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/faasd/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 im
    
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).
			sc, err := b.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{HealthCheckEnabled: b.config.HealthCheck})
			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 {
			b.cc.RemoveSubConn(sc)
			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
}