Parser does not work in serverless environment

[czarny]

Environment information

Version:
"body-parser: 1.20.3
"express": "^5.1.0",
"serverless-http": "^3.2.0",

Platform:
Service is deployed to as AWS Lambda.

Any other relevant information:

Latest express release uses body-parser which uses on-finished to determine if body should be parsed.

The on-finished checks socket.readable property to determine if request is finished (https://github.com/jshttp/on-finished/blob/master/index.js#L76).

The serverless-http sets readable to false (https://github.com/dougmoscrop/serverless-http/blob/master/lib/request.js#L9) when creating request object for express.

This causes that body-parser skips body parsing (https://github.com/expressjs/body-parser/blob/master/lib/types/json.js#L87) because request is considered finished.

[Phillip9587]

Hey @czarny, Thanks for your report.

I just read the serverless-http README and noticed that since v4 the library switched to using a PassThrough stream internally (instead of a stub).

Note: v4.0.0 doesn't intentionally intorudce any breaking changes, but uses a PassThrough stream internally instead of a stub - however, this is a sensitive area, so in order to avoid unintentional breaks, a semver major version was used. You should hopefully not have to change anything, but test thoroughly please.

That stream remains readable: true, so on-finished and body-parser should no longer treat the request as finished. In the issue @bjohansebas created it is confirmed v4 works: dougmoscrop/serverless-http#274. Upgrading to serverless-http@^4 should resolve the parsing behavior you’re seeing.

I’m going to close this as not planned on the body-parser side. Express targets Node.js directly. We can’t reasonably test or guarantee behavior across third-party serverless adapters/runtimes. For broader context, see: expressjs/discussions#365