The Tor Browser: toolkit/components/thumbnails/PageThumbs.jsm@129ffea94266 (annotated)

toolkit/components/thumbnails/PageThumbs.jsm@129ffea94266 (annotated)

toolkit/components/thumbnails/PageThumbs.jsm

Sat, 03 Jan 2015 20:18:00 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Sat, 03 Jan 2015 20:18:00 +0100
branch: TOR_BUG_3246
changeset 7: 129ffea94266
permissions: -rw-r--r--

Conditionally enable double key logic according to:
private browsing mode or privacy.thirdparty.isolate preference and
implement in GetCookieStringCommon and FindCookie where it counts...
With some reservations of how to convince FindCookie users to test
condition and pass a nullptr when disabling double key logic.

 /* 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/. */
 "use strict";
 this.EXPORTED_SYMBOLS = ["PageThumbs", "PageThumbsStorage"];
 const Cu = Components.utils;
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const HTML_NAMESPACE = "http://www.w3.org/1999/xhtml";
 const PREF_STORAGE_VERSION = "browser.pagethumbnails.storage_version";
 const LATEST_STORAGE_VERSION = 3;
 const EXPIRATION_MIN_CHUNK_SIZE = 50;
 const EXPIRATION_INTERVAL_SECS = 3600;
 // If a request for a thumbnail comes in and we find one that is "stale"
 // (or don't find one at all) we automatically queue a request to generate a
 // new one.
 const MAX_THUMBNAIL_AGE_SECS = 172800; // 2 days == 60*60*24*2 == 172800 secs.
 /**
  * Name of the directory in the profile that contains the thumbnails.
  */
 const THUMBNAIL_DIRECTORY = "thumbnails";
 /**
  * The default background color for page thumbnails.
  */
 const THUMBNAIL_BG_COLOR = "#fff";
 Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
 Cu.import("resource://gre/modules/osfile/_PromiseWorker.jsm", this);
 Cu.import("resource://gre/modules/Promise.jsm", this);
 Cu.import("resource://gre/modules/osfile.jsm", this);
 XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
   "resource://gre/modules/NetUtil.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Services",
   "resource://gre/modules/Services.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
   "resource://gre/modules/FileUtils.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
   "resource://gre/modules/PlacesUtils.jsm");
 XPCOMUtils.defineLazyServiceGetter(this, "gUpdateTimerManager",
   "@mozilla.org/updates/timer-manager;1", "nsIUpdateTimerManager");
 XPCOMUtils.defineLazyGetter(this, "gCryptoHash", function () {
   return Cc["@mozilla.org/security/hash;1"].createInstance(Ci.nsICryptoHash);
 });
 XPCOMUtils.defineLazyGetter(this, "gUnicodeConverter", function () {
   let converter = Cc["@mozilla.org/intl/scriptableunicodeconverter"]
                     .createInstance(Ci.nsIScriptableUnicodeConverter);
   converter.charset = 'utf8';
   return converter;
 });
 XPCOMUtils.defineLazyModuleGetter(this, "Task",
   "resource://gre/modules/Task.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Deprecated",
   "resource://gre/modules/Deprecated.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "AsyncShutdown",
   "resource://gre/modules/AsyncShutdown.jsm");
 /**
  * Utilities for dealing with promises and Task.jsm
  */
 const TaskUtils = {
   /**
    * Add logging to a promise.
    *
    * @param {Promise} promise
    * @return {Promise} A promise behaving as |promise|, but with additional
    * logging in case of uncaught error.
    */
   captureErrors: function captureErrors(promise) {
     return promise.then(
       null,
       function onError(reason) {
         Cu.reportError("Uncaught asynchronous error: " + reason + " at\n"
           + reason.stack + "\n");
         throw reason;
       }
     );
   },
   /**
    * Spawn a new Task from a generator.
    *
    * This function behaves as |Task.spawn|, with the exception that it
    * adds logging in case of uncaught error. For more information, see
    * the documentation of |Task.jsm|.
    *
    * @param {generator} gen Some generator.
    * @return {Promise} A promise built from |gen|, with the same semantics
    * as |Task.spawn(gen)|.
    */
   spawn: function spawn(gen) {
     return this.captureErrors(Task.spawn(gen));
   },
   /**
    * Read the bytes from a blob, asynchronously.
    *
    * @return {Promise}
    * @resolve {ArrayBuffer} In case of success, the bytes contained in the blob.
    * @reject {DOMError} In case of error, the underlying DOMError.
    */
   readBlob: function readBlob(blob) {
     let deferred = Promise.defer();
     let reader = Cc["@mozilla.org/files/filereader;1"].createInstance(Ci.nsIDOMFileReader);
     reader.onloadend = function onloadend() {
       if (reader.readyState != Ci.nsIDOMFileReader.DONE) {
         deferred.reject(reader.error);
       } else {
         deferred.resolve(reader.result);
       }
     };
     reader.readAsArrayBuffer(blob);
     return deferred.promise;
   }
 };
 /**
  * Singleton providing functionality for capturing web page thumbnails and for
  * accessing them if already cached.
  */
 this.PageThumbs = {
   _initialized: false,
   /**
    * The calculated width and height of the thumbnails.
    */
   _thumbnailWidth : 0,
   _thumbnailHeight : 0,
   /**
    * The scheme to use for thumbnail urls.
    */
   get scheme() "moz-page-thumb",
   /**
    * The static host to use for thumbnail urls.
    */
   get staticHost() "thumbnail",
   /**
    * The thumbnails' image type.
    */
   get contentType() "image/png",
   init: function PageThumbs_init() {
     if (!this._initialized) {
       this._initialized = true;
       PlacesUtils.history.addObserver(PageThumbsHistoryObserver, false);
       // Migrate the underlying storage, if needed.
       PageThumbsStorageMigrator.migrate();
       PageThumbsExpiration.init();
     }
   },
   uninit: function PageThumbs_uninit() {
     if (this._initialized) {
       this._initialized = false;
       PlacesUtils.history.removeObserver(PageThumbsHistoryObserver);
     }
   },
   /**
    * Gets the thumbnail image's url for a given web page's url.
    * @param aUrl The web page's url that is depicted in the thumbnail.
    * @return The thumbnail image's url.
    */
   getThumbnailURL: function PageThumbs_getThumbnailURL(aUrl) {
     return this.scheme + "://" + this.staticHost +
            "?url=" + encodeURIComponent(aUrl);
   },
    /**
     * Gets the path of the thumbnail file for a given web page's
     * url. This file may or may not exist depending on whether the
     * thumbnail has been captured or not.
     *
     * @param aUrl The web page's url.
     * @return The path of the thumbnail file.
     */
    getThumbnailPath: function PageThumbs_getThumbnailPath(aUrl) {
      return PageThumbsStorage.getFilePathForURL(aUrl);
    },
   /**
    * Captures a thumbnail for the given window.
    * @param aWindow The DOM window to capture a thumbnail from.
    * @param aCallback The function to be called when the thumbnail has been
    *                  captured. The first argument will be the data stream
    *                  containing the image data.
    */
   capture: function PageThumbs_capture(aWindow, aCallback) {
     if (!this._prefEnabled()) {
       return;
     }
     let canvas = this._createCanvas();
     this.captureToCanvas(aWindow, canvas);
     // Fetch the canvas data on the next event loop tick so that we allow
     // some event processing in between drawing to the canvas and encoding
     // its data. We want to block the UI as short as possible. See bug 744100.
     Services.tm.currentThread.dispatch(function () {
       canvas.mozFetchAsStream(aCallback, this.contentType);
     }.bind(this), Ci.nsIThread.DISPATCH_NORMAL);
   },
   /**
    * Captures a thumbnail for the given window.
    *
    * @param aWindow The DOM window to capture a thumbnail from.
    * @return {Promise}
    * @resolve {Blob} The thumbnail, as a Blob.
    */
   captureToBlob: function PageThumbs_captureToBlob(aWindow) {
     if (!this._prefEnabled()) {
       return null;
     }
     let canvas = this._createCanvas();
     this.captureToCanvas(aWindow, canvas);
     let deferred = Promise.defer();
     let type = this.contentType;
     // Fetch the canvas data on the next event loop tick so that we allow
     // some event processing in between drawing to the canvas and encoding
     // its data. We want to block the UI as short as possible. See bug 744100.
     canvas.toBlob(function asBlob(blob) {
       deferred.resolve(blob, type);
     });
     return deferred.promise;
   },
   /**
    * Captures a thumbnail from a given window and draws it to the given canvas.
    * @param aWindow The DOM window to capture a thumbnail from.
    * @param aCanvas The canvas to draw to.
    */
   captureToCanvas: function PageThumbs_captureToCanvas(aWindow, aCanvas) {
     let telemetryCaptureTime = new Date();
     this._captureToCanvas(aWindow, aCanvas);
     let telemetry = Services.telemetry;
     telemetry.getHistogramById("FX_THUMBNAILS_CAPTURE_TIME_MS")
       .add(new Date() - telemetryCaptureTime);
   },
   // The background thumbnail service captures to canvas but doesn't want to
   // participate in this service's telemetry, which is why this method exists.
   _captureToCanvas: function PageThumbs__captureToCanvas(aWindow, aCanvas) {
     let [sw, sh, scale] = this._determineCropSize(aWindow, aCanvas);
     let ctx = aCanvas.getContext("2d");
     // Scale the canvas accordingly.
     ctx.save();
     ctx.scale(scale, scale);
     try {
       // Draw the window contents to the canvas.
       ctx.drawWindow(aWindow, 0, 0, sw, sh, THUMBNAIL_BG_COLOR,
                      ctx.DRAWWINDOW_DO_NOT_FLUSH);
     } catch (e) {
       // We couldn't draw to the canvas for some reason.
     }
     ctx.restore();
   },
   /**
    * Captures a thumbnail for the given browser and stores it to the cache.
    * @param aBrowser The browser to capture a thumbnail for.
    * @param aCallback The function to be called when finished (optional).
    */
   captureAndStore: function PageThumbs_captureAndStore(aBrowser, aCallback) {
     if (!this._prefEnabled()) {
       return;
     }
     let url = aBrowser.currentURI.spec;
     let channel = aBrowser.docShell.currentDocumentChannel;
     let originalURL = channel.originalURI.spec;
     // see if this was an error response.
     let wasError = this._isChannelErrorResponse(channel);
     TaskUtils.spawn((function task() {
       let isSuccess = true;
       try {
         let blob = yield this.captureToBlob(aBrowser.contentWindow);
         let buffer = yield TaskUtils.readBlob(blob);
         yield this._store(originalURL, url, buffer, wasError);
       } catch (_) {
         isSuccess = false;
       }
       if (aCallback) {
         aCallback(isSuccess);
       }
     }).bind(this));
   },
   /**
    * Checks if an existing thumbnail for the specified URL is either missing
    * or stale, and if so, captures and stores it.  Once the thumbnail is stored,
    * an observer service notification will be sent, so consumers should observe
    * such notifications if they want to be notified of an updated thumbnail.
    *
    * @param aBrowser The content window of this browser will be captured.
    * @param aCallback The function to be called when finished (optional).
    */
   captureAndStoreIfStale: function PageThumbs_captureAndStoreIfStale(aBrowser, aCallback) {
     let url = aBrowser.currentURI.spec;
     PageThumbsStorage.isFileRecentForURL(url).then(recent => {
       if (!recent.ok &&
           // Careful, the call to PageThumbsStorage is async, so the browser may
           // have navigated away from the URL or even closed.
           aBrowser.currentURI &&
           aBrowser.currentURI.spec == url) {
         this.captureAndStore(aBrowser, aCallback);
       } else if (aCallback) {
         aCallback(true);
       }
     }, err => {
       if (aCallback)
         aCallback(false);
     });
   },
   /**
    * Stores data to disk for the given URLs.
    *
    * NB: The background thumbnail service calls this, too.
    *
    * @param aOriginalURL The URL with which the capture was initiated.
    * @param aFinalURL The URL to which aOriginalURL ultimately resolved.
    * @param aData An ArrayBuffer containing the image data.
    * @param aNoOverwrite If true and files for the URLs already exist, the files
    *                     will not be overwritten.
    * @return {Promise}
    */
   _store: function PageThumbs__store(aOriginalURL, aFinalURL, aData, aNoOverwrite) {
     return TaskUtils.spawn(function () {
       let telemetryStoreTime = new Date();
       yield PageThumbsStorage.writeData(aFinalURL, aData, aNoOverwrite);
       Services.telemetry.getHistogramById("FX_THUMBNAILS_STORE_TIME_MS")
         .add(new Date() - telemetryStoreTime);
       Services.obs.notifyObservers(null, "page-thumbnail:create", aFinalURL);
       // We've been redirected. Create a copy of the current thumbnail for
       // the redirect source. We need to do this because:
       //
       // 1) Users can drag any kind of links onto the newtab page. If those
       //    links redirect to a different URL then we want to be able to
       //    provide thumbnails for both of them.
       //
       // 2) The newtab page should actually display redirect targets, only.
       //    Because of bug 559175 this information can get lost when using
       //    Sync and therefore also redirect sources appear on the newtab
       //    page. We also want thumbnails for those.
       if (aFinalURL != aOriginalURL) {
         yield PageThumbsStorage.copy(aFinalURL, aOriginalURL, aNoOverwrite);
         Services.obs.notifyObservers(null, "page-thumbnail:create", aOriginalURL);
       }
     });
   },
   /**
    * Register an expiration filter.
    *
    * When thumbnails are going to expire, each registered filter is asked for a
    * list of thumbnails to keep.
    *
    * The filter (if it is a callable) or its filterForThumbnailExpiration method
    * (if the filter is an object) is called with a single argument.  The
    * argument is a callback function.  The filter must call the callback
    * function and pass it an array of zero or more URLs.  (It may do so
    * asynchronously.)  Thumbnails for those URLs will be except from expiration.
    *
    * @param aFilter callable, or object with filterForThumbnailExpiration method
    */
   addExpirationFilter: function PageThumbs_addExpirationFilter(aFilter) {
     PageThumbsExpiration.addFilter(aFilter);
   },
   /**
    * Unregister an expiration filter.
    * @param aFilter A filter that was previously passed to addExpirationFilter.
    */
   removeExpirationFilter: function PageThumbs_removeExpirationFilter(aFilter) {
     PageThumbsExpiration.removeFilter(aFilter);
   },
   /**
    * Determines the crop size for a given content window.
    * @param aWindow The content window.
    * @param aCanvas The target canvas.
    * @return An array containing width, height and scale.
    */
   _determineCropSize: function PageThumbs_determineCropSize(aWindow, aCanvas) {
     let utils = aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
                        .getInterface(Ci.nsIDOMWindowUtils);
     let sbWidth = {}, sbHeight = {};
     try {
       utils.getScrollbarSize(false, sbWidth, sbHeight);
     } catch (e) {
       // This might fail if the window does not have a presShell.
       Cu.reportError("Unable to get scrollbar size in _determineCropSize.");
       sbWidth.value = sbHeight.value = 0;
     }
     // Even in RTL mode, scrollbars are always on the right.
     // So there's no need to determine a left offset.
     let sw = aWindow.innerWidth - sbWidth.value;
     let sh = aWindow.innerHeight - sbHeight.value;
     let {width: thumbnailWidth, height: thumbnailHeight} = aCanvas;
     let scale = Math.min(Math.max(thumbnailWidth / sw, thumbnailHeight / sh), 1);
     let scaledWidth = sw * scale;
     let scaledHeight = sh * scale;
     if (scaledHeight > thumbnailHeight)
       sh -= Math.floor(Math.abs(scaledHeight - thumbnailHeight) * scale);
     if (scaledWidth > thumbnailWidth)
       sw -= Math.floor(Math.abs(scaledWidth - thumbnailWidth) * scale);
     return [sw, sh, scale];
   },
   /**
    * Creates a new hidden canvas element.
    * @param aWindow The document of this window will be used to create the
    *                canvas.  If not given, the hidden window will be used.
    * @return The newly created canvas.
    */
   _createCanvas: function PageThumbs_createCanvas(aWindow) {
     let doc = (aWindow || Services.appShell.hiddenDOMWindow).document;
     let canvas = doc.createElementNS(HTML_NAMESPACE, "canvas");
     canvas.mozOpaque = true;
     canvas.mozImageSmoothingEnabled = true;
     let [thumbnailWidth, thumbnailHeight] = this._getThumbnailSize();
     canvas.width = thumbnailWidth;
     canvas.height = thumbnailHeight;
     return canvas;
   },
   /**
    * Calculates the thumbnail size based on current desktop's dimensions.
    * @return The calculated thumbnail size or a default if unable to calculate.
    */
   _getThumbnailSize: function PageThumbs_getThumbnailSize() {
     if (!this._thumbnailWidth || !this._thumbnailHeight) {
       let screenManager = Cc["@mozilla.org/gfx/screenmanager;1"]
                             .getService(Ci.nsIScreenManager);
       let left = {}, top = {}, width = {}, height = {};
       screenManager.primaryScreen.GetRectDisplayPix(left, top, width, height);
       this._thumbnailWidth = Math.round(width.value / 3);
       this._thumbnailHeight = Math.round(height.value / 3);
     }
     return [this._thumbnailWidth, this._thumbnailHeight];
   },
   /**
    * Given a channel, returns true if it should be considered an "error
    * response", false otherwise.
    */
   _isChannelErrorResponse: function(channel) {
     // No valid document channel sounds like an error to me!
     if (!channel)
       return true;
     if (!(channel instanceof Ci.nsIHttpChannel))
       // it might be FTP etc, so assume it's ok.
       return false;
     try {
       return !channel.requestSucceeded;
     } catch (_) {
       // not being able to determine success is surely failure!
       return true;
     }
   },
   _prefEnabled: function PageThumbs_prefEnabled() {
     try {
       return !Services.prefs.getBoolPref("browser.pagethumbnails.capturing_disabled");
     }
     catch (e) {
       return true;
     }
   },
 };
 this.PageThumbsStorage = {
   // The path for the storage
   _path: null,
   get path() {
     if (!this._path) {
       this._path = OS.Path.join(OS.Constants.Path.localProfileDir, THUMBNAIL_DIRECTORY);
     }
     return this._path;
   },
   ensurePath: function Storage_ensurePath() {
     // Create the directory (ignore any error if the directory
     // already exists). As all writes are done from the PageThumbsWorker
     // thread, which serializes its operations, this ensures that
     // future operations can proceed without having to check whether
     // the directory exists.
     return PageThumbsWorker.post("makeDir",
       [this.path, {ignoreExisting: true}]).then(
         null,
         function onError(aReason) {
           Components.utils.reportError("Could not create thumbnails directory" + aReason);
         });
   },
   getLeafNameForURL: function Storage_getLeafNameForURL(aURL) {
     if (typeof aURL != "string") {
       throw new TypeError("Expecting a string");
     }
     let hash = this._calculateMD5Hash(aURL);
     return hash + ".png";
   },
   getFilePathForURL: function Storage_getFilePathForURL(aURL) {
     return OS.Path.join(this.path, this.getLeafNameForURL(aURL));
   },
   /**
    * Write the contents of a thumbnail, off the main thread.
    *
    * @param {string} aURL The url for which to store a thumbnail.
    * @param {ArrayBuffer} aData The data to store in the thumbnail, as
    * an ArrayBuffer. This array buffer is neutered and cannot be
    * reused after the copy.
    * @param {boolean} aNoOverwrite If true and the thumbnail's file already
    * exists, the file will not be overwritten.
    *
    * @return {Promise}
    */
   writeData: function Storage_writeData(aURL, aData, aNoOverwrite) {
     let path = this.getFilePathForURL(aURL);
     this.ensurePath();
     aData = new Uint8Array(aData);
     let msg = [
       path,
       aData,
       {
         tmpPath: path + ".tmp",
         bytes: aData.byteLength,
         noOverwrite: aNoOverwrite,
         flush: false /*thumbnails do not require the level of guarantee provided by flush*/
       }];
     return PageThumbsWorker.post("writeAtomic", msg,
       msg /*we don't want that message garbage-collected,
            as OS.Shared.Type.void_t.in_ptr.toMsg uses C-level
            memory tricks to enforce zero-copy*/).
       then(null, this._eatNoOverwriteError(aNoOverwrite));
   },
   /**
    * Copy a thumbnail, off the main thread.
    *
    * @param {string} aSourceURL The url of the thumbnail to copy.
    * @param {string} aTargetURL The url of the target thumbnail.
    * @param {boolean} aNoOverwrite If true and the target file already exists,
    * the file will not be overwritten.
    *
    * @return {Promise}
    */
   copy: function Storage_copy(aSourceURL, aTargetURL, aNoOverwrite) {
     this.ensurePath();
     let sourceFile = this.getFilePathForURL(aSourceURL);
     let targetFile = this.getFilePathForURL(aTargetURL);
     let options = { noOverwrite: aNoOverwrite };
     return PageThumbsWorker.post("copy", [sourceFile, targetFile, options]).
       then(null, this._eatNoOverwriteError(aNoOverwrite));
   },
   /**
    * Remove a single thumbnail, off the main thread.
    *
    * @return {Promise}
    */
   remove: function Storage_remove(aURL) {
     return PageThumbsWorker.post("remove", [this.getFilePathForURL(aURL)]);
   },
   /**
    * Remove all thumbnails, off the main thread.
    *
    * @return {Promise}
    */
   wipe: Task.async(function* Storage_wipe() {
     //
     // This operation may be launched during shutdown, so we need to
     // take a few precautions to ensure that:
     //
     // 1. it is not interrupted by shutdown, in which case we
     //    could be leaving privacy-sensitive files on disk;
     // 2. it is not launched too late during shutdown, in which
     //    case this could cause shutdown freezes (see bug 1005487,
     //    which will eventually be fixed by bug 965309)
     //
     let blocker = () => promise;
     // The following operation will rise an error if we have already
     // reached profileBeforeChange, in which case it is too late
     // to clear the thumbnail wipe.
     AsyncShutdown.profileBeforeChange.addBlocker(
       "PageThumbs: removing all thumbnails",
       blocker);
     // Start the work only now that `profileBeforeChange` has had
     // a chance to throw an error.
     let promise = PageThumbsWorker.post("wipe", [this.path]);
     try {
       yield promise;
     }  finally {
        // Generally, we will be done much before profileBeforeChange,
        // so let's not hoard blockers.
        if ("removeBlocker" in AsyncShutdown.profileBeforeChange) {
          // `removeBlocker` was added with bug 985655. In the interest
          // of backporting, let's degrade gracefully if `removeBlocker`
          // doesn't exist.
          AsyncShutdown.profileBeforeChange.removeBlocker(blocker);
        }
     }
   }),
   fileExistsForURL: function Storage_fileExistsForURL(aURL) {
     return PageThumbsWorker.post("exists", [this.getFilePathForURL(aURL)]);
   },
   isFileRecentForURL: function Storage_isFileRecentForURL(aURL) {
     return PageThumbsWorker.post("isFileRecent",
                                  [this.getFilePathForURL(aURL),
                                   MAX_THUMBNAIL_AGE_SECS]);
   },
   _calculateMD5Hash: function Storage_calculateMD5Hash(aValue) {
     let hash = gCryptoHash;
     let value = gUnicodeConverter.convertToByteArray(aValue);
     hash.init(hash.MD5);
     hash.update(value, value.length);
     return this._convertToHexString(hash.finish(false));
   },
   _convertToHexString: function Storage_convertToHexString(aData) {
     let hex = "";
     for (let i = 0; i < aData.length; i++)
       hex += ("0" + aData.charCodeAt(i).toString(16)).slice(-2);
     return hex;
   },
   /**
    * For functions that take a noOverwrite option, OS.File throws an error if
    * the target file exists and noOverwrite is true.  We don't consider that an
    * error, and we don't want such errors propagated.
    *
    * @param {aNoOverwrite} The noOverwrite option used in the OS.File operation.
    *
    * @return {function} A function that should be passed as the second argument
    * to then() (the `onError` argument).
    */
   _eatNoOverwriteError: function Storage__eatNoOverwriteError(aNoOverwrite) {
     return function onError(err) {
       if (!aNoOverwrite ||
           !(err instanceof OS.File.Error) ||
           !err.becauseExists) {
         throw err;
       }
     };
   },
   // Deprecated, please do not use
   getFileForURL: function Storage_getFileForURL_DEPRECATED(aURL) {
     Deprecated.warning("PageThumbs.getFileForURL is deprecated. Please use PageThumbs.getFilePathForURL and OS.File",
                        "https://developer.mozilla.org/docs/JavaScript_OS.File");
     // Note: Once this method has been removed, we can get rid of the dependency towards FileUtils
     return new FileUtils.File(PageThumbsStorage.getFilePathForURL(aURL));
   }
 };
 let PageThumbsStorageMigrator = {
   get currentVersion() {
     try {
       return Services.prefs.getIntPref(PREF_STORAGE_VERSION);
     } catch (e) {
       // The pref doesn't exist, yet. Return version 0.
       return 0;
     }
   },
   set currentVersion(aVersion) {
     Services.prefs.setIntPref(PREF_STORAGE_VERSION, aVersion);
   },
   migrate: function Migrator_migrate() {
     let version = this.currentVersion;
     // Storage version 1 never made it to beta.
     // At the time of writing only Windows had (ProfD != ProfLD) and we
     // needed to move thumbnails from the roaming profile to the locale
     // one so that they're not needlessly included in backups and/or
     // written via SMB.
     // Storage version 2 also never made it to beta.
     // The thumbnail folder structure has been changed and old thumbnails
     // were not migrated. Instead, we just renamed the current folder to
     // "<name>-old" and will remove it later.
     if (version < 3) {
       this.migrateToVersion3();
     }
     this.currentVersion = LATEST_STORAGE_VERSION;
   },
   /**
    * Bug 239254 added support for having the disk cache and thumbnail
    * directories on a local path (i.e. ~/.cache/) under Linux. We'll first
    * try to move the old thumbnails to their new location. If that's not
    * possible (because ProfD might be on a different file system than
    * ProfLD) we'll just discard them.
    *
    * @param {string*} local The path to the local profile directory.
    * Used for testing. Default argument is good for all non-testing uses.
    * @param {string*} roaming The path to the roaming profile directory.
    * Used for testing. Default argument is good for all non-testing uses.
    */
   migrateToVersion3: function Migrator_migrateToVersion3(
     local = OS.Constants.Path.localProfileDir,
     roaming = OS.Constants.Path.profileDir) {
     PageThumbsWorker.post(
       "moveOrDeleteAllThumbnails",
       [OS.Path.join(roaming, THUMBNAIL_DIRECTORY),
        OS.Path.join(local, THUMBNAIL_DIRECTORY)]
     );
   }
 };
 let PageThumbsExpiration = {
   _filters: [],
   init: function Expiration_init() {
     gUpdateTimerManager.registerTimer("browser-cleanup-thumbnails", this,
                                       EXPIRATION_INTERVAL_SECS);
   },
   addFilter: function Expiration_addFilter(aFilter) {
     this._filters.push(aFilter);
   },
   removeFilter: function Expiration_removeFilter(aFilter) {
     let index = this._filters.indexOf(aFilter);
     if (index > -1)
       this._filters.splice(index, 1);
   },
   notify: function Expiration_notify(aTimer) {
     let urls = [];
     let filtersToWaitFor = this._filters.length;
     let expire = function expire() {
       this.expireThumbnails(urls);
     }.bind(this);
     // No registered filters.
     if (!filtersToWaitFor) {
       expire();
       return;
     }
     function filterCallback(aURLs) {
       urls = urls.concat(aURLs);
       if (--filtersToWaitFor == 0)
         expire();
     }
     for (let filter of this._filters) {
       if (typeof filter == "function")
         filter(filterCallback)
       else
         filter.filterForThumbnailExpiration(filterCallback);
     }
   },
   expireThumbnails: function Expiration_expireThumbnails(aURLsToKeep) {
     let path = this.path;
     let keep = [PageThumbsStorage.getLeafNameForURL(url) for (url of aURLsToKeep)];
     let msg = [
       PageThumbsStorage.path,
       keep,
       EXPIRATION_MIN_CHUNK_SIZE
     ];
     return PageThumbsWorker.post(
       "expireFilesInDirectory",
       msg
     );
   }
 };
 /**
  * Interface to a dedicated thread handling I/O
  */
 let PageThumbsWorker = (function() {
   let worker = new PromiseWorker("resource://gre/modules/PageThumbsWorker.js",
     OS.Shared.LOG.bind("PageThumbs"));
   return {
     post: function post(...args) {
       let promise = worker.post.apply(worker, args);
       return promise.then(
         null,
         function onError(error) {
           // Decode any serialized error
           if (error instanceof PromiseWorker.WorkerError) {
             throw OS.File.Error.fromMsg(error.data);
           } else {
             throw error;
           }
         }
       );
     }
   };
 })();
 let PageThumbsHistoryObserver = {
   onDeleteURI: function Thumbnails_onDeleteURI(aURI, aGUID) {
     PageThumbsStorage.remove(aURI.spec);
   },
   onClearHistory: function Thumbnails_onClearHistory() {
     PageThumbsStorage.wipe();
   },
   onTitleChanged: function () {},
   onBeginUpdateBatch: function () {},
   onEndUpdateBatch: function () {},
   onVisit: function () {},
   onPageChanged: function () {},
   onDeleteVisits: function () {},
   QueryInterface: XPCOMUtils.generateQI([Ci.nsINavHistoryObserver])
 };

The Tor Browser / annotate

toolkit/components/thumbnails/PageThumbs.jsm@129ffea94266 (annotated)

toolkit/components/thumbnails/PageThumbs.jsm