fix(stream): handle S3 upload errors without crashing the process#220
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fix(stream): handle S3 upload errors without crashing the process#220
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When an S3 upload fails (e.g., RequestTimeout), the error flows through
toS3()'s .catch() handler which calls toS3Stream.emit("error", err).
If no error listener is attached to that stream, emit("error") throws,
and since the throw happens inside a .catch() handler, it creates a new
unhandled promise rejection that crashes the Lambda runtime.
Three changes:
1. toS3() .catch(): Stop calling emit("error") on the stream. Just
store the error and set the emittedError flag. The error propagates
through the _final callback when the stream is ended.
2. leos3.js newStream(): Add an error listener on the internal s3
upload stream so any error events have a listener and don't throw.
3. leos3.js submitStream(): Listen for both "error" and "finish"
events with a callback guard. Previously only "finish" was handled,
but _final(callback) with a truthy error emits "error" not "finish".
Task: ES-2976
Made-with: Cursor
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Revert the leo-stream.js change from 9f65041. The original behavior of emitting the error on toS3Stream is correct — the fix in leos3.js adds the missing error listener that catches it. Task: ES-2976
czirker
approved these changes
Apr 2, 2026
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Summary
leos3.jssoemit("error")fromtoS3()has a handler and doesn't throwerrorandfinishevents insubmitStream()with a callback guard, since_final(callback)with a truthy error emitserrornotfinishTask Reference
Changes Made
lib/stream/helper/leos3.js— Add.on('error')handler when creating the S3 stream innewStream(), and handle botherror/finishevents insubmitStream()Root Cause
When an S3 upload fails (e.g.,
RequestTimeout),toS3()'s.catch()callstoS3Stream.emit("error", err). Inleos3.js, the internals3 = ls.toS3(...)stream had no error listener, soemit("error")throws (Node.js EventEmitter behavior). Since the throw happens inside a.catch()handler, it creates a new unhandled promise rejection →Runtime.ExitError→ Lambda crash.Testing