gzip-uncompressed-size/index.js

Determine the estimated uncompressed size from a GZIP file (uses ISIZE)

/*
 * The MIT License
 *
 * Copyright (c) 2016 Juan Cruz Viotti. https://github.com/jviotti
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

'use strict';

const fs = require('fs');
const ISIZE_LENGTH = 4;

const openStat = (filename, callback) => {
  fs.open(filename, 'r', (error, fd) => {
    if (error) {
      return callback(error);
    }
    fs.fstat(fd, (error, stats) => {
      callback(error, fd, stats);
    });
  });
};

exports.fromFile = (file, callback) => {
  const isize = Buffer.alloc(ISIZE_LENGTH, 0);
  openStat(file, (error, fd, stats) => {
    fs.read(fd, isize, 0, ISIZE_LENGTH, stats.size - ISIZE_LENGTH, (error, bytesRead) => {
      if (error) {
        return callback(error);
      } else if (bytesRead !== ISIZE_LENGTH) {
        error = new Error(`Bytes read mismatch: ${bytesRead} != ${ISIZE_LENGTH}`);
        return callback(error);
      }
      callback(null, isize.readUInt32LE(0));
    });
  });
};