[Bug] [Electron] Can't enable blocking in multiple sessions

[KaKi87]

Hi,

The enableBlockingInSession method works fine when only having only one Session instance to enable blocking in, but when having multiple, the following error is thrown :

Error: Attempted to register a second handler for '@ghostery/adblocker/inject-cosmetic-filters'
    at IpcMainImpl.handle (node:electron/js2c/browser_init:2:109431)
    at BlockingContext.enable (node_modules/@ghostery/adblocker-electron/dist/commonjs/index.js:95:21)
    at ElectronBlocker.enableBlockingInSession (node_modules/@ghostery/adblocker-electron/dist/commonjs/index.js:237:17)

Thanks

[Kamiikaze]

Having the same issue. I tried to create a new blocker for each window but getting the same error.

[seia-soto]

I quickly generated a reproduction code with Gemini then plan to try reproducing. I might lack specialties on Electron knowledge, so please correct me if I'm picking the wrong one.

const { app, BrowserWindow, session } = require('electron');
const { ElectronBlocker } = require('@ghostery/adblocker-electron');
const fetch = require('cross-fetch');

async function createWindow() {
  const blocker = await ElectronBlocker.fromPrebuiltAdsAndTracking(fetch);

  // Session 1: Default Session
  const ses1 = session.defaultSession;
  blocker.enableBlockingInSession(ses1);
  console.log('Blocker enabled for Session 1');

  // Session 2: A separate partition (The issue occurs here)
  const ses2 = session.fromPartition('persist:test-session');
  blocker.enableBlockingInSession(ses2);
  console.log('Blocker enabled for Session 2');

  // Open windows for both sessions to verify blocking
  const win1 = new BrowserWindow({ session: ses1 });
  win1.loadURL('https://google.com/'); // Should block

  const win2 = new BrowserWindow({ session: ses2 });
  win2.loadURL('https://google.com/'); // Issue: May fail to block ads in this session
}

app.whenReady().then(createWindow);

[KaKi87]

Here's what I ended up doing instead :

const
    {
        FiltersEngine,
        Request
    } = require('@ghostery/adblocker'),
    filterEngine = await FiltersEngine.fromLists(fetch, [
        'https://ublockorigin.pages.dev/thirdparties/easylist.txt',
        'https://filters.adtidy.org/extension/ublock/filters/2_without_easylist.txt',
        'https://filters.adtidy.org/extension/ublock/filters/3.txt',
        'https://pgl.yoyo.org/adservers/serverlist.php?hostformat=hosts&showintro=1&mimetype=plaintext'
    ]);
electron.app.on('web-contents-created', (_, webContents) => {
    webContents.debugger.attach('1.3');
    webContents.debugger.sendCommand('Network.enable');
    webContents.debugger.sendCommand('Fetch.enable', { patterns: [{ urlPattern: '*' }] });
    webContents.debugger.on(
        'message',
        async (_, method, params) => {
            if(method !== 'Fetch.requestPaused') return;
            if(filterEngine.match(Request.fromRawDetails({ url: params.request.url })).match)
                await webContents.debugger.sendCommand(
                    'Fetch.failRequest',
                    {
                        requestId: params.requestId,
                        errorReason: 'Aborted'
                    }
                );
            else
                await webContents.debugger.sendCommand(
                    'Fetch.continueRequest',
                    {
                        requestId: params.requestId
                    }
                );
        }
    );
});

This block ads in all windows and webviews of an app.