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: nsq_to_nsq.go
    path of file: ./repos/nsq/apps/nsq_to_nsq
    
    the code of the file until where you have to start completion: // This is an NSQ client that reads the specified topic/channel
// and re-publishes the messages to destination nsqd via TCP

package main

import (
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"log"
	"os"
	"os/signal"
	"strconv"
	"sync/atomic"
	"syscall"
	"time"

	"github.com/bitly/go-hostpool"
	"github.com/bitly/timer_metrics"
	"github.com/nsqio/go-nsq"
	"github.com/nsqio/nsq/internal/app"
	"github.com/nsqio/nsq/internal/protocol"
	"github.com/nsqio/nsq/internal/version"
)

const (
	ModeRoundRobin = iota
	ModeHostPool
)

var (
	showVersion = fl
    
func (ph *PublishHandler) responder() {
	var msg *nsq.Message
	var startTime time.Time
	var address string
	var hostPoolResponse hostpool.HostPoolResponse

	for t := range ph.respChan {
		switch ph.mode {
		case ModeRoundRobin:
			msg = t.Args[0].(*nsq.Message)
			startTime = t.Args[1].(time.Time)
			hostPoolResponse = nil
			address = t.Args[2].(string)
		case ModeHostPool:
			msg = t.Args[0].(*nsq.Message)
			startTime = t.Args[1].(time.Time)
			hostPoolResponse = t.Args[2].(hostpool.HostPoolResponse)
			address = hostPoolResponse.Host()
		}

		success := t.Error == nil

		if hostPoolResponse != nil {
			if !success {
				hostPoolResponse.Mark(errors.New("failed"))
			} else {
				hostPoolResponse.Mark(nil)
			}
		}

		if success {
			msg.Finish()
		} else {
			msg.Requeue(-1)
		}

		ph.perAddressStatus[address].Status(startTime)
		ph.timermetrics.Status(startTime)
	}
}