security: allow to block desktopCapturer.getSources() calls

docs/api/app.md

@@ -398,6 +398,16 @@ non-minimized.
 This event is guaranteed to be emitted after the `ready` event of `app`
 gets emitted.
 
+### Event: 'desktop-capturer-get-sources'
+
+Returns:
+
+* `event` Event
+* `webContents` [WebContents](web-contents.md)
+
+Emitted when `desktopCapturer.getSources()` is called in the renderer process of `webContents`.
+Calling `event.preventDefault()` will make it throw an error.
+
 ### Event: 'remote-require'
 
 Returns:

docs/api/web-contents.md

@@ -663,6 +663,15 @@ Returns:
 Emitted when the associated window logs a console message. Will not be emitted
 for windows with *offscreen rendering* enabled.
 
+#### Event: 'desktop-capturer-get-sources'
+
+Returns:
+
+* `event` Event
+
+Emitted when `desktopCapturer.getSources()` is called in the renderer process.
+Calling `event.preventDefault()` will make it throw an error.
+
 #### Event: 'remote-require'
 
 Returns:

lib/browser/api/web-contents.js

@@ -368,6 +368,10 @@ WebContents.prototype._init = function () {
     })
   })
 
+  this.on('desktop-capturer-get-sources', (event, ...args) => {
+    app.emit('desktop-capturer-get-sources', event, this, ...args)
+  })
+
   this.on('remote-require', (event, ...args) => {
     app.emit('remote-require', event, this, ...args)
   })

lib/browser/desktop-capturer.js

@@ -1,7 +1,10 @@
 'use strict'
 
 const ipcMain = require('@electron/internal/browser/ipc-main-internal')
+const errorUtils = require('@electron/internal/common/error-utils')
+
 const { desktopCapturer } = process.atomBinding('desktop_capturer')
+const eventBinding = process.atomBinding('event')
 
 const deepEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b)
 
@@ -12,6 +15,15 @@ const electronSources = 'ELECTRON_BROWSER_DESKTOP_CAPTURER_GET_SOURCES'
 const capturerResult = (id) => `ELECTRON_RENDERER_DESKTOP_CAPTURER_RESULT_${id}`
 
 ipcMain.on(electronSources, (event, captureWindow, captureScreen, thumbnailSize, fetchWindowIcons, id) => {
+  const customEvent = eventBinding.createWithSender(event.sender)
+  event.sender.emit('desktop-capturer-get-sources', customEvent)
+
+  if (customEvent.defaultPrevented) {
+    const error = new Error('desktopCapturer.getSources() blocked')
+    event.sender._sendInternal(capturerResult(id), errorUtils.serialize(error))
+    return
+  }
+
   const request = {
     id,
     options: {
@@ -51,15 +63,15 @@ desktopCapturer.emit = (event, name, sources, fetchWindowIcons) => {
   })
 
   if (handledWebContents) {
-    handledWebContents._sendInternal(capturerResult(handledRequest.id), result)
+    handledWebContents._sendInternal(capturerResult(handledRequest.id), null, result)
   }
 
   // Check the queue to see whether there is another identical request & handle
   requestsQueue.forEach(request => {
     const webContents = request.webContents
     if (deepEqual(handledRequest.options, request.options)) {
       if (webContents) {
-        webContents._sendInternal(capturerResult(request.id), result)
+        webContents._sendInternal(capturerResult(request.id), null, result)
       }
     } else {
       unhandledRequestsQueue.push(request)

lib/renderer/api/desktop-capturer.js

@@ -1,7 +1,9 @@
 'use strict'
 
 const { nativeImage } = require('electron')
+
 const ipcRenderer = require('@electron/internal/renderer/ipc-renderer-internal')
+const errorUtils = require('@electron/internal/common/error-utils')
 
 const includes = [].includes
 let currentId = 0
@@ -17,6 +19,16 @@ function isValid (options) {
   return Array.isArray(types)
 }
 
+function mapSources (sources) {
+  return sources.map(source => ({
+    id: source.id,
+    name: source.name,
+    thumbnail: nativeImage.createFromDataURL(source.thumbnail),
+    display_id: source.display_id,
+    appIcon: source.appIcon ? nativeImage.createFromDataURL(source.appIcon) : null
+  }))
+}
+
 exports.getSources = function (options, callback) {
   if (!isValid(options)) return callback(new Error('Invalid options'))
   const captureWindow = includes.call(options.types, 'window')
@@ -34,19 +46,11 @@ exports.getSources = function (options, callback) {
 
   const id = incrementId()
   ipcRenderer.send('ELECTRON_BROWSER_DESKTOP_CAPTURER_GET_SOURCES', captureWindow, captureScreen, options.thumbnailSize, options.fetchWindowIcons, id)
-  return ipcRenderer.once(`ELECTRON_RENDERER_DESKTOP_CAPTURER_RESULT_${id}`, (event, sources) => {
-    callback(null, (() => {
-      const results = []
-      sources.forEach(source => {
-        results.push({
-          id: source.id,
-          name: source.name,
-          thumbnail: nativeImage.createFromDataURL(source.thumbnail),
-          display_id: source.display_id,
-          appIcon: source.appIcon ? nativeImage.createFromDataURL(source.appIcon) : null
-        })
-      })
-      return results
-    })())
+  return ipcRenderer.once(`ELECTRON_RENDERER_DESKTOP_CAPTURER_RESULT_${id}`, (event, error, sources) => {
+    if (error) {
+      callback(errorUtils.deserialize(error))
+    } else {
+      callback(null, mapSources(sources))
+    }
   })
 }

spec/api-app-spec.js

@@ -370,6 +370,16 @@ describe('app module', () => {
       w = new BrowserWindow({ show: false })
     })
 
+    it('should emit desktop-capturer-get-sources event when desktopCapturer.getSources() is invoked', (done) => {
+      app.once('desktop-capturer-get-sources', (event, webContents) => {
+        expect(webContents).to.equal(w.webContents)
+        done()
+      })
+      w = new BrowserWindow({ show: false })
+      w.loadURL('about:blank')
+      w.webContents.executeJavaScript(`require('electron').desktopCapturer.getSources({ types: ['screen'] }, () => {})`)
+    })
+
     it('should emit remote-require event when remote.require() is invoked', (done) => {
       app.once('remote-require', (event, webContents, moduleName) => {
         expect(webContents).to.equal(w.webContents)

spec/api-desktop-capturer-spec.js

@@ -1,6 +1,6 @@
 const chai = require('chai')
 const dirtyChai = require('dirty-chai')
-const { desktopCapturer, remote } = require('electron')
+const { desktopCapturer, ipcRenderer, remote } = require('electron')
 const { screen } = remote
 const features = process.atomBinding('features')
 
@@ -39,6 +39,15 @@ describe('desktopCapturer', () => {
     })
   })
 
+  it('throws an error when blocked', done => {
+    ipcRenderer.send('handle-next-desktop-capturer-get-sources')
+    desktopCapturer.getSources({ types: ['screen'] }, (error, sources) => {
+      expect(error.message).to.equal('desktopCapturer.getSources() blocked')
+      expect(sources).to.be.undefined()
+      done()
+    })
+  })
+
   it('does not throw an error when called more than once (regression)', (done) => {
     let callCount = 0
     const callback = (error, sources) => {

spec/static/main.js

@@ -233,6 +233,12 @@ app.on('ready', function () {
   })
 })
 
+ipcMain.on('handle-next-desktop-capturer-get-sources', function (event) {
+  event.sender.once('desktop-capturer-get-sources', (event) => {
+    event.preventDefault()
+  })
+})
+
 ipcMain.on('handle-next-remote-require', function (event, modulesMap = {}) {
   event.sender.once('remote-require', (event, moduleName) => {
     event.preventDefault()