fix: fix possible non-termination in ingest_drop().

[zicklag]

Fixes an issue where ingest_drop() may not terminate.

I ran into this issue while adding a way to import drops in earthstar. I'm honestly not sure why the same issue isn't run into in the willow test cases, but I do have a failing test case in a PR to the Earthstar repo.

The issue is that we are pushing chunks into the FIFO and then later here, we are triggering a for await loop that will never end because the FIFO has no concept of an EOF or terminating message.

Then a little bit further down the code we are awaiting on the promise running that endless loop, so that we never finish.

This gets around the issue by wrapping the FIFO in a generator that will properly exit when we push an undefined to it. That way we can indicate the end of the stream.

[sgwilym]

Interesting that there were no failing test cases here for so long! As you're right, this FIFO should never end.

Would you be so kind as to make one modification? This kind of stopping pattern is used elsewhere in the codebase, but uses a symbol instead of undefined (e.g.

willow-js/src/wgps/data/payload_ingester.ts

Line 22 in 6c22c02

fifo: FIFO<Uint8Array | typeof CANCELLATION>;

). This makes it a little clearer what's happening.

Thank you!

[zicklag]

Ah, great idea I'll do that!