stations.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <json-c/json.h>
#include <iwinfo.h>
#include <net/if.h>
#include <glob.h>
#include <alloca.h>

#define NETIF_PREFIX "/sys/class/net/"
#define VIRTIF_PREFIX "/sys/devices/virtual/net/"
#define LOWERGLOB_SUFFIX "/lower_*"

static struct json_object *get_stations(const struct iwinfo_ops *iw, const char *ifname) {
	int len;
	char buf[IWINFO_BUFSIZE];
	struct json_object *stations = json_object_new_object();

	if (iw->assoclist(ifname, buf, &len) == -1)
		return stations;

	// This is just: for entry in assoclist(ifname)
	for (struct iwinfo_assoclist_entry *entry = (struct iwinfo_assoclist_entry *)buf;
			(char*)(entry+1) <= buf + len; entry++) {
		struct json_object *station = json_object_new_object();

		json_object_object_add(station, "signal", json_object_new_int(entry->signal));
		json_object_object_add(station, "noise", json_object_new_int(entry->noise));
		json_object_object_add(station, "inactive", json_object_new_int(entry->inactive));

		char macstr[18];

		snprintf(macstr, sizeof(macstr), "%02x:%02x:%02x:%02x:%02x:%02x",
				entry->mac[0], entry->mac[1], entry->mac[2],
				entry->mac[3], entry->mac[4], entry->mac[5]);

		json_object_object_add(stations, macstr, station);
	}

	return stations;
}

static void badrequest() {
	printf("Status: 400 Bad Request\n\n");
	exit(1);
}

// recurse down to the lowest layer-2 interface
static int interface_get_lowest(const char *ifname, char *hwifname);
static int interface_get_lowest(const char *ifname, char *hwifname) {
	glob_t globbuf;
	char *fnamebuf = alloca(1 + strlen(VIRTIF_PREFIX) + IF_NAMESIZE +
			strlen(LOWERGLOB_SUFFIX));
	char *lowentry = NULL;


	sprintf(fnamebuf, "%s%s%s", VIRTIF_PREFIX, ifname, LOWERGLOB_SUFFIX);
	glob(fnamebuf, GLOB_NOSORT | GLOB_NOESCAPE, NULL, &globbuf);

	if (globbuf.gl_pathc == 1) {
		lowentry = alloca(1 + strlen(globbuf.gl_pathv[0]));
		strncpy(lowentry, globbuf.gl_pathv[0], 1 + strlen(globbuf.gl_pathv[0]));
	}

	globfree(&globbuf);

	if (!lowentry) {
		char *path = alloca(1 + strlen(NETIF_PREFIX) + strlen(ifname));
		sprintf(path, "%s%s", NETIF_PREFIX, ifname);

		if(access(path, F_OK) != 0)
			return false;

		strncpy(hwifname, ifname, IF_NAMESIZE - 1);
		return true;
	} else {
		char buf[PATH_MAX];
		ssize_t len;

		if ((len = readlink(lowentry, buf, sizeof(buf)-1)) != -1)
			buf[len] = '\0';
		else
			return false;

		if (strncmp(buf, "../", 3) == 0) {
			return interface_get_lowest(strrchr(buf, '/') + 1, hwifname);
		} else {
			return false;
		}
	}
}

int main(int argc, char *argv[]) {
	if (argc != 2)
		badrequest();

	const char *ifname = argv[1];
	char hwifname[IF_NAMESIZE] = "";

	if (strlen(ifname) >= IF_NAMESIZE)
		badrequest();

	if (strcspn(ifname, "/\\[]{}*?") != strlen(ifname))
		badrequest();

	if (!interface_get_lowest(ifname, hwifname))
		badrequest();

	const struct iwinfo_ops *iw = iwinfo_backend(hwifname);

	if (iw == NULL)
		badrequest();

	printf("Content-type: text/event-stream\n\n");

	while (true) {
		struct json_object *obj;
		obj = get_stations(iw, hwifname);
		printf("data: %s\n\n", json_object_to_json_string_ext(obj, JSON_C_TO_STRING_PLAIN));
		fflush(stdout);
		json_object_put(obj);
		usleep(150000);
	}

	return 0;
}