pkg/download/save.go

package download

import (
	"io"
	"os"

	"github.com/go-kit/kit/log"
	"github.com/pkg/errors"
)

const (
	writeBufSize = 1024 * 8
)

// SaveTo uses given downloader to fetch the resource with retries and saves the
// given file. Directory of dst is not created by this function. If a file at
// dst exists, it will be truncated. If a new file is created, mode is used to
// set the permission bits. Written number of bytes are returned on success.
func SaveTo(ctx *log.Context, downloaders []Downloader, dst string, mode os.FileMode) (int64, error) {
	f, err := os.OpenFile(dst, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, mode)
	if err != nil {
		return 0, errors.Wrapf(err, "failed to open file for writing: %s", dst)
	}
	defer f.Close()

	body, err := WithRetries(ctx, downloaders, ActualSleep)
	if err != nil {
		return 0, errors.Wrapf(err, "failed to download file '%s'", dst)
	}
	defer body.Close()

	n, err := io.CopyBuffer(f, body, make([]byte, writeBufSize))
	return n, errors.Wrapf(err, "failed to write to file: %s", dst)
}