Server on different ip's - c

Question

I'm trying to create TCP Server that should run on a machine with multiple NIC's (eth0, eth1). Each NIC has its own IP from the network and I basically want to be able to connect to the servers running on each of the IP's at the same time. However currently I am able only to connect (netcat) to the first interface IP eth0 and when I try with eth1 I get a "Connection refused" even when I have the server only running on eth1.
I'm not sure if it is a problem with my server code (below). I bind to the required interface with setsockopt() and also use the interface IP (retrieved via ioctl), and netstat shows that the server is listening on the correct ip:port, however I am not able to connect to the one on eth1.
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 255
struct in_addr getIfIp(char* ifName)
{
int sockfd;
struct ifreq ifr;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
ifr.ifr_addr.sa_family = AF_INET;
strncpy(ifr.ifr_name, ifName, IFNAMSIZ-1);
if (ioctl(sockfd, SIOCGIFADDR, &ifr) < 0) {
fprintf(stderr, "ioctl failed\n");
}
close(sockfd);
return ((struct sockaddr_in*)&ifr.ifr_addr)->sin_addr;
}
int startServer(char* ifName, unsigned short port)
{
int sock_descriptor, conn_desc;
struct sockaddr_in serv_addr, client_addr;
socklen_t size = sizeof(client_addr);
char buff[MAX_SIZE];
if (ifName == NULL || port == 0) {
fprintf(stderr, "invalid server parameters\n");
return -1;
}
sock_descriptor = socket(AF_INET, SOCK_STREAM, 0);
if(sock_descriptor < 0) {
fprintf(stderr, "Failed creating socket\n");
return sock_descriptor;
}
if (setsockopt(sock_descriptor, SOL_SOCKET, SO_BINDTODEVICE, ifName, strlen(ifName)) < 0) {
fprintf(stderr, "Failed setting socket option\n");
return -1;
}
bzero((char *)&serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET; // AddressFamily = Internet address
serv_addr.sin_addr = getIfIp(ifName);//INADDR_ANY;
serv_addr.sin_port = htons(port);
// bind the address to the socket file descriptor
if (bind(sock_descriptor, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
fprintf(stderr, "Failed to bind\n");
return -1;
} else {
printf("bound to %s\n", inet_ntoa(serv_addr.sin_addr));
}
// Now start listening
if (listen(sock_descriptor, 0) < 0){
fprintf(stderr, "Listen failed");
return -1;
} else {// max queue of pending connections
printf("Listening on port %hu ...\n", port);
}
conn_desc = accept(sock_descriptor, (struct sockaddr *)&client_addr, &size);
if (conn_desc == -1) {
fprintf(stderr, "Failed accepting connection\n");
} else {
fprintf(stderr, "Connected\n");
}
close(conn_desc);
close(sock_descriptor);
return 0;
}
Any help with this would be appreciated.
[EDIT]
As mentioned in my comment, one funny thing I noticed is that once I connect to either of the interfaces I can only connect to this interface again and connect attempts to the other fail (for both eth0 and eth1) until a reboot.
Also I guess I would go ahead with INADDR_ANY for now but would really like to hear if anyone could shed some light as to why I can't connect to separate listeners (with my code here) in this case?

Answer 1

To have the socket listen on any interface use INADDR_ANY as listener address ...
serv_addr.sin_addr = INADDR_ANY;
and remove the call to setsockopt().
I'm not sure whether a back-log size of 0 makes sense. Also the code misses to test the outcome of the call to listen().
Finally int size should be socklen_t size.