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Synchronous throws (and rejected promises) from engine.use middlewares now reach the same callback(err) path as next(err), so they surface as MIDDLEWARE_FAILURE / connection_error instead of being lost. Fixes socketio#5263
Yahiro025
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The kind of change this PR does introduce
Current behavior
Synchronous throws inside
engine.use(...)/io.engine.use(...)middlewares are not caught in_applyMiddlewares. Unlikenext(err), a thrown error never reaches the middleware failure path, so it is not reported asMIDDLEWARE_FAILURE/connection_error.Fixes #5263
New behavior
_applyMiddlewareswraps each middleware call so:callback(err)callback(err)That matches the existing
next(err)failure path (HTTP 400 +connection_errorwithMIDDLEWARE_FAILURE).Other information (e.g. related issues)
packages/engine.io/test/middlewares.jsmirroring the existingnext(err)polling case.npm test --workspace=engine.io.