1 files changed, 140 insertions, 0 deletions
diff --git a/browser/components/newtab/lib/Screenshots.sys.mjs b/browser/components/newtab/lib/Screenshots.sys.mjs
new file mode 100644
index 0000000000..e5423bd52f
--- /dev/null
+++ b/browser/components/newtab/lib/Screenshots.sys.mjs
@@ -0,0 +1,140 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// We use importESModule here instead of static import so that
+// the Karma test environment won't choke on this module. This
+// is because the Karma test environment already stubs out
+// XPCOMUtils, and overrides importESModule to be a no-op (which
+// can't be done for a static import statement).
+
+// eslint-disable-next-line mozilla/use-static-import
+const { XPCOMUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/XPCOMUtils.sys.mjs"
+);
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  BackgroundPageThumbs: "resource://gre/modules/BackgroundPageThumbs.sys.mjs",
+  PageThumbs: "resource://gre/modules/PageThumbs.sys.mjs",
+  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.sys.mjs",
+});
+
+const GREY_10 = "#F9F9FA";
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  lazy,
+  "gPrivilegedAboutProcessEnabled",
+  "browser.tabs.remote.separatePrivilegedContentProcess",
+  false
+);
+
+export const Screenshots = {
+  /**
+   * Get a screenshot / thumbnail for a url. Either returns the disk cached
+   * image or initiates a background request for the url.
+   *
+   * @param url {string} The url to get a thumbnail
+   * @return {Promise} Resolves a custom object or null if failed
+   */
+  async getScreenshotForURL(url) {
+    try {
+      await lazy.BackgroundPageThumbs.captureIfMissing(url, {
+        backgroundColor: GREY_10,
+      });
+
+      // The privileged about content process is able to use the moz-page-thumb
+      // protocol, so if it's enabled, send that down.
+      if (lazy.gPrivilegedAboutProcessEnabled) {
+        return lazy.PageThumbs.getThumbnailURL(url);
+      }
+
+      // Otherwise, for normal content processes, we fallback to using
+      // Blob URIs for the screenshots.
+      const imgPath = lazy.PageThumbs.getThumbnailPath(url);
+
+      const filePathResponse = await fetch(`file://${imgPath}`);
+      const fileContents = await filePathResponse.blob();
+
+      // Check if the file is empty, which indicates there isn't actually a
+      // thumbnail, so callers can show a failure state.
+      if (fileContents.size === 0) {
+        return null;
+      }
+
+      return { path: imgPath, data: fileContents };
+    } catch (err) {
+      console.error(`getScreenshot(${url}) failed:`, err);
+    }
+
+    // We must have failed to get the screenshot, so persist the failure by
+    // storing an empty file. Future calls will then skip requesting and return
+    // failure, so do the same thing here. The empty file should not expire with
+    // the usual filtering process to avoid repeated background requests, which
+    // can cause unwanted high CPU, network and memory usage - Bug 1384094
+    try {
+      await lazy.PageThumbs._store(url, url, null, true);
+    } catch (err) {
+      // Probably failed to create the empty file, but not much more we can do.
+    }
+    return null;
+  },
+
+  /**
+   * Checks if all the open windows are private browsing windows. If so, we do not
+   * want to collect screenshots. If there exists at least 1 non-private window,
+   * we are ok to collect screenshots.
+   */
+  _shouldGetScreenshots() {
+    for (let win of Services.wm.getEnumerator("navigator:browser")) {
+      if (!lazy.PrivateBrowsingUtils.isWindowPrivate(win)) {
+        // As soon as we encounter 1 non-private window, screenshots are fair game.
+        return true;
+      }
+    }
+    return false;
+  },
+
+  /**
+   * Conditionally get a screenshot for a link if there's no existing pending
+   * screenshot. Updates the cached link's desired property with the result.
+   *
+   * @param link {object} Link object to update
+   * @param url {string} Url to get a screenshot of
+   * @param property {string} Name of property on object to set
+   @ @param onScreenshot {function} Callback for when the screenshot loads
+   */
+  async maybeCacheScreenshot(link, url, property, onScreenshot) {
+    // If there are only private windows open, do not collect screenshots
+    if (!this._shouldGetScreenshots()) {
+      return;
+    }
+    // __sharedCache may not exist yet for links from default top sites that
+    // don't have a default tippy top icon.
+    if (!link.__sharedCache) {
+      link.__sharedCache = {
+        updateLink(prop, val) {
+          link[prop] = val;
+        },
+      };
+    }
+    const cache = link.__sharedCache;
+    // Nothing to do if we already have a pending screenshot or
+    // if a previous request failed and returned null.
+    if (cache.fetchingScreenshot || link[property] !== undefined) {
+      return;
+    }
+
+    // Save the promise to the cache so other links get it immediately
+    cache.fetchingScreenshot = this.getScreenshotForURL(url);
+
+    // Clean up now that we got the screenshot
+    const screenshot = await cache.fetchingScreenshot;
+    delete cache.fetchingScreenshot;
+
+    // Update the cache for future links and call back for existing content
+    cache.updateLink(property, screenshot);
+    onScreenshot(screenshot);
+  },
+};