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

问题:

(English is not my native tongue, don't worry if some sentences are strange ;) ).

I was developing a PONG game and by the way creating some classes to help me managing window, event ... and network because I added a LAN feature to the game but currently you have to enter the address of the one with who you want to play with. And a solution to that was a broadcast (scanning LAN for player). This was easy with ipv4, just use the address 255.255.255.255 but we are in 2017 and provide a feature that works only with ipv4 sucks...

Then I look for a way to broadcast with ipv6 and I learn about multi-cast but this part just get me lost. =(

I use standard libraries on Linux in C++, I found several example of multi-cast that didn't work with me. The best I have done at this time is sending a udp packet from one instance of the program to an other on the same computer.

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

The best code found on Internet (I rearranged it) that almost work (there is client and serv all in one, 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 have try with ff01:: and ff02::.

I need help, I have not found any simple documentation about that. Thanks in advance for any answer.

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

Edit : THANKS Jeremy ! Your advice to use ff12::blah:blah(...) instead of ff0e:: works ! Should I write answer to my question to close the thread ?

回答1:

This code below is right:
The only thing wrong is the address used for the multicast.
Like Jeremy said it, ff0e:: is not correct, I used instead ff12::feed:a:dead:beef and it works.

It is possible to get the name and index of the available interface by using if_nameindex().

Update : I try to remove some code to see if it work without it and I manage to get this :

server :

// 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); 

client :

// 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); 

文章来源: How to multicast with ipv6 udp socket in C/C++ on linux?