How do I make two socket multicast transmitters talk to each other? - c++

Question

I am trying to establish two sockets that are both able to multicast transmit. And the should both be members of each others multicast group.
I have two problems.
I have tried to disable the loopback, so that a transmitter does not receive its own messages. This does not seem to work.
The two transmitters should be the same, but only one of them receives the message sent on their multicast group.
The code looks like this:
#define ERROR_CODE -1
int init(const char *rx, const char *tx, uint16_t port, struct sockaddr_in& txaddress)
{
int status = 0;
int enable = 1;
int disable = 0;
int mainSocket = ::socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, 0);
if (mainSocket == ERROR_CODE)
std::cout << "Error creating socket." << std::endl;
if (::setsockopt(mainSocket, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) == ERROR_CODE)
std::cout << "System failed to set reuse address." << std::endl;
if (::setsockopt(mainSocket, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(enable)) == ERROR_CODE)
std::cout << "System failed to set reuse port." << std::endl;
status = setsockopt(mainSocket, IPPROTO_IP, IP_MULTICAST_LOOP, &disable, sizeof(disable));
if (status == ERROR_CODE)
std::cout << "Unable to disable multicast loopback." << std::endl;
struct sockaddr_in rxaddress = address(INADDR_ANY, port);
txaddress = address(inet_addr(tx), port);
status = ::bind(mainSocket, reinterpret_cast<sockaddr*>(&rxaddress), sizeof(sockaddr_in));
if (status == ERROR_CODE)
std::cout << "Error binding socket." << std::endl;
struct in_addr localInterface;
memset(&localInterface, 0, sizeof(localInterface));
localInterface.s_addr = inet_addr("127.0.0.1");
status = setsockopt(mainSocket, IPPROTO_IP, IP_MULTICAST_IF, (char*) &localInterface, sizeof(localInterface));
if (status == ERROR_CODE)
std::cout << "Unable to set interface to multicast." << std::endl;
struct ip_mreq group;
memset(&group, 0, sizeof(group));
group.imr_multiaddr.s_addr = inet_addr(rx);
group.imr_interface.s_addr = INADDR_ANY;
status = setsockopt(mainSocket, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &group, sizeof(group));
if (status == ERROR_CODE)
std::cout << "Unable to add to multicast group." << std::endl;
return mainSocket;
}
Where
struct sockaddr_in address(uint32_t ip, uint16_t port)
{
struct sockaddr_in address;
memset(&address, 0, sizeof(sockaddr_in));
address.sin_family = AF_INET;
if (ip == INADDR_BROADCAST)
address.sin_addr.s_addr = htonl(INADDR_BROADCAST);
else
if (ip == INADDR_ANY)
address.sin_addr.s_addr = htonl(INADDR_ANY);
else
address.sin_addr.s_addr = ip;
address.sin_port = htons(port);
return address;
}
And the testcode is
#include <iostream>
#include <arpa/inet.h>
#include <cstring>
#include <thread>
#define MULTICAST_SERVER_ADDRESS "224.0.0.1"
#define MULTICAST_CLIENT_ADDRESS "224.0.0.0"
int main (int argc, char** argv)
{
char message1[16] = "server says hi.";
char message2[16] = "client says hi.";
char buffer1[100] = {0};
char buffer2[100] = {0};
socklen_t length = sizeof(sockaddr_in);
struct sockaddr_in servertxaddress;
struct sockaddr_in clienttxaddress;
memset(&servertxaddress, 0, length);
memset(&clienttxaddress, 0, length);
int serversocket = init(MULTICAST_CLIENT_ADDRESS, MULTICAST_SERVER_ADDRESS, 2000, servertxaddress);
int clientsocket = init(MULTICAST_SERVER_ADDRESS, MULTICAST_CLIENT_ADDRESS, 2000, clienttxaddress);
sendto(serversocket, message1, 16, 0, (const sockaddr*) &servertxaddress, length);
std::this_thread::sleep_for(std::chrono::milliseconds(100));
recvfrom(clientsocket, buffer1, 16, 0, nullptr, nullptr);
std::this_thread::sleep_for(std::chrono::milliseconds(100));
std::cout << buffer1 << std::endl;
sendto(clientsocket, message2, 16, 0, (const sockaddr*) &clienttxaddress, length);
std::this_thread::sleep_for(std::chrono::milliseconds(100));
recvfrom(serversocket, buffer2, 160, 0, nullptr, nullptr);
std::this_thread::sleep_for(std::chrono::milliseconds(100));
std::cout << buffer2 << std::endl;
return 0;
}
When I run the program, both sockets receive the multicast message (message1), so the IP_MULTICAST_LOOP I tried does not work, as I would expect it to. And the last transmit seems to get transmitted, but it does not arrive in the other end.
So the output is:
server says hi.
server says hi.
And I would like it to be:
server says hi.
client says hi.
Please advise.