Direct fetch is incompatible with express.js

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
express, node.js, nuxt
Domain
api, backend

Research direction

Start with the reproduction and the linked unenv runtime/fetch/call.ts and Nitro src/types/runtime/nitro.ts entry points. Trace which request and response implementations direct local fetch uses, then verify the Express prototype setup no longer causes res.setHeader to throw and that local request errors can be sent correctly.

Written by the indexing model from the issue text.

Description

bug
Environment

Nuxt with default node env

Reproduction
import createApp from 'express';
import {IncomingMessage} from 'unenv/runtime/node/http/_request'
import {ServerResponse} from 'unenv/runtime/node/http/_response'

const req = new IncomingMessage();
const res = new ServerResponse(req);

// Taken from express init middleware implementation
const app = createApp();
Object.setPrototypeOf(res, app.response);

res.setHeader('vary', 'test'); // TypeError: Cannot set properties of undefined (setting 'vary')
Describe the bug

When sending a local request to an express server using fetch, a server error occurs

Additional context

This is very problematic in nuxt with useFetch and a legacy endpoint that uses an express server behind the scenes (This issue took me about 20h to debug because it's such a complex chain of events to follow and the errors hidden behind 3 layers could not even be sent properly because the response object was broken)

It seems the problem is that unenv's fetch always uses its internal node/http/request,response even if build with the node env preset and this is problematic because then local requests behave differently than external requests
https://github.com/unjs/unenv/blob/main/src/runtime/fetch/call.ts#L1-L2

unenv's fetch is then used by nitro even if env is set to node
https://github.com/unjs/nitro/blob/a399e189576d4c18d7f837bd454e0503e1f53980/src/types/runtime/nitro.ts#L7

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Dominant language
TypeScript
Stars
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Forks
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