How to multicast with ipv6 udp socket in C / C ++ on Linux?

Question

(English is not my native language, do not worry if some sentences are strange;)).

I developed a PONG game and, by the way, created several classes to help me manage the window, the event ... and the network , because I added a LAN , but for now you have to enter the address of the person you want to play with. And the solution for this was broadcast (LAN scan for the player) . It was easy with ipv4, just use the address 255.255.255.255, but we are in 2017 and provide a function that works only with ipv4 sucks ...

Then I look for a way to broadcast from ipv6, and I learn about multi-casting, but this part just lost me. = (

I use standard libraries for Linux in C ++ , I found some examples of multi-throw that did not work with me. The best I did at this time was sending the udp package from one instance of the program to another on the same computer.

How can I use multi-cast with ipv6 udp socket on Linux in C / C ++?

The best code found on the Internet (I rebuilt it) that almost works (client and service are all in one, the choice is made by adding 1 or 0 to argv):

int main(int argc, char const *argv[]) {

struct sockaddr_in6 groupSock;
int sd = -1;

char databuf[10];
int datalen = sizeof databuf;

/* Create a datagram socket on which to send/receive. */
if((sd = socket(AF_INET6, SOCK_DGRAM, 0)) < 0) {
    perror("Opening datagram socket error");
    return 1;
} else {
    cout << "Opening the datagram socket...OK." << endl;;
}

/* Enable SO_REUSEADDR to allow multiple instances of this */
/* application to receive copies of the multicast datagrams. */
int reuse = 1;
if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof reuse) < 0) {
    perror("Setting SO_REUSEADDR error");
    close(sd);
    return 1;
} else {
    cout << "Setting SO_REUSEADDR...OK." << endl;
}

/* Initialize the group sockaddr structure with a */
memset((char *) &groupSock, 0, sizeof groupSock);
groupSock.sin6_family = AF_INET6;
// address of the group
inet_pton(AF_INET6, "ff0e::/16", &groupSock.sin6_addr);
groupSock.sin6_port = htons(4321);

/* Set local interface for outbound multicast datagrams. */
/* The IP address specified must be associated with a local, */
/* multicast capable interface. */
int ifindex = if_nametoindex ("enp3s0");
cout << "ifindex is " << ifindex << endl;

if(setsockopt(sd, IPPROTO_IPV6, IPV6_MULTICAST_IF, &ifindex, sizeof ifindex)) {
    perror("Setting local interface error");
    return 1;
} else {
    cout << "Setting the local interface...OK" << endl;
}

// choice is 0 for sending and 1 for receiving
int choice;
if (argc < 2) {
    cout << "missing argv[1]" << endl;
    return 1;
}
sscanf (argv[1], "%d", &choice);

// if sending
if (choice == 0) {
    memset(databuf, 'a', datalen);
    databuf[sizeof databuf - 1] = '\0';

    if (sendto(sd, databuf, datalen, 0, (sockaddr*)&groupSock, sizeof groupSock) < 0) {
        cout << "Error in send" << endl;
    } else {
        cout << "Send okay!" << endl;
    }
}

// if receiving
else if (choice == 1) {
    groupSock.sin6_addr = in6addr_any;
    if(bind(sd, (sockaddr*)&groupSock, sizeof groupSock)) {
        perror("Binding datagram socket error");
        close(sd);
        return 1;
    } else {
        cout << "Binding datagram socket...OK." << endl;
    }

    /* Join the multicast group ff0e::/16 on the local  */
    /* interface. Note that this IP_ADD_MEMBERSHIP option must be */
    /* called for each local interface over which the multicast */
    /* datagrams are to be received. */
    struct ipv6_mreq group;
    inet_pton (AF_INET6, "ff0e::", &group.ipv6mr_multiaddr.s6_addr);
    group.ipv6mr_interface = ifindex;

    if(setsockopt(sd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, (char *)&group, sizeof group) < 0) {
        perror("Adding multicast group error");
        close(sd);
        return 1;
    } else {
        cout << "Adding multicast group...OK." << endl;
    }

    if (read(sd, databuf, datalen) < 0) {
        perror("Error in read");
    } else {
        databuf[sizeof databuf - 1] = '\0';// just for safety
        cout << "Read Okay" << endl;
        cout << "Message is : " << databuf << endl;
    }
}

return 0;
}

Here the address is ff0e :: but I tried ff01 :: and ff02 ::.

I need help, I did not find simple documentation about this. Thanks in advance for any response.

Edit: Thanks to Ron Maupin and Jeremy Friesner for these comments, this helps me.

: ! ff12:: blah: blah (...) ff0e:: works! , ?

Answer 1

:
, , , . , ff0e:: , ff12:: feed: a: dead: beef .

, if_nameindex().

: - , , , :

:

// OPEN
int fd = socket(AF_INET6, SOCK_DGRAM, 0);

// BIND
struct sockaddr_in6 address = {AF_INET6, htons(4321)};
bind(fd, (struct sockaddr*)&address, sizeof address);

// JOIN MEMBERSHIP
struct ipv6_mreq group;
group.ipv6mr_interface = 0;
inet_pton(AF_INET6, "ff12::1234", &group.ipv6mr_multiaddr);
setsockopt(fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &group, sizeof group);

// READ
char buffer[128];
read(fd, buffer, sizeof buffer);

:

// OPEN
int fd = socket(AF_INET6, SOCK_DGRAM, 0);

// ADDRESS
struct sockaddr_in6 address = {AF_INET6, htons(4321)};
inet_pton(AF_INET6, "ff12::1234", &address.sin6_addr);

// SEND TO
char buffer[128];
strcpy(buffer, "hello world!");
sendto(fd, buffer, sizeof buffer, 0, (struct sockaddr*)&address, sizeof address);