Attaching 'data' listeners immediately

Support plan

• Which support plan is this issue covered by? (Community, Sponsor, Enterprise): Community
• Currently blocking your project/work? (yes/no): yes
• Affecting a production system? (yes/no): OSS - we can't update to formidable v3

Context

• Node.js version: 22
• Release Line of Formidable (Legacy, Current, Next): Current
• Formidable exact version: v3
• Environment (node, browser, native, OS): Node.js/macOS
• Used with (popular names of modules):

What are you trying to achieve or the steps to reproduce?

In formidable v2/v3 the parsing is async and the 'data' handlers are attached not directly. This causes an issue that if you have multiple async things happening after the request was started other consumers might consume the buffered 'data' chunks. Then formidable is not able to parse the request anymore since it receives only a part of it.

An easy fix for that would be to attach the handlers earlier - at the beginning when calling parse.

Currently they are attached after writeHeaders: https://github.com/node-formidable/formidable/blob/d0fbec13edc8add54a1afb9ce1a8d3db803f8d47/src/Formidable.js#L233

See https://github.com/microsoft/playwright/issues/35823#issuecomment-2847667026 for more information. We would appreciate if this could considered since it breaks our use-case and potentially also other customers with async/await hops.

What was the result you got?

When there is an async hop which is consuming 'data' as well, formidable is not able to parse the request body.

What result did you expect?

It works like in formidable v1 - there the parsing was sync.

Start in src/Formidable.js around the current listener attachment after writeHeaders, then compare the reported behavior with Formidable v1. Reproduce the async-hop case where another consumer receives data, and verify that formidable can still parse the complete request body when listeners are attached earlier.