oven-sh/bun

Remove the undici polyfill

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#17799 opened on Feb 28, 2025

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 (1 comment) (11 reactions) (0 assignees)Rust (90,348 stars) (4,486 forks)batch import
enhancementgood first issue

Description

What is the problem this feature would solve?

Bun's fetch and WebSocket have an issue with headers casing (they're not the same as the ones we give, see https://github.com/Vexcited/tcp-websocket#why-not-directly-use-undici- for an example)

Using undici completely fixes that since it uses node:net and node:tls to make the requests instead of builtins.

What is the feature you are proposing to solve the problem?

Today, Bun supports undici out of the box.

Removing this polyfill would allow us to not do forks of it or import tweaks to prevent Bun pollyfing the import (see https://github.com/Vexcited/tcp-websocket/blob/main/src/index.ts)

Also it would help to have a package that does requests with the exact same API and outputs the same thing on all runtimes (I tested Deno, Node.js and Bun and it always produces the same output!)

undici is pollyfilled in

What alternatives have you considered?

Writing my own package that tweaks the imports to make sure Bun does not polyfill it, https://github.com/Vexcited/tcp-websocket

Contributor guide

Tech stack
javascripttypescriptnodejscpp
Domain
backenddeveloper experienceapi
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
JavaScript/TypeScriptNode.js API knowledgeBun internalsC++ basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Remove the undici polyfill by deleting or modifying the files mentioned: test/js/first party/undici, src/js/thirdparty/undici.js, src/bun.js/bindings/Undici.h, and src/bun.js/bindings/Undici.cpp. Ensure that undici can be imported normally without Bun intercepting, and that the native fetch and WebSocket still work. Check the tcp websocket issue for context on header casing differences. Run existing tests to confirm no regressions.