Fix document creation race condition #221
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rolyatmax
approved these changes
Apr 16, 2024
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When a client attempts to create a new doc with a given name, we first check if the doc exists and if not we put an empty doc on S3. There is a potential race condition where if two requests check if a doc exists, they will both write an empty file. If the file has since changed, those changes will be erased.
I thought this was mostly theoretical, but I want to rule it out as it seems to be happening.
The fix is that, instead of attempting to create the empty file from the stateless worker, we delegate file creation to the durable object itself. This means instantiating the durable object earlier in the connection lifecycle, but has the advantage that the document will only be created if it does not already exist (since there is guaranteed to only be one instance of the durable object).