Response built by express is broken if res and req don't extend node's http.IncomingMessage and http.ServerResponse

[Tofandel]

To reproduce

import createApp from 'express';

const app = createApp();
console.log(app.response);

console.log(app.response.getHeader('vary'));

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')

node:_http_outgoing:747
  const entry = headers[name.toLowerCase()];
                       ^

TypeError: Cannot read properties of undefined (reading 'vary')
    at ServerResponse.getHeader (node:_http_outgoing:747:24)

Because response is initialized from prototype without constructor, headers is empty and fails

Solution:

var request = require('./request');

/**
 * Response prototype.
 * @public
 */

var res = new http.ServerResponse(request)

[Tofandel]

See also #2548 and unjs/unenv#328

[Tofandel]

The issue is actually coming from the use of sePrototypeOf and not really the reproduction in the end

We should rewrite the initExpress middleware like this

  app._router.stack[1].handle = (req, res, next) => {
    req.res = res;
    res.req = req;
    req.next = next;

    app.request.res = res;

    const setProtoKey = (obj, proto, prop) => {
      Object.defineProperty(obj, prop, {
        get: function () {
          return proto[prop];
        },
        set: function (val) {
          delete obj[prop];
          obj[prop] = val;
        },
        enumerable: proto.propertyIsEnumerable(prop),
        configurable: true,
      });
    };

    const reqKeys = [
      'app',
      'header',          'get',
      'accepts',         'acceptsEncodings',
      'acceptsEncoding', 'acceptsCharsets',
      'acceptsCharset',  'acceptsLanguages',
      'acceptsLanguage', 'range',
      'param',           'is',
      'protocol',        'secure',
      'ip',              'ips',
      'subdomains',      'path',
      'hostname',        'host',
      'fresh',           'stale',
      'xhr'
    ];

    const resKeys = [
      'app',
      'status',
      'links',
      'send',
      'json',
      'jsonp',
      'sendStatus',
      'sendFile',
      'sendfile',
      'download',
      'type',
      'contentType',
      'format',
      'attachment',
      'append',
      'header',
      'set',
      'get',
      'clearCookie',
      'cookie',
      'location',
      'redirect',
      'vary',
      'render',
    ];

    reqKeys.forEach((key) => {
      setProtoKey(req, app.request, key);
    });
    resKeys.forEach((key) => {
      setProtoKey(res, app.response, key);
    });

    res.locals = res.locals || Object.create(null);

    next();
  };