NebulaBrowser/README-PLUGINS.md

Nebula Plugins (Early Preview)

This document explains how to build simple plugins for Nebula. The initial API is intentionally small and will grow with feedback.

Overview

• Plugins live under either of these folders:
  • App folder: <app>/plugins/<plugin-id>/
  • User folder: %APPDATA%/Nebula/plugins/<plugin-id>/ (Windows) – preferred for user-installed plugins.
• Each plugin has a plugin.json manifest. Optional main.js runs in the main process. Optional renderer-preload.js runs in the renderer preload context and can expose safe APIs via contextBridge.
• Plugins are loaded on app start. Toggle a plugin by setting "enabled": false in its manifest.

Manifest (plugin.json)

Example:

{
  "id": "my-plugin",
  "name": "My Plugin",
  "version": "0.1.0",
  "description": "What it does",
  "main": "main.js",
  "rendererPreload": "renderer-preload.js",
  "enabled": true
}

Fields:

• id: Unique id. Defaults to folder name if omitted.
• main: Optional entry for main process integration.
• rendererPreload: Optional file injected into the preload. Use it to expose limited APIs.
• enabled: Defaults to true.

Main process API (activate)

If main is present, export an activate(ctx) function. The ctx contains:

• Electron: app, BrowserWindow, ipcMain, session, Menu, dialog, shell
• paths: { appPath, userData, pluginDir }
• log/warn/error: prefix logs with your plugin id
• on(event, cb): subscribe to lifecycle events (experimental)
• registerIPC(channel, handler): quickly expose an ipcMain.handle
• registerWebRequest(filter, listener): attach session.webRequest.onBeforeRequest

Example:

module.exports.activate = (ctx) => { ctx.log('hello'); ctx.registerIPC('my-plugin:do', async (_evt, payload) => ({ ok: true })); ctx.registerWebRequest({ urls: [':///*'] }, (details) => ({ cancel: false })); };

Renderer preload API

If rendererPreload is present, it will be require()-d from the app preload. You can use contextBridge to expose a safe surface to the page:

const { contextBridge, ipcRenderer } = require('electron'); contextBridge.exposeInMainWorld('myPlugin', { hello: () => ipcRenderer.invoke('my-plugin:do'), });

Your exposed API will be available on window.myPlugin in renderer/ code (e.g., script.js).

Sample plugin

A working sample is included at plugins/sample-hello/:

• Adds menu item "Say Hello (Sample Plugin)" under Help.
• Exposes window.sampleHello.ping() and window.sampleHello.onHello(cb).

Try it from the DevTools console:

await window.sampleHello.ping(); window.sampleHello.onHello((m) => console.log('got hello', m));

Click Help -> Say Hello (Sample Plugin) to see the message delivered to the page.

Loading order and safety

• Plugins load after the app is ready. Renderer preloads run after Nebula's own preload has exposed its APIs.
• Context isolation stays enabled. Only data explicitly exposed via contextBridge is available to pages.
• Avoid long blocking work in plugin activation.

Debugging

• See logs with a [Plugin:<id>] prefix in the app console.
• Temporarily disable a plugin by setting enabled: false in plugin.json.

Roadmap

This is a first pass. Planned next:

• Enable plugin settings UI
• Hot reload/reload button
• More lifecycle hooks (tab events, context menu contributions)
• Theming hooks