RUST-522 Implement resume functionality for change streams #547
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abr-egn
commented
Jan 7, 2022
| @@ -227,11 +220,47 @@ where | |||
| T: DeserializeOwned + Unpin + Send + Sync, | |||
| { | |||
| fn poll_next_in_batch(&mut self, cx: &mut Context<'_>) -> Poll<Result<BatchValue>> { | |||
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This is essentially the manual state machine version of SessionChangeStream::next_if_any. Hopefully at some point Rust gets reasonable first-class syntax for streams.
I considered trying to write this by wrapping an async function in a stream adaptor for clarity, but that ended up needing to be self-referential.
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Overall looks good! Great work with handling this, I know it has been a lot more complicated than originally anticipated. I have a few minor questions and one concern about handling implicit sessions. I agree with the approach to cutting out the Stream + SessionChangeStream combo for now as we discussed in triage.
patrickfreed
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Jan 13, 2022
isabelatkinson
approved these changes
Jan 14, 2022
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RUST-522
This lets change streams resume when encountering appropriate errors.
Unfortunately, I couldn't find a way to implement
SessionChangeStream::valueswithout resorting to unsafe code to dodge around lifetime restrictions; for now, I've removed that interface and filed RUST-1139 to track implementing it in the future. SinceSessionChangeStreamexposes bothnextandnext_if_any, iteration is still possible and reasonably convenient; the main loss is the API consistency with cursors and the convenient combinators available forStream.