
    boost::asio::io_service m_ioservice;
    boost::asio::ip::tcp::acceptor m_acceptor;
    std::list<Connection> m_connections;
    using con_handle_t = std::list<Connection>::iterator;

public:

    CServer() : m_ioservice(), m_acceptor(m_ioservice), m_connections() { }

    void handle_read(con_handle_t con_handle, boost::system::error_code const & err, size_t bytes_transfered) {
        if (bytes_transfered > 0) {
            std::istream is(&con_handle->read_buffer);
            std::string line;
            std::getline(is, line);
            std::cout << "Message Received: " << line << std::endl;
        }

        if (!err) {
            do_async_read(con_handle);
        }
        else {
            std::cerr << "Error on read: " << err.message() << std::endl;
            m_connections.erase(con_handle);
        }
    }

    void do_async_read(con_handle_t con_handle) {
        auto handler = boost::bind(&CServer::handle_read, this, con_handle, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred);
        boost::asio::async_read(con_handle->socket, con_handle->read_buffer, boost::asio::transfer_exactly(READ_BUF_SIZE), handler);
    }

    void handle_write(con_handle_t con_handle, std::shared_ptr<std::string> msg_buffer, boost::system::error_code const & err) {
        if (!err) {
            std::cout << "Finished sending message\n";
            if (con_handle->socket.is_open()) {
                // Write completed successfully and connection is open
            }
        }
        else {
            std::cerr << "Error on write: " << err.message() << std::endl;
            m_connections.erase(con_handle);
        }
    }

    void handle_accept(con_handle_t con_handle, boost::system::error_code const & err) {
        if (!err) {
            std::cout << "Connection from: " << con_handle->socket.remote_endpoint().address().to_string() << "\n";
            std::cout << "Sending message\n";
            auto buff = std::make_shared<std::string>("Hello World!\r\n\r\n");
            auto handler = boost::bind(&CServer::handle_write, this, con_handle, buff, boost::asio::placeholders::error);
            boost::asio::async_write(con_handle->socket, boost::asio::buffer(*buff), handler);
            do_async_read(con_handle);
        }
        else {
            std::cerr << "We had an error: " << err.message() << std::endl;
            m_connections.erase(con_handle);
        }
        start_accept();
    }

    void start_accept() {
        auto con_handle = m_connections.emplace(m_connections.begin(), m_ioservice);
        auto handler = boost::bind(&CServer::handle_accept, this, con_handle, boost::asio::placeholders::error);
        m_acceptor.async_accept(con_handle->socket, handler);
    }

    void listen(uint16_t port) {
        auto endpoint = boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), port);
        m_acceptor.open(endpoint.protocol());
        m_acceptor.set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));
        m_acceptor.bind(endpoint);
        m_acceptor.listen();
        start_accept();
    }

    void run() {
        m_ioservice.run();
    }
};

这个类是先通过第一个使用它的listen功能,然后通过使用其run指令通过构造函数创建,然后调用。

虽然“世界,你好!”测试邮件被发送,服务器不接收任何信息传回来自客户端(handle_read()不会被调用)

Client::Client() : io_context(), resolver(io_context), endpoints(resolver.resolve("localhost", "daytime")), socket(io_context)
{
    try
    {
        boost::asio::connect(socket, endpoints);

        boost::array<unsigned char, PACKET_LENGTH> buf;
        boost::system::error_code error;

        socket.read_some(boost::asio::buffer(buf), error);
        std::cout << "Got message." << std::endl;

        boost::asio::write(socket, boost::asio::buffer("test message"), error);
    }
    catch (std::exception& e)
    {
        std::cerr << e.what() << std::endl;
    }
}

最后,这是我的客户端类。它包含一个io_context对象,一个插座,分解,并呼吁tcp::resolver::results_type一个endpoints对象类型。

调试“得到的消息”进入实际输出到控制台,使服务器可以写入到客户端,而“测试消息”项实际上从未在服务器中看到的,大概是因为它无法读取它。

当这里是什么问题?提前致谢。

c++ boost boost-asio
1个回答
1
投票

问题是在这里

boost::asio::async_read(con_handle->socket, con_handle->read_buffer,
      boost::asio::transfer_exactly(READ_BUF_SIZE), handler);
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ where READ_BUF_SIZE is 512

当被准确读数为512字节或插座在客户端被破坏或它的发送操作被禁止socket.shutdown()您的处理程序被调用。

所以问题是Client对象在客户端代码的寿命。如果您的客户端代码是这样的:

int main() {
  Client c; // send data, delete object, socket is destroyed
  return 0;
}

在服务器handle_read被调用error_code == boost::asio::error::eof (end of file or stream)什么方式,在客户端插座被摧毁。但你可以检查流缓冲的内容,它包含“测试消息”。

但如果你的客户端的代码如下所示:

int main() {
  Client c;
  // wait here for X seconds
  return 0;
}

在服务器端,你将不会看到任何输出,直到X秒过去了。您可以使用

boost::asio::write(socket, boost::asio::buffer("test message"), error);
socket.shutdown(boost::asio::ip::tcp::socket::shutdown_send);  // <---

shutdown使得end_of_file被发送到服务器,读取操作被中止,对于handle_read处理程序被调用,您可以检查是否error_code为error::eof,如果是的话,你可以打印strambuf的内容。

如果你不知道有多少字节发送,则可以使用async_read_until()功能与分隔符来表示信息的结束(在本例中为换行符):

// server side
boost::asio::async_read_until(con_handle->socket, con_handle->read_buffer, "\n", handler);
                                                                           ^^^^ delimiter
// client side
boost::asio::write(socket, boost::asio::buffer("test message\n"), error);
                                                         ^^^^ added delimiter
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