hss/docs/hss_get_eth_ips.md

hss_get_eth_ips

Source: hss-probe.h:62

Enumerates the machine's active, non-loopback IPv4 addresses.

Signature

static int hss_get_eth_ips(char ips[][INET_ADDRSTRLEN], int max);

Parameter	Description
ips	Output array of IP address strings (each INET_ADDRSTRLEN bytes)
max	Maximum number of IPs to return

Returns the number of IPs found.

Implementation

struct ifaddrs *ifaddr, *ifa;
int count = 0;
if (getifaddrs(&ifaddr) == -1) return 0;
for (ifa = ifaddr; ifa && count < max; ifa = ifa->ifa_next) {
    if (!ifa->ifa_addr || ifa->ifa_addr->sa_family != AF_INET ||
        !(ifa->ifa_flags & IFF_UP) || (ifa->ifa_flags & IFF_LOOPBACK)) continue;
    inet_ntop(AF_INET, &((struct sockaddr_in *)ifa->ifa_addr)->sin_addr,
              ips[count++], INET_ADDRSTRLEN);
}
freeifaddrs(ifaddr);
return count;

1. getifaddrs() builds a linked list of all interfaces.
2. For each interface, keep only those that:
   • Have an address (ifa_addr is non-NULL).
   • Are IPv4 (AF_INET).
   • Are up (IFF_UP).
   • Are not the loopback interface (IFF_LOOPBACK).
3. Convert the binary address to a string with inet_ntop.
4. freeifaddrs() frees the list.

Why this is needed

When hss probes localhost, a listener may be bound to 0.0.0.0 (all interfaces) or to specific IPs. To replicate ss's per-interface "Local Address:Port" display, hss needs to know the machine's IPs so it can test each one.

In hss.c, the IPs are fetched once and passed to every hss_probe_port call:

char eth_ips[10][INET_ADDRSTRLEN];
int num_eth_ips = hss_get_eth_ips(eth_ips, 10);

A limit of 10 is arbitrary but sufficient for typical machines.

Why not Linux-specific

getifaddrs/freeifaddrs are POSIX-standard (from ifaddrs.h) and work on any system with a libc that implements them, including GNU/Hurd. The tool does not use netlink, /proc/net/dev, or any Linux-only interface enumeration mechanism.