download file questions

Hello, I’m implementing a download module, want to try node-fetch and have a few questions:

1. How can i get the total fileSize so i can implement a progress?
2. How can i pause/resume/cancel a download?

Thank you!

const fetch = require('node-fetch');
const fs = require('fs');

const url = 'https://images.pexels.com/photos/45201/kitty-cat-kitten-pet-45201.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940'

async function download() {
  const nfetch = await fetch(url);

  const fileStream = fs.createWriteStream('./octocat.png');
  nfetch.body.pipe(fileStream);

  nfetch.body.on("response", (data) => {
    console.log('response ???');
  });

  nfetch.body.on("data", (chunk) => {
    console.log(chunk.length);
  });

  nfetch.body.on("error", (err) => {
    console.log('err:', err)
  });

  fileStream.on("finish", function () {
    console.log('finish');
  });
}

download();

[jimmywarting]

here is some psudo code of how to write a downloader that can monitor progress, abort and resume

ctrl = new AbortController()
signal = ctrl.signal
url = 'https://images.pexels.com/photos/45201/kitty-cat-kitten-pet-45201.jpeg?d='+Date.now()
res = await fetch(url, { signal })
acceptRanges = res.headers.get('accept-ranges') === 'bytes'
contentLength = parseInt(res.headers.get('content-length'))
chunks = []
downloaded = 0

res.body.pipeTo(new WritableStream({
  write(chunk) {
    chunks.push(chunk) // uint8array
    downloaded += chunk.byteLength
    console.log(downloaded, contentLength)
    ctrl.abort()
    console.log(URL.createObjectURL(new Blob(chunks, {type:'image/jpeg'})))
    resumePartialRequest(url, downloaded)
  }
}))

async function resumePartialRequest (url, start = 0, end = '') {
  const res = await fetch(url, {
    headers: {
      'range': `bytes=${start}-${end}` 
    }
  })
  await res.body.pipeTo(new WritableStream({
    write(chunk) {
      chunks.push(chunk)
      downloaded += chunk.byteLength
      console.log(downloaded, contentLength)
    }
  }))
  console.log(URL.createObjectURL(new Blob(chunks, {type:'image/jpeg'})))
}

I wrote this in chrome’s devtool, so it’s not 100% adopted for node-fetch with major differences being pipeTo/pipe and node/whatwg WritableStream Note that there is a lot more to it. You have to check if it accepts byte ranges, you should pipe to some file destination. if it don’t accept byte ranges then you can’t technically “pause & resume” you can only abort then

read more about partial request here: https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests

[frvi]

For the filesize, you should be able to get it from the content-length response header, e g nfetch.headers.get('content-length');