zs-extract/lib/extract.mjs

import vm from 'vm';
import url from 'url';
import request from 'request';
import cheerio from 'cheerio';
/**
 * A request promise wrapper.
 *
 * @param req Request function.
 * @param options Request options.
 * @returns Request response and body.
 */

async function requestP(req, options) {
  const r = await new Promise((resolve, reject) => {
    req(options, (error, response, body) => {
      if (error) {
        reject(error);
        return;
      }

      resolve({
        response,
        body
      });
    });
  });
  return r;
}
/**
 * Extract script code from HTML code.
 *
 * @param html HTML code.
 * @returns Script code.
 */


function extractScripts(html) {
  const r = [];
  const $ = cheerio.load(html);
  $('script').each((elI, el) => {
    const data = $(el).html();

    if (data) {
      r.push(data);
    }
  });
  return r;
}
/**
 * Attempt to extract info from script.
 *
 * @param script Script code.
 * @returns Result object or null.
 */


function extractScript(script) {
  let result = null;

  if (!script.includes('dlbutton')) {
    return result;
  } // Create a context with wich to run code in
  // Creating the object with a null prototype is very important.
  // Prevents host variables from leaking into the sanbox.


  const ctx = vm.createContext(Object.create(null));
  const runOpts = {
    timeout: 1000
  }; // Setup environment.

  const codePre = [
  /* eslint-disable @typescript-eslint/indent */
  'window = this;', 'document = (function(r) {', 'var elements = {', '"dlbutton": {},', '"fimage": {}', '};', 'r.getElementById = function(id) {', 'return elements[id];', '}', 'return r;', '})({});'
  /* eslint-enable @typescript-eslint/indent */
  ].join('\n'); // Extract info from environment.

  const codePost = [
  /* eslint-disable @typescript-eslint/indent */
  'JSON.stringify({', '"dlbutton": document.getElementById("dlbutton").href', '})'
  /* eslint-enable @typescript-eslint/indent */
  ].join('\n'); // Attempt to run code in sanbox and extract the info.

  try {
    // Run the pre script.
    vm.runInContext(codePre, ctx, runOpts); // Run the script code.

    vm.runInContext(script, ctx, runOpts); // Run the post script.
    // Force return value to be string, with concatenation, NOT casting.
    // This prevents any funny business from sandboxed code.
    // eslint-disable-next-line

    result = JSON.parse('' + vm.runInContext(codePost, ctx, runOpts));
  } catch (err) {// Ignore failure.
  }

  return result;
}
/**
 * Extract file info from a URL.
 *
 * @param uri The URI to extract info from.
 * @param req Optional custom request function or null.
 * @returns File info.
 */


export async function extract(uri, req = null) {
  const requester = req || request;
  const {
    response,
    body
  } = await requestP(requester, {
    url: uri
  });
  const {
    statusCode
  } = response;

  if (statusCode !== 200) {
    throw new Error(`Invalid status code: ${statusCode}`);
  }

  const bodyType = typeof body;

  if (bodyType !== 'string') {
    throw new Error(`Invalid body type: ${bodyType}`);
  }

  const scripts = extractScripts(body);
  let result = null;

  for (const script of scripts) {
    result = extractScript(script);

    if (result) {
      break;
    }
  }

  if (!result || !result.dlbutton) {
    throw new Error('Failed to extract info');
  }

  const download = url.resolve(uri, result.dlbutton);
  const filename = decodeURI((url.parse(download).pathname || '').split('/').pop() || '') || null;
  return {
    download,
    filename
  };
}
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