an express router that downloads and caches files.

file-download-router.js

import express from 'express'
import fs from 'fs'
import http from 'http'
import u from 'url'
import path from 'path'

const downloadRouter = express.Router()

let downloadedFiles = {}

downloadRouter.get('/', async (req, res) => {
  console.log(downloadedFiles)
  const url = new u.URL(req.query.url)
  const extension = req.query.ext
  const decoded = decodeURI(url.pathname)

  if (downloadedFiles[decoded])
    return fs.createReadStream(downloadedFiles[decoded]).pipe(res)

  downloadedFiles[decoded] = 'files/' + filenameFromUrl(url, extension)
  const file = await download(url, downloadedFiles[decoded])
  file.pipe(res)
})

const filenameFromUrl = (url, fileExt) => {
  const decoded = decodeURI(url.pathname)
  const base = path.basename(decoded)
  const pathExt = path.extname(decoded)

  if (!pathExt) return base.replaceAll(' ', '-').substring(0, 20) + fileExt

  return base.split(pathExt)[0].replaceAll(' ', '-').substring(0, 20) + pathExt
}

const download = async (url, destination) => {
  console.log('download:', url.toString())
  const file = fs.createWriteStream(destination)

  await new Promise((resolve, reject) => {
    http.get(url, function (response) {
      response.pipe(file)

      // after download completed close filestream
      file.on('finish', () => {
        file.close()
        resolve()
        console.log(decodeURI(url.pathname) + ' downloaded')
      })

      file.on('error', (e) => reject(err))
    })
  })

  return fs.createReadStream(destination)
}

export default downloadRouter