Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 1186 insertions, 0 deletions

diff --git a/services/sync/modules/engines/clients.js b/services/sync/modules/engines/clients.js
new file mode 100644
index 0000000000..60715d73bd
--- /dev/null
+++ b/services/sync/modules/engines/clients.js
@@ -0,0 +1,1186 @@
+/* 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/. */
+
+/**
+ * How does the clients engine work?
+ *
+ * - We use 2 files - commands.json and commands-syncing.json.
+ *
+ * - At sync upload time, we attempt a rename of commands.json to
+ *   commands-syncing.json, and ignore errors (helps for crash during sync!).
+ * - We load commands-syncing.json and stash the contents in
+ *   _currentlySyncingCommands which lives for the duration of the upload process.
+ * - We use _currentlySyncingCommands to build the outgoing records
+ * - Immediately after successful upload, we delete commands-syncing.json from
+ *   disk (and clear _currentlySyncingCommands). We reconcile our local records
+ *   with what we just wrote in the server, and add failed IDs commands
+ *   back in commands.json
+ * - Any time we need to "save" a command for future syncs, we load
+ *   commands.json, update it, and write it back out.
+ */
+
+var EXPORTED_SYMBOLS = ["ClientEngine", "ClientsRec"];
+
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+const { Async } = ChromeUtils.import("resource://services-common/async.js");
+const {
+  DEVICE_TYPE_DESKTOP,
+  DEVICE_TYPE_MOBILE,
+  SCORE_INCREMENT_XLARGE,
+  SINGLE_USER_THRESHOLD,
+  SYNC_API_VERSION,
+} = ChromeUtils.import("resource://services-sync/constants.js");
+const { Store, SyncEngine, LegacyTracker } = ChromeUtils.import(
+  "resource://services-sync/engines.js"
+);
+const { CryptoWrapper } = ChromeUtils.import(
+  "resource://services-sync/record.js"
+);
+const { Resource } = ChromeUtils.import("resource://services-sync/resource.js");
+const { Svc, Utils } = ChromeUtils.import("resource://services-sync/util.js");
+
+ChromeUtils.defineModuleGetter(
+  this,
+  "fxAccounts",
+  "resource://gre/modules/FxAccounts.jsm"
+);
+
+const { PREF_ACCOUNT_ROOT } = ChromeUtils.import(
+  "resource://gre/modules/FxAccountsCommon.js"
+);
+
+const CLIENTS_TTL = 1814400; // 21 days
+const CLIENTS_TTL_REFRESH = 604800; // 7 days
+const STALE_CLIENT_REMOTE_AGE = 604800; // 7 days
+
+// TTL of the message sent to another device when sending a tab
+const NOTIFY_TAB_SENT_TTL_SECS = 1 * 3600; // 1 hour
+
+// How often we force a refresh of the FxA device list.
+const REFRESH_FXA_DEVICE_INTERVAL_MS = 2 * 60 * 60 * 1000; // 2 hours
+
+// Reasons behind sending collection_changed push notifications.
+const COLLECTION_MODIFIED_REASON_SENDTAB = "sendtab";
+const COLLECTION_MODIFIED_REASON_FIRSTSYNC = "firstsync";
+
+const SUPPORTED_PROTOCOL_VERSIONS = [SYNC_API_VERSION];
+const LAST_MODIFIED_ON_PROCESS_COMMAND_PREF =
+  "services.sync.clients.lastModifiedOnProcessCommands";
+
+function hasDupeCommand(commands, action) {
+  if (!commands) {
+    return false;
+  }
+  return commands.some(
+    other =>
+      other.command == action.command &&
+      Utils.deepEquals(other.args, action.args)
+  );
+}
+
+function ClientsRec(collection, id) {
+  CryptoWrapper.call(this, collection, id);
+}
+ClientsRec.prototype = {
+  __proto__: CryptoWrapper.prototype,
+  _logName: "Sync.Record.Clients",
+  ttl: CLIENTS_TTL,
+};
+
+Utils.deferGetSet(ClientsRec, "cleartext", [
+  "name",
+  "type",
+  "commands",
+  "version",
+  "protocols",
+  "formfactor",
+  "os",
+  "appPackage",
+  "application",
+  "device",
+  "fxaDeviceId",
+]);
+
+function ClientEngine(service) {
+  SyncEngine.call(this, "Clients", service);
+
+  this.fxAccounts = fxAccounts;
+  this.addClientCommandQueue = Async.asyncQueueCaller(this._log);
+  Utils.defineLazyIDProperty(this, "localID", "services.sync.client.GUID");
+}
+ClientEngine.prototype = {
+  __proto__: SyncEngine.prototype,
+  _storeObj: ClientStore,
+  _recordObj: ClientsRec,
+  _trackerObj: ClientsTracker,
+  allowSkippedRecord: false,
+  _knownStaleFxADeviceIds: null,
+  _lastDeviceCounts: null,
+  _lastFxaDeviceRefresh: 0,
+
+  async initialize() {
+    // Reset the last sync timestamp on every startup so that we fetch all clients
+    await this.resetLastSync();
+  },
+
+  // These two properties allow us to avoid replaying the same commands
+  // continuously if we cannot manage to upload our own record.
+  _localClientLastModified: 0,
+  get _lastModifiedOnProcessCommands() {
+    return Services.prefs.getIntPref(LAST_MODIFIED_ON_PROCESS_COMMAND_PREF, -1);
+  },
+
+  set _lastModifiedOnProcessCommands(value) {
+    Services.prefs.setIntPref(LAST_MODIFIED_ON_PROCESS_COMMAND_PREF, value);
+  },
+
+  get isFirstSync() {
+    return !this.lastRecordUpload;
+  },
+
+  // Always sync client data as it controls other sync behavior
+  get enabled() {
+    return true;
+  },
+
+  get lastRecordUpload() {
+    return Svc.Prefs.get(this.name + ".lastRecordUpload", 0);
+  },
+  set lastRecordUpload(value) {
+    Svc.Prefs.set(this.name + ".lastRecordUpload", Math.floor(value));
+  },
+
+  get remoteClients() {
+    // return all non-stale clients for external consumption.
+    return Object.values(this._store._remoteClients).filter(v => !v.stale);
+  },
+
+  remoteClient(id) {
+    let client = this._store._remoteClients[id];
+    return client && !client.stale ? client : null;
+  },
+
+  remoteClientExists(id) {
+    return !!this.remoteClient(id);
+  },
+
+  // Aggregate some stats on the composition of clients on this account
+  get stats() {
+    let stats = {
+      hasMobile: this.localType == DEVICE_TYPE_MOBILE,
+      names: [this.localName],
+      numClients: 1,
+    };
+
+    for (let id in this._store._remoteClients) {
+      let { name, type, stale } = this._store._remoteClients[id];
+      if (!stale) {
+        stats.hasMobile = stats.hasMobile || type == DEVICE_TYPE_MOBILE;
+        stats.names.push(name);
+        stats.numClients++;
+      }
+    }
+
+    return stats;
+  },
+
+  /**
+   * Obtain information about device types.
+   *
+   * Returns a Map of device types to integer counts. Guaranteed to include
+   * "desktop" (which will have at least 1 - this device) and "mobile" (which
+   * may have zero) counts. It almost certainly will include only these 2.
+   */
+  get deviceTypes() {
+    let counts = new Map();
+
+    counts.set(this.localType, 1); // currently this must be DEVICE_TYPE_DESKTOP
+    counts.set(DEVICE_TYPE_MOBILE, 0);
+
+    for (let id in this._store._remoteClients) {
+      let record = this._store._remoteClients[id];
+      if (record.stale) {
+        continue; // pretend "stale" records don't exist.
+      }
+      let type = record.type;
+      if (!counts.has(type)) {
+        counts.set(type, 0);
+      }
+
+      counts.set(type, counts.get(type) + 1);
+    }
+
+    return counts;
+  },
+
+  get brandName() {
+    let brand = Services.strings.createBundle(
+      "chrome://branding/locale/brand.properties"
+    );
+    return brand.GetStringFromName("brandShortName");
+  },
+
+  get localName() {
+    return this.fxAccounts.device.getLocalName();
+  },
+  set localName(value) {
+    this.fxAccounts.device.setLocalName(value);
+  },
+
+  get localType() {
+    return this.fxAccounts.device.getLocalType();
+  },
+
+  getClientName(id) {
+    if (id == this.localID) {
+      return this.localName;
+    }
+    let client = this._store._remoteClients[id];
+    return client ? client.name : "";
+  },
+
+  getClientFxaDeviceId(id) {
+    if (this._store._remoteClients[id]) {
+      return this._store._remoteClients[id].fxaDeviceId;
+    }
+    return null;
+  },
+
+  getClientByFxaDeviceId(fxaDeviceId) {
+    for (let id in this._store._remoteClients) {
+      let client = this._store._remoteClients[id];
+      if (client.stale) {
+        continue;
+      }
+      if (client.fxaDeviceId == fxaDeviceId) {
+        return client;
+      }
+    }
+    return null;
+  },
+
+  getClientType(id) {
+    const client = this._store._remoteClients[id];
+    if (client.type == DEVICE_TYPE_DESKTOP) {
+      return "desktop";
+    }
+    if (client.formfactor && client.formfactor.includes("tablet")) {
+      return "tablet";
+    }
+    return "phone";
+  },
+
+  async _readCommands() {
+    let commands = await Utils.jsonLoad("commands", this);
+    return commands || {};
+  },
+
+  /**
+   * Low level function, do not use directly (use _addClientCommand instead).
+   */
+  async _saveCommands(commands) {
+    try {
+      await Utils.jsonSave("commands", this, commands);
+    } catch (error) {
+      this._log.error("Failed to save JSON outgoing commands", error);
+    }
+  },
+
+  async _prepareCommandsForUpload() {
+    try {
+      await Utils.jsonMove("commands", "commands-syncing", this);
+    } catch (e) {
+      // Ignore errors
+    }
+    let commands = await Utils.jsonLoad("commands-syncing", this);
+    return commands || {};
+  },
+
+  async _deleteUploadedCommands() {
+    delete this._currentlySyncingCommands;
+    try {
+      await Utils.jsonRemove("commands-syncing", this);
+    } catch (err) {
+      this._log.error("Failed to delete syncing-commands file", err);
+    }
+  },
+
+  // Gets commands for a client we are yet to write to the server. Doesn't
+  // include commands for that client which are already on the server.
+  // We should rename this!
+  async getClientCommands(clientId) {
+    const allCommands = await this._readCommands();
+    return allCommands[clientId] || [];
+  },
+
+  async removeLocalCommand(command) {
+    // the implementation of this engine is such that adding a command to
+    // the local client is how commands are deleted! ¯\_(ツ)_/¯
+    await this._addClientCommand(this.localID, command);
+  },
+
+  async _addClientCommand(clientId, command) {
+    this.addClientCommandQueue.enqueueCall(async () => {
+      try {
+        const localCommands = await this._readCommands();
+        const localClientCommands = localCommands[clientId] || [];
+        const remoteClient = this._store._remoteClients[clientId];
+        let remoteClientCommands = [];
+        if (remoteClient && remoteClient.commands) {
+          remoteClientCommands = remoteClient.commands;
+        }
+        const clientCommands = localClientCommands.concat(remoteClientCommands);
+        if (hasDupeCommand(clientCommands, command)) {
+          return false;
+        }
+        localCommands[clientId] = localClientCommands.concat(command);
+        await this._saveCommands(localCommands);
+        return true;
+      } catch (e) {
+        // Failing to save a command should not "break the queue" of pending operations.
+        this._log.error(e);
+        return false;
+      }
+    });
+
+    return this.addClientCommandQueue.promiseCallsComplete();
+  },
+
+  async _removeClientCommands(clientId) {
+    const allCommands = await this._readCommands();
+    delete allCommands[clientId];
+    await this._saveCommands(allCommands);
+  },
+
+  async updateKnownStaleClients() {
+    this._log.debug("Updating the known stale clients");
+    // _fetchFxADevices side effect updates this._knownStaleFxADeviceIds.
+    await this._fetchFxADevices();
+    let localFxADeviceId = await fxAccounts.device.getLocalId();
+    // Process newer records first, so that if we hit a record with a device ID
+    // we've seen before, we can mark it stale immediately.
+    let clientList = Object.values(this._store._remoteClients).sort(
+      (a, b) => b.serverLastModified - a.serverLastModified
+    );
+    let seenDeviceIds = new Set([localFxADeviceId]);
+    for (let client of clientList) {
+      // Clients might not have an `fxaDeviceId` if they fail the FxA
+      // registration process.
+      if (!client.fxaDeviceId) {
+        continue;
+      }
+      if (this._knownStaleFxADeviceIds.includes(client.fxaDeviceId)) {
+        this._log.info(
+          `Hiding stale client ${client.id} - in known stale clients list`
+        );
+        client.stale = true;
+      } else if (seenDeviceIds.has(client.fxaDeviceId)) {
+        this._log.info(
+          `Hiding stale client ${client.id}` +
+            ` - duplicate device id ${client.fxaDeviceId}`
+        );
+        client.stale = true;
+      } else {
+        seenDeviceIds.add(client.fxaDeviceId);
+      }
+    }
+  },
+
+  async _fetchFxADevices() {
+    // We only force a refresh periodically to keep the load on the servers
+    // down, and because we expect FxA to have received a push message in
+    // most cases when the FxA device list would have changed. For this reason
+    // we still go ahead and check the stale list even if we didn't force a
+    // refresh.
+    let now = this.fxAccounts._internal.now(); // tests mock this .now() impl.
+    if (now - REFRESH_FXA_DEVICE_INTERVAL_MS > this._lastFxaDeviceRefresh) {
+      this._lastFxaDeviceRefresh = now;
+      try {
+        await this.fxAccounts.device.refreshDeviceList();
+      } catch (e) {
+        this._log.error("Could not refresh the FxA device list", e);
+      }
+    }
+
+    // We assume that clients not present in the FxA Device Manager list have been
+    // disconnected and so are stale
+    this._log.debug("Refreshing the known stale clients list");
+    let localClients = Object.values(this._store._remoteClients)
+      .filter(client => client.fxaDeviceId) // iOS client records don't have fxaDeviceId
+      .map(client => client.fxaDeviceId);
+    const fxaClients = this.fxAccounts.device.recentDeviceList
+      ? this.fxAccounts.device.recentDeviceList.map(device => device.id)
+      : [];
+    this._knownStaleFxADeviceIds = Utils.arraySub(localClients, fxaClients);
+  },
+
+  async _syncStartup() {
+    // Reupload new client record periodically.
+    if (Date.now() / 1000 - this.lastRecordUpload > CLIENTS_TTL_REFRESH) {
+      await this._tracker.addChangedID(this.localID);
+    }
+    return SyncEngine.prototype._syncStartup.call(this);
+  },
+
+  async _processIncoming() {
+    // Fetch all records from the server.
+    await this.resetLastSync();
+    this._incomingClients = {};
+    try {
+      await SyncEngine.prototype._processIncoming.call(this);
+      // Update FxA Device list.
+      await this._fetchFxADevices();
+      // Since clients are synced unconditionally, any records in the local store
+      // that don't exist on the server must be for disconnected clients. Remove
+      // them, so that we don't upload records with commands for clients that will
+      // never see them. We also do this to filter out stale clients from the
+      // tabs collection, since showing their list of tabs is confusing.
+      for (let id in this._store._remoteClients) {
+        if (!this._incomingClients[id]) {
+          this._log.info(`Removing local state for deleted client ${id}`);
+          await this._removeRemoteClient(id);
+        }
+      }
+      let localFxADeviceId = await fxAccounts.device.getLocalId();
+      // Bug 1264498: Mobile clients don't remove themselves from the clients
+      // collection when the user disconnects Sync, so we mark as stale clients
+      // with the same name that haven't synced in over a week.
+      // (Note we can't simply delete them, or we re-apply them next sync - see
+      // bug 1287687)
+      this._localClientLastModified = Math.round(
+        this._incomingClients[this.localID]
+      );
+      delete this._incomingClients[this.localID];
+      let names = new Set([this.localName]);
+      let seenDeviceIds = new Set([localFxADeviceId]);
+      let idToLastModifiedList = Object.entries(this._incomingClients).sort(
+        (a, b) => b[1] - a[1]
+      );
+      for (let [id, serverLastModified] of idToLastModifiedList) {
+        let record = this._store._remoteClients[id];
+        // stash the server last-modified time on the record.
+        record.serverLastModified = serverLastModified;
+        if (
+          record.fxaDeviceId &&
+          this._knownStaleFxADeviceIds.includes(record.fxaDeviceId)
+        ) {
+          this._log.info(
+            `Hiding stale client ${id} - in known stale clients list`
+          );
+          record.stale = true;
+        }
+        if (!names.has(record.name)) {
+          if (record.fxaDeviceId) {
+            seenDeviceIds.add(record.fxaDeviceId);
+          }
+          names.add(record.name);
+          continue;
+        }
+        let remoteAge = Resource.serverTime - this._incomingClients[id];
+        if (remoteAge > STALE_CLIENT_REMOTE_AGE) {
+          this._log.info(`Hiding stale client ${id} with age ${remoteAge}`);
+          record.stale = true;
+          continue;
+        }
+        if (record.fxaDeviceId && seenDeviceIds.has(record.fxaDeviceId)) {
+          this._log.info(
+            `Hiding stale client ${record.id}` +
+              ` - duplicate device id ${record.fxaDeviceId}`
+          );
+          record.stale = true;
+        } else if (record.fxaDeviceId) {
+          seenDeviceIds.add(record.fxaDeviceId);
+        }
+      }
+    } finally {
+      this._incomingClients = null;
+    }
+  },
+
+  async _uploadOutgoing() {
+    this._currentlySyncingCommands = await this._prepareCommandsForUpload();
+    const clientWithPendingCommands = Object.keys(
+      this._currentlySyncingCommands
+    );
+    for (let clientId of clientWithPendingCommands) {
+      if (this._store._remoteClients[clientId] || this.localID == clientId) {
+        this._modified.set(clientId, 0);
+      }
+    }
+    let updatedIDs = this._modified.ids();
+    await SyncEngine.prototype._uploadOutgoing.call(this);
+    // Record the response time as the server time for each item we uploaded.
+    let lastSync = await this.getLastSync();
+    for (let id of updatedIDs) {
+      if (id == this.localID) {
+        this.lastRecordUpload = lastSync;
+      } else {
+        this._store._remoteClients[id].serverLastModified = lastSync;
+      }
+    }
+  },
+
+  async _onRecordsWritten(succeeded, failed) {
+    // Reconcile the status of the local records with what we just wrote on the
+    // server
+    for (let id of succeeded) {
+      const commandChanges = this._currentlySyncingCommands[id];
+      if (id == this.localID) {
+        if (this.isFirstSync) {
+          this._log.info(
+            "Uploaded our client record for the first time, notifying other clients."
+          );
+          this._notifyClientRecordUploaded();
+        }
+        if (this.localCommands) {
+          this.localCommands = this.localCommands.filter(
+            command => !hasDupeCommand(commandChanges, command)
+          );
+        }
+      } else {
+        const clientRecord = this._store._remoteClients[id];
+        if (!commandChanges || !clientRecord) {
+          // should be impossible, else we wouldn't have been writing it.
+          this._log.warn(
+            "No command/No record changes for a client we uploaded"
+          );
+          continue;
+        }
+        // fixup the client record, so our copy of _remoteClients matches what we uploaded.
+        this._store._remoteClients[id] = await this._store.createRecord(id);
+        // we could do better and pass the reference to the record we just uploaded,
+        // but this will do for now
+      }
+    }
+
+    // Re-add failed commands
+    for (let id of failed) {
+      const commandChanges = this._currentlySyncingCommands[id];
+      if (!commandChanges) {
+        continue;
+      }
+      await this._addClientCommand(id, commandChanges);
+    }
+
+    await this._deleteUploadedCommands();
+
+    // Notify other devices that their own client collection changed
+    const idsToNotify = succeeded.reduce((acc, id) => {
+      if (id == this.localID) {
+        return acc;
+      }
+      const fxaDeviceId = this.getClientFxaDeviceId(id);
+      return fxaDeviceId ? acc.concat(fxaDeviceId) : acc;
+    }, []);
+    if (idsToNotify.length > 0) {
+      this._notifyOtherClientsModified(idsToNotify);
+    }
+  },
+
+  _notifyOtherClientsModified(ids) {
+    // We are not waiting on this promise on purpose.
+    this._notifyCollectionChanged(
+      ids,
+      NOTIFY_TAB_SENT_TTL_SECS,
+      COLLECTION_MODIFIED_REASON_SENDTAB
+    );
+  },
+
+  _notifyClientRecordUploaded() {
+    // We are not waiting on this promise on purpose.
+    this._notifyCollectionChanged(
+      null,
+      0,
+      COLLECTION_MODIFIED_REASON_FIRSTSYNC
+    );
+  },
+
+  /**
+   * @param {?string[]} ids FxA Client IDs to notify. null means everyone else.
+   * @param {number} ttl TTL of the push notification.
+   * @param {string} reason Reason for sending this push notification.
+   */
+  async _notifyCollectionChanged(ids, ttl, reason) {
+    const message = {
+      version: 1,
+      command: "sync:collection_changed",
+      data: {
+        collections: ["clients"],
+        reason,
+      },
+    };
+    let excludedIds = null;
+    if (!ids) {
+      const localFxADeviceId = await fxAccounts.device.getLocalId();
+      excludedIds = [localFxADeviceId];
+    }
+    try {
+      await this.fxAccounts.notifyDevices(ids, excludedIds, message, ttl);
+    } catch (e) {
+      this._log.error("Could not notify of changes in the collection", e);
+    }
+  },
+
+  async _syncFinish() {
+    // Record histograms for our device types, and also write them to a pref
+    // so non-histogram telemetry (eg, UITelemetry) and the sync scheduler
+    // has easy access to them, and so they are accurate even before we've
+    // successfully synced the first time after startup.
+    let deviceTypeCounts = this.deviceTypes;
+    for (let [deviceType, count] of deviceTypeCounts) {
+      let hid;
+      let prefName = this.name + ".devices.";
+      switch (deviceType) {
+        case DEVICE_TYPE_DESKTOP:
+          hid = "WEAVE_DEVICE_COUNT_DESKTOP";
+          prefName += "desktop";
+          break;
+        case DEVICE_TYPE_MOBILE:
+          hid = "WEAVE_DEVICE_COUNT_MOBILE";
+          prefName += "mobile";
+          break;
+        default:
+          this._log.warn(
+            `Unexpected deviceType "${deviceType}" recording device telemetry.`
+          );
+          continue;
+      }
+      Services.telemetry.getHistogramById(hid).add(count);
+      // Optimization: only write the pref if it changed since our last sync.
+      if (
+        this._lastDeviceCounts == null ||
+        this._lastDeviceCounts.get(prefName) != count
+      ) {
+        Svc.Prefs.set(prefName, count);
+      }
+    }
+    this._lastDeviceCounts = deviceTypeCounts;
+    return SyncEngine.prototype._syncFinish.call(this);
+  },
+
+  async _reconcile(item) {
+    // Every incoming record is reconciled, so we use this to track the
+    // contents of the collection on the server.
+    this._incomingClients[item.id] = item.modified;
+
+    if (!(await this._store.itemExists(item.id))) {
+      return true;
+    }
+    // Clients are synced unconditionally, so we'll always have new records.
+    // Unfortunately, this will cause the scheduler to use the immediate sync
+    // interval for the multi-device case, instead of the active interval. We
+    // work around this by updating the record during reconciliation, and
+    // returning false to indicate that the record doesn't need to be applied
+    // later.
+    await this._store.update(item);
+    return false;
+  },
+
+  // Treat reset the same as wiping for locally cached clients
+  async _resetClient() {
+    await this._wipeClient();
+  },
+
+  async _wipeClient() {
+    await SyncEngine.prototype._resetClient.call(this);
+    this._knownStaleFxADeviceIds = null;
+    delete this.localCommands;
+    await this._store.wipe();
+    try {
+      await Utils.jsonRemove("commands", this);
+    } catch (err) {
+      this._log.warn("Could not delete commands.json", err);
+    }
+    try {
+      await Utils.jsonRemove("commands-syncing", this);
+    } catch (err) {
+      this._log.warn("Could not delete commands-syncing.json", err);
+    }
+  },
+
+  async removeClientData() {
+    let res = this.service.resource(this.engineURL + "/" + this.localID);
+    await res.delete();
+  },
+
+  // Override the default behavior to delete bad records from the server.
+  async handleHMACMismatch(item, mayRetry) {
+    this._log.debug("Handling HMAC mismatch for " + item.id);
+
+    let base = await SyncEngine.prototype.handleHMACMismatch.call(
+      this,
+      item,
+      mayRetry
+    );
+    if (base != SyncEngine.kRecoveryStrategy.error) {
+      return base;
+    }
+
+    // It's a bad client record. Save it to be deleted at the end of the sync.
+    this._log.debug("Bad client record detected. Scheduling for deletion.");
+    await this._deleteId(item.id);
+
+    // Neither try again nor error; we're going to delete it.
+    return SyncEngine.kRecoveryStrategy.ignore;
+  },
+
+  /**
+   * A hash of valid commands that the client knows about. The key is a command
+   * and the value is a hash containing information about the command such as
+   * number of arguments, description, and importance (lower importance numbers
+   * indicate higher importance.
+   */
+  _commands: {
+    resetAll: {
+      args: 0,
+      importance: 0,
+      desc: "Clear temporary local data for all engines",
+    },
+    resetEngine: {
+      args: 1,
+      importance: 0,
+      desc: "Clear temporary local data for engine",
+    },
+    wipeAll: {
+      args: 0,
+      importance: 0,
+      desc: "Delete all client data for all engines",
+    },
+    wipeEngine: {
+      args: 1,
+      importance: 0,
+      desc: "Delete all client data for engine",
+    },
+    logout: { args: 0, importance: 0, desc: "Log out client" },
+    displayURI: {
+      args: 3,
+      importance: 1,
+      desc: "Instruct a client to display a URI",
+    },
+  },
+
+  /**
+   * Sends a command+args pair to a specific client.
+   *
+   * @param command Command string
+   * @param args Array of arguments/data for command
+   * @param clientId Client to send command to
+   */
+  async _sendCommandToClient(command, args, clientId, telemetryExtra) {
+    this._log.trace("Sending " + command + " to " + clientId);
+
+    let client = this._store._remoteClients[clientId];
+    if (!client) {
+      throw new Error("Unknown remote client ID: '" + clientId + "'.");
+    }
+    if (client.stale) {
+      throw new Error("Stale remote client ID: '" + clientId + "'.");
+    }
+
+    let action = {
+      command,
+      args,
+      // We send the flowID to the other client so *it* can report it in its
+      // telemetry - we record it in ours below.
+      flowID: telemetryExtra.flowID,
+    };
+
+    if (await this._addClientCommand(clientId, action)) {
+      this._log.trace(`Client ${clientId} got a new action`, [command, args]);
+      await this._tracker.addChangedID(clientId);
+      try {
+        telemetryExtra.deviceID = this.service.identity.hashedDeviceID(
+          clientId
+        );
+      } catch (_) {}
+
+      this.service.recordTelemetryEvent(
+        "sendcommand",
+        command,
+        undefined,
+        telemetryExtra
+      );
+    } else {
+      this._log.trace(`Client ${clientId} got a duplicate action`, [
+        command,
+        args,
+      ]);
+    }
+  },
+
+  /**
+   * Check if the local client has any remote commands and perform them.
+   *
+   * @return false to abort sync
+   */
+  async processIncomingCommands() {
+    return this._notify("clients:process-commands", "", async function() {
+      if (
+        !this.localCommands ||
+        (this._lastModifiedOnProcessCommands == this._localClientLastModified &&
+          !this.ignoreLastModifiedOnProcessCommands)
+      ) {
+        return true;
+      }
+      this._lastModifiedOnProcessCommands = this._localClientLastModified;
+
+      const clearedCommands = await this._readCommands()[this.localID];
+      const commands = this.localCommands.filter(
+        command => !hasDupeCommand(clearedCommands, command)
+      );
+      let didRemoveCommand = false;
+      let URIsToDisplay = [];
+      // Process each command in order.
+      for (let rawCommand of commands) {
+        let shouldRemoveCommand = true; // most commands are auto-removed.
+        let { command, args, flowID } = rawCommand;
+        this._log.debug("Processing command " + command, args);
+
+        this.service.recordTelemetryEvent(
+          "processcommand",
+          command,
+          undefined,
+          { flowID }
+        );
+
+        let engines = [args[0]];
+        switch (command) {
+          case "resetAll":
+            engines = null;
+          // Fallthrough
+          case "resetEngine":
+            await this.service.resetClient(engines);
+            break;
+          case "wipeAll":
+            engines = null;
+          // Fallthrough
+          case "wipeEngine":
+            await this.service.wipeClient(engines);
+            break;
+          case "logout":
+            this.service.logout();
+            return false;
+          case "displayURI":
+            let [uri, clientId, title] = args;
+            URIsToDisplay.push({ uri, clientId, title });
+            break;
+          default:
+            this._log.warn("Received an unknown command: " + command);
+            break;
+        }
+        // Add the command to the "cleared" commands list
+        if (shouldRemoveCommand) {
+          await this.removeLocalCommand(rawCommand);
+          didRemoveCommand = true;
+        }
+      }
+      if (didRemoveCommand) {
+        await this._tracker.addChangedID(this.localID);
+      }
+
+      if (URIsToDisplay.length) {
+        this._handleDisplayURIs(URIsToDisplay);
+      }
+
+      return true;
+    })();
+  },
+
+  /**
+   * Validates and sends a command to a client or all clients.
+   *
+   * Calling this does not actually sync the command data to the server. If the
+   * client already has the command/args pair, it won't receive a duplicate
+   * command.
+   * This method is async since it writes the command to a file.
+   *
+   * @param command
+   *        Command to invoke on remote clients
+   * @param args
+   *        Array of arguments to give to the command
+   * @param clientId
+   *        Client ID to send command to. If undefined, send to all remote
+   *        clients.
+   * @param flowID
+   *        A unique identifier used to track success for this operation across
+   *        devices.
+   */
+  async sendCommand(command, args, clientId = null, telemetryExtra = {}) {
+    let commandData = this._commands[command];
+    // Don't send commands that we don't know about.
+    if (!commandData) {
+      this._log.error("Unknown command to send: " + command);
+      return;
+    } else if (!args || args.length != commandData.args) {
+      // Don't send a command with the wrong number of arguments.
+      this._log.error(
+        "Expected " +
+          commandData.args +
+          " args for '" +
+          command +
+          "', but got " +
+          args
+      );
+      return;
+    }
+
+    // We allocate a "flowID" here, so it is used for each client.
+    telemetryExtra = Object.assign({}, telemetryExtra); // don't clobber the caller's object
+    if (!telemetryExtra.flowID) {
+      telemetryExtra.flowID = Utils.makeGUID();
+    }
+
+    if (clientId) {
+      await this._sendCommandToClient(command, args, clientId, telemetryExtra);
+    } else {
+      for (let [id, record] of Object.entries(this._store._remoteClients)) {
+        if (!record.stale) {
+          await this._sendCommandToClient(command, args, id, telemetryExtra);
+        }
+      }
+    }
+  },
+
+  /**
+   * Send a URI to another client for display.
+   *
+   * A side effect is the score is increased dramatically to incur an
+   * immediate sync.
+   *
+   * If an unknown client ID is specified, sendCommand() will throw an
+   * Error object.
+   *
+   * @param uri
+   *        URI (as a string) to send and display on the remote client
+   * @param clientId
+   *        ID of client to send the command to. If not defined, will be sent
+   *        to all remote clients.
+   * @param title
+   *        Title of the page being sent.
+   */
+  async sendURIToClientForDisplay(uri, clientId, title) {
+    this._log.trace(
+      "Sending URI to client: " + uri + " -> " + clientId + " (" + title + ")"
+    );
+    await this.sendCommand("displayURI", [uri, this.localID, title], clientId);
+
+    this._tracker.score += SCORE_INCREMENT_XLARGE;
+  },
+
+  /**
+   * Handle a bunch of received 'displayURI' commands.
+   *
+   * Interested parties should observe the "weave:engine:clients:display-uris"
+   * topic. The callback will receive an array as the subject parameter
+   * containing objects with the following keys:
+   *
+   *   uri         URI (string) that is requested for display.
+   *   sender.id   ID of client that sent the command.
+   *   sender.name Name of client that sent the command.
+   *   title       Title of page that loaded URI (likely) corresponds to.
+   *
+   * The 'data' parameter to the callback will not be defined.
+   *
+   * @param uris
+   *        An array containing URI objects to display
+   * @param uris[].uri
+   *        String URI that was received
+   * @param uris[].clientId
+   *        ID of client that sent URI
+   * @param uris[].title
+   *        String title of page that URI corresponds to. Older clients may not
+   *        send this.
+   */
+  _handleDisplayURIs(uris) {
+    uris.forEach(uri => {
+      uri.sender = {
+        id: uri.clientId,
+        name: this.getClientName(uri.clientId),
+      };
+    });
+    Svc.Obs.notify("weave:engine:clients:display-uris", uris);
+  },
+
+  async _removeRemoteClient(id) {
+    delete this._store._remoteClients[id];
+    await this._tracker.removeChangedID(id);
+    await this._removeClientCommands(id);
+    this._modified.delete(id);
+  },
+};
+
+function ClientStore(name, engine) {
+  Store.call(this, name, engine);
+}
+ClientStore.prototype = {
+  __proto__: Store.prototype,
+
+  _remoteClients: {},
+
+  async create(record) {
+    await this.update(record);
+  },
+
+  async update(record) {
+    if (record.id == this.engine.localID) {
+      // Only grab commands from the server; local name/type always wins
+      this.engine.localCommands = record.commands;
+    } else {
+      this._remoteClients[record.id] = record.cleartext;
+    }
+  },
+
+  async createRecord(id, collection) {
+    let record = new ClientsRec(collection, id);
+
+    const commandsChanges = this.engine._currentlySyncingCommands
+      ? this.engine._currentlySyncingCommands[id]
+      : [];
+
+    // Package the individual components into a record for the local client
+    if (id == this.engine.localID) {
+      try {
+        record.fxaDeviceId = await this.engine.fxAccounts.device.getLocalId();
+      } catch (error) {
+        this._log.warn("failed to get fxa device id", error);
+      }
+      record.name = this.engine.localName;
+      record.type = this.engine.localType;
+      record.version = Services.appinfo.version;
+      record.protocols = SUPPORTED_PROTOCOL_VERSIONS;
+
+      // Substract the commands we recorded that we've already executed
+      if (
+        commandsChanges &&
+        commandsChanges.length &&
+        this.engine.localCommands &&
+        this.engine.localCommands.length
+      ) {
+        record.commands = this.engine.localCommands.filter(
+          command => !hasDupeCommand(commandsChanges, command)
+        );
+      }
+
+      // Optional fields.
+      record.os = Services.appinfo.OS; // "Darwin"
+      record.appPackage = Services.appinfo.ID;
+      record.application = this.engine.brandName; // "Nightly"
+
+      // We can't compute these yet.
+      // record.device = "";            // Bug 1100723
+      // record.formfactor = "";        // Bug 1100722
+    } else {
+      record.cleartext = Object.assign({}, this._remoteClients[id]);
+      delete record.cleartext.serverLastModified; // serverLastModified is a local only attribute.
+
+      // Add the commands we have to send
+      if (commandsChanges && commandsChanges.length) {
+        const recordCommands = record.cleartext.commands || [];
+        const newCommands = commandsChanges.filter(
+          command => !hasDupeCommand(recordCommands, command)
+        );
+        record.cleartext.commands = recordCommands.concat(newCommands);
+      }
+
+      if (record.cleartext.stale) {
+        // It's almost certainly a logic error for us to upload a record we
+        // consider stale, so make log noise, but still remove the flag.
+        this._log.error(
+          `Preparing to upload record ${id} that we consider stale`
+        );
+        delete record.cleartext.stale;
+      }
+    }
+    if (record.commands) {
+      const maxPayloadSize = this.engine.service.getMemcacheMaxRecordPayloadSize();
+      let origOrder = new Map(record.commands.map((c, i) => [c, i]));
+      // we sort first by priority, and second by age (indicated by order in the
+      // original list)
+      let commands = record.commands.slice().sort((a, b) => {
+        let infoA = this.engine._commands[a.command];
+        let infoB = this.engine._commands[b.command];
+        // Treat unknown command types as highest priority, to allow us to add
+        // high priority commands in the future without worrying about clients
+        // removing them on each-other unnecessarially.
+        let importA = infoA ? infoA.importance : 0;
+        let importB = infoB ? infoB.importance : 0;
+        // Higher importantance numbers indicate that we care less, so they
+        // go to the end of the list where they'll be popped off.
+        let importDelta = importA - importB;
+        if (importDelta != 0) {
+          return importDelta;
+        }
+        let origIdxA = origOrder.get(a);
+        let origIdxB = origOrder.get(b);
+        // Within equivalent priorities, we put older entries near the end
+        // of the list, so that they are removed first.
+        return origIdxB - origIdxA;
+      });
+      let truncatedCommands = Utils.tryFitItems(commands, maxPayloadSize);
+      if (truncatedCommands.length != record.commands.length) {
+        this._log.warn(
+          `Removing commands from client ${id} (from ${record.commands.length} to ${truncatedCommands.length})`
+        );
+        // Restore original order.
+        record.commands = truncatedCommands.sort(
+          (a, b) => origOrder.get(a) - origOrder.get(b)
+        );
+      }
+    }
+    return record;
+  },
+
+  async itemExists(id) {
+    return id in (await this.getAllIDs());
+  },
+
+  async getAllIDs() {
+    let ids = {};
+    ids[this.engine.localID] = true;
+    for (let id in this._remoteClients) {
+      ids[id] = true;
+    }
+    return ids;
+  },
+
+  async wipe() {
+    this._remoteClients = {};
+  },
+};
+
+function ClientsTracker(name, engine) {
+  LegacyTracker.call(this, name, engine);
+}
+ClientsTracker.prototype = {
+  __proto__: LegacyTracker.prototype,
+
+  _enabled: false,
+
+  onStart() {
+    Svc.Obs.add("fxaccounts:new_device_id", this.asyncObserver);
+    Services.prefs.addObserver(
+      PREF_ACCOUNT_ROOT + "device.name",
+      this.asyncObserver
+    );
+  },
+  onStop() {
+    Services.prefs.removeObserver(
+      PREF_ACCOUNT_ROOT + "device.name",
+      this.asyncObserver
+    );
+    Svc.Obs.remove("fxaccounts:new_device_id", this.asyncObserver);
+  },
+
+  async observe(subject, topic, data) {
+    switch (topic) {
+      case "nsPref:changed":
+        this._log.debug("client.name preference changed");
+      // Fallthrough intended.
+      case "fxaccounts:new_device_id":
+        await this.addChangedID(this.engine.localID);
+        this.score += SINGLE_USER_THRESHOLD + 1; // ALWAYS SYNC NOW.
+        break;
+    }
+  },
+};