reverseproxy: allow 0 as weighted round robin value

modules/caddyhttp/reverseproxy/selectionpolicies.go

@@ -136,8 +136,15 @@ func (r *WeightedRoundRobinSelection) Select(pool UpstreamPool, _ *http.Request,
 		return pool[0]
 	}
 	var index, totalWeight int
+	var weights []int
+
+	for _, w := range r.Weights {
+		if w > 0 {
+			weights = append(weights, w)
+		}
+	}
 	currentWeight := int(atomic.AddUint32(&r.index, 1)) % r.totalWeight
-	for i, weight := range r.Weights {
+	for i, weight := range weights {
 		totalWeight += weight
 		if currentWeight < totalWeight {
 			index = i
@@ -145,9 +152,9 @@ func (r *WeightedRoundRobinSelection) Select(pool UpstreamPool, _ *http.Request,
 		}
 	}
 
-	upstreams := make([]*Upstream, 0, len(r.Weights))
-	for _, upstream := range pool {
-		if !upstream.Available() {
+	upstreams := make([]*Upstream, 0, len(weights))
+	for i, upstream := range pool {
+		if !upstream.Available() || r.Weights[i] == 0 {
 			continue
 		}
 		upstreams = append(upstreams, upstream)

modules/caddyhttp/reverseproxy/selectionpolicies_test.go

@@ -131,6 +131,50 @@ func TestWeightedRoundRobinPolicy(t *testing.T) {
 	}
 }
 
+func TestWeightedRoundRobinPolicyWithZeroWeight(t *testing.T) {
+	pool := testPool()
+	wrrPolicy := WeightedRoundRobinSelection{
+		Weights:     []int{0, 2, 1},
+		totalWeight: 3,
+	}
+	req, _ := http.NewRequest("GET", "/", nil)
+
+	h := wrrPolicy.Select(pool, req, nil)
+	if h != pool[1] {
+		t.Error("Expected first weighted round robin host to be second host in the pool.")
+	}
+
+	h = wrrPolicy.Select(pool, req, nil)
+	if h != pool[2] {
+		t.Error("Expected second weighted round robin host to be third host in the pool.")
+	}
+
+	h = wrrPolicy.Select(pool, req, nil)
+	if h != pool[1] {
+		t.Error("Expected third weighted round robin host to be second host in the pool.")
+	}
+
+	// mark second host as down
+	pool[1].setHealthy(false)
+	h = wrrPolicy.Select(pool, req, nil)
+	if h != pool[2] {
+		t.Error("Expect select next available host.")
+	}
+
+	h = wrrPolicy.Select(pool, req, nil)
+	if h != pool[2] {
+		t.Error("Expect select only available host.")
+	}
+
+	pool[1].setHealthy(true)
+
+	h = wrrPolicy.Select(pool, req, nil)
+	if h != pool[1] {
+		t.Error("Expect select first host on availability.")
+	}
+
+}
+
 func TestLeastConnPolicy(t *testing.T) {
 	pool := testPool()
 	lcPolicy := LeastConnSelection{}