setsockopt() fails

hnasr2001 · 02-05-2015, 12:40 PM

I am trying to open and set options for socket. I am getting "protocol error" for the setsockopt() function. I did not include the libraries here.
All functions above the setsockopt, return 0.
Any help will be appreciated.

--------------------------------------------------------------
#define MCAST_GROUP "239.255.0.1"
#define MCAST_PORT 30785
#define NONBLOCKING 1

int main(int argc , char *argv[])
{
int sock;
int ctl;
int on = 1;
int mode = 0;
struct sockaddr_in addr;
struct ip_mreq mreq;
mode = NONBLOCKING;
sock = socket(AF_INET , SOCK_STREAM , 0);
ctl = ioctl(sock, FIONBIO, &mode);

setsock = setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on));

memset(&addr, 0, sizeof(addr)); /* fill memory with 0*/
addr.sin_family=AF_INET;
addr.sin_port=htons(MCAST_PORT);
addr.sin_addr.s_addr=htonl(INADDR_ANY);
mreq.imr_multiaddr.s_addr=inet_addr(MCAST_GROUP);
mreq.imr_interface.s_addr=htonl(INADDR_ANY);
setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,&mreq, sizeof(mreq));
if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0)
{
perror("setsockopt");
exit(1);
}
return 0;
}

rtmistler · 02-10-2015, 01:14 PM

For what it's worth, I did stage this program and see the EXACT same problem you're seeing. I searched a bit for information or examples related to multicast. I don't see what's wrong. I did feel that you ought to have looked at your interim results from socket(), setsockopt(), and so forth.

The other comments are when you perform the setsockopt() for IP_ADD_MEMBERSHIP, you do that twice, I'm guessing because you added debug via copy/paste. Either case, keep the second iteration of it and remove the first one.

Next, in the line where you set up mreg.imr_multiaddr.s_addr I think you need to use addr and perform a memcpy of the structure:

Code:

    memset(&addr, 0, sizeof(addr)); /* fill memory with 0*/
    addr.sin_family=AF_INET;
    addr.sin_port=htons(MCAST_PORT);
    addr.sin_addr.s_addr=MCAST_GROUP;
    memcpy(&mreq.imr_multiaddr.s_addr, &addr, sizeof(struct in_addr));
    mreq.imr_interface.s_addr=htonl(INADDR_ANY);

However this doesn't work either. My editing of your code ended up getting the same errno you're seeing.

Maybe search for some examples of multicast out there in code and copy exactly to see if they work first and then edit them to match what you specifically want.

Here's my total effort, sorry I was not able to find a resolution either.

In the future, it's more helpful if you use [code][/code] tags to put in code, it retains the format and allows for better cut/paste. Further, adding the includes and your entire file is helpful so that other programmers won't have to search for the thread of needed include files. There's a link in my signature to describe how to do that.

Code:

#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <errno.h>

#define MCAST_GROUP "239.255.0.1"
#define MCAST_PORT 30785
#define NONBLOCKING 1

int main(int argc , char *argv[])
{
    int sock;
    int ctl;
    int on = 1;
    int mode = 0;
    int retval;
    struct sockaddr_in addr;
    struct ip_mreq mreq;

    mode = NONBLOCKING;
    if((sock = socket(AF_INET , SOCK_STREAM , 0)) <= 0) {
        printf("socket create error: %d:%s\n", errno, strerror(errno));
        return -1;
    }

    if((ctl = ioctl(sock, FIONBIO, &mode)) < 0) {
        printf("ioctl error: %d:%s\n", errno, strerror(errno));
        return -1;
    }

    if((retval = setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on))) < 0) {
        printf("set option error(1): %d:%s\n", errno, strerror(errno));
        return -1;
    }

    memset(&addr, 0, sizeof(addr)); /* fill memory with 0*/
    addr.sin_family=AF_INET;
    addr.sin_port=htons(MCAST_PORT);
    addr.sin_addr.s_addr=MCAST_GROUP;
    memcpy(&mreq.imr_multiaddr.s_addr, &addr, sizeof(struct in_addr));
    mreq.imr_interface.s_addr=htonl(INADDR_ANY);

    //setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,&mreq, sizeof(mreq));
    // Why was that there?

    if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0) {
        printf("set option error(2): %d:%s\n", errno, strerror(errno));
        return -1;
    }

    return 0;
}

Upd4ting · 12-04-2017, 02:40 PM

Hello,

For future googlers that still have this error.

The error is at this line:

Code:

if((sock = socket(AF_INET , SOCK_STREAM , 0)) <= 0) {

You need to change that by

Code:

if((sock = socket(AF_INET , SOCK_DGRAM, 0)) <= 0) {

To ensure that you are working with UDP socket.