The fetch crate is about to serve downloads whose file names, sizes and addresses come from a user-editable list,
so it checks them before touching the disk: an ordinary, unique file name (no separators, drive or stream
syntax, control characters, trailing dots, Windows device names or .part suffix), a non-zero size within the
caller's bound, a well-formed SHA-256, bounded file, mirror and attempt counts, and URLs capped at 16 KiB.
FileSpec now borrows its strings (callers with static names are unchanged) so a name read from a file needs no
leaking. download_url fetches one file from an exact address, query string included, for signed links.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
MarekSpodBiedry