[Feature] Monitored: Support random lookups

src/libserver/monitored.c

 	gdouble check_tm;
 };
 
+static void
+rspamd_monitored_dns_random (struct rspamd_monitored *m,
+							 struct rspamd_dns_monitored_conf *conf)
+{
+	gchar random_prefix[64];
+	const gchar dns_chars[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_";
+	gint len;
+
+	len = rspamd_random_uint64_fast () % sizeof (random_prefix);
+
+	if (len < 8) {
+		len = 8;
+	}
+
+	for (guint i = 0; i < len; i ++) {
+		guint idx = rspamd_random_uint64_fast () % sizeof (dns_chars);
+		random_prefix[i] = dns_chars[idx];
+	}
+
+	conf->request->len = 0;
+	rspamd_printf_gstring (conf->request, "%*.s.%s", len, random_prefix, m->url);
+}
+
 static void *
 rspamd_monitored_dns_conf (struct rspamd_monitored *m,
 		struct rspamd_monitored_ctx *ctx,
 			}
 		}
 
-		elt = ucl_object_lookup (opts, "prefix");
+		if (!(m->flags & RSPAMD_MONITORED_RANDOM)) {
+			/* Prefix is useless for random monitored */
+			elt = ucl_object_lookup (opts, "prefix");
 
-		if (elt && ucl_object_type (elt) == UCL_STRING) {
-			rspamd_printf_gstring (req, "%s.", ucl_object_tostring (elt));
+			if (elt && ucl_object_type (elt) == UCL_STRING) {
+				rspamd_printf_gstring (req, "%s.", ucl_object_tostring (elt));
+			}
 		}
 
 		elt = ucl_object_lookup (opts, "ipnet");
 		}
 	}
 
-	rspamd_printf_gstring (req, "%s", m->url);
+	if (!(m->flags & RSPAMD_MONITORED_RANDOM)) {
+		rspamd_printf_gstring (req, "%s", m->url);
+	}
+
 	conf->request = req;
 
 	return conf;
 {
 	struct rspamd_dns_monitored_conf *conf = ud;
 
+	if (m->flags & RSPAMD_MONITORED_RANDOM) {
+		rspamd_monitored_dns_random (m, conf);
+	}
+
 	if (!rdns_make_request_full (ctx->resolver, rspamd_monitored_dns_cb,
 			conf, ctx->cfg->dns_timeout, ctx->cfg->dns_retransmits,
 			1, conf->request->str, conf->rt)) {
 	gchar *cksum_encoded, cksum[rspamd_cryptobox_HASHBYTES];
 
 	g_assert (ctx != NULL);
-	g_assert (line != NULL);
 
 	m = g_malloc0 (sizeof (*m));
 	m->type = type;
 	m->flags = flags;
+
 	m->url = g_strdup (line);
 	m->ctx = ctx;
 	m->monitoring_mult = 1.0;
 		return NULL;
 	}
 
+	if (opts) {
+		const ucl_object_t *rnd_obj;
+
+		rnd_obj = ucl_object_lookup (opts, "random");
+
+		if (rnd_obj && ucl_object_type (rnd_obj) == UCL_BOOLEAN) {
+			if (ucl_object_toboolean (rnd_obj)) {
+				m->flags |= RSPAMD_MONITORED_RANDOM;
+			}
+		}
+	}
+
 	m->proc.ud = m->proc.monitored_config (m, ctx, opts);
 
 	if (m->proc.ud == NULL) {

src/libserver/monitored.h

 };
 
 enum rspamd_monitored_flags {
-	RSPAMD_MONITORED_DEFAULT = 0,
-	RSPAMD_MONITORED_RBL = (1 << 0),
+	RSPAMD_MONITORED_DEFAULT = 0u,
+	RSPAMD_MONITORED_RBL = (1u << 0u),
+	RSPAMD_MONITORED_RANDOM = (1u << 1u)
 };
 
 /**