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: dhcp6.go
    path of file: ./repos/router7/cmd/dhcp6
    
    the code of the file until where you have to start completion: // Copyright 2018 Google Inc.
//
// 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.

// Binary dhcp6 obtains a DHCPv6 lease, persists it to
// /perm/dhcp6/wire/lease.json and notifies netconfigd.
package main

import (
	"encoding/json"
	"flag"
	"io/ioutil"
	"os"
	"os/signal"
	"path/filepath"
	"syscall"
	"time"

	"github.com/google/renameio"
	"github.com/jpillora/backoff"
	"github.com/rtr7/router7/internal/dhcp6"
	"github.com/rtr7/router7/internal/notify"
	"github.com/rtr7/router7/internal/teelogger"
)

var log = teelogger.NewConsole()

func logic() error {
	const leasePath = "/perm/dhcp6/wire/lease.json"
	if err := os.MkdirAll(filepath.Dir(leasePath), 0755); err != nil {
		return err
	}

	duid, err := ioutil.ReadFile("/perm/dhcp6/duid")
	if err != nil {
		log.Printf("could not read /perm/dhcp6/duid (%v), proceeding with DUID-LLT", err)
	}

	c, err := dhcp6.NewClient(dh
    
func logic() error {
	const leasePath = "/perm/dhcp6/wire/lease.json"
	if err := os.MkdirAll(filepath.Dir(leasePath), 0755); err != nil {
		return err
	}

	duid, err := ioutil.ReadFile("/perm/dhcp6/duid")
	if err != nil {
		log.Printf("could not read /perm/dhcp6/duid (%v), proceeding with DUID-LLT", err)
	}

	c, err := dhcp6.NewClient(dhcp6.ClientConfig{
		InterfaceName: "uplink0",
		DUID:          duid,
	})
	if err != nil {
		return err
	}
	usr2 := make(chan os.Signal, 1)
	signal.Notify(usr2, syscall.SIGUSR2)
	backoff := backoff.Backoff{
		Factor: 2,
		Jitter: true,
		Min:    10 * time.Second,
		Max:    1 * time.Minute,
	}

	for c.ObtainOrRenew() {
		if err := c.Err(); err != nil {
			dur := backoff.Duration()
			log.Printf("Temporary error: %v (waiting %v)", err, dur)
			time.Sleep(dur)
			continue
		}
		backoff.Reset()
		log.Printf("lease: %+v", c.Config())
		b, err := json.Marshal(c.Config())
		if err != nil {
			return err
		}
		if err := renameio.WriteFile(leasePath, b, 0644); err != nil {
			return err
		}
		if err := notify.Process("/user/netconfigd", syscall.SIGUSR1); err != nil {
			log.Printf("notifying netconfig: %v", err)
		}
		if err := notify.Process("/user/radvd", syscall.SIGUSR1); err != nil {
			log.Printf("notifying radvd: %v", err)
		}
		select {
		case <-time.After(time.Until(c.Config().RenewAfter)):
			// fallthrough and renew the DHCP lease
		case <-usr2:
			log.Printf("SIGUSR2 received, sending DHCPRELEASE")
			if _, _, err := c.Release(); err != nil {
				return err
			}
			os.Exit(125) // quit supervision by gokrazy
		}
	}
	return c.Err() // permanent error
}