seek-bzip
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Package description
The seek-bzip npm package is a pure-Javascript implementation of the BZIP2 decompression algorithm, which allows for random access seeking within bzip2 files. This package is particularly useful for applications that need to extract portions of large compressed files without having to decompress the entire file.
Random Access Decompression
This feature allows users to decompress a specific block of data from a bzip2 compressed file, starting at a specified byte. This is useful for extracting data from large files without the need to decompress the entire file.
const fs = require('fs');
const seekBzip = require('seek-bzip');
const compressedData = fs.readFileSync('path/to/compressed-file.bz2');
const start = 12345; // start byte for decompression
const decompressedData = seekBzip.decodeBlock(compressedData, start);unbzip2-stream is a streaming bzip2 decompressor in pure JavaScript for Node.js. Unlike seek-bzip, it does not support random access seeking, but it is useful for streaming decompression of bzip2 files.
compressjs is a collection of pure JavaScript implementations of various data compression algorithms, including bzip2. It provides a broader range of compression algorithms compared to seek-bzip, but it may not support random access seeking within bzip2 files.
node-bzip is a bzip2 compression and decompression library for Node.js. It is a wrapper around the C++ libbz2 library, which means it is not pure JavaScript like seek-bzip. It offers fast performance but does not support random access seeking.
Readme
seek-bzip is a pure-javascript Node.JS module adapted from node-bzip and before that antimatter15's pure-javascript bzip2 decoder. Like these projects, seek-bzip only does decompression (see compressjs if you need compression code). Unlike those other projects, seek-bzip can seek to and decode single blocks from the bzip2 file.
seek-bzip primarily decodes buffers into other buffers, synchronously.
With the help of the fibers
package, it can operate on node streams; see test/stream.js for an
example.
npm install seek-bzip
This package uses Typed Arrays, which are present in node.js >= 0.5.5.
After compressing some example data into example.bz2, the following will recreate that original data and save it to example:
var Bunzip = require('seek-bzip');
var fs = require('fs');
var compressedData = fs.readFileSync('example.bz2');
var data = Bunzip.decode(compressedData);
fs.writeFileSync('example', data);
See the tests in the tests/ directory for further usage examples.
For uncompressing single blocks of bzip2-compressed data, you will need
an out-of-band index listing the start of each bzip2 block. (Presumably
you generate this at the same time as you index the start of the information
you wish to seek to inside the compressed file.) The seek-bzip module
has been designed to be compatible with the C implementation seek-bzip2
available from https://bitbucket.org/james_taylor/seek-bzip2. That codebase
contains a bzip-table tool which will generate bzip2 block start indices.
There is also a pure-JavaScript seek-bzip-table tool in this package's
bin directory.
require('seek-bzip') returns a Bunzip object. It contains three static
methods. The first is a function accepting one or two parameters:
Bunzip.decode = function(input, [Number expectedSize] or [output], [boolean multistream])
The input argument can be a "stream" object (which must implement the
readByte method), or a Buffer.
If expectedSize is not present, decodeBzip simply decodes input and
returns the resulting Buffer.
If expectedSize is present (and numeric), decodeBzip will store
the results in a Buffer of length expectedSize, and throw an error
in the case that the size of the decoded data does not match
expectedSize.
If you pass a non-numeric second parameter, it can either be a Buffer
object (which must be of the correct length; an error will be thrown if
the size of the decoded data does not match the buffer length) or
a "stream" object (which must implement a writeByte method).
The optional third multistream parameter, if true, attempts to continue
reading past the end of the bzip2 file. This supports "multistream"
bzip2 files, which are simply multiple bzip2 files concatenated together.
If this argument is true, the input stream must have an eof method
which returns true when the end of the input has been reached.
The second exported method is a function accepting two or three parameters:
Bunzip.decodeBlock = function(input, Number blockStartBits, [Number expectedSize] or [output])
The input and expectedSize/output parameters are as above.
The blockStartBits parameter gives the start of the desired block, in bits.
If passing a stream as the input parameter, it must implement the
seek method.
The final exported method is a function accepting two or three parameters:
Bunzip.table = function(input, Function callback, [boolean multistream])
The input and multistream parameters are identical to those for the
decode method.
This function will invoke callback(position, size) once per bzip2 block,
where position gives the starting position of the block (in bits), and
size gives the uncompressed size of the block (in bytes).
This can be used to construct an index allowing direct access to a particular
block inside a bzip2 file, using the decodeBlock method.
There are binaries available in bin. The first generates an index of all the blocks in a bzip2-compressed file:
$ bin/seek-bzip-table test/sample4.bz2
32 99981
320555 99981
606348 99981
847568 99981
1089094 99981
1343625 99981
1596228 99981
1843336 99981
2090919 99981
2342106 39019
$
The first field is the starting position of the block, in bits, and the second field is the length of the block, in bytes.
The second binary decodes an arbitrary block of a bzip2 file:
$ bin/seek-bunzip -d -b 2342106 test/sample4.bz2 | tail
élan's
émigré
émigré's
émigrés
épée
épée's
épées
étude
étude's
études
$
Use --help to see other options.
Improvements to this module would be generally useful. Feel free to fork on github and submit pull requests!
Copyright © 2013 C. Scott Ananian
Copyright © 2012 Eli Skeggs
Copyright © 2011 Kevin Kwok
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, see http://www.gnu.org/licenses/lgpl-2.1.html
FAQs
a pure-JavaScript Node.JS module for random-access decoding bzip2 data
The npm package seek-bzip receives a total of 2,814,181 weekly downloads. As such, seek-bzip popularity was classified as popular.
We found that seek-bzip demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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