perf(mtp): try parent=0xFFFFFFFF for root listing before fallback

[num13ru]

Summary

• Root listing (list_objects_stream(None)) now tries parent=0xFFFFFFFF first for all devices, not just Android. Falls back to parent=0 only when the device rejects the request with an error.
• Fixes a 110x over-fetch on Kindle Paperwhite (and likely other non-Android MTP devices) where GetObjectHandles(parent=0) returned every object on the storage (2541) instead of the 23 root-level items.
• Adds tests for the fast path, fallback on error, empty-storage edge case, Kindle-specific vendor extension, and subfolder-skips-fast-path.

Approach

Instead of adding device-specific detection, make the fast path universal:

1. Root listing → try GetObjectHandles(parent=0xFFFFFFFF) first
2. Ok(handles) → return immediately with AndroidRoot parent filter (accepts parent 0 or 0xFFFFFFFF)
3. Ok([]) → treat as empty storage (no fallback — an empty result is valid)
4. Err(_) → fall through to parent=0 + Exact(ROOT) filter (existing behaviour)
5. Subfolder listing → unchanged, goes directly to the specified parent handle

Worst case for a device that rejects 0xFFFFFFFF: one extra USB round-trip before the existing path runs. Samsung InvalidObjectHandle fallback and Fuji parent filtering are preserved in the fallback path.

Tests

• stream_root_falls_back_on_error — device rejects 0xFFFFFFFF, listing uses parent=0 with Exact(ROOT) filter
• stream_root_empty_is_not_fallback — empty Ok([]) is accepted as empty storage
• stream_kindle_root_uses_fast_path — non-Android vendor extension takes the fast path
• stream_subfolder_skips_fast_path — subfolder listings don't attempt 0xFFFFFFFF
• Existing tests updated: stream_filters_by_parent and stream_root_accepts_both_parent_values no longer require is_android()
• Integration test on physical Kindle Paperwhite (tested manually, 2541 → 23 handles)

Closes #8

[vdavid]

Hey @num13ru! Great work!
I ran the full suite against my Pixel 9 Pro XL, and I saw all unit+int tests and checks pass. Root listing returned 17 objects in ~1.7s on the Pixel (correct).
I'll merge this now and cut a release shortly.
Thanks for making the lib better for everyone! ❤️

[vdavid]

Just shipped this in https://crates.io/crates/mtp-rs/0.13.2.

[num13ru]

@vdavid thanks a lot! I really like this library and I'm glad I could help improve it

I will keep testing it on real devices and will continue contributing possible correctness fixes and performance improvements when I find them

Thanks for maintaining the project and for the quick release!

[vdavid]

@num13ru, just curious, what are you building?

[num13ru]

@vdavid this https://github.com/num13ru/mtp-tui
I'm constantly transferring books to my Kindle and I'm tired of OpenMTP’s clunky GUI
So I decided to build my own tool that would be faster and more user-friendly (thanks to mtp-rs & ratatui) 🙂

[vdavid]

@num13ru Nice! Not sure if you're in this for the hacking itself, but if you want to see another solution and you're on a mac, I also recommend my file manager Cmdr, built on top of this lib and 100% free for copying books to Kindles :)