On Node 26.11, reading duplex on the lightweight request throws ERR_INVALID_THIS, so new Request(url, c.req.raw) fails #408

Versions

• @hono/node-server 2.1.5 (also 2.1.4)
• hono 4.13.12
• Node 26.11.1 fails (also 26.11.0). Node 26.10.0 works.

What happens

Any code that passes the request c.req.raw from @hono/node-server as a RequestInit now throws on Node 26.11. A common example is rewriting the URL before handing the request to an auth library:

new Request(new URL('/rewritten', c.req.url), c.req.raw)

TypeError [ERR_INVALID_THIS]: Illegal invocation

Every Better Auth endpoint that is routed through this rewrite returns 500.

Minimal reproduction

// package.json: { "type": "module", "dependencies": { "@hono/node-server": "2.1.5", "hono": "4.13.12" } }
import { serve } from '@hono/node-server'
import { Hono } from 'hono'

const app = new Hono()
app.all('*', (c) => {
  try {
    const r = new Request(new URL('/rewritten', c.req.url), c.req.raw)
    return c.text(`OK method=${r.method}`)
  } catch (e) {
    return c.text(`FAIL ${e.name} code=${e.code} ${e.message}`, 500)
  }
})

const server = serve({ fetch: app.fetch, port: 0 }, async (info) => {
  const base = `http://127.0.0.1:${info.port}`
  const get = await fetch(`${base}/api/x`)
  const post = await fetch(`${base}/api/x`, { method: 'POST', body: '{"a":1}' })
  console.log(`node ${process.version} | GET: ${get.status} ${await get.text()} | POST: ${post.status} ${await post.text()}`)
  server.close()
})

Output (docker run node:<version>-alpine):

node v26.10.0 | GET: 200 OK method=GET | POST: 200 OK method=POST
node v26.11.1 | GET: 500 FAIL TypeError code=ERR_INVALID_THIS Illegal invocation | POST: 500 FAIL TypeError code=ERR_INVALID_THIS Illegal invocation

To find the failing property, I read each Request property on c.req.raw. On 26.11.1 only one throws:

node v26.10.0 | no property throws
node v26.11.1 | throws: duplex(ERR_INVALID_THIS)

Cause

• Node 26.11.0 updated undici to 8.11.2. undici 8.11.0 includes use private fields for brand checks nodejs/undici#5792 ("use private fields for brand checks"). Since then, the getters on Request.prototype throw unless this is a real undici Request.
• The lightweight request in src/request.ts forwards a fixed list of properties to the real request through getRequestCache(): cache, credentials, destination, integrity, mode, redirect, referrer, referrerPolicy and keepalive. duplex is not on that list. Reading duplex therefore falls through to undici's own Request.prototype.duplex getter, which now fails its brand check.
• The Request constructor reads init.duplex, so passing the lightweight request as init throws.

Suggested fix

Add duplex to the forwarded properties in src/request.ts:

;[
  'cache',
  'credentials',
  'destination',
  'duplex',
  'integrity',
  // ...

Two other fixes are possible, depending on what you want to support: forward every remaining Request.prototype getter so that a future undici getter can't hit the same problem, or return the constant 'half'.

Related

• bodyLimit answers 500 for a body without Content-Length when node-server runs with overrideGlobalObjects: false hono#5538: the same kind of failure in bodyLimit (new Request(c.req.raw, init)) with overrideGlobalObjects: false.
• use private fields for brand checks nodejs/undici#5792: the brand-check change.