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: s3.go
    path of file: ./repos/client/go/release/update
    
    the code of the file until where you have to start completion: // Copyright 2015 Keybase, Inc. All rights reserved. Use of
// this source code is governed by the included BSD license.

package update

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"text/tabwriter"
	"time"

	"github.com/alecthomas/template"
	"github.com/blang/semver"
	"github.com/keybase/client/go/release/version"

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

const defaultCacheControl = "max-age=60"

const defaultChannel = "v2"

// Section defines a set of releases
type Section struct {
	Header   string
	Releases []Release
}

// Release defines a release bundle
type Release struct {
	Name       string
	Key        string
	URL        string
	Version    string
	DateString string
	Date       time.Time
	Commit     string
}

// ByRelease defines how to sort releases
type ByRelease []Release

func (s ByRelease) Len() int {
	return len(s)
}

func (s ByRelease) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

func (s ByR
    
func (c *Client) promoteAReleaseToProd(releaseName string, bucketName string, platform Platform, env string, toChannel string, dryRun bool) (release *Release, err error) {
	var filePath string
	switch platform.Name {
	case PlatformTypeDarwin, PlatformTypeDarwinArm64:
		filePath = fmt.Sprintf("Keybase-%s.dmg", releaseName)
	case PlatformTypeWindows:
		filePath = fmt.Sprintf("Keybase_%s.amd64.msi", releaseName)
	default:
		return nil, fmt.Errorf("Unsupported for this platform: %s", platform.Name)
	}

	release, err = platform.FindRelease(bucketName, func(r Release) bool {
		return r.Name == filePath
	})
	if err != nil {
		return nil, err
	}
	if release == nil {
		return nil, fmt.Errorf("No matching release found")
	}
	log.Printf("Found %s release %s (%s), %s", platform.Name, release.Name, time.Since(release.Date), release.Version)
	jsonName := updateJSONName(toChannel, platform.Name, env)
	jsonURL := urlString(bucketName, platform.PrefixSupport, fmt.Sprintf("update-%s-%s-%s.json", platform.Name, env, release.Version))

	if dryRun {
		log.Printf("DRYRUN: Would PutCopy %s to %s\n", jsonURL, jsonName)
		return release, nil
	}
	log.Printf("PutCopying %s to %s\n", jsonURL, jsonName)
	_, err = c.svc.CopyObject(&s3.CopyObjectInput{
		Bucket:       aws.String(bucketName),
		CopySource:   aws.String(jsonURL),
		Key:          aws.String(jsonName),
		CacheControl: aws.String(defaultCacheControl),
		ACL:          aws.String("public-read"),
	})
	return release, err
}