reverseproxy: Allow `0` as weights for `weighted_round_robin` (#6681)

* Allow 0 as weights

Change positive to non-negative

* reverseproxy: allow 0 as weighted round robin value

* test: add more wrr select test

---------

Co-authored-by: peanutduck <[email protected]>

1 files changed, 13 insertions, 6 deletions

diff --git a/modules/caddyhttp/reverseproxy/selectionpolicies.go b/modules/caddyhttp/reverseproxy/selectionpolicies.go
index 293ff75e2..fcf7f90f6 100644
--- a/modules/caddyhttp/reverseproxy/selectionpolicies.go
+++ b/modules/caddyhttp/reverseproxy/selectionpolicies.go
@@ -111,8 +111,8 @@ func (r *WeightedRoundRobinSelection) UnmarshalCaddyfile(d *caddyfile.Dispenser)
 		if err != nil {
 			return d.Errf("invalid weight value '%s': %v", weight, err)
 		}
-		if weightInt < 1 {
-			return d.Errf("invalid weight value '%s': weight should be non-zero and positive", weight)
+		if weightInt < 0 {
+			return d.Errf("invalid weight value '%s': weight should be non-negative", weight)
 		}
 		r.Weights = append(r.Weights, weightInt)
 	}
@@ -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)