Electron application packaging

To relieve Windows problem under the path name is too long issues , slightly faster require speed and simplicity hidden source code, we can choose to use packaged into asar archive, only need to make some minor changes to the source code. Most users can easily implement this function, because it is electron-packager in 060bdcb042b99b, electron-forge and electron-builder , and can be used out of the box.

Generate asar package

asar tar style archive format that combines multiple files into one file. Electron not need to decompress the entire file, you can read any file content from it.
The application can be packaged into asar according to the following steps:

• Install asar :

$ npm install -g asar

• Use asar pack package:

$ asar pack your-app app.asar

Use asar package

In Electron There are two types of APIs , respectively Node.js provided Node API and Chromium provided Web API . Both types of API support reading files from the asar

Node API

Since Electron in particular hit a patch, Node API in such fs.readFile or require method and the like can be asar regarded as virtual folders, read asar inside and read from a file on the file system as the real.

Example:

For example, suppose we have a example.asar package /path/to

$ asar list /path/to/example.asar
/app.js
/file.txt
/dir/module.js
/static/index.html
/static/main.css
/static/jquery.min.js

Read a file from the asar

const fs = require('fs');
fs.readFileSync('/path/to/example.asar/file.txt');

List all files in the root directory of the asar

const fs = require('fs');
fs.readdirSync('/path/to/example.asar');

Use a module in the asar

const BrowserWindow = require('electron').BrowserWindow;
var win = new BrowserWindow({width: 800, height: 600});
win.loadURL('file:///path/to/example.asar/static/index.html');

Web API

In the Web page, the file: protocol can be used to obtain the files in the asar Like Node API , the asar package is regarded as a virtual folder.

Example:

For example, you can use $.get to get the file:

<script>
var $ = require('./jquery.min.js');
$.get('file:///path/to/example.asar/file.txt', function(data) {
  console.log(data);
});
</script>

Treat the asar package as a normal file

In some cases, for example, to asar package file of 060bdcb042bc6c, we need to read the package file of asar For this reason we can not use the built-in asar function and the original fs module identical original-fs module.

Example:

const originalFs = require('original-fs')
originalFs.readFileSync('/path/to/example.asar')

You can also set process.noAsar to true to disable the support for asar fs

const fs = require('fs')
process.noAsar = true
fs.readFileSync('/path/to/example.asar')

Node API flaws

Although we have done our best to make asar package under Node API tend to the real directory structure as much as possible, there are still some underlying Node API we cannot guarantee its normal operation.

asar package file is read-only

asar contents of the package can not be changed, so Node APIs in those methods can be used to modify the file in treating asar can not work properly package.

The working directory is invalid in the asar package

Although the asar package is a virtual folder, there is no real directory structure corresponding to the file system, so it is impossible for us to set the working directory working Directory to a folder in the asar asar the folder in cwd API in the form of 060bdcb042bd5a as a parameter will also report an error.

Certain APIs require additional decompressed asar packages

Most fs can read files or file information from the asar package without decompression, but when dealing with some underlying system methods that rely on the real file path, Electron will extract the required files to the temporary directory, and then the temporary directory The real file path is passed to the underlying system method to make it work properly. For this type of API , the cost will be slightly more.

The following are some API that need additional decompression:

• child_process.execFile
• child_process.execFileSync
• fs.open
• fs.openSync
• process.dlopen

Untrue statistics of fs.stat

fs.stat for the files in the asar package. The returned Stats object is not an accurate value because these files do not actually exist in the file system. So apart from file size and file type, we should not rely on the value of the Stats

Execute the binary file in the asar package

Node that can execute programs in API , such as child_process.exec , child_process.spawn and child_process.execFile , but only execFile can execute the programs in the asar

Because exec and spawn allow command replace file as input, and command needs to be shell under 060bdcb042beef, there is currently no reliable method to determine command is operating in a asar package, and we can’t guarantee that we can still judge the file in the package. Replace the file path in command without any side effects.

Add unpackaged files to the asar package

Some Node API will decompress the file into the file system when invoking it. In addition to efficiency issues, it may also attract the attention of anti-virus software!

To solve this problem, we can use the --unpack asar package to exclude some files from being packaged in the asar package. Here is how to exclude some native modules for sharing purposes:

$ asar pack app app.asar --unpack *.node

After the above command, in addition to the generated app.asar package, there is also a app.asar.unpacked folder that contains excluded files. We need to copy this folder together and provide it to users.