streams.mjs

// ---------------------------------
//      write data to a file
// ---------------------------------
// import fs from 'fs';

// const heros =  [
//                   { name: "Tyrion Lannister", minutes: 166, seconds: 15, episodes: 28, family: "Lannister", url: "http://gameofthrones.wikia.com/wiki/Tyrion_Lannister" },
//                   { name: "Daenerys Targaryen", minutes: 127, seconds: 35, episodes: 25, family: "Targaryen", url: "http://gameofthrones.wikia.com/wiki/Daenerys_Targaryen"},
//                   { name: "Jon Snow", minutes: 126, seconds: 41, episodes: 24, family: "Night's Watch", url: "http://gameofthrones.wikia.com/wiki/Jon_Snow" },
//                   { name: "Arya Stark", minutes: 100, seconds: 11, episodes: 27, family: "Stark", url: "http://gameofthrones.wikia.com/wiki/Arya_Stark"},
//                   { name: "Eddard Stark", minutes: 94, seconds: 35, episodes: 9, family: "Stark", url: "http://gameofthrones.wikia.com/wiki/Eddard_Stark" },
//                   { name: "Catelyn Stark", minutes: 91, seconds: 14, episodes: 25, family: "Stark", url: "http://gameofthrones.wikia.com/wiki/Catelyn_Stark"},
//                   { name: "Cersei Lannister", minutes: 90, seconds: 2, episodes: 27, family: "Lannister", url: "http://gameofthrones.wikia.com/wiki/Cersei_Lannister" },
//                   { name: "Robb Stark", minutes: 89, seconds: 16, episodes: 22, family: "Stark", url: "http://gameofthrones.wikia.com/wiki/Robb_Stark"},
//                   { name: "Sansa Stark", minutes: 85, seconds: 42, episodes: 24, family: "Stark", url: "http://gameofthrones.wikia.com/wiki/Sansa_Stark" },
//               ];

// const wstream  = fs.createWriteStream('./data/heros.json');
// wstream.write(JSON.stringify(heros,null,2));
// wstream.end();  


//---------------------------------
//       download an image
//---------------------------------
import fs from 'fs';
import fetch from 'node-fetch';
import log from '@ajar/marker'

// const url = 'https://www.rivernetwork.org/wp-content/uploads/2015/08/Our-Work-landing-page-big-image.jpg';
// const writeStream = fs.createWriteStream('./images/big-image.jpg');

// const url = 'https://joannachayes.files.wordpress.com/2015/06/nightsking.jpg';
// const writeStream = fs.createWriteStream('./images/nights-king.jpg')

const url = 'http://orig14.deviantart.net/dbcb/f/2016/152/b/c/white_walker_4k_by_blaufosc-da4n3yi.jpg';
const writeStream = fs.createWriteStream('./images/white-walker.jpg');

// (async ()=> {
//   const response = await fetch(url);
//   // fetch() returns a promise that
//   // resolves once headers have been received
//   log.obj(response.headers,'headers:');
//   const total = Number(response.headers.get('content-length'));

//   // response.body is a readable stream.
//   const readStream = response.body;
//   let loaded = 0;

//   readStream.on('data', data => {
//     loaded += data.length;
//     const progress = ((loaded / total) * 100).toFixed(2); 
//     log.v(`${progress}%`); 
//     writeStream.write(data)
//   });

//   readStream.on('end', ()=> {
//     log.info(`Finished fetching ${loaded} bytes`);
//     writeStream.end()
//   });

//   readStream.on('error', err => {
//     log.info(`Error: ${err.message}`);
//     writeStream.close();
//   });
// })().catch(log.error)


(async ()=> {
  const response = await fetch(url);
  const total = Number(response.headers.get('content-length'));
  let loaded = 0;
  for await(const data of response.body) {
    loaded += data.length;
    const progress = ((loaded / total) * 100).toFixed(2); 
    log.v(`${progress}%`); 
    writeStream.write(data)
  }
  log.info(`Finished fetching ${loaded} bytes`);
})().catch(log.error)

//--------------------------------------
//    in the browser you could...
//--------------------------------------
// (async ()=> {
//   const response = await fetch(url);
//   const total = Number(response.headers.get('content-length'));
//   let loaded = 0;
//   for await(const {length} of response.body.getReader()) {
//     loaded += length;
//     const progress = ((loaded / total) * 100).toFixed(2); 
//     log.v(`${progress}%`); // or yourDiv.textContent = `${progress}%`;
//   }
//   log.info(`Finished fetching ${loaded} bytes`);
// })().catch(err=>log.error(err))


//--------------------------------------
//       stream a response in express
//--------------------------------------

// router.get('/visual',async (req,res)=> {
//   // response.body is a readable stream.
//   // res is a writable stream
//   const {url} = req.query;
//   const response = await fetch(url);
//   response.body.pipe(res);
// })