fix no rate limiting if average is 0

pkg/middlewares/ratelimiter/rate_limiter.go

@@ -79,10 +79,12 @@ func New(ctx context.Context, next http.Handler, config dynamic.RateLimit, name
 		period = time.Second
 	}
 
-	// if config.Average == 0, in that case,
+	// Initialized at rate.Inf to enforce no rate limiting when config.Average == 0
-	// the value of maxDelay does not matter since the reservation will (buggily) give us a delay of 0 anyway.
+	rtl := float64(rate.Inf)
+	// No need to set any particular value for maxDelay as the reservation's delay
+	// will be <= 0 in the Inf case (i.e. the average == 0 case).
 	var maxDelay time.Duration
-	var rtl float64
+
 	if config.Average > 0 {
 		rtl = float64(config.Average*int64(time.Second)) / float64(period)
 		// maxDelay does not scale well for rates below 1,
@@ -153,10 +155,6 @@ func (rl *rateLimiter) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		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)

pkg/middlewares/ratelimiter/rate_limiter_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/traefik/traefik/v2/pkg/config/dynamic"
 	"github.com/traefik/traefik/v2/pkg/testhelpers"
 	"github.com/vulcand/oxy/v2/utils"
+	"golang.org/x/time/rate"
 )
 
 func TestNewRateLimiter(t *testing.T) {
@@ -25,7 +26,16 @@ func TestNewRateLimiter(t *testing.T) {
 		expectedSourceIP string
 		requestHeader    string
 		expectedError    string
+		expectedRTL      rate.Limit
 	}{
+		{
+			desc: "no ratelimit on Average == 0",
+			config: dynamic.RateLimit{
+				Average: 0,
+				Burst:   10,
+			},
+			expectedRTL: rate.Inf,
+		},
 		{
 			desc: "maxDelay computation",
 			config: dynamic.RateLimit{
@@ -120,6 +130,9 @@ func TestNewRateLimiter(t *testing.T) {
 				assert.NoError(t, err)
 				assert.Equal(t, test.requestHeader, hd)
 			}
+			if test.expectedRTL != 0 {
+				assert.Equal(t, test.expectedRTL, rtl.rate)
+			}
 		})
 	}
 }