Copy operations are (relatively) slow

[valoq]

It takes my setup about 1 second to copy a 1GB file using "cp"
But the same operation takes about 5 seconds in lf.

After digging through the code I am still unsure what causes this issue.

[MahouShoujoMivutilde]

Lf copies a file in relatively small chunks of fixed size (4KB)

lf/copy.go

Lines 51 to 86 in ce12116

	buf := make([]byte, 4096)
	r, err := os.Open(src)
	if err != nil {
	return err
	}
	defer r.Close()
	w, err := os.OpenFile(dst, os.O_RDWR|os.O_CREATE|os.O_TRUNC, dst_mode)
	if err != nil {
	return err
	}
	for {
	n, err := r.Read(buf)
	if err != nil && err != io.EOF {
	w.Close()
	os.Remove(dst)
	return err
	}
	if n == 0 {
	break
	}
	if _, err := w.Write(buf[:n]); err != nil {
	return err
	}
	nums <- int64(n)
	}
	if err := w.Close(); err != nil {
	os.Remove(dst)
	return err
	}

which could be suboptimal.

In an ideal world it would use io.Copy() (which could benefit from copy_file_range() to speed things up, allowing e.g. CoW fs reflinks, samba server side file copy, etc) instead of a custom implementation (which exists for a reason ⬇️).

However, it's also nice to have a % progress of an ongoing copy, which io.Copy() doesn't provide an easy way* to implement while keeping full scope of its benefits.

Increasing it to 4MB decreases the copy duration by about 30%.

* - at least I haven't found any in 2021.