fast-asar

A faster implementation of Electron's ASAR archive format.

This is both a library and a CLI tool.

Installation

You can install fast-asar from NPM (or your preferred package manager):

npm install fast-asar
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Usage

CLI

You can use the CLI tool to extract and create ASAR archives.

npx fast-asar help
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Library

The library exports an Asar class, which can be used to read and write ASAR archives.

For example, to extract an ASAR archive to a directory:

import { Asar } from "fast-asar";
import { readFile } from "fs/promises";

const asarBytes = await readFile("./app.asar");

const asar = new Asar(asarBytes);

await asar.extract("./app-extracted");
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For more information, see the API documentation.

Compatibility

This library can be run with Node.js and Bun.

Browser support is planned.

Benchmarks

The following benchmarks were run with hyperfine on a 2016 MacBook Pro with a 2.9 GHz Quad-Core Intel Core i7 processor and 16 GB of RAM.

Extract files

This benchmark extracts all files in the Replit Desktop app's app.asar file.

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./node_modules/.bin/asar extract test/ignore/app.asar test/ignore/app1	670.0 ± 52.6	614.6	739.4	1.54 ± 0.41
bun ./src/cli/index.ts extract test/ignore/app.asar test/ignore/app2	435.1 ± 110.9	373.7	632.3	1.00

Summary: fast-asar is 1.54 ± 0.41 times faster than @electron/asar.

To run this benchmark yourself, run bun run benchmark:extract.

Pack directories

This benchmark packs the src directory into an ASAR archive at test/ignore/src.asar.

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./node_modules/.bin/asar pack src test/ignore/src.asar	154.7 ± 45.3	123.4	231.7	1.93 ± 0.57
bun ./src/cli/index.ts pack src test/ignore/src.asar	80.0 ± 3.1	77.6	85.4	1.00

Summary: fast-asar is 1.93 ± 0.57 times faster than @electron/asar.

To run this benchmark yourself, run bun run benchmark:pack.

List files

This benchmark lists all files in the Replit Desktop app's app.asar file.

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./node_modules/.bin/asar list test/ignore/app.asar	136.0 ± 31.3	117.5	191.5	1.28 ± 0.30
bun ./src/cli/index.ts list test/ignore/app.asar	106.0 ± 5.9	101.3	116.2	1.00

Summary: fast-asar is 1.28 ± 0.30 times faster than @electron/asar.

To run this benchmark yourself, run bun run benchmark:list.

Contributing

Running tests

For the tests, you must have the Replit Desktop app's app.asar file in the test/ignore directory. You can get this file by installing the Replit Desktop app and copying the app.asar file from the installation directory.

Then, to run all tests:

bun pretest
bun test
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