func gzipDisk()

in cli_tools/gce_export/main.go [135:206]
62 lines of code
12 McCabe index (conditional complexity)

func gzipDisk(file *os.File, size int64, writer io.WriteCloser) error {
	wp := &progress{}
	gw, err := gzip.NewWriterLevel(io.MultiWriter(wp, writer), *level)
	if err != nil {
		return err
	}
	rp := &progress{}
	tw := tar.NewWriter(io.MultiWriter(rp, gw))

	ls := splitLicenses(*licenses)
	if ls != nil {
		fmt.Printf("GCEExport: Creating gzipped image of %q with licenses %q.\n", file.Name(), ls)
	} else {
		fmt.Printf("GCEExport: Creating gzipped image of %q.\n", file.Name())
	}
	start := time.Now()

	if ls != nil {
		type lsJSON struct {
			Licenses []string `json:"licenses"`
		}
		body, err := json.Marshal(lsJSON{Licenses: ls})
		if err != nil {
			return err
		}

		if err := tw.WriteHeader(&tar.Header{
			Name:   "manifest.json",
			Mode:   0600,
			Size:   int64(len(body)),
			Format: tar.FormatGNU,
		}); err != nil {
			return err
		}
		if _, err := tw.Write([]byte(body)); err != nil {
			return err
		}
	}
	if err := tw.WriteHeader(&tar.Header{
		Name:   "disk.raw",
		Mode:   0600,
		Size:   size,
		Format: tar.FormatGNU,
	}); err != nil {
		return err
	}

	go writeGzipProgress(start, size, rp, wp)

	if _, err := io.CopyN(tw, file, size); err != nil {
		return err
	}

	if err := tw.Close(); err != nil {
		return err
	}

	if err := gw.Close(); err != nil {
		return err
	}

	if err := writer.Close(); err != nil {
		return err
	}

	since := time.Since(start)
	spd := humanize.IBytes(uint64(size / int64(since.Seconds())))
	ratio := size / wp.total
	log.Printf("GCEExport: Finished creating gzipped image of %q in %s [%s/s] with a compression ratio of %d.", file.Name(), since, spd, ratio)

	return nil
}