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: backend.go
    path of file: ./repos/zrok/endpoints/tcpTunnel
    
    the code of the file until where you have to start completion: package tcpTunnel

import (
	"github.com/openziti/sdk-golang/ziti"
	"github.com/openziti/sdk-golang/ziti/edge"
	"github.com/openziti/zrok/endpoints"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"net"
	"time"
)

type BackendConfig struct {
	IdentityPath    string
	EndpointAddress string
	ShrTok
    
func NewBackend(cfg *BackendConfig) (*Backend, error) {
	options := ziti.ListenOptions{
		ConnectTimeout:               5 * time.Minute,
		WaitForNEstablishedListeners: 1,
	}
	zcfg, err := ziti.NewConfigFromFile(cfg.IdentityPath)
	if err != nil {
		return nil, errors.Wrap(err, "error loading config")
	}
	zctx, err := ziti.NewContext(zcfg)
	if err != nil {
		return nil, errors.Wrap(err, "error loading ziti context")
	}
	listener, err := zctx.ListenWithOptions(cfg.ShrToken, &options)
	if err != nil {
		return nil, errors.Wrap(err, "error listening")
	}
	b := &Backend{
		cfg:      cfg,
		listener: listener,
	}
	return b, nil
}