download.js

/**
 * The example of usage for [mt-downloader](https://www.npmjs.com/package/mt-downloader).
 *
 * ## Installation
 *
 *   npm install mt-downloader muxer
 *
 * ## Usage
 *
 *   // the URL to download from
 *   var url = 'https://assets-cdn.github.com/pinned-octocat.svg';
 *
 *   // the output file name
 *   var destPath = 'pinned-octocat.svg';
 *
 *   // the maximum number of parallel downloads
 *   var concurrence = 10;
 *
 *   var download = createDownload({
 *      url: url,
 *      path: destPath,
 *      range: concurrence
 *   }).toPromise();
 *
 *   download
 *     .then(() => console.log('done'))
 *     .catch((err) => console.log(err));
 *
 * Based on tushar.mathur's
 * https://github.com/tusharmath/Multi-threaded-downloader/blob/master/perf/TestHelpers.js
 */

'use strict'
const Rx = require('rx').Rx;
const O = require('rx').Observable;
const R = require('ramda');
const CreateMTDFile = require('mt-downloader').CreateMTDFile;
const DownloadFromMTDFile = require('mt-downloader').DownloadFromMTDFile;
const FILE = require('mt-downloader').FILE;
const FinalizeDownload = require('mt-downloader').FinalizeDownload;
const MTDPath = require('mt-downloader').MTDPath;
const demux = require('muxer').demux;


/**
 * Test UTILS for doing a real download.
 *
 * @param options
 * @returns {Observable}
 */
function createDownload(options) {
  /**
   * Create MTD File
   */
  const createMTDFile$ = CreateMTDFile(options).share()
  const [{fdW$}] = demux(createMTDFile$, 'fdW$')

  /**
   * Download From MTD File
   */
  const downloadFromMTDFile$ = createMTDFile$.last()
    .map(MTDPath(options.path)).flatMap(DownloadFromMTDFile).share()

  const [{fdR$, meta$}] = demux(downloadFromMTDFile$, 'meta$', 'fdR$')

  /**
   * Finalize Downloaded FILE
   */
  const finalizeDownload$ = downloadFromMTDFile$.last()
    .withLatestFrom(fdR$, meta$, (_, fd, meta) => ({
      fd$: O.just(fd),
      meta$: O.just(meta)
    }))
    .flatMap(FinalizeDownload)
    .share()
    .last()

  /**
   * Close File Descriptors
   */
  const fd$ = finalizeDownload$
    .withLatestFrom(fdW$, fdR$)
    .map(R.tail)
    .flatMap(R.map(R.of))

  return FILE.close(fd$)
}

module.exports.createDownload = createDownload;