fetch-to-node

fetch-to-node

A library providing Node.js-compatible request and response objects for WinterTC (fetch-like) runtimes, such as Cloudflare Workers, Bun, Deno and Fastly Compute.

Useful for when you're using a Node.js library in one of these environments that expects Node.js-style req and res objects, for example Express.

This is basically the inverse of libraries like @mjackson/node-fetch-server that allow the use of Request/Response signatures in Node.js servers.

This library is a copy/fork of Katsuyuki Omuro's great @fastly/http-compute-js project and wouldn't be possible without the hard work put in there. The changes here were largely made to remove dependencies and make the interfaces more generic.

That said, this library does depend on a certain level of Node.js compatibility (Readable, Writable from node:stream and Buffer from node:buffer). So please check out @fastly/http-compute-js if this library doesn't work for you.

Usage

import { toReqRes, toFetchResponse } from "fetch-to-node";

export default {
  async fetch(request: Request): Promise<Response> {
    // Create Node.js-compatible req and res from request
    const { req, res } = toReqRes(request);

    // Use req/res as you would in a Node.js application
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(
      JSON.stringify({
        data: "Hello World!",
      })
    );

    // Create a Response object based on res, and return it
    return await toFetchResponse(res);
  },
};

NB: If you're using Cloudflare Workers, be sure to set the nodejs_compat flag.

req and res are implementations of IncomingMessage and ServerResponse, respectively, and can be used as in a Node.js program.

API

toReqRes(request)

• Converts from a Request object to a pair of Node.js-compatible request and response objects.
• Parameters:
  • request - A Request object. You would typically obtain this from the request received by your fetch handler.
• Returns: an object with the following properties.
  • req - An http.IncomingMessage object whose Readable interface has been wired to the Request object's body. NOTE: This is an error if the Request's body has already been used.
  • res - An http.ServerResponse object whose Writable interface has been wired to an in-memory buffer.

toFetchResponse(res)

• Creates a new Response object from the res object above, based on the status code, headers, and body that has been written to it.
• Parameters:
  • res - An http.ServerResponse object created by toReqRes().
• Returns: a promise that resolves to a Response object.
• NOTE: This function returns a Promise that resolves to a Response once the res object emits the 'finish' event, which typically happens when you call res.end(). If your application never signals the end of output, this promise will never resolve, and your application will likely error or time out.
• If an error occurs, the promise will reject with that error.

Notes / Known Issues

• HTTP Version is currently always reported as 1.1.
• The socket property of these objects is always null, and cannot be assigned.
• The ServerResponse write stream must be finished before the Response object is generated.
• Trailers are not supported, as there's no support for these in the fetch API.
• Client APIs not supported: http.Agent, http.ClientRequest, http.get(), http.request(), to name a few.

License

MIT.

In order for this library to function without requiring a direct dependency on Node.js itself, portions of the code in this library are adapted / copied from Node.js. Those portions are Copyright Joyent, Inc. and other Node contributors. See the LICENSE file for details.

Changelog

[2.1.0] - 2025-04-26

Changed

• Bring codebase up to date with latest Node.js source (~v22.15.0)
• Fix chunked encoding support
• Add FixedLengthStream for responses with a content-length header