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: gateway.go
    path of file: ./repos/learning/golang/practice/go-crontab/gopath/src/github.com/coreos/etcd/etcdmain
    
    the code of the file until where you have to start completion: // Copyright 2016 The etcd 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 etcdmain

import (
	"fmt"
	"net"
	"net/url"
	"os"
	"time"

	"github.com/coreos/etcd/proxy/tcpproxy"

	"github.com/spf13/cobra"
	"go.uber.org/zap"
)

var (
	gatewayListenAddr        string
	gatewayEndpoints         []string
	gatewayDNSCluster        string
	gatewayInsecureDiscovery bool
	getewayRetryDelay  
    
func startGateway(cmd *cobra.Command, args []string) {
	var lg *zap.Logger
	lg, err := zap.NewProduction()
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	srvs := discoverEndpoints(lg, gatewayDNSCluster, gatewayCA, gatewayInsecureDiscovery)
	if len(srvs.Endpoints) == 0 {
		// no endpoints discovered, fall back to provided endpoints
		srvs.Endpoints = gatewayEndpoints
	}
	// Strip the schema from the endpoints because we start just a TCP proxy
	srvs.Endpoints = stripSchema(srvs.Endpoints)
	if len(srvs.SRVs) == 0 {
		for _, ep := range srvs.Endpoints {
			h, p, serr := net.SplitHostPort(ep)
			if serr != nil {
				fmt.Printf("error parsing endpoint %q", ep)
				os.Exit(1)
			}
			var port uint16
			fmt.Sscanf(p, "%d", &port)
			srvs.SRVs = append(srvs.SRVs, &net.SRV{Target: h, Port: port})
		}
	}

	if len(srvs.Endpoints) == 0 {
		fmt.Println("no endpoints found")
		os.Exit(1)
	}

	var l net.Listener
	l, err = net.Listen("tcp", gatewayListenAddr)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	tp := tcpproxy.TCPProxy{
		Logger:          lg,
		Listener:        l,
		Endpoints:       srvs.SRVs,
		MonitorInterval: getewayRetryDelay,
	}

	// At this point, etcd gateway listener is initialized
	notifySystemd(lg)

	tp.Run()
}