node-fetch file URL

node-fetch-file-url.js

const fs = require('fs');
const path = require('path');
const nodeFetch = require('node-fetch');
const Request = nodeFetch.Request;
const Request = nodeFetch.Response;

  fetch = function (url, options) {
    const request = new Request(url, options);
    if (request.url.substring(0, 5) === 'file:') {
      return new Promise((resolve, reject) => {
        const filePath = path.normalize(url.substring('file:///'.length));
        if (!fs.existsSync(filePath)) {
          reject(`File not found: ${filePath}`);
        }
        const readStream = fs.createReadStream(filePath);
        readStream.on('open', function () {
          resolve(new Response(readStream, {
            url: request.url,
            status: 200,
            statusText: 'OK',
            size: fs.statSync(filePath).size,
            timeout: request.timeout
          }));
        });
      });
    } else {
      return nodeFetch(url, options);
    }
  };

• rename Request variable to Response on line 5
• size: fs.statSync(filePath).size, should be changed to
  headers: { "Content-Length": fs.statSync(filePath).size }
• timeout should be replaced with AbortController

Node.js' undici fetch() implementation can be modified at or around https://github.com/nodejs/undici/blob/main/lib/web/fetch/index.js#L129 to include something like

  const p = createDeferredPromise()
  const url = new URL(input);
  if (url.protocol === "file:") {
    return import("node:fs").then((fs) => {
      p.resolve(new Response(fs.readFileSync(url)));
      return p.promise;
    })       
  }

see https://gist.github.com/guest271314/a4f005d9a6b5b433ae6d6e6c5c6d7595 for some other options I tried.