// WriteHeaders writes the response headers for conditional requests
func (oi ObjectInfo) WriteHeaders(w http.ResponseWriter, preamble, statusCode func()) {
	preamble()

	if !oi.ModTime.IsZero() {
		w.Header().Set(xhttp.LastModified, oi.ModTime.UTC().Format(http.TimeFormat))
	}

	if oi.ETag != "" {
		w.Header()[xhttp.ETag] = []string{"\"" + oi.ETag + "\""}
	}

	if oi.Expires != "" {
		w.Header().Set(xhttp.Expires, oi.Expires)
	}

	for obj := range objCh {
		if obj.Err != nil {
			log.Fatalf("Listing error: %v", obj.Err)
		}
		fmt.Printf("Key: %s\nSize: %d\nLast Modified: %s\n===\n", obj.Key, obj.Size, obj.LastModified)
	}

	for obj := range objCh {
		if obj.Err != nil {
			log.Fatalf("Listing error: %v", obj.Err)
		}
		fmt.Printf("Key: %s\nSize: %d\nLast Modified: %s\n===\n", obj.Key, obj.Size, obj.LastModified)
	}

	// set common headers
	setCommonHeaders(w)

	// Set last modified time.
	lastModified := objInfo.ModTime.UTC().Format(http.TimeFormat)
	w.Header().Set(xhttp.LastModified, lastModified)

	// Set Etag if available.
	if objInfo.ETag != "" {
		w.Header()[xhttp.ETag] = []string{"\"" + objInfo.ETag + "\""}
	}

	if objInfo.ContentType != "" {

		for object := range s3Client.ListObjects(context.Background(), bucket, opts) {
			if object.Err != nil {
				log.Println("FAILED: LIST with error:", object.Err)
				continue
			}
			if !minModTime.IsZero() && object.LastModified.Before(minModTime) {
				continue
			}
			if object.IsDeleteMarker {
				log.Println("SKIPPED: DELETE marker object:", objFullPath(object))
				continue
			}

	nextObject := func(ch <-chan minio.ObjectInfo) (ctnt minio.ObjectInfo, ok bool) {
		for {
			ctnt, ok := <-ch
			if !ok {
				return minio.ObjectInfo{}, false
			}
			if ctnt.LastModified.Before(maxObjectModTime) {
				return ctnt, ok
			}
		}
	}

	sclnt, err := buildS3Client(sourceEndpoint, sourceAccessKey, sourceSecretKey, insecure)
	if err != nil {
		log.Fatalln(err)
	}

	for obj := range objCh {
		if obj.Err != nil {
			log.Fatalf("Listing error: %v", obj.Err)
		}
		fmt.Printf("Key: %s\nSize: %d\nLast Modified: %s\n===\n", obj.Key, obj.Size, obj.LastModified)
	}