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: statistics.go
    path of file: ./repos/trojan-go/statistic
    
    the code of the file until where you have to start completion: package statistic

import (
	"context"
	"io"
	"strings"
	"sync"

	"github.com/p4gefau1t/trojan-go/common"
	"github.com/p4gefau1t/trojan-go/log"
)

type TrafficMeter interface {
	io.Closer
	Hash() string
	AddTraffic(sent, recv
    
func NewAuthenticator(ctx context.Context, name string) (Authenticator, error) {
	// allocate a unique authenticator for each context
	createdAuthLock.Lock() // avoid concurrent map read/write
	defer createdAuthLock.Unlock()
	if auth, found := createdAuth[ctx]; found {
		log.Debug("authenticator has been created:", name)
		return auth, nil
	}
	creator, found := authCreators[strings.ToUpper(name)]
	if !found {
		return nil, common.NewError("auth driver name " + name + " not found")
	}
	auth, err := creator(ctx)
	if err != nil {
		return nil, err
	}
	createdAuth[ctx] = auth
	return auth, err
}