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asar
Advanced tools
Readme
Asar is a simple extensive archive format, it works like tar
that concatenates
all files together without compression, while having random access support.
This module requires Node 10 or later.
$ npm install --engine-strict asar
$ 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
Given:
app
(a) ├── x1
(b) ├── x2
(c) ├── y3
(d) │ ├── x1
(e) │ └── z1
(f) │ └── x2
(g) └── z4
(h) └── w1
Exclude: a, b
$ asar pack app app.asar --unpack-dir "{x1,x2}"
Exclude: a, b, d, f
$ asar pack app app.asar --unpack-dir "**/{x1,x2}"
Exclude: a, b, d, f, h
$ asar pack app app.asar --unpack-dir "{**/x1,**/x2,z4/w1}"
const asar = require('asar');
const src = 'some/path/';
const dest = 'name.asar';
await asar.createPackage(src, dest);
console.log('done.');
Please note that there is currently no error handling provided!
You can pass in a transform
option, that is a function, which either returns
nothing, or a stream.Transform
. The latter will be used on files that will be
in the .asar
file to transform them (e.g. compress).
const asar = require('asar');
const src = 'some/path/';
const dest = 'name.asar';
function transform (filename) {
return new CustomTransformStream()
}
await asar.createPackageWithOptions(src, dest, { transform: transform });
console.log('done.');
There is also an unofficial grunt plugin to generate asar archives at bwin/grunt-asar.
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,
"integrity": {
"algorithm": "SHA256",
"hash": "...",
"blockSize": 1024,
"blocks": ["...", "..."]
}
},
"cd": {
"offset": "100",
"size": 100,
"executable": true,
"integrity": {
"algorithm": "SHA256",
"hash": "...",
"blockSize": 1024,
"blocks": ["...", "..."]
}
}
}
}
}
},
"etc": {
"files": {
"hosts": {
"offset": "200",
"size": 32,
"integrity": {
"algorithm": "SHA256",
"hash": "...",
"blockSize": 1024,
"blocks": ["...", "..."]
}
}
}
}
}
}
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.
integrity
is an object consisting of a few keys:
algorithm
, currently only SHA256
is supported.hash
value representing the hash of the entire file.blocks
of the file. i.e. for a blockSize of 4KB this array contains the hash of every block if you split the file into N 4KB blocks.blockSize
representing the size in bytes of each block in the blocks
hashes aboveFAQs
Creating Electron app packages
The npm package asar receives a total of 218,757 weekly downloads. As such, asar popularity was classified as popular.
We found that asar demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 2 open source maintainers collaborating on the project.
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