[Bug]: JS SDK: passing logger makes every API call fail on Node with "onResponse: must return new Response() when modifying the response" #1986

Sandbox ID or Build ID

None. The call fails before a sandbox is created.

Environment

• e2b 2.32.0 and 2.56.0 (latest). Both reproduce.
• Node.js 24.14.1 (macOS and Linux/Alpine)
• openapi-fetch 0.14.1 (bundled with 2.32.0) and 0.17.0 (bundled with 2.56.0)
• undici resolvable, which is always the case because e2b depends on it

Timestamp of the issue

2026-10-14 20:00 UTC onwards (when we started passing logger). It reproduces every time.

Frequency

Happens every time

Expected behavior

Passing a logger in the connection options (for example Sandbox.create({ logger })) only adds logging, and the request behaves as it does without one.

Actual behavior

On Node, every API call made through ApiClient throws before the response is handled:

Error: onResponse: must return new Response() when modifying the response
    at coreFetch (node_modules/openapi-fetch/dist/index.mjs:...)

Without logger, the same call works.

Cause: On Node the SDK fetches through the npm undici (loadUndici() / buildApiFetcher in src/api/http2.ts), so responses are instances of undici.Response, not globalThis.Response. When a logger is set, createApiLogger (packages/js-sdk/src/logs.ts) installs a middleware whose onResponse returns the response it received. openapi-fetch treats any truthy onResponse result as a replacement response and requires result instanceof Response, checked against the global Response. undici.Response !== globalThis.Response, so the check fails.

Under Bun (and in browsers) the SDK uses the global fetch, so the classes match and the bug doesn't show. That's probably why it hasn't been noticed.

Suggested fix: don't return the unchanged response (or request). In openapi-fetch, returning undefined from a middleware means "unchanged":

export function createApiLogger(logger: Logger): Middleware {
  return {
    async onRequest({ request }) {
      logger.info?.(`Request ${request.method} ${request.url}`)
    },
    async onResponse({ response }) {
      if (response.status >= 400) {
        logger.error?.('Response:', response.status, response.statusText)
      } else {
        logger.info?.('Response:', response.status, response.statusText)
      }
    },
  }
}

Reproduction

No E2B account needed; a local stub server stands in for the API. Run with node repro.mjs (Node 24, npm i e2b):

import http from 'node:http'
import { Sandbox } from 'e2b'

const server = http
  .createServer((req, res) => {
    res.writeHead(500, { 'content-type': 'application/json' })
    res.end('{"code":500,"message":"stub api reached"}')
  })
  .listen(0)
await new Promise((r) => server.once('listening', r))
const apiUrl = `http://127.0.0.1:${server.address().port}`
const apiKey = 'e2b_' + '0'.repeat(40)

for (const logger of [undefined, { warn() {}, error() {} }]) {
  try {
    await Sandbox.create({ apiKey, apiUrl, logger })
  } catch (e) {
    console.log(logger ? 'with logger:   ' : 'without logger:', e.message)
  }
}
const undici = await import('undici')
console.log('undici.Response === globalThis.Response:', undici.Response === globalThis.Response)
server.close()

Output:

without logger: 500: stub api reached
with logger:    onResponse: must return new Response() when modifying the response
undici.Response === globalThis.Response: false

Under bun repro.mjs, both lines print 500: stub api reached.