ratelimit: Avoid replicating "zero" pipes excessively

This patch makes it so any time a pipe's `.counter` value reaches 0, it
will only get broadcasted to neighbouring cluster nodes exactly 3 more
times, after which it will be completely skipped from being included in
the replication packet.  This counter is then reset to 3 as soon as the
pipe's value is incremented locally.

modules/ratelimit/ratelimit.h

@@ -95,6 +95,7 @@ typedef struct rl_pipe {
 	time_t last_used;			/* timestamp when the pipe was last accessed */
 	time_t last_local_used;		/* timestamp when the pipe was last locally accessed */
 	rl_repl_counter_t *dsts;	/* counters per destination */
+	int repl_zero_cnt;			/* only broadcast a zero counter N times */
 	rl_window_t rwin;			/* window of requests */
 } rl_pipe_t;
 

modules/ratelimit/ratelimit_helper.c

@@ -486,6 +486,7 @@ int w_rl_check(struct sip_msg *_m, str *name, int *limit, str *algorithm)
 		}
 	} else {
 		pipe->counter++;
+		pipe->repl_zero_cnt = 3;
 	}
 
 	ret = rl_pipe_check(pipe);
@@ -1057,11 +1058,12 @@ void rl_timer_repl(utime_t ticks, void *param)
 				LM_ERR("[BUG] bogus map[%d] state\n", i);
 				goto next_pipe;
 			}
-			if (!RL_USE_BIN(pipe))
-			        goto next_pipe;
-
-			/* do not replicate if about to expire */
-			if (pipe->last_local_used + rl_expire_time < now)
+			/* ignore cachedb replicated stuff */
+			if (!RL_USE_BIN(pipe)
+			        /* ... or pipes with value: 0 after 'cnt' broadcasts */
+			        || (pipe->counter == 0 && pipe->repl_zero_cnt-- <= 0)
+			        /* ... and do not replicate if about to expire */
+			        || pipe->last_local_used + rl_expire_time < now)
 				goto next_pipe;
 
 			key = iterator_key(&it);