I am trying to open a SocketCAN J1939 and receive and send J1939 messages. I am very confused with type “sockaddr_can”. This structure has j1939.addr, j1939.pgn, j1939.name etc. When I receive a message with
recvfrom(s, &lCANFrame.data, sizeof(lCANFrame.data), 0x0, (struct sockaddr*)&j1939_addr, &recv_data_len)
where sockaddr_can j1939_addr;, the address of the sender is in j1939_addr.can_addr.j1939.addr and PGN of received message is in j1939_addr.can_addr.j1939.pgn. However, I assigned the these values to be my SRC address and NAME as seen below when I am initializing the socket.

    // J1939 CAN Socket
    j1939_addr.can_family = AF_CAN;
    j1939_addr.can_ifindex = ifr.ifr_ifindex;
    j1939_addr.can_addr.j1939.name = J1939_NAME;     //J1939 Name
    j1939_addr.can_addr.j1939.addr = CAN_SRC_ADDR;   //J1939: this is the SRC address of this device transmitting
    //j1939_addr.can_addr.j1939.addr = J1939_IDLE_ADDR;   //J1939: this is the SRC address of this device transmitting
    j1939_addr.can_addr.j1939.pgn =  J1939_NO_PGN;        //This is a filter for receive function. This will only recieve PGN that is mentioned

So, when a message is received, ADDR and PGN are over written by the received message. If that is the case, how do I compare my NAME to received NAME and update my address if these is a conflict (for address claiming).

Does the Kernel take care of address claim?

Also, how do I send a message out. Below is not working. What am I doing wrong please?
send_response = sendto(s, &lCANFrame.data[1], 1, 0, (const struct sockaddr*)&j1939_addr, sizeof(j1939_addr)); //Send OUT CAN data to the interface //Send one byte CAN message OUT

I have tried send() and write() and I still can not send a message out. For CAN_RAW, everything works fine. Once I change the protocol to J1939, it does not work. Can you please give me a sample C code example. Here is my initialization:

   s = socket(PF_CAN, SOCK_DGRAM, CAN_J1939); //Open J1939 socket
    strcpy(ifr.ifr_name, can_int_name); //can_int_name is the can interface name "vcan0", can0 etc.
    ioctl(s, SIOCGIFINDEX, &ifr); //Retreive the index to the CAN interface
    // J1939 CAN Socket
    j1939_addr.can_family = AF_CAN;
    j1939_addr.can_ifindex = ifr.ifr_ifindex;
    j1939_addr.can_addr.j1939.name = J1939_NAME;     //J1939 Name
    j1939_addr.can_addr.j1939.addr = CAN_SRC_ADDR;   //J1939: this is the SRC address of this device transmitting
    j1939_addr.can_addr.j1939.pgn =  J1939_NO_PGN;   //This is a filter for receive function. This will only recieve PGN that is mentioned

   if(bind(s, (struct sockaddr*)&j1939_addr, sizeof(j1939_addr)))      // Check to make sure Socket Binding is successful
    {
        perror("Error in Binding Socket");
    }

Thank you