@lpfreelance/electron-bridge NPM

electron-bridge

This library provides common main process modules (bridges) to be used from a renderer process in your Electron application (cf Process Model).

This package follows Electron' recommendations to provides you a reusable structured pattern while working in the safest environment possible.

Therefore, electron-bridge use Inter-Process Communication through context isolation and context bridge compatible with a sandbox environment.

Repository

This is a monorepo containing two packages:

electron-bridge
├── demo/         # a demo to quickly test common modules.
├── cli/          # electron-bridge-cli package to generate schemas.
├── schemas/      # schemas of the Electron's main process modules to generate and expose.
└── src/          # source files generated from schemas.

Install

$ npm install --save @lpfreelance/electron-bridge

Naming convention

Here is a brief description of the names used, so that we are on the same page:

Path	File	Symbol	Description
./bridge/main/	my-something.bridge.ts	MySomethingBridge	Class used in the main process.
./bridge/preload/	my-something.module.ts	MySomethingModule	Object used in the preload script.
./bridge/renderer/	my-something.api.ts	MySomethingApi	Interface used in the renderer process.

./bridge/renderer/	renderer.ts	Window	Augment Window with bridge's api.

With this example, you must expect IPC channels to be named eb.mySomething.<functionName>.

Finally common bridges means exposed Electron's main features (e.g. nativeTheme, powerMonitor, etc.). It also contains homebrew bridges for the benefit of all developers.

Bridges

This table shows you currently implemented bridges:

1. Electron

Bridge	Description
autoUpdater	cf Documentation
dialog	cf Documentation
nativeTheme	cf Documentation
powerMonitor	cf Documentation
powerSaveBlocker	cf Documentation
safeStorage	cf Documentation

2. Homebrew

Bridge	Description
fileSystem	Very simple wrapper for Node.js file system module.
path	Wrapper for Node.js path module.
store	JSON key/value storage solution using `safeStorage` to encrypt / decrypt data.

You can see usage of each bridge in demo/.

Usage

1. Main process side

In your electron entry-point:

Instantiate a BridgeService.
Add bridges you which to use on the renderer process side.
Register all modules to actually listen to IPC handlers.

electron.dev.ts

import {app, BrowserWindow} from 'electron';
import {BridgeService, DialogBridge} from '@lpfreelance/electron-bridge/main';

let win: BrowserWindow; let bridgeService: BridgeService;

app.enableSandbox();

const createWindow = () => { win = new BrowserWindow({ width: 1024, height: 768, webPreferences: { nativeWindowOpen: true, nodeIntegration: false, contextIsolation: true, enableRemoteModule: false, // ... } });

win.loadFile('index.html');

// Create bridge service. bridgeService = new BridgeService();

// Append bridges that you need and register all IPC handlers. bridgeService.add(new DialogBridge()) .registerAll();

win.on('closed', () => { // Release bridges resources bridgeService.releaseAll();

win = null;
bridgeService = null;

}); };

You can also add your own bridge ([see Custom bridge](#custom-bridge)).
Now that we have registered IPC handlers, we must declare a preload script.

### 2. Preload script
Using `context bridge`, it will allow us to expose bridges on the renderer process.
With `PreloadService`, we can expose only what we want to use:

> electron.preload.ts
```typescript
import {PreloadService} from '@lpfreelance/electron-bridge/preload';

const preloadService = new PreloadService();

preloadService.add('dialog')
              .expose();

Here you add the modules matching the bridges you added in electron.dev.ts file. You just need to use the camelCase name of the bridge, like in Electron documentation (e.g. nativeTheme, powerMonitor, etc.).

You can also add your own module. This is further explained below (see Create a module).

You must call expose() in order to expose your modules using context bridge.

Now Electron needs to know that this script must be preloaded. When creating a BrowserWindow, we just need to set the preload path of our script like below:

electron.dev.ts
import * as path from 'path';

// ... win = new BrowserWindow({ // ... webPreferences: { // ... preload: path.join(__dirname, 'electron.preload.js') } });

### 3. Renderer process side
In your renderer process, aka your application. You can now access exposed bridges like this:

> index.html
```html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>electron-bridge-test</title>
</head>
<body>
<script>
window.dialog.showOpenDialog({title: 'My Awesome Native Dialog', properties: ['openDirectory']})
      .then(result => {
        if (result.canceled || result.filePaths.length !== 1) {
          console.error(`<i-need-a-file-and-only-one-file />`);
          return;
        }
        console.info(`<directory path="${result.filePaths[0]}" />`);
      });
</script>
</body>
</html>

As you can see, you can simply use the native dialog module from your renderer process. You'll notice that it reflects the same API exposed by Electron. This way, you can directly look at Electron's documentation.

4. Test it

You can now execute the following command to run electron:

$ tsc electron.dev.ts electron.preload.ts && electron electron.dev.js

Custom bridge

You will now learn how to write your own bridge which is composed of three files.

You should first take a look to understand how things works together. But ultimately you'll want to use a Schema thanks to electron-bridge-cli in cli/.

1. Create a bridge

Side: main process

You must implement a Bridge interface in order to register it in the main process:

src/bridge/main/app.bridge.ts

import {App, ipcMain} from 'electron';
import {Bridge} from '@lpfreelance/electron-bridge/main';

export class AppBridge implements Bridge {

constructor(private app: App) {
    
}

public register(): void {
    ipcMain.handle('eb.app.getVersion', (event: any) => {
        return this.app.getVersion();
    });
    ipcMain.handle('eb.app.getName', (event: any) => {
        return this.app.getName();
    });
    ipcMain.handle('eb.app.getPath', (event: any, path: string) => {
        return this.app.getPath(path);
    });
    // allocate resources you'll need.
}

public release(): void {
    ipcMain.removeHandler('eb.app.getVersion');
    ipcMain.removeHandler('eb.app.getName');
    ipcMain.removeHandler('eb.app.getPath');
    // release resources you no longer need.
}

}

### 2. Create a module
> Side: preload script

Then, you must write your module using BridgeModule interface:

> src/bridge/preload/app.module.ts
```typescript
import {ipcRenderer} from 'electron';
import {BridgeModule} from '@lpfreelance/electron-bridge/preload';

export const AppModule: BridgeModule = {
    name: 'app',
    readonly: true,
    api: {
        getVersion: async () => {
            return await ipcRenderer.invoke('eb.app.getVersion');
        },
        getName: async () => {
            return await ipcRenderer.invoke('eb.app.getName');
        },
        getPath: async (path: string) => {
            return await ipcRenderer.invoke('eb.app.getPath', path);
        }
    }
};

You can now import and add your custom module in the preload script:

src/electron.preload.ts

import {PreloadService} from '@lpfreelance/electron-bridge/preload';
import {AppModule} from './bridge/module/app.module.ts';

const preloadService = new PreloadService();

preloadService.add('dialog') .add(AppModule) .expose();

### 3. Create an api interface
> Side: your beloved IDE

Let's write an exported interface for our bridge:

> src/bridge/renderer/app.api.ts
```typescript
export interface AppApi {
    
    getName(): Promise<string>;
    getVersion(): Promise<number>;
    getPath(path: string): Promise<string>;

}

And augment the Window interface:

src/bridge/renderer/renderer.ts
import {AppApi} from './app.api';

declare global { interface Window { app: AppApi; } }

### 4. Build it
Use your preferred bundler to bundle your application and target each Electron's process. You can find an example using
[webpack](https://webpack.js.org/) with this repository configuration file: `./webpack.dev.js`.
You should edit this configuration to match your project.

You can then bundle with:
```bash script
$ webpack --config webpack.dev.js

5. Test it

Side: renderer process

We can now use our custom module:

index.html

<!-- ... -->
<script>
  // ...
  Promise.all([
    window.app.getName(),
    window.app.getVersion(),
    window.app.getPath('userData')
  ]).then(([name, version, path]) => {
    console.log(`<app name="${name}" version="${version}" user-data="${path}" />`);
  });
</script>
<!-- ... -->

Security

This library provides a pattern to quickly access main process features. You are still responsible regarding features you expose to the renderer process (cf Context Isolation).

You can quickly implement a logic in your application using the fileSystem module and test it. But at the end, you should create your own custom module and always check for bad behaviors.

You can see an example with the store bridge. When StoreBridge is created, you give an absolute path (parent) where to store JSON files. You can then create multiple JSON files in this directory using store.withStore('my/path/db'). Without safety checks, calling store.withStore('/root/my-store') would allow any users to create a file outside the given parent path.

In this implementation, attempting to resolve the store's path outside the given parent path will throw an error.

Schemas

A schema allows you to write a single file to describe a bridge between the main process and the renderer process. You can then use electron-bridge-cli in cli/ to generate a bridge file, a module file and an api file.

Actually, this package uses schemas/ with electron-bridge-cli to generate all files under src/.

This is the way.

Contributing

Feel free to contribute by creating an issue / submitting a pull-request.

If you wish to propose a new bridge, create an issue to discuss it, or just submit a PR if you already wrote it. Please remember that one bridge = one schema.

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