PanicException('called `Option::unwrap()` on a `None` value')

[chwzr]

When using a yjs-websocket server (https://github.com/yjs/y-websocket) the ypy-websocket provider does not sync properly:

thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', /root/.cargo/registry/src/github.qkg1.top-1ecc6299db9ec823/yrs-0.11.1/src/block.rs:1073:54

Traceback (most recent call last):
  File "/root/yspine-client/.venv/lib/python3.10/site-packages/ypy_websocket/websocket_provider.py", line 34, in _run
    await process_sync_message(message[1:], self._ydoc, self._websocket, self.log)
  File "/root/yspine-client/.venv/lib/python3.10/site-packages/ypy_websocket/yutils.py", line 130, in process_sync_message
    Y.apply_update(ydoc, update)
pyo3_runtime.PanicException: called `Option::unwrap()` on a `None` value

Other yjs clients on the same server work fine.
Please let me know if you need further details or something to reproduce.

Cheers,
chwzr

[davidbrochart]

Thanks for reporting @chwzr, yes a reproducible example would help a lot.

[chwzr]

hi @davidbrochart thanks for the quick reply!

here is a repo to reproduce the bug:

https://github.com/chwzr/ypy-sync-issue

[davidbrochart]

Thanks a lot @chwzr, I could reproduce the issue.
It happens when the ypy client receives a SYNC_STEP2 message from yjs, and could be linked to y-crdt/ypy#94.
cc @dmonad @Horusiath @Waidhoferj

[chwzr]

I saw this in the ypy drawing example:
https://github.com/y-crdt/ypy/blob/792dc96c8a55052b9123f1620856b977234188cf/examples/drawing/client.py#L30

so i updated the put_updates function to look like this:

def put_updates(update_queue: asyncio.Queue, ydoc: Y.YDoc, event: Y.AfterTransactionEvent) -> None:
    update = event.get_update()
    if update != b'\x00\x00':
        update_queue.put_nowait(update)

this will fix it for me now, but resolving y-crdt/ypy#94 would feel better, as even the Y.encode_state_vector function is producing empty updates.