185 lines
6.8 KiB
Markdown
185 lines
6.8 KiB
Markdown
# seek-bzip
|
|
|
|
[![Build Status][1]][2] [![dependency status][3]][4] [![dev dependency status][5]][6]
|
|
|
|
`seek-bzip` is a pure-javascript Node.JS module adapted from [node-bzip](https://github.com/skeggse/node-bzip) and before that [antimatter15's pure-javascript bzip2 decoder](https://github.com/antimatter15/bzip2.js). Like these projects, `seek-bzip` only does decompression (see [compressjs](https://github.com/cscott/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](https://github.com/laverdet/node-fibers)
|
|
package, it can operate on node streams; see `test/stream.js` for an
|
|
example.
|
|
|
|
## How to Install
|
|
|
|
```
|
|
npm install seek-bzip
|
|
```
|
|
|
|
This package uses
|
|
[Typed Arrays](https://developer.mozilla.org/en-US/docs/JavaScript/Typed_arrays), which are present in node.js >= 0.5.5.
|
|
|
|
## Usage
|
|
|
|
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.
|
|
|
|
## Documentation
|
|
|
|
`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.
|
|
|
|
## Command-line
|
|
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.
|
|
|
|
## Help wanted
|
|
|
|
Improvements to this module would be generally useful.
|
|
Feel free to fork on github and submit pull requests!
|
|
|
|
## Related projects
|
|
|
|
* https://github.com/skeggse/node-bzip node-bzip (original upstream source)
|
|
* https://github.com/cscott/compressjs
|
|
Lots of compression/decompression algorithms from the same author as this
|
|
module, including bzip2 compression code.
|
|
* https://github.com/cscott/lzjb fast LZJB compression/decompression
|
|
|
|
## License
|
|
|
|
#### MIT License
|
|
|
|
> Copyright © 2013-2015 C. Scott Ananian
|
|
>
|
|
> Copyright © 2012-2015 Eli Skeggs
|
|
>
|
|
> Copyright © 2011 Kevin Kwok
|
|
>
|
|
> 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.
|
|
|
|
[1]: https://travis-ci.org/cscott/seek-bzip.png
|
|
[2]: https://travis-ci.org/cscott/seek-bzip
|
|
[3]: https://david-dm.org/cscott/seek-bzip.png
|
|
[4]: https://david-dm.org/cscott/seek-bzip
|
|
[5]: https://david-dm.org/cscott/seek-bzip/dev-status.png
|
|
[6]: https://david-dm.org/cscott/seek-bzip#info=devDependencies
|