[Typescript] fix prevent message cache size from becoming zero #418
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Fixes a critical bug where the message cache size calculation could result in 0, causing "Consume was already called" errors and stopping message processing. ## Root Cause When consumption was slow or message rate was low, #messageCacheMaxSize calculated to 0. JavaScript's truthy check (0 && callback is falsy) caused consume(0, callback) to call _consumeLoop() instead of _consumeNum(), starting a persistent background loop that blocked all other workers. ## Solution Added Math.max(1, ...) to ensure cache size is always at least 1, plus defensive validation in the consume() method. ## When This Occurs The bug triggers when messagesPerMillisecondSingleWorker < 0.000333, which happens with: - Slow eachMessage/eachBatch callbacks (DB writes, HTTP calls, etc.) - Low message volumes across multiple partitions - High partitionsConsumedConcurrently settings ## Example Processing 3 messages across 5 partitions taking 6 seconds: ```javascript messagesPerMillisecondSingleWorker = 3 / 5 / 6000 = 0.0001 Math.round(1500 * 0.0001) = 0 // Bug triggers ``` Fixes confluentinc#415
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Pull request overview
This PR fixes a critical bug where the message cache size calculation could incorrectly evaluate to 0, causing message processing to halt with "Consume was already called" errors. The fix ensures the cache size is always at least 1 by adding 1 inside the Math.ceil() call before performing the calculation.
Key Changes:
- Modified cache size calculation to guarantee minimum value of 1
- Prevents division-by-zero-like behavior when message consumption is slow or message rates are low
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Fixes a critical bug where the message cache size calculation could result in 0, causing "Consume was already called" errors and stopping message processing.
Root Cause
When consumption was slow or message rate was low, #messageCacheMaxSize calculated to 0. JavaScript's truthy check (0 && callback is falsy) caused consume(0, callback) to call _consumeLoop() instead of _consumeNum(), starting a persistent background loop that blocked all other workers.
Solution
Added Math.max(1, ...) to ensure cache size is always at least 1, plus defensive validation in the consume() method.
When This Occurs
The bug triggers when messagesPerMillisecondSingleWorker < 0.000333, which happens with:
Example
Processing 3 messages across 5 partitions taking 6 seconds:
Fixes #415