Function copy_one_checked

pub fn copy_one_checked(
    source: &Path,
    destination: &Path,
    expected_size: u64,
    verify: bool,
    replace: bool,
    verify_existing: bool,
) -> Result<Wrote, String>

Copies a file, optionally requiring matching bytes for an existing output.

A mismatching existing output is retained and reported as an error; explicit replacement is required to refresh it. Verification has fixed memory use.