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
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
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
has been designed to be compatible with the C implementation
available from https://bitbucket.org/james_taylor/seek-bzip2. That codebase
bzip-table tool which will generate bzip2 block start indices.
seek-bzip-table tool in this package's
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])
input argument can be a "stream" object (which must implement the
readByte method), or a
expectedSize is not present,
decodeBzip simply decodes
returns the resulting
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
If you pass a non-numeric second parameter, it can either be a
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
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
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])
output parameters are as above.
blockStartBits parameter gives the start of the desired block, in bits.
If passing a stream as the
input parameter, it must implement the
The final exported method is a function accepting two or three parameters:
Bunzip.table = function(input, Function callback, [boolean multistream])
multistream parameters are identical to those for the
This function will invoke
callback(position, size) once per bzip2 block,
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
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.bz232 99981320555 99981606348 99981847568 999811089094 999811343625 999811596228 999811843336 999812090919 999812342106 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 | tailélan'sémigréémigré'sémigrésépéeépée'sépéesétudeétude'sétudes$
--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