setsockopt returning error 10014

Question

I'm trying to write a simple UDP server that advertises its service port on a multicast group but I'm having trouble getting the multicast to work. I tried looking around on the Microsoft documentation and copy/pasted some of their code but it's not working. Here is the problematic code:

    this->port = srvc_port; //11129 in my example
    this->mcast_port = mcast_port; //11130 in my example
    this->mcast_ip = mcast_ip; //230.0.0.30 in my example

    int iResult = WSAStartup(MAKEWORD(2,2), &service_wsaData);
    if (iResult != NO_ERROR)
    {
        cout << "WSAstartup failed" << endl;
        return -1;
    }

    service_sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (service_sock == INVALID_SOCKET) {
        closesocket(service_sock);
        WSACleanup();
        cout << "Error at socket" << endl;
        return -1;
    }

    mcast_sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if(mcast_sock == INVALID_SOCKET) {
        closesocket(mcast_sock);
        WSACleanup();
        cout << "Error at socket" << endl;
        return -1;
    }

    multicast.sin_family = AF_INET; // multicast is a sockaddr_in struct
    multicast.sin_addr.s_addr = INADDR_ANY;
    multicast.sin_port = htons(mcast_port);

    service.sin_family = AF_INET; //same for service
    service.sin_addr.s_addr = INADDR_ANY;
    service.sin_port = htons(port);

    if(::bind( service_sock, (sockaddr *)&service, sizeof(service) ) == SOCKET_ERROR) {
        closesocket(mcast_sock);
        closesocket(service_sock);
        WSACleanup();
        cout << "Error binding service socket" << endl;
        return -1;
    };

    if(::bind( mcast_sock, (sockaddr *)&multicast, sizeof(multicast) ) == SOCKET_ERROR) {
        closesocket(mcast_sock);
        closesocket(service_sock);
        WSACleanup();
        cout << "Error binding multicast socket" << endl;
        return -1;
    };

    mreq.imr_multiaddr.s_addr = inet_addr(mcast_ip.c_str()); //mreq is declared like so "struct ip_mreq mreq;" in the class
    mreq.imr_interface.s_addr = htonl(INADDR_ANY);

    if(setsockopt(mcast_sock,IPPROTO_IP,IP_ADD_SOURCE_MEMBERSHIP,(char *) &mreq, sizeof(mreq)) == SOCKET_ERROR)
    {
            //I get error 10014 here
        cout << "Error: " << WSAGetLastError() << endl;
        return -1;
    }

Any help would be appreciated.

Answer 1

10014 is WSAEFAULT, which means "The buffer pointed to by the optval parameter is not in a valid part of the process address space or the optlen parameter is too small."

Read the documentation:

IPPROTO_IP Socket Options

IP_ADD_SOURCE_MEMBERSHIP expects a pointer to an ip_mreq_source structure:

typedef struct ip_mreq_source {
  struct in_addr  imr_multiaddr;
  struct in_addr  imr_sourceaddr;
  struct in_addr  imr_interface;
} IP_MREQ_SOURCE, *PIP_MREQ_SOURCE;

You are passing it a pointer to an ip_mreq structure instead:

typedef struct ip_mreq {
  struct in_addr  imr_multiaddr;
  struct in_addr  imr_interface;
} IP_MREQ, *PIP_MREQ;

ip_mreq is smaller than ip_mreq_source, thus sizeof(mreq) is too small for IP_ADD_SOURCE_MEMBERSHIP. You need to change your mreq variable to ip_mreq_source, and be sure to fill in its imr_sourceaddr member.

ip_mreq is used for IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP.

ip_mreq_source is used for IP_ADD_SOURCE_MEMBERSHIP, IP_DROP_SOURCE_MEMBERSHIP, IP_BLOCK_SOURCE, and IP_UNBLOCK_SOURCE.