asar-lib
v0.7.2
Published
Creating atom-shell app packages
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asar - Atom-Shell Archive
Asar is a simple extensive archive format, it works like tar
that concatenates
all files together without compression, while having random access support.
Features
- Support random access
- Use JSON to store files' information
- Very easy to write a parser
Command line utility
Install
$ npm install asar
Usage
$ asar --help
Usage: asar [options] [command]
Commands:
pack|p <dir> <output>
create asar archive
list|l <archive>
list files of asar archive
extract-file|ef <archive> <filename>
extract one file from archive
extract|e <archive> <dest>
extract archive
Options:
-h, --help output usage information
-V, --version output the version number
Using programatically
Example
var asar = require('asar');
var src = 'some/path/';
var dest = 'name.asar';
asar.createPackage(src, dest, function() {
console.log('done.');
})
Please note that there is currently no error handling provided!
Using with grunt
There is also an unofficial grunt plugin to generate asar archives at bwin/grunt-asar.
Format
Asar uses Pickle to safely serialize binary value to file, there is
also a node.js binding of Pickle
class.
The format of asar is very flat:
| UInt32: header_size | String: header | Bytes: file1 | ... | Bytes: file42 |
The header_size
and header
are serialized with Pickle class, and
header_size
's Pickle object is 8 bytes.
The header
is a JSON string, and the header_size
is the size of header
's
Pickle
object.
Structure of header
is something like this:
{
"files": {
"tmp": {
"files": {}
},
"usr" : {
"files": {
"bin": {
"files": {
"ls": {
"offset": "0",
"size": 100,
"executable": true
},
"cd": {
"offset": "100",
"size": 100,
"executable": true
}
}
}
}
},
"etc": {
"files": {
"hosts": {
"offset": "200",
"size": 32
}
}
}
}
}
offset
and size
records the information to read the file from archive, the
offset
starts from 0 so you have to manually add the size of header_size
and
header
to the offset
to get the real offset of the file.
offset
is a UINT64 number represented in string, because there is no way to
precisely represent UINT64 in JavaScript Number
. size
is a JavaScript
Number
that is no larger than Number.MAX_SAFE_INTEGER
, which has a value of
9007199254740991
and is about 8PB in size. We didn't store size
in UINT64
because file size in Node.js is represented as Number
and it is not safe to
convert Number
to UINT64.