refactor: re-implement desktop-capturer in TypeScript (#18580)

lib/browser/desktop-capturer.ts

@@ -0,0 +1,66 @@
+import { EventEmitter } from 'events'
+
+const { createDesktopCapturer } = process.electronBinding('desktop_capturer')
+
+const deepEqual = (a: ElectronInternal.GetSourcesOptions, b: ElectronInternal.GetSourcesOptions) => JSON.stringify(a) === JSON.stringify(b)
+
+let currentlyRunning: {
+  options: ElectronInternal.GetSourcesOptions;
+  getSources: Promise<ElectronInternal.GetSourcesResult[]>;
+}[] = []
+
+export const getSources = (event: Electron.IpcMainEvent, options: ElectronInternal.GetSourcesOptions) => {
+  for (const running of currentlyRunning) {
+    if (deepEqual(running.options, options)) {
+      // If a request is currently running for the same options
+      // return that promise
+      return running.getSources
+    }
+  }
+
+  const getSources = new Promise<ElectronInternal.GetSourcesResult[]>((resolve, reject) => {
+    const stopRunning = () => {
+      // Remove from currentlyRunning once we resolve or reject
+      currentlyRunning = currentlyRunning.filter(running => running.options !== options)
+    }
+
+    const emitter = new EventEmitter()
+
+    emitter.once('error', (event, error: string) => {
+      stopRunning()
+      reject(error)
+    })
+
+    emitter.once('finished', (event, sources: Electron.DesktopCapturerSource[], fetchWindowIcons: boolean) => {
+      stopRunning()
+      resolve(sources.map(source => ({
+        id: source.id,
+        name: source.name,
+        thumbnail: source.thumbnail.toDataURL(),
+        display_id: source.display_id,
+        appIcon: (fetchWindowIcons && source.appIcon) ? source.appIcon.toDataURL() : null
+      })))
+    })
+
+    let capturer: ElectronInternal.DesktopCapturer | null = createDesktopCapturer()
+
+    capturer.emit = emitter.emit.bind(emitter)
+    capturer.startHandling(options.captureWindow, options.captureScreen, options.thumbnailSize, options.fetchWindowIcons)
+
+    // If the WebContents is destroyed before receiving result, just remove the
+    // reference to emit and the capturer itself so that it never dispatches
+    // back to the renderer
+    event.sender.once('destroyed', () => {
+      capturer!.emit = null
+      capturer = null
+      stopRunning()
+    })
+  })
+
+  currentlyRunning.push({
+    options,
+    getSources
+  })
+
+  return getSources
+}