ratelimiter: use correct ttlSeconds value, and always call Set

Co-authored-by: Romain <rtribotte@users.noreply.github.com>
Co-authored-by: Daniel Tomcej <daniel.tomcej@gmail.com>

pkg/middlewares/ratelimiter/rate_limiter.go

@@ -30,7 +30,12 @@ type rateLimiter struct {
 	burst int64
 	// maxDelay is the maximum duration we're willing to wait for a bucket reservation to become effective, in nanoseconds.
 	// For now it is somewhat arbitrarily set to 1/(2*rate).
-	maxDelay      time.Duration
+	maxDelay time.Duration
+	// each rate limiter for a given source is stored in the buckets ttlmap.
+	// To keep this ttlmap constrained in size,
+	// each ratelimiter is "garbage collected" when it is considered expired.
+	// It is considered expired after it hasn't been used for ttl seconds.
+	ttl           int
 	sourceMatcher utils.SourceExtractor
 	next          http.Handler
 
@@ -66,12 +71,15 @@ func New(ctx context.Context, next http.Handler, config dynamic.RateLimit, name
 	}
 
 	period := time.Duration(config.Period)
+	if period < 0 {
+		return nil, fmt.Errorf("negative value not valid for period: %v", period)
+	}
 	if period == 0 {
 		period = time.Second
 	}
 
-	// Logically, we should set maxDelay to infinity when config.Average == 0 (because it means no rate limiting),
-	// but since the reservation will give us a delay = 0 anyway in this case, we're good even with any maxDelay >= 0.
+	// if config.Average == 0, in that case,
+	// the value of maxDelay does not matter since the reservation will (buggily) give us a delay of 0 anyway.
 	var maxDelay time.Duration
 	var rtl float64
 	if config.Average > 0 {
@@ -86,6 +94,17 @@ func New(ctx context.Context, next http.Handler, config dynamic.RateLimit, name
 		}
 	}
 
+	// Make the ttl inversely proportional to how often a rate limiter is supposed to see any activity (when maxed out),
+	// for low rate limiters.
+	// Otherwise just make it a second for all the high rate limiters.
+	// Add an extra second in both cases for continuity between the two cases.
+	ttl := 1
+	if rtl >= 1 {
+		ttl++
+	} else if rtl > 0 {
+		ttl += int(1 / rtl)
+	}
+
 	return &rateLimiter{
 		name:          name,
 		rate:          rate.Limit(rtl),
@@ -94,6 +113,7 @@ func New(ctx context.Context, next http.Handler, config dynamic.RateLimit, name
 		next:          next,
 		sourceMatcher: sourceMatcher,
 		buckets:       buckets,
+		ttl:           ttl,
 	}, nil
 }
 
@@ -121,13 +141,21 @@ func (rl *rateLimiter) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		bucket = rlSource.(*rate.Limiter)
 	} else {
 		bucket = rate.NewLimiter(rl.rate, int(rl.burst))
-		if err := rl.buckets.Set(source, bucket, int(rl.maxDelay)*10+1); err != nil {
-			logger.Errorf("could not insert bucket: %v", err)
-			http.Error(w, "could not insert bucket", http.StatusInternalServerError)
-			return
-		}
 	}
 
+	// We Set even in the case where the source already exists,
+	// because we want to update the expiryTime everytime we get the source,
+	// as the expiryTime is supposed to reflect the activity (or lack thereof) on that source.
+	if err := rl.buckets.Set(source, bucket, rl.ttl); err != nil {
+		logger.Errorf("could not insert/update bucket: %v", err)
+		http.Error(w, "could not insert/update bucket", http.StatusInternalServerError)
+		return
+	}
+
+	// time/rate is bugged, since a rate.Limiter with a 0 Limit not only allows a Reservation to take place,
+	// but also gives a 0 delay below (because of a division by zero, followed by a multiplication that flips into the negatives),
+	// regardless of the current load.
+	// However, for now we take advantage of this behavior to provide the no-limit ratelimiter when config.Average is 0.
 	res := bucket.Reserve()
 	if !res.OK() {
 		http.Error(w, "No bursty traffic allowed", http.StatusTooManyRequests)