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<h1 class="page-title">Source: packet/compressed.js</h1>
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<pre class="prettyprint source"><code>// GPG4Browsers - An OpenPGP implementation in javascript
// Copyright (C) 2011 Recurity Labs GmbH
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
/**
* Implementation of the Compressed Data Packet (Tag 8)<br/>
* <br/>
* RFC4880 5.6: The Compressed Data packet contains compressed data. Typically,
* this packet is found as the contents of an encrypted packet, or following
* a Signature or One-Pass Signature packet, and contains a literal data packet.
* @requires compression/jxg
* @requires encoding/base64
* @requires enums
* @module packet/compressed
*/
var enums = require('../enums.js'),
JXG = require('../compression/jxg.js'),
base64 = require('../encoding/base64.js');
/**
* @constructor
*/
module.exports = function compressed() {
/**
* List of packets
* @type {module:packet/packetlist}
*/
this.packets = null;
/**
* Compression algorithm
* @type {compression}
*/
this.algorithm = 'uncompressed';
/**
* Compressed packet data
* @type {String}
*/
this.compressed = null;
/**
* Parsing function for the packet.
* @param {String} bytes Payload of a tag 8 packet
*/
this.read = function(bytes) {
// One octet that gives the algorithm used to compress the packet.
this.algorithm = enums.read(enums.compression, bytes.charCodeAt(0));
// Compressed data, which makes up the remainder of the packet.
this.compressed = bytes.substr(1);
this.decompress();
}
/**
* Return the compressed packet.
* @return {String} binary compressed packet
*/
this.write = function() {
if (this.compressed == null)
this.compress();
return String.fromCharCode(enums.write(enums.compression, this.algorithm)) + this.compressed;
}
/**
* Decompression method for decompressing the compressed data
* read by read_packet
*/
this.decompress = function() {
var decompressed;
switch (this.algorithm) {
case 'uncompressed':
decompressed = this.compressed;
break;
case 'zip':
var compData = this.compressed;
var radix = base64.encode(compData).replace(/\n/g, "");
// no header in this case, directly call deflate
var jxg_obj = new JXG.Util.Unzip(JXG.Util.Base64.decodeAsArray(radix));
decompressed = unescape(jxg_obj.deflate()[0][0]);
break;
case 'zlib':
//RFC 1950. Bits 0-3 Compression Method
var compressionMethod = this.compressed.charCodeAt(0) % 0x10;
//Bits 4-7 RFC 1950 are LZ77 Window. Generally this value is 7 == 32k window size.
// 2nd Byte in RFC 1950 is for "FLAGs" Allows for a Dictionary
// (how is this defined). Basic checksum, and compression level.
if (compressionMethod == 8) { //CM 8 is for DEFLATE, RFC 1951
// remove 4 bytes ADLER32 checksum from the end
var compData = this.compressed.substring(0, this.compressed.length - 4);
var radix = base64.encode(compData).replace(/\n/g, "");
//TODO check ADLER32 checksum
decompressed = JXG.decompress(radix);
break;
} else {
throw new Error("Compression algorithm ZLIB only supports " +
"DEFLATE compression method.");
}
break;
case 'bzip2':
// TODO: need to implement this
throw new Error('Compression algorithm BZip2 [BZ2] is not implemented.');
break;
default:
throw new Error("Compression algorithm unknown :" + this.alogrithm);
break;
}
this.packets.read(decompressed);
}
/**
* Compress the packet data (member decompressedData)
*/
this.compress = function() {
switch (this.algorithm) {
case 'uncompressed':
// - Uncompressed
this.compressed = this.packets.write();
break;
case 'zip':
// - ZIP [RFC1951]
throw new Error("Compression algorithm ZIP [RFC1951] is not implemented.");
break;
case 'zlib':
// - ZLIB [RFC1950]
// TODO: need to implement this
throw new Error("Compression algorithm ZLIB [RFC1950] is not implemented.");
break;
case 'bzip2':
// - BZip2 [BZ2]
// TODO: need to implement this
throw new Error("Compression algorithm BZip2 [BZ2] is not implemented.");
break;
default:
throw new Error("Compression algorithm unknown :" + this.type);
break;
}
}
};
</code></pre>
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