UDP communication using c++ boost asio

问题:

I need to communicate with a different device in a private network over UDP. I am new to using boost, but based on what I searched online and also the tutorials on Boost website, I came up with below code.. I am currently trying to send and receive data from my own device. Just to unit test and finalize the code.

Question: I am unable to receive any message. What am I missing?

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include "boost/asio.hpp"
#include <thread>
#include <boost/array.hpp>
#include <boost/bind.hpp>

#define SRVR_UDP_PORT  10251
#define CLNT_UDP_PORT 10252

boost::array<char, 1024> recv_buffer;

void Sender(std::string in)
{
    boost::asio::io_service io_service;
    boost::asio::ip::udp::socket socket(io_service);
    boost::asio::ip::udp::endpoint remote_endpoint;
    socket.open(boost::asio::ip::udp::v4());
    remote_endpoint = boost::asio::ip::udp::endpoint(boost::asio::ip::address::from_string("192.168.1.64"), SRVR_UDP_PORT);

    boost::system::error_code err;
    socket.send_to(boost::asio::buffer(in.c_str(), in.size()), remote_endpoint, 0, err);
    socket.close();
    //int i =0;
    printf("Sending Payload --- \n");
}

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


void Receiver()
{
    while(1)
    {
        boost::asio::io_service io_service;
        boost::asio::ip::udp::socket socket(io_service);
        boost::asio::ip::udp::endpoint remote_endpoint;

        //socket.open(boost::asio::ip::udp::v4());
        boost::system::error_code err;
        remote_endpoint = boost::asio::ip::udp::endpoint(boost::asio::ip::address::from_string("192.168.1.64"), CLNT_UDP_PORT);

        socket.open(boost::asio::ip::udp::v4());
        //https://stackoverflow.com/questions/26820215/boost-asio-udp-client-async-receive-from-calls-handler-even-when-there-are-no-in
        socket.async_receive_from(boost::asio::buffer(recv_buffer),
                                    remote_endpoint,
                                    boost::bind(handle_receive,
                                    boost::asio::placeholders::error,
                                    boost::asio::placeholders::bytes_transferred));                                    
                                    //socket.close();
    }
    int i = 0;
    printf("Received Payload --- %d", i);

}

int main(int argc, char *argv[])
{
    //std::thread s(Sender);
    std::thread r(Receiver);
    //s.join();
    std::string input = argv[1];
    printf("Input is %s\nSending it to Sender Function...\n", input.c_str());
    Sender(input);
    r.join();
    return 0;
}

回答1:

You forget to

1. bind the receiving socket
2. run the io_service
3. use the same UDP port for the receiver

There's no use doing async_* calls in a loop, because all it does is queue tasks, which won't get executed unless a thread runs io_service::run.

Live On Coliru

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

#define IPADDRESS "127.0.0.1" // "192.168.1.64"
#define UDP_PORT 13251

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

void Sender(std::string in) {
    boost::asio::io_service io_service;
    udp::socket socket(io_service);
    udp::endpoint remote_endpoint = udp::endpoint(address::from_string(IPADDRESS), UDP_PORT);
    socket.open(udp::v4());

    boost::system::error_code err;
    auto sent = socket.send_to(boost::asio::buffer(in), remote_endpoint, 0, err);
    socket.close();
    std::cout << "Sent Payload --- " << sent << "\n";
}

struct Client {
    boost::asio::io_service io_service;
    udp::socket socket{io_service};
    boost::array<char, 1024> recv_buffer;
    udp::endpoint remote_endpoint;

    int count = 3;

    void handle_receive(const boost::system::error_code& error, size_t bytes_transferred) {
        if (error) {
            std::cout << "Receive failed: " << error.message() << "\n";
            return;
        }
        std::cout << "Received: '" << std::string(recv_buffer.begin(), recv_buffer.begin()+bytes_transferred) << "' (" << error.message() << ")\n";

        if (--count > 0) {
            std::cout << "Count: " << count << "\n";
            wait();
        }
    }

    void wait() {
        socket.async_receive_from(boost::asio::buffer(recv_buffer),
            remote_endpoint,
            boost::bind(&Client::handle_receive, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));
    }

    void Receiver()
    {
        socket.open(udp::v4());
        socket.bind(udp::endpoint(address::from_string(IPADDRESS), UDP_PORT));

        wait();

        std::cout << "Receiving\n";
        io_service.run();
        std::cout << "Receiver exit\n";
    }
};

int main(int argc, char *argv[])
{
    Client client;
    std::thread r([&] { client.Receiver(); });

    std::string input = argc>1? argv[1] : "hello world";
    std::cout << "Input is '" << input.c_str() << "'\nSending it to Sender Function...\n";

    for (int i = 0; i < 3; ++i) {
        std::this_thread::sleep_for(std::chrono::milliseconds(200));
        Sender(input);
    }

    r.join();
}

Prints

Input is 'hello'
Sending it to Sender Function...
Receiving
Sent Payload --- 5
Received: 'hello' (Success)
Count: 2
Sent Payload --- 5
Received: 'hello' (Success)
Count: 1
Sent Payload --- 5
Received: 'hello' (Success)
Receiver exit