weightedroundrobin: Move functions to manage Endpoint weights into a new internal package (#8087)

Author: arjan-bal

balancer/weightedroundrobin/balancer.go

@@ -16,6 +16,15 @@
  *
  */
 
+// Package weightedroundrobin provides an implementation of the weighted round
+// robin LB policy, as defined in [gRFC A58].
+//
+// # Experimental
+//
+// Notice: This package is EXPERIMENTAL and may be changed or removed in a
+// later release.
+//
+// [gRFC A58]: https://github.com/grpc/proposal/blob/master/A58-client-side-weighted-round-robin-lb-policy.md
 package weightedroundrobin
 
 import (

balancer/weightedroundrobin/weightedroundrobin.go

@@ -0,0 +1,66 @@
+/*
+ *
+ * Copyright 2025 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+// Package weight contains utilities to manage endpoint weights. Weights are
+// used by LB policies such as ringhash to distribute load across multiple
+// endpoints.
+package weight
+
+import (
+	"fmt"
+
+	"google.golang.org/grpc/resolver"
+)
+
+// attributeKey is the type used as the key to store EndpointInfo in the
+// Attributes field of resolver.Endpoint.
+type attributeKey struct{}
+
+// EndpointInfo will be stored in the Attributes field of Endpoints in order to
+// use the ringhash balancer.
+type EndpointInfo struct {
+	Weight uint32
+}
+
+// Equal allows the values to be compared by Attributes.Equal.
+func (a EndpointInfo) Equal(o any) bool {
+	oa, ok := o.(EndpointInfo)
+	return ok && oa.Weight == a.Weight
+}
+
+// Set returns a copy of endpoint in which the Attributes field is updated with
+// EndpointInfo.
+func Set(endpoint resolver.Endpoint, epInfo EndpointInfo) resolver.Endpoint {
+	endpoint.Attributes = endpoint.Attributes.WithValue(attributeKey{}, epInfo)
+	return endpoint
+}
+
+// String returns a human-readable representation of EndpointInfo.
+// This method is intended for logging, testing, and debugging purposes only.
+// Do not rely on the output format, as it is not guaranteed to remain stable.
+func (a EndpointInfo) String() string {
+	return fmt.Sprintf("Weight: %d", a.Weight)
+}
+
+// FromEndpoint returns the EndpointInfo stored in the Attributes field of an
+// endpoint. It returns an empty EndpointInfo if attribute is not found.
+func FromEndpoint(endpoint resolver.Endpoint) EndpointInfo {
+	v := endpoint.Attributes.Value(attributeKey{})
+	ei, _ := v.(EndpointInfo)
+	return ei
+}

balancer/weightedroundrobin/weightedroundrobin_test.go

@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 2025 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package weight_test
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"google.golang.org/grpc/attributes"
+	"google.golang.org/grpc/internal/balancer/weight"
+	"google.golang.org/grpc/internal/grpctest"
+	"google.golang.org/grpc/resolver"
+)
+
+type s struct {
+	grpctest.Tester
+}
+
+func Test(t *testing.T) {
+	grpctest.RunSubTests(t, s{})
+}
+
+func (s) TestEndpointInfoToAndFromAttributes(t *testing.T) {
+	tests := []struct {
+		desc              string
+		inputEndpointInfo weight.EndpointInfo
+		inputAttributes   *attributes.Attributes
+		wantEndpointInfo  weight.EndpointInfo
+	}{
+		{
+			desc:              "empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{Weight: 100},
+			inputAttributes:   nil,
+			wantEndpointInfo:  weight.EndpointInfo{Weight: 100},
+		},
+		{
+			desc:              "non-empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{Weight: 100},
+			inputAttributes:   attributes.New("foo", "bar"),
+			wantEndpointInfo:  weight.EndpointInfo{Weight: 100},
+		},
+		{
+			desc:              "endpointInfo_not_present_in_empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{},
+			inputAttributes:   nil,
+			wantEndpointInfo:  weight.EndpointInfo{},
+		},
+		{
+			desc:              "endpointInfo_not_present_in_non-empty_attributes",
+			inputEndpointInfo: weight.EndpointInfo{},
+			inputAttributes:   attributes.New("foo", "bar"),
+			wantEndpointInfo:  weight.EndpointInfo{},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			endpoint := resolver.Endpoint{Attributes: test.inputAttributes}
+			endpoint = weight.Set(endpoint, test.inputEndpointInfo)
+			gotEndpointInfo := weight.FromEndpoint(endpoint)
+			if !cmp.Equal(gotEndpointInfo, test.wantEndpointInfo) {
+				t.Errorf("gotEndpointInfo: %v, wantEndpointInfo: %v", gotEndpointInfo, test.wantEndpointInfo)
+			}
+
+		})
+	}
+}

internal/balancer/weight/weight.go

@@ -23,7 +23,7 @@ import (
 	"fmt"
 	"sort"
 
-	"google.golang.org/grpc/balancer/weightedroundrobin"
+	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/hierarchy"
 	internalserviceconfig "google.golang.org/grpc/internal/serviceconfig"
 	"google.golang.org/grpc/resolver"
@@ -281,7 +281,7 @@ func priorityLocalitiesToClusterImpl(localities []xdsresource.Locality, priority
 			if endpoint.Weight != 0 {
 				ew = endpoint.Weight
 			}
-			resolverEndpoint = weightedroundrobin.SetAddrInfoInEndpoint(resolverEndpoint, weightedroundrobin.AddrInfo{Weight: lw * ew})
+			resolverEndpoint = weight.Set(resolverEndpoint, weight.EndpointInfo{Weight: lw * ew})
 			retEndpoints = append(retEndpoints, resolverEndpoint)
 		}
 	}

internal/balancer/weight/weight_test.go

@@ -30,7 +30,7 @@ import (
 	"google.golang.org/grpc/attributes"
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/roundrobin"
-	"google.golang.org/grpc/balancer/weightedroundrobin"
+	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/internal/hierarchy"
 	iserviceconfig "google.golang.org/grpc/internal/serviceconfig"
 	"google.golang.org/grpc/internal/xds/bootstrap"
@@ -653,7 +653,7 @@ func testEndpointWithAttrs(addrStrs []string, localityWeight, endpointWeight uin
 	}
 	endpoint = hierarchy.SetInEndpoint(endpoint, path)
 	endpoint = wrrlocality.SetAddrInfoInEndpoint(endpoint, wrrlocality.AddrInfo{LocalityWeight: localityWeight})
-	endpoint = weightedroundrobin.SetAddrInfoInEndpoint(endpoint, weightedroundrobin.AddrInfo{Weight: localityWeight * endpointWeight})
+	endpoint = weight.Set(endpoint, weight.EndpointInfo{Weight: localityWeight * endpointWeight})
 	return endpoint
 }
 

xds/internal/balancer/clusterresolver/configbuilder.go

@@ -23,9 +23,10 @@ import (
 	"math"
 	"testing"
 
-	xxhash "github.com/cespare/xxhash/v2"
-	"google.golang.org/grpc/balancer/weightedroundrobin"
+	"google.golang.org/grpc/internal/balancer/weight"
 	"google.golang.org/grpc/resolver"
+
+	xxhash "github.com/cespare/xxhash/v2"
 )
 
 var testEndpoints []resolver.Endpoint
@@ -43,9 +44,9 @@ func init() {
 	testEndpointStateMap.Set(testEndpoints[2], &endpointState{firstAddr: "c", weight: 4})
 }
 
-func testEndpoint(addr string, weight uint32) resolver.Endpoint {
+func testEndpoint(addr string, endpointWeight uint32) resolver.Endpoint {
 	ep := resolver.Endpoint{Addresses: []resolver.Address{{Addr: addr}}}
-	return weightedroundrobin.SetAddrInfoInEndpoint(ep, weightedroundrobin.AddrInfo{Weight: weight})
+	return weight.Set(ep, weight.EndpointInfo{Weight: endpointWeight})
 }
 
 func (s) TestRingNew(t *testing.T) {