You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: balancer.go
    path of file: ./repos/streamdal/apps/server/vendor/google.golang.org/grpc/balancer/base
    
    the code of the file until where you have to start completion: /*
 *
 * Copyright 2017 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 base

import (
	"errors"
	"fmt"

	"google.golang.org/grpc/balancer"
	"google.golang.org/grpc/connectivity"
	"google.golang.org/grpc/grpclog"
	"google.golang.org/grpc/resolver"
)

var logger = grpclog.Component("balancer")

type baseBuilder struct {
	name          string
	pickerBuilder PickerBuilder
	config        Config
}

func (bb *baseBuilder) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
	bal := &baseBalancer{
		cc:            cc,
		pickerBuilder: bb.pickerBuilder,

		subConns: resolver.NewAddressMap(),
		scStates: make(map[balancer.SubConn]connectivity.State),
		csEvltr:  &balancer.ConnectivityStateEvaluator{},
		config:   bb.config,
		state:    connectivity.Connecting,
	}
	// Initialize picker to a picker that always returns
	// ErrNoSubConnAvailable, because when state of a SubConn changes, we
	// may call UpdateState with this picker.
	bal.picker = NewErrPicker(balancer.ErrNoSubConnAvailable)
	return bal
}

func (bb *baseBuilder) Name() string {
	return bb.name
}

type baseBalancer struct {
	cc            balancer.ClientConn
	pickerBuilder PickerBuilder

	csEvltr *balancer.ConnectivityState
    
func (b *baseBalancer) UpdateClientConnState(s balancer.ClientConnState) error {
	// TODO: handle s.ResolverState.ServiceConfig?
	if logger.V(2) {
		logger.Info("base.baseBalancer: got new ClientConn state: ", s)
	}
	// Successful resolution; clear resolver error and ensure we return nil.
	b.resolverErr = nil
	// addrsSet is the set converted from addrs, it's used for quick lookup of an address.
	addrsSet := resolver.NewAddressMap()
	for _, a := range s.ResolverState.Addresses {
		addrsSet.Set(a, nil)
		if _, ok := b.subConns.Get(a); !ok {
			// a is a new address (not existing in b.subConns).
			var sc balancer.SubConn
			opts := balancer.NewSubConnOptions{
				HealthCheckEnabled: b.config.HealthCheck,
				StateListener:      func(scs balancer.SubConnState) { b.updateSubConnState(sc, scs) },
			}
			sc, err := b.cc.NewSubConn([]resolver.Address{a}, opts)
			if err != nil {
				logger.Warningf("base.baseBalancer: failed to create new SubConn: %v", err)
				continue
			}
			b.subConns.Set(a, sc)
			b.scStates[sc] = connectivity.Idle
			b.csEvltr.RecordTransition(connectivity.Shutdown, connectivity.Idle)
			sc.Connect()
		}
	}
	for _, a := range b.subConns.Keys() {
		sci, _ := b.subConns.Get(a)
		sc := sci.(balancer.SubConn)
		// a was removed by resolver.
		if _, ok := addrsSet.Get(a); !ok {
			sc.Shutdown()
			b.subConns.Delete(a)
			// Keep the state of this sc in b.scStates until sc's state becomes Shutdown.
			// The entry will be deleted in updateSubConnState.
		}
	}
	// If resolver state contains no addresses, return an error so ClientConn
	// will trigger re-resolve. Also records this as an resolver error, so when
	// the overall state turns transient failure, the error message will have
	// the zero address information.
	if len(s.ResolverState.Addresses) == 0 {
		b.ResolverError(errors.New("produced zero addresses"))
		return balancer.ErrBadResolverState
	}

	b.regeneratePicker()
	b.cc.UpdateState(balancer.State{ConnectivityState: b.state, Picker: b.picker})
	return nil
}