Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 820 insertions, 0 deletions

diff --git a/services/sync/modules/engines/addons.sys.mjs b/services/sync/modules/engines/addons.sys.mjs
new file mode 100644
index 0000000000..d1b766a957
--- /dev/null
+++ b/services/sync/modules/engines/addons.sys.mjs
@@ -0,0 +1,820 @@
+/* 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/. */
+
+/*
+ * This file defines the add-on sync functionality.
+ *
+ * There are currently a number of known limitations:
+ *  - We only sync XPI extensions and themes available from addons.mozilla.org.
+ *    We hope to expand support for other add-ons eventually.
+ *  - We only attempt syncing of add-ons between applications of the same type.
+ *    This means add-ons will not synchronize between Firefox desktop and
+ *    Firefox mobile, for example. This is because of significant add-on
+ *    incompatibility between application types.
+ *
+ * Add-on records exist for each known {add-on, app-id} pair in the Sync client
+ * set. Each record has a randomly chosen GUID. The records then contain
+ * basic metadata about the add-on.
+ *
+ * We currently synchronize:
+ *
+ *  - Installations
+ *  - Uninstallations
+ *  - User enabling and disabling
+ *
+ * Synchronization is influenced by the following preferences:
+ *
+ *  - services.sync.addons.ignoreUserEnabledChanges
+ *  - services.sync.addons.trustedSourceHostnames
+ *
+ *  and also influenced by whether addons have repository caching enabled and
+ *  whether they allow installation of addons from insecure options (both of
+ *  which are themselves influenced by the "extensions." pref branch)
+ *
+ * See the documentation in all.js for the behavior of these prefs.
+ */
+
+import { Preferences } from "resource://gre/modules/Preferences.sys.mjs";
+
+import { AddonUtils } from "resource://services-sync/addonutils.sys.mjs";
+import { AddonsReconciler } from "resource://services-sync/addonsreconciler.sys.mjs";
+import {
+  Store,
+  SyncEngine,
+  LegacyTracker,
+} from "resource://services-sync/engines.sys.mjs";
+import { CryptoWrapper } from "resource://services-sync/record.sys.mjs";
+import { Svc, Utils } from "resource://services-sync/util.sys.mjs";
+
+import { SCORE_INCREMENT_XLARGE } from "resource://services-sync/constants.sys.mjs";
+import { CollectionValidator } from "resource://services-sync/collection_validator.sys.mjs";
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  AddonManager: "resource://gre/modules/AddonManager.sys.mjs",
+  AddonRepository: "resource://gre/modules/addons/AddonRepository.sys.mjs",
+});
+
+// 7 days in milliseconds.
+const PRUNE_ADDON_CHANGES_THRESHOLD = 60 * 60 * 24 * 7 * 1000;
+
+/**
+ * AddonRecord represents the state of an add-on in an application.
+ *
+ * Each add-on has its own record for each application ID it is installed
+ * on.
+ *
+ * The ID of add-on records is a randomly-generated GUID. It is random instead
+ * of deterministic so the URIs of the records cannot be guessed and so
+ * compromised server credentials won't result in disclosure of the specific
+ * add-ons present in a Sync account.
+ *
+ * The record contains the following fields:
+ *
+ *  addonID
+ *    ID of the add-on. This correlates to the "id" property on an Addon type.
+ *
+ *  applicationID
+ *    The application ID this record is associated with.
+ *
+ *  enabled
+ *    Boolean stating whether add-on is enabled or disabled by the user.
+ *
+ *  source
+ *    String indicating where an add-on is from. Currently, we only support
+ *    the value "amo" which indicates that the add-on came from the official
+ *    add-ons repository, addons.mozilla.org. In the future, we may support
+ *    installing add-ons from other sources. This provides a future-compatible
+ *    mechanism for clients to only apply records they know how to handle.
+ */
+function AddonRecord(collection, id) {
+  CryptoWrapper.call(this, collection, id);
+}
+AddonRecord.prototype = {
+  _logName: "Record.Addon",
+};
+Object.setPrototypeOf(AddonRecord.prototype, CryptoWrapper.prototype);
+
+Utils.deferGetSet(AddonRecord, "cleartext", [
+  "addonID",
+  "applicationID",
+  "enabled",
+  "source",
+]);
+
+/**
+ * The AddonsEngine handles synchronization of add-ons between clients.
+ *
+ * The engine maintains an instance of an AddonsReconciler, which is the entity
+ * maintaining state for add-ons. It provides the history and tracking APIs
+ * that AddonManager doesn't.
+ *
+ * The engine instance overrides a handful of functions on the base class. The
+ * rationale for each is documented by that function.
+ */
+export function AddonsEngine(service) {
+  SyncEngine.call(this, "Addons", service);
+
+  this._reconciler = new AddonsReconciler(this._tracker.asyncObserver);
+}
+
+AddonsEngine.prototype = {
+  _storeObj: AddonsStore,
+  _trackerObj: AddonsTracker,
+  _recordObj: AddonRecord,
+  version: 1,
+
+  syncPriority: 5,
+
+  _reconciler: null,
+
+  async initialize() {
+    await SyncEngine.prototype.initialize.call(this);
+    await this._reconciler.ensureStateLoaded();
+  },
+
+  /**
+   * Override parent method to find add-ons by their public ID, not Sync GUID.
+   */
+  async _findDupe(item) {
+    let id = item.addonID;
+
+    // The reconciler should have been updated at the top of the sync, so we
+    // can assume it is up to date when this function is called.
+    let addons = this._reconciler.addons;
+    if (!(id in addons)) {
+      return null;
+    }
+
+    let addon = addons[id];
+    if (addon.guid != item.id) {
+      return addon.guid;
+    }
+
+    return null;
+  },
+
+  /**
+   * Override getChangedIDs to pull in tracker changes plus changes from the
+   * reconciler log.
+   */
+  async getChangedIDs() {
+    let changes = {};
+    const changedIDs = await this._tracker.getChangedIDs();
+    for (let [id, modified] of Object.entries(changedIDs)) {
+      changes[id] = modified;
+    }
+
+    let lastSync = await this.getLastSync();
+    let lastSyncDate = new Date(lastSync * 1000);
+
+    // The reconciler should have been refreshed at the beginning of a sync and
+    // we assume this function is only called from within a sync.
+    let reconcilerChanges = this._reconciler.getChangesSinceDate(lastSyncDate);
+    let addons = this._reconciler.addons;
+    for (let change of reconcilerChanges) {
+      let changeTime = change[0];
+      let id = change[2];
+
+      if (!(id in addons)) {
+        continue;
+      }
+
+      // Keep newest modified time.
+      if (id in changes && changeTime < changes[id]) {
+        continue;
+      }
+
+      if (!(await this.isAddonSyncable(addons[id]))) {
+        continue;
+      }
+
+      this._log.debug("Adding changed add-on from changes log: " + id);
+      let addon = addons[id];
+      changes[addon.guid] = changeTime.getTime() / 1000;
+    }
+
+    return changes;
+  },
+
+  /**
+   * Override start of sync function to refresh reconciler.
+   *
+   * Many functions in this class assume the reconciler is refreshed at the
+   * top of a sync. If this ever changes, those functions should be revisited.
+   *
+   * Technically speaking, we don't need to refresh the reconciler on every
+   * sync since it is installed as an AddonManager listener. However, add-ons
+   * are complicated and we force a full refresh, just in case the listeners
+   * missed something.
+   */
+  async _syncStartup() {
+    // We refresh state before calling parent because syncStartup in the parent
+    // looks for changed IDs, which is dependent on add-on state being up to
+    // date.
+    await this._refreshReconcilerState();
+    return SyncEngine.prototype._syncStartup.call(this);
+  },
+
+  /**
+   * Override end of sync to perform a little housekeeping on the reconciler.
+   *
+   * We prune changes to prevent the reconciler state from growing without
+   * bound. Even if it grows unbounded, there would have to be many add-on
+   * changes (thousands) for it to slow things down significantly. This is
+   * highly unlikely to occur. Still, we exercise defense just in case.
+   */
+  async _syncCleanup() {
+    let lastSync = await this.getLastSync();
+    let ms = 1000 * lastSync - PRUNE_ADDON_CHANGES_THRESHOLD;
+    this._reconciler.pruneChangesBeforeDate(new Date(ms));
+    return SyncEngine.prototype._syncCleanup.call(this);
+  },
+
+  /**
+   * Helper function to ensure reconciler is up to date.
+   *
+   * This will load the reconciler's state from the file
+   * system (if needed) and refresh the state of the reconciler.
+   */
+  async _refreshReconcilerState() {
+    this._log.debug("Refreshing reconciler state");
+    return this._reconciler.refreshGlobalState();
+  },
+
+  // Returns a promise
+  isAddonSyncable(addon, ignoreRepoCheck) {
+    return this._store.isAddonSyncable(addon, ignoreRepoCheck);
+  },
+};
+Object.setPrototypeOf(AddonsEngine.prototype, SyncEngine.prototype);
+
+/**
+ * This is the primary interface between Sync and the Addons Manager.
+ *
+ * In addition to the core store APIs, we provide convenience functions to wrap
+ * Add-on Manager APIs with Sync-specific semantics.
+ */
+function AddonsStore(name, engine) {
+  Store.call(this, name, engine);
+}
+AddonsStore.prototype = {
+  // Define the add-on types (.type) that we support.
+  _syncableTypes: ["extension", "theme"],
+
+  _extensionsPrefs: new Preferences("extensions."),
+
+  get reconciler() {
+    return this.engine._reconciler;
+  },
+
+  /**
+   * Override applyIncoming to filter out records we can't handle.
+   */
+  async applyIncoming(record) {
+    // The fields we look at aren't present when the record is deleted.
+    if (!record.deleted) {
+      // Ignore records not belonging to our application ID because that is the
+      // current policy.
+      if (record.applicationID != Services.appinfo.ID) {
+        this._log.info(
+          "Ignoring incoming record from other App ID: " + record.id
+        );
+        return;
+      }
+
+      // Ignore records that aren't from the official add-on repository, as that
+      // is our current policy.
+      if (record.source != "amo") {
+        this._log.info(
+          "Ignoring unknown add-on source (" +
+            record.source +
+            ")" +
+            " for " +
+            record.id
+        );
+        return;
+      }
+    }
+
+    // Ignore incoming records for which an existing non-syncable addon
+    // exists. Note that we do not insist that the addon manager already have
+    // metadata for this addon - it's possible our reconciler previously saw the
+    // addon but the addon-manager cache no longer has it - which is fine for a
+    // new incoming addon.
+    // (Note that most other cases where the addon-manager cache is invalid
+    // doesn't get this treatment because that cache self-repairs after some
+    // time - but it only re-populates addons which are currently installed.)
+    let existingMeta = this.reconciler.addons[record.addonID];
+    if (
+      existingMeta &&
+      !(await this.isAddonSyncable(existingMeta, /* ignoreRepoCheck */ true))
+    ) {
+      this._log.info(
+        "Ignoring incoming record for an existing but non-syncable addon",
+        record.addonID
+      );
+      return;
+    }
+
+    await Store.prototype.applyIncoming.call(this, record);
+  },
+
+  /**
+   * Provides core Store API to create/install an add-on from a record.
+   */
+  async create(record) {
+    // This will throw if there was an error. This will get caught by the sync
+    // engine and the record will try to be applied later.
+    const results = await AddonUtils.installAddons([
+      {
+        id: record.addonID,
+        syncGUID: record.id,
+        enabled: record.enabled,
+        requireSecureURI: this._extensionsPrefs.get(
+          "install.requireSecureOrigin",
+          true
+        ),
+      },
+    ]);
+
+    if (results.skipped.includes(record.addonID)) {
+      this._log.info("Add-on skipped: " + record.addonID);
+      // Just early-return for skipped addons - we don't want to arrange to
+      // try again next time because the condition that caused up to skip
+      // will remain true for this addon forever.
+      return;
+    }
+
+    let addon;
+    for (let a of results.addons) {
+      if (a.id == record.addonID) {
+        addon = a;
+        break;
+      }
+    }
+
+    // This should never happen, but is present as a fail-safe.
+    if (!addon) {
+      throw new Error("Add-on not found after install: " + record.addonID);
+    }
+
+    this._log.info("Add-on installed: " + record.addonID);
+  },
+
+  /**
+   * Provides core Store API to remove/uninstall an add-on from a record.
+   */
+  async remove(record) {
+    // If this is called, the payload is empty, so we have to find by GUID.
+    let addon = await this.getAddonByGUID(record.id);
+    if (!addon) {
+      // We don't throw because if the add-on could not be found then we assume
+      // it has already been uninstalled and there is nothing for this function
+      // to do.
+      return;
+    }
+
+    this._log.info("Uninstalling add-on: " + addon.id);
+    await AddonUtils.uninstallAddon(addon);
+  },
+
+  /**
+   * Provides core Store API to update an add-on from a record.
+   */
+  async update(record) {
+    let addon = await this.getAddonByID(record.addonID);
+
+    // update() is called if !this.itemExists. And, since itemExists consults
+    // the reconciler only, we need to take care of some corner cases.
+    //
+    // First, the reconciler could know about an add-on that was uninstalled
+    // and no longer present in the add-ons manager.
+    if (!addon) {
+      await this.create(record);
+      return;
+    }
+
+    // It's also possible that the add-on is non-restartless and has pending
+    // install/uninstall activity.
+    //
+    // We wouldn't get here if the incoming record was for a deletion. So,
+    // check for pending uninstall and cancel if necessary.
+    if (addon.pendingOperations & lazy.AddonManager.PENDING_UNINSTALL) {
+      addon.cancelUninstall();
+
+      // We continue with processing because there could be state or ID change.
+    }
+
+    await this.updateUserDisabled(addon, !record.enabled);
+  },
+
+  /**
+   * Provide core Store API to determine if a record exists.
+   */
+  async itemExists(guid) {
+    let addon = this.reconciler.getAddonStateFromSyncGUID(guid);
+
+    return !!addon;
+  },
+
+  /**
+   * Create an add-on record from its GUID.
+   *
+   * @param guid
+   *        Add-on GUID (from extensions DB)
+   * @param collection
+   *        Collection to add record to.
+   *
+   * @return AddonRecord instance
+   */
+  async createRecord(guid, collection) {
+    let record = new AddonRecord(collection, guid);
+    record.applicationID = Services.appinfo.ID;
+
+    let addon = this.reconciler.getAddonStateFromSyncGUID(guid);
+
+    // If we don't know about this GUID or if it has been uninstalled, we mark
+    // the record as deleted.
+    if (!addon || !addon.installed) {
+      record.deleted = true;
+      return record;
+    }
+
+    record.modified = addon.modified.getTime() / 1000;
+
+    record.addonID = addon.id;
+    record.enabled = addon.enabled;
+
+    // This needs to be dynamic when add-ons don't come from AddonRepository.
+    record.source = "amo";
+
+    return record;
+  },
+
+  /**
+   * Changes the id of an add-on.
+   *
+   * This implements a core API of the store.
+   */
+  async changeItemID(oldID, newID) {
+    // We always update the GUID in the reconciler because it will be
+    // referenced later in the sync process.
+    let state = this.reconciler.getAddonStateFromSyncGUID(oldID);
+    if (state) {
+      state.guid = newID;
+      await this.reconciler.saveState();
+    }
+
+    let addon = await this.getAddonByGUID(oldID);
+    if (!addon) {
+      this._log.debug(
+        "Cannot change item ID (" +
+          oldID +
+          ") in Add-on " +
+          "Manager because old add-on not present: " +
+          oldID
+      );
+      return;
+    }
+
+    addon.syncGUID = newID;
+  },
+
+  /**
+   * Obtain the set of all syncable add-on Sync GUIDs.
+   *
+   * This implements a core Store API.
+   */
+  async getAllIDs() {
+    let ids = {};
+
+    let addons = this.reconciler.addons;
+    for (let id in addons) {
+      let addon = addons[id];
+      if (await this.isAddonSyncable(addon)) {
+        ids[addon.guid] = true;
+      }
+    }
+
+    return ids;
+  },
+
+  /**
+   * Wipe engine data.
+   *
+   * This uninstalls all syncable addons from the application. In case of
+   * error, it logs the error and keeps trying with other add-ons.
+   */
+  async wipe() {
+    this._log.info("Processing wipe.");
+
+    await this.engine._refreshReconcilerState();
+
+    // We only wipe syncable add-ons. Wipe is a Sync feature not a security
+    // feature.
+    let ids = await this.getAllIDs();
+    for (let guid in ids) {
+      let addon = await this.getAddonByGUID(guid);
+      if (!addon) {
+        this._log.debug(
+          "Ignoring add-on because it couldn't be obtained: " + guid
+        );
+        continue;
+      }
+
+      this._log.info("Uninstalling add-on as part of wipe: " + addon.id);
+      await Utils.catch.call(this, () => addon.uninstall())();
+    }
+  },
+
+  /** *************************************************************************
+   * Functions below are unique to this store and not part of the Store API  *
+   ***************************************************************************/
+
+  /**
+   * Obtain an add-on from its public ID.
+   *
+   * @param id
+   *        Add-on ID
+   * @return Addon or undefined if not found
+   */
+  async getAddonByID(id) {
+    return lazy.AddonManager.getAddonByID(id);
+  },
+
+  /**
+   * Obtain an add-on from its Sync GUID.
+   *
+   * @param  guid
+   *         Add-on Sync GUID
+   * @return DBAddonInternal or null
+   */
+  async getAddonByGUID(guid) {
+    return lazy.AddonManager.getAddonBySyncGUID(guid);
+  },
+
+  /**
+   * Determines whether an add-on is suitable for Sync.
+   *
+   * @param  addon
+   *         Addon instance
+   * @param ignoreRepoCheck
+   *         Should we skip checking the Addons repository (primarially useful
+   *         for testing and validation).
+   * @return Boolean indicating whether it is appropriate for Sync
+   */
+  async isAddonSyncable(addon, ignoreRepoCheck = false) {
+    // Currently, we limit syncable add-ons to those that are:
+    //   1) In a well-defined set of types
+    //   2) Installed in the current profile
+    //   3) Not installed by a foreign entity (i.e. installed by the app)
+    //      since they act like global extensions.
+    //   4) Is not a hotfix.
+    //   5) The addons XPIProvider doesn't veto it (i.e not being installed in
+    //      the profile directory, or any other reasons it says the addon can't
+    //      be synced)
+    //   6) Are installed from AMO
+
+    // We could represent the test as a complex boolean expression. We go the
+    // verbose route so the failure reason is logged.
+    if (!addon) {
+      this._log.debug("Null object passed to isAddonSyncable.");
+      return false;
+    }
+
+    if (!this._syncableTypes.includes(addon.type)) {
+      this._log.debug(
+        addon.id + " not syncable: type not in allowed list: " + addon.type
+      );
+      return false;
+    }
+
+    if (!(addon.scope & lazy.AddonManager.SCOPE_PROFILE)) {
+      this._log.debug(addon.id + " not syncable: not installed in profile.");
+      return false;
+    }
+
+    // If the addon manager says it's not syncable, we skip it.
+    if (!addon.isSyncable) {
+      this._log.debug(addon.id + " not syncable: vetoed by the addon manager.");
+      return false;
+    }
+
+    // This may be too aggressive. If an add-on is downloaded from AMO and
+    // manually placed in the profile directory, foreignInstall will be set.
+    // Arguably, that add-on should be syncable.
+    // TODO Address the edge case and come up with more robust heuristics.
+    if (addon.foreignInstall) {
+      this._log.debug(addon.id + " not syncable: is foreign install.");
+      return false;
+    }
+
+    // If the AddonRepository's cache isn't enabled (which it typically isn't
+    // in tests), getCachedAddonByID always returns null - so skip the check
+    // in that case. We also provide a way to specifically opt-out of the check
+    // even if the cache is enabled, which is used by the validators.
+    if (ignoreRepoCheck || !lazy.AddonRepository.cacheEnabled) {
+      return true;
+    }
+
+    let result = await new Promise(res => {
+      lazy.AddonRepository.getCachedAddonByID(addon.id, res);
+    });
+
+    if (!result) {
+      this._log.debug(
+        addon.id + " not syncable: add-on not found in add-on repository."
+      );
+      return false;
+    }
+
+    return this.isSourceURITrusted(result.sourceURI);
+  },
+
+  /**
+   * Determine whether an add-on's sourceURI field is trusted and the add-on
+   * can be installed.
+   *
+   * This function should only ever be called from isAddonSyncable(). It is
+   * exposed as a separate function to make testing easier.
+   *
+   * @param  uri
+   *         nsIURI instance to validate
+   * @return bool
+   */
+  isSourceURITrusted: function isSourceURITrusted(uri) {
+    // For security reasons, we currently limit synced add-ons to those
+    // installed from trusted hostname(s). We additionally require TLS with
+    // the add-ons site to help prevent forgeries.
+    let trustedHostnames = Svc.Prefs.get(
+      "addons.trustedSourceHostnames",
+      ""
+    ).split(",");
+
+    if (!uri) {
+      this._log.debug("Undefined argument to isSourceURITrusted().");
+      return false;
+    }
+
+    // Scheme is validated before the hostname because uri.host may not be
+    // populated for certain schemes. It appears to always be populated for
+    // https, so we avoid the potential NS_ERROR_FAILURE on field access.
+    if (uri.scheme != "https") {
+      this._log.debug("Source URI not HTTPS: " + uri.spec);
+      return false;
+    }
+
+    if (!trustedHostnames.includes(uri.host)) {
+      this._log.debug("Source hostname not trusted: " + uri.host);
+      return false;
+    }
+
+    return true;
+  },
+
+  /**
+   * Update the userDisabled flag on an add-on.
+   *
+   * This will enable or disable an add-on. It has no return value and does
+   * not catch or handle exceptions thrown by the addon manager. If no action
+   * is needed it will return immediately.
+   *
+   * @param addon
+   *        Addon instance to manipulate.
+   * @param value
+   *        Boolean to which to set userDisabled on the passed Addon.
+   */
+  async updateUserDisabled(addon, value) {
+    if (addon.userDisabled == value) {
+      return;
+    }
+
+    // A pref allows changes to the enabled flag to be ignored.
+    if (Svc.Prefs.get("addons.ignoreUserEnabledChanges", false)) {
+      this._log.info(
+        "Ignoring enabled state change due to preference: " + addon.id
+      );
+      return;
+    }
+
+    AddonUtils.updateUserDisabled(addon, value);
+    // updating this flag doesn't send a notification for appDisabled addons,
+    // meaning the reconciler will not update its state and may resync the
+    // addon - so explicitly rectify the state (bug 1366994)
+    if (addon.appDisabled) {
+      await this.reconciler.rectifyStateFromAddon(addon);
+    }
+  },
+};
+
+Object.setPrototypeOf(AddonsStore.prototype, Store.prototype);
+
+/**
+ * The add-ons tracker keeps track of real-time changes to add-ons.
+ *
+ * It hooks up to the reconciler and receives notifications directly from it.
+ */
+function AddonsTracker(name, engine) {
+  LegacyTracker.call(this, name, engine);
+}
+AddonsTracker.prototype = {
+  get reconciler() {
+    return this.engine._reconciler;
+  },
+
+  get store() {
+    return this.engine._store;
+  },
+
+  /**
+   * This callback is executed whenever the AddonsReconciler sends out a change
+   * notification. See AddonsReconciler.addChangeListener().
+   */
+  async changeListener(date, change, addon) {
+    this._log.debug("changeListener invoked: " + change + " " + addon.id);
+    // Ignore changes that occur during sync.
+    if (this.ignoreAll) {
+      return;
+    }
+
+    if (!(await this.store.isAddonSyncable(addon))) {
+      this._log.debug(
+        "Ignoring change because add-on isn't syncable: " + addon.id
+      );
+      return;
+    }
+
+    const added = await this.addChangedID(addon.guid, date.getTime() / 1000);
+    if (added) {
+      this.score += SCORE_INCREMENT_XLARGE;
+    }
+  },
+
+  onStart() {
+    this.reconciler.startListening();
+    this.reconciler.addChangeListener(this);
+  },
+
+  onStop() {
+    this.reconciler.removeChangeListener(this);
+    this.reconciler.stopListening();
+  },
+};
+
+Object.setPrototypeOf(AddonsTracker.prototype, LegacyTracker.prototype);
+
+export class AddonValidator extends CollectionValidator {
+  constructor(engine = null) {
+    super("addons", "id", ["addonID", "enabled", "applicationID", "source"]);
+    this.engine = engine;
+  }
+
+  async getClientItems() {
+    return lazy.AddonManager.getAllAddons();
+  }
+
+  normalizeClientItem(item) {
+    let enabled = !item.userDisabled;
+    if (item.pendingOperations & lazy.AddonManager.PENDING_ENABLE) {
+      enabled = true;
+    } else if (item.pendingOperations & lazy.AddonManager.PENDING_DISABLE) {
+      enabled = false;
+    }
+    return {
+      enabled,
+      id: item.syncGUID,
+      addonID: item.id,
+      applicationID: Services.appinfo.ID,
+      source: "amo", // check item.foreignInstall?
+      original: item,
+    };
+  }
+
+  async normalizeServerItem(item) {
+    let guid = await this.engine._findDupe(item);
+    if (guid) {
+      item.id = guid;
+    }
+    return item;
+  }
+
+  clientUnderstands(item) {
+    return item.applicationID === Services.appinfo.ID;
+  }
+
+  async syncedByClient(item) {
+    return (
+      !item.original.hidden &&
+      !item.original.isSystem &&
+      !(
+        item.original.pendingOperations & lazy.AddonManager.PENDING_UNINSTALL
+      ) &&
+      // No need to await the returned promise explicitely:
+      // |expr1 && expr2| evaluates to expr2 if expr1 is true.
+      this.engine.isAddonSyncable(item.original, true)
+    );
+  }
+}