core: add rate-limiting helper

It can be used to perform an action like logging a message with
simple rate limiting.

src/core/nm-core-utils.c

@@ -5568,3 +5568,59 @@ out_removed:
                 feature);
     return FALSE;
 }
+
+/*****************************************************************************/
+
+/**
+ * nm_rate_limit_check():
+ * @rate_limit: the NMRateLimit instance
+ * @window_sec: the time window in seconds, between 1 and 864000 (ten days)
+ * @burst: the number of max allowed event occurrences in the given time
+ *   window
+ *
+ * The function rate limits an event. Call it multiple times with the
+ * same @window_sec, and @burst values.
+ *
+ * Returns: TRUE if the event is allowed, FALSE if it is rate-limited
+ */
+gboolean
+nm_rate_limit_check(NMRateLimit *rate_limit, gint32 window_sec, gint32 burst)
+{
+    gint64 now;
+    gint64 old_ts_msec;
+    gint64 window_msec;
+    gint64 capacity;
+    gint64 elapsed;
+
+    nm_assert(window_sec >= 1 && window_sec <= 864000);
+    nm_assert(burst >= 1);
+
+    /* This implements a simple token bucket algorithm. For each millisecond,
+     * refill "burst" tokens. Thus, during a full time window we
+     * refill (window_msec * burst) tokens. Each event consumes @window_msec
+     * tokens. */
+
+    window_msec         = (gint64) window_sec * NM_UTILS_MSEC_PER_SEC;
+    capacity            = window_msec * (gint64) burst;
+    old_ts_msec         = rate_limit->ts_msec;
+    now                 = nm_utils_get_monotonic_timestamp_msec();
+    rate_limit->ts_msec = now;
+
+    elapsed = now - old_ts_msec;
+    if (old_ts_msec == 0 || elapsed > window_msec) {
+        /* On the first call, or in case a whole window passed, (re)start with
+         * a full budget */
+        rate_limit->tokens = capacity;
+    } else {
+        rate_limit->tokens += elapsed * (gint64) burst;
+        rate_limit->tokens = NM_MIN(rate_limit->tokens, capacity);
+    }
+
+    /* Consume the tokens */
+    if (rate_limit->tokens >= window_msec) {
+        rate_limit->tokens -= window_msec;
+        return TRUE;
+    }
+
+    return FALSE;
+}

src/core/nm-core-utils.h

@@ -494,4 +494,13 @@ gid_t nm_utils_get_nm_gid(void);
 
 gboolean nm_utils_connection_supported(NMConnection *connection, GError **error);
 
+/*****************************************************************************/
+
+typedef struct {
+    gint64 ts_msec;
+    gint64 tokens;
+} NMRateLimit;
+
+gboolean nm_rate_limit_check(NMRateLimit *rate_limit, gint32 window_sec, gint32 burst);
+
 #endif /* __NM_CORE_UTILS_H__ */

src/core/tests/test-utils.c

@@ -260,6 +260,73 @@ test_shorten_hostname(void)
     do_test_shorten_hostname(".name1", FALSE, NULL);
 }
 
+/*****************************************************************************/
+typedef struct {
+    NMRateLimit ratelimit;
+    GMainLoop  *loop;
+    GSource    *source1;
+    GSource    *source2;
+    guint       num;
+} RateLimitData;
+
+static int
+rate_limit_window_expire_cb(gpointer user_data)
+{
+    RateLimitData *data = user_data;
+
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+
+    g_assert(!nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(!nm_rate_limit_check(&data->ratelimit, 1, 5));
+
+    g_main_loop_quit(data->loop);
+
+    nm_clear_g_source_inst(&data->source1);
+
+    return G_SOURCE_CONTINUE;
+}
+
+static int
+rate_limit_check_cb(gpointer user_data)
+{
+    RateLimitData *data = user_data;
+
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(nm_rate_limit_check(&data->ratelimit, 1, 5));
+
+    g_assert(!nm_rate_limit_check(&data->ratelimit, 1, 5));
+    g_assert(!nm_rate_limit_check(&data->ratelimit, 1, 5));
+
+    nm_clear_g_source_inst(&data->source2);
+
+    return G_SOURCE_CONTINUE;
+}
+
+static void
+test_rate_limit_check(void)
+{
+    RateLimitData data;
+
+    data = (RateLimitData) {
+        .loop      = g_main_loop_new(NULL, FALSE),
+        .ratelimit = {},
+        .num       = 0,
+    };
+
+    data.source1 = nm_g_timeout_add_source(1100, rate_limit_window_expire_cb, &data);
+    data.source2 = nm_g_timeout_add_source(10, rate_limit_check_cb, &data);
+
+    g_main_loop_run(data.loop);
+    g_main_loop_unref(data.loop);
+}
+
 /*****************************************************************************/
 
 NMTST_DEFINE();
@@ -272,6 +339,7 @@ main(int argc, char **argv)
     g_test_add_func("/utils/stable_privacy", test_stable_privacy);
     g_test_add_func("/utils/hw_addr_gen_stable_eth", test_hw_addr_gen_stable_eth);
     g_test_add_func("/utils/shorten-hostname", test_shorten_hostname);
+    g_test_add_func("/utils/rate-limit-check", test_rate_limit_check);
 
     return g_test_run();
 }