node http fetch proxy

Inside a standard nodejs http handler like this

function handler(request, result) {
  // ...
}

you want to forward the request to another url, and then stream the result back using the nodejs result. You want to use the new and shiny fetch, because it is now included in nodejs by default, and your longtime favorite node library request is deprecated.

With good old request you could just do the following:

function handler(req, res) {
  const newUrl = 'https://the-url-you-want-to-send-your-requests-to.com'

  function onError(e) {
    console.error('something bad happended', e)
    res.statusCode = 500
    res.end()
  }

  // prettier-ignore
  req
    .pipe(request(newUrl))
    .on('error', onError)
    .pipe(res)
    .on('error', onError)
}

With this library you get some helpers that assist you to achieve the same using fetch:

import {
  forwardFetchResult,
  forwardRequestHeadersToFetch,
  makeErrorHandler,
} from 'node-fetch-request-proxy'

async function handler(request, result) {
  const newUrl = 'https://the-url-you-want-to-send-your-requests-to.com'

  const headers = new Headers()
  // you can add your own custom headers here as well

  // this forwards relevant headers of the request to your new destination
  // ommitting some headers that can cause problems when forwarded
  forwardRequestHeadersToFetch(request, headers)

  // this creates an error handler that logs the error and closes
  // the result stream with a given error message and status code.
  // use your own if you like.
  const onError = makeErrorHandler(result, 'something bad happened', 500)

  try {
    // make your fetch request as usual
    const fetchResult = await fetch(newUrl, {
      method: request.method,
      headers,
      // add more configuration as you see fit...
    })

    // then stream the body of the fetchResult to your node http result
    return forwardFetchResult(fetchResult, result, onError)
  } catch (e) {
    return onError(e)
  }
}

A little more verbose, but hey, it's fetch :)

Requires nodejs >= 18.0.0 because this is when fetch became natively available.

This library is published as ESM only. With commonjs, use this code:

const makeProxyHelpers = () => import('node-fetch-request-proxy')

async function handler(request, result) {
  const { forwardFetchResult, forwardRequestHeadersToFetch, makeErrorHandler } =
    await makeProxyHelpers()

  // proceed as before ...
}

Look at the source code, if you want to implement the details yourself, it is roughly 90 lines of sparsely commented code.

License

MIT, see the LICENSE file in the repository.

Copyright (c) 2022 Thomas Gorny