UDP Socket does not connect

[mickes27]

Hey, I want to send some packet which contains: command, pin number and value from my PC to Raspberry Pi via UDP. I made this code:

PC:

#include <SFML/Network.hpp>
#include <iostream>

int main() {

        sf::UdpSocket socket;
        socket.setBlocking(false);

        sf::Packet packet;
        sf::String command = "write";
        sf::Uint16 pin = 23;
        sf::Uint16 value = 0;

        packet << command << pin << value;

        sf::IpAddress recipient = "192.168.1.102";
        unsigned short port = 54000;

        while (1) {
                if (socket.send(packet, recipient, port) != sf::Socket::Done)
                {
                        std::cout << "Couldn't send" << std::endl;
                }
                else {
                        std::cout << value << std::endl;
                        value++;
                }
        }


        return 0;
}

Rpi:

#include <SFML/Network.hpp>
#include <iostream>

int main() {

        sf::UdpSocket socket;
        socket.setBlocking(false);

        if (socket.bind(54000) != sf::Socket::Done)
        {
                std::cout << "Cannot bind socket" << std::endl;
        }

        sf::Packet packet;
        sf::IpAddress remoteIP = "192.168.1.101";
        unsigned short remotePort = 54000;
       
        while (1) {
                if (socket.receive(packet, remoteIP, remotePort) == sf::Socket::Done) {
                        std::cout << "Got it" << std::endl;
                        sf::String command;
                        sf::Uint16 pin;
                        sf::Uint16 value;

                        packet >> command >> pin >> value;
                        std::cout << "Command: " << command.toAnsiString().c_str() << " " << pin << " " << value << std::endl;
                }
                else if (socket.receive(packet, remoteIP, remotePort) == sf::Socket::NotReady) {
                        std::cout << "Some error while recieving" << std::endl;
                }
        }


        return 0;
}
 

But I have some error while running both programs, cause it says packet is sent from PC, but it's still "Some error while recieving" on Rpi. What thing I failed and missunderstand?

[Laurent]

You're calling the function (ie. trying to receive data) twice, just for testing the return value. Which doesn't make sense and is of course wrong.

Do this instead:

auto status = socket.receive(packet, remoteIP, remotePort);
if (status == sf::Socket::Done)
{
    // ...
}
else if (status == sf::Socket::NotReady)
{
    // ...
}

And by the way, "NotReady" is not an error, it just means that there's nothing to be received yet on your non-blocking socket.

[mickes27]

Oh, you are right, my bad. But even in this way, application never get packet. It is send from PC, but on Rpi there is always NotReady, and never Done. Something like it lost package meanwhile.

EDIT: I think I got it:

PC:

#include <SFML/Network.hpp>
#include <iostream>

int main() {

        sf::UdpSocket socket;
        socket.setBlocking(false);

        sf::Packet packet;
        sf::String command = "write";
        sf::Uint16 pin = 23;
        sf::Uint16 value = 0;

        packet << command << pin << value;

        sf::IpAddress recipient = "192.168.1.102";
        unsigned short port = 54000;

        while (1) {
                packet.clear();
                packet << command << pin << value;
                if (socket.send(packet, recipient, port) != sf::Socket::Done)
                {
                        std::cout << "Some error" << std::endl;
                }
                else {
                        std::cout << value << std::endl;
                        if (value < 10) {
                                value++;
                        }
                        else {
                                value = 0;
                        }
                       
                }
        }

                system("PAUSE");

        return 0;
}

Rpi:

#include <SFML/Network.hpp>
#include <SFML/Network.hpp>
#include <iostream>

int main() {

        sf::UdpSocket socket;
        socket.setBlocking(false);

        if (socket.bind(54000) != sf::Socket::Done)
        {
                std::cout << "Cannot bind socket" << std::endl;
        }

        sf::Packet packet;
        sf::IpAddress remoteIP;// = "192.168.1.100";
        unsigned short remotePort;// = 54000;
       
        while (1) {
                auto status = socket.receive(packet, remoteIP, remotePort);
                if (status == sf::Socket::Done){
                        std::cout << "Got it" << std::endl;
                        sf::String command;
                        sf::Uint16 pin;
                        sf::Uint16 value;

                        packet >> command >> pin >> value;
                        std::cout << remoteIP  << ": "<< "Command: " << command.toAnsiString().c_str() << " " << pin << " " << value << std::endl;
                }
                else if (status == sf::Socket::NotReady){
                        std::cout << "No data" << std::endl;
                }
        }


        return 0;
}

 

Does remoteIP and remotePort has to be empty?

[Laurent]

Does remoteIP and remotePort has to be empty?

It doesn't matter, they are out arguments, which means that they are overwritten by the function if something is received.

[eXpl0it3r]

Start up Wireshark and similar and check your network traffic.