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: server.go
    path of file: ./repos/awless/vendor/github.com/aws/aws-sdk-go/example/service/s3/presignURL/server
    
    the code of the file until where you have to start completion: // +build example

package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"net"
	"net/http"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/endpoints"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/s3"
	"github.com/aws/aws-sdk-go/service/s3/s3iface"
	"github.com/aws/aws-sdk-go/service/s3/s3manager"
)

// server.go is an example of a service that vends lists for requests for presigned
// URL
    
func loadConfig() (addr, bucket, region string) {
	flag.StringVar(&bucket, "b", "", "S3 `bucket` object should be uploaded to.")
	flag.StringVar(&region, "r", "", "AWS `region` the bucket exists in, If not set region will be looked up, only valid for AWS Regions, not AWS China or Gov Cloud.")
	flag.StringVar(&addr, "a", "127.0.0.1:8080", "The TCP `address` the server will be started on.")
	flag.Parse()

	if len(bucket) == 0 {
		fmt.Fprintln(os.Stderr, "bucket is required")
		flag.PrintDefaults()
		os.Exit(1)
	}

	return addr, bucket, region
}