internal/balancer/weight/weight.go

/*
 *
 * 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
}