c++ - 即使没有传入消息，Boost ASIO UDP 客户端 async_receive_from 也会调用处理程序

Question

我已将 Boost 白天客户端教程中的 UDP 客户端代码修改为以下内容:

class UDPClient
{
public:
    udp::socket* socket;
    udp::endpoint* receiver_endpoint;
    boost::array<char, 1024> recv_buffer;

    UDPClient();
    void do_receive();
    void handle_receive(const boost::system::error_code& error, size_t);
};

UDPClient::UDPClient()
{
    boost::asio::io_service io_service;

    udp::resolver resolver(io_service);
    udp::resolver::query query(udp::v4(), "127.0.0.1", "8888");
    receiver_endpoint = new udp::endpoint(*resolver.resolve(query));

    socket = new udp::socket(io_service);
    socket->open(udp::v4());

    do_receive();

    while (true)
    {
        io_service.poll();
        Sleep(1);
    }
}

void UDPClient::do_receive()
{
    socket->async_receive_from(boost::asio::buffer(recv_buffer), *receiver_endpoint,
                               boost::bind(&UDPClient::handle_receive, this,
                               boost::asio::placeholders::error,
                               boost::asio::placeholders::bytes_transferred));
}

void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
    cout << "ulala" << endl;

    if (!error || error == boost::asio::error::message_size)
        do_receive();
}

如果一切按计划进行，只有在有传入消息时才会打印“ulala”。然而，这里不是这种情况......无论是否有传入消息，都会立即调用处理程序并打印“ulala”。我尝试了一些不同的方法:将 io_service.poll() 与 io_service.run() 和 io_service.run_one() 交换，以及删除 Sleep(1)，但这些更改都没有对问题产生任何影响。我该怎么办？

提前致谢!

Answer 1

socket = new udp::socket(io_service);
socket->open(udp::v4());

设置一个用于发送到任意端点的套接字。要接收(“收听”)，请使用

socket = new udp::socket(io_service, udp::endpoint(udp::v4(), 8888));

除此之外，socket 和 receiver_endpoint 现在已经泄露。要解决这个问题:

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

using boost::asio::ip::udp;

class UDPClient
{
public:
    boost::asio::io_service io_service;
    udp::socket socket;
    udp::endpoint receiver_endpoint;
    boost::array<char, 1024> recv_buffer;

    UDPClient();
    void do_receive();
    void handle_receive(const boost::system::error_code& error, size_t);
};

UDPClient::UDPClient()
    : io_service(),
      socket(io_service, {udp::v4(), 8888})
{
    do_receive();
    io_service.run();
}

void UDPClient::do_receive()
{
    socket.async_receive_from(boost::asio::buffer(recv_buffer), receiver_endpoint,
                               boost::bind(&UDPClient::handle_receive, this,
                               boost::asio::placeholders::error,
                               boost::asio::placeholders::bytes_transferred));
}

void UDPClient::handle_receive(const boost::system::error_code& error, size_t bytes_transferred)
{
    std::cout << "ulala" << std::endl;
    std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "'\n";

    if (!error || error == boost::asio::error::message_size)
        do_receive();
}

int main()
{
    UDPClient updclient;
}

这也会打印收到的消息(假设它是可打印的)。见

• boost::asio async_receive_from UDP endpoint shared between threads?

寻求一种可以同时处理多个 UDP 请求的方法。