Function CopyWithCtx

pkg/utils/io.go:26–51

CopyWithCtx slightly modified function signature: - context has been added in order to propagate cancellation - I do not return the number of bytes written, has it is not useful in my use case

(ctx context.Context, out io.Writer, in io.Reader, size int64, progress func(percentage float64))

// - context has been added in order to propagate cancellation
// - I do not return the number of bytes written, has it is not useful in my use case
func CopyWithCtx(ctx context.Context, out io.Writer, in io.Reader, size int64, progress func(percentage float64)) error {
	// Copy will call the Reader and Writer interface multiple time, in order
	// to copy by chunk (avoiding loading the whole file in memory).
	// I insert the ability to cancel before read time as it is the earliest
	// possible in the call process.
	var finish int64 = 0
	s := size / 100
	_, err := CopyWithBuffer(out, readerFunc(func(p []byte) (int, error) {
		// golang non-blocking channel: https://gobyexample.com/non-blocking-channel-operations
		select {
		// if context has been canceled
		case <-ctx.Done():
			// stop process and propagate "context canceled" error
			return 0, ctx.Err()
		default:
			// otherwise just run default io.Reader implementation
			n, err := in.Read(p)
			if s > 0 && (err == nil || err == io.EOF) {
				finish += int64(n)
				progress(float64(finish) / float64(s))
			}
			return n, err
		}
	}))
	return err
}

type limitWriter struct {
	w     io.Writer