hss_probe_port

Source: hss-probe.h:43

Probes a single port and, if a listener is found, formats the local address string — including multi-address display for localhost.

Signature

static int hss_probe_port(const char *host, int port, char *out, size_t len,
                          char (*ips)[INET_ADDRSTRLEN], int nips);

Parameter	Description
`host`	Target host (e.g., `"localhost"`, `"192.168.1.100"`)
`port`	Port number to probe
`out`	Output buffer for the formatted `"address:port"` string
`len`	Size of `out`
`ips`	Array of the machine's ethernet IPs (from `hss_get_eth_ips`)
`nips`	Number of entries in `ips`

Returns 1 if a listener is detected, 0 otherwise.

Initial probe

if (!hss_try_connect(host, port)) return 0;

First, confirm something is listening at host:port. If not, return immediately — no address formatting needed.

Localhost multi-address display

int local = !strcmp(host, "localhost") || !strcmp(host, "127.0.0.1");
if (local && nips > 0) {
    size_t off = 0;
    int shown = 0;
    for (int i = 0; i < nips && shown < 3; i++)
        if (hss_try_connect(ips[i], port))
            off += snprintf(out + off, len - off, "%s%s:%d",
                            shown++ ? ", " : "", ips[i], port);
    if (shown) {
        if (nips > 3) snprintf(out + off, len - off, ", +more");
        return 1;
    }
}

When the target is localhost or 127.0.0.1, a listener may be bound to 0.0.0.0 (all interfaces) or to specific IPs. To replicate ss's per-interface display, hss cross-checks the listener against each of the machine's ethernet IPs (obtained earlier via hss_get_eth_ips).

Probes each ethernet IP at the same port.
Lists up to 3 matching addresses, comma-separated.
If more than 3 match, appends ", +more".

This produces output like:

192.168.86.42:22, 10.0.0.5:22, +more

Remote / fallback

snprintf(out, len, "%s:%d", host, port);
return 1;

For non-localhost targets, or localhost listeners that don't match any specific ethernet IP (e.g., bound only to 127.0.0.1), the output is simply host:port.

Why ethernet IPs matter

On Linux, ss reads bound interface addresses from the kernel. On Hurd, there is no centralized table to query. hss enumerates the machine's active ethernet interfaces via getifaddrs and tests each one, building the same multi-address view from userspace.

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