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75 lines
2.2 KiB
JavaScript
75 lines
2.2 KiB
JavaScript
/*
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* Copyright 2016 resin.io
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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const Bluebird = require('bluebird');
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const fs = Bluebird.promisifyAll(require('fs'));
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/**
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* @summary The byte length of ISIZE
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* @type {Number}
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* @constant
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* @description
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* See https://tools.ietf.org/html/rfc1952
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*/
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const ISIZE_LENGTH = 4;
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/**
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* @summary Get a gzip file uncompressed size
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* @function
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* @public
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*
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* @description
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* This function determines the uncompressed size of the gzip file
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* by reading its `ISIZE`. The specification clarifies that this
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* value is just an estimation.
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*
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* @param {String} file - path to gzip file
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* @fulfil {Number} - uncompressed size
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* @returns {Promise}
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*
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* @example
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* gzip.getUncompressedSize('path/to/file.gz').then((uncompressedSize) => {
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* console.log(`The uncompressed size is: ${uncompressedSize}`);
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* });
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*/
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exports.getUncompressedSize = (file) => {
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return Bluebird.using(fs.openAsync(file, 'r').disposer((fileDescriptor) => {
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return fs.closeAsync(fileDescriptor);
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}), (fileDescriptor) => {
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return fs.fstatAsync(fileDescriptor).then((stats) => {
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const ISIZE_BUFFER_FILL_VALUE = 0;
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const ISIZE_BUFFER_START = 0;
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const isizeBuffer = Buffer.alloc(ISIZE_LENGTH, ISIZE_BUFFER_FILL_VALUE);
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return fs.readAsync(
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fileDescriptor,
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isizeBuffer,
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ISIZE_BUFFER_START,
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ISIZE_LENGTH,
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stats.size - ISIZE_LENGTH
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).then((bytesRead) => {
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if (bytesRead !== ISIZE_LENGTH) {
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throw new Error(`Bytes read mismatch: ${bytesRead} != ${ISIZE_LENGTH}`);
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}
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return isizeBuffer.readUInt32LE(ISIZE_BUFFER_START);
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});
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});
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});
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};
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