# All files / local indexeddb_persistence.ts

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     /**
     * Copyright 2017 Google Inc.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *   http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    import { User } from '../auth/user';
    import { DatabaseInfo } from '../core/database_info';
    import { JsonProtoSerializer } from '../remote/serializer';
    import { assert } from '../util/assert';
    import { Code, FirestoreError } from '../util/error';
    import * as log from '../util/log';
    import { AutoId } from '../util/misc';

    import { IndexedDbMutationQueue } from './indexeddb_mutation_queue';
    import { IndexedDbQueryCache } from './indexeddb_query_cache';
    import { IndexedDbRemoteDocumentCache } from './indexeddb_remote_document_cache';
    import {
      ALL_STORES,
      createOrUpgradeDb,
      DbOwner,
      DbOwnerKey,
      SCHEMA_VERSION
    } from './indexeddb_schema';
    import { LocalSerializer } from './local_serializer';
    import { MutationQueue } from './mutation_queue';
    import { Persistence } from './persistence';
    import { PersistencePromise } from './persistence_promise';
    import { QueryCache } from './query_cache';
    import { RemoteDocumentCache } from './remote_document_cache';
    import { SimpleDb, SimpleDbTransaction } from './simple_db';

    const LOG_TAG = 'IndexedDbPersistence';

    /** If the owner lease is older than 5 seconds, try to take ownership. */
    const OWNER_LEASE_MAX_AGE_MS = 5000;
    /** Refresh the owner lease every 4 seconds while owner. */
    const OWNER_LEASE_REFRESH_INTERVAL_MS = 4000;

    /** LocalStorage location to indicate a zombied ownerId (see class comment). */
    const ZOMBIE_OWNER_LOCALSTORAGE_SUFFIX = 'zombiedOwnerId';
    /** Error when the owner lease cannot be acquired or is lost. */
    const EXISTING_OWNER_ERROR_MSG =
      'There is another tab open with offline' +
      ' persistence enabled. Only one such tab is allowed at a time. The' +
      ' other tab must be closed or persistence must be disabled.';
    const UNSUPPORTED_PLATFORM_ERROR_MSG =
      'This platform is either missing' +
      ' IndexedDB or is known to have an incomplete implementation. Offline' +
      ' persistence has been disabled.';

    /**
     * An IndexedDB-backed instance of Persistence. Data is stored persistently
     * across sessions.
     *
     * Currently the Firestore SDK only supports a single consumer of the database,
     * but browsers obviously support multiple tabs. IndexedDbPersistence ensures a
     * single consumer of the database via an "owner lease" stored in the database.
     *
     * On startup, IndexedDbPersistence assigns itself a random "ownerId" and writes
     * it to a special "owner" object in the database (if no entry exists already or
     * the current entry is expired). This owner lease is then verified inside every
     * transaction to ensure the lease has not been lost.
     *
     * If a tab opts not to acquire the owner lease (because there's an existing
     * non-expired owner) or loses the owner lease, IndexedDbPersistence enters a
     * failed state and all subsequent operations will automatically fail.
     *
     * The current owner regularly refreshes the owner lease with new timestamps to
     * prevent newly-opened tabs from taking over ownership.
     *
     * Additionally there is an optimization so that when a tab is closed, the owner
     * lease is released immediately (this is especially important to make sure that
     * a refreshed tab is able to immediately re-acquire the owner lease).
     * Unfortunately, IndexedDB cannot be reliably used in window.unload since it is
     * an asynchronous API. So in addition to attempting to give up the lease,
     * the owner writes its ownerId to a "zombiedOwnerId" entry in LocalStorage
     * which acts as an indicator that another tab should go ahead and take the
     * owner lease immediately regardless of the current lease timestamp.
     */
    export class IndexedDbPersistence implements Persistence {
      /**
       * The name of the main (and currently only) IndexedDB database. this name is
       * appended to the prefix provided to the IndexedDbPersistence constructor.
       */
      static MAIN_DATABASE = 'main';

      private simpleDb: SimpleDb;
      private started: boolean;
      private dbName: string;
      private localStoragePrefix: string;
      private ownerId: string = this.generateOwnerId();

      /**
       * Set to an Error object if we encounter an unrecoverable error. All further
       * transactions will be failed with this error.
       */
      private persistenceError: Error | null;
      /** The setInterval() handle tied to refreshing the owner lease. */
      // tslint:disable-next-line:no-any setTimeout() type differs on browser / node
      private ownerLeaseRefreshHandle: any;
      /** Our window.unload handler, if registered. */
      private windowUnloadHandler: (() => void) | null;

      private serializer: LocalSerializer;

      constructor(prefix: string, serializer: JsonProtoSerializer) {
        this.dbName = prefix + IndexedDbPersistence.MAIN_DATABASE;
        this.serializer = new LocalSerializer(serializer);
        this.localStoragePrefix = prefix;
      }

      start(): Promise<void> {
        Iif (!IndexedDbPersistence.isAvailable()) {
          this.persistenceError = new FirestoreError(
            Code.UNIMPLEMENTED,
            UNSUPPORTED_PLATFORM_ERROR_MSG
          );
          return Promise.reject(this.persistenceError);
        }

        assert(!this.started, 'IndexedDbPersistence double-started!');
        this.started = true;

        return SimpleDb.openOrCreate(this.dbName, SCHEMA_VERSION, createOrUpgradeDb)
          .then(db => {
            this.simpleDb = db;
          })
          .then(() => this.tryAcquireOwnerLease())
          .then(() => {
            this.scheduleOwnerLeaseRefreshes();
            this.attachWindowUnloadHook();
          });
      }

      shutdown(): Promise<void> {
        assert(this.started, 'IndexedDbPersistence shutdown without start!');
        this.started = false;
        this.detachWindowUnloadHook();
        this.stopOwnerLeaseRefreshes();
        return this.releaseOwnerLease().then(() => {
          this.simpleDb.close();
        });
      }

      getMutationQueue(user: User): MutationQueue {
        return IndexedDbMutationQueue.forUser(user, this.serializer);
      }

      getQueryCache(): QueryCache {
        return new IndexedDbQueryCache(this.serializer);
      }

      getRemoteDocumentCache(): RemoteDocumentCache {
        return new IndexedDbRemoteDocumentCache(this.serializer);
      }

      runTransaction<T>(
        action: string,
        operation: (transaction: SimpleDbTransaction) => PersistencePromise<T>
      ): Promise<T> {
        Iif (this.persistenceError) {
          return Promise.reject(this.persistenceError);
        }

        log.debug(LOG_TAG, 'Starting transaction:', action);

        // Do all transactions as readwrite against all object stores, since we
        // are the only reader/writer.
        return this.simpleDb.runTransaction('readwrite', ALL_STORES, txn => {
          // Verify that we still have the owner lease as part of every transaction.
          return this.ensureOwnerLease(txn).next(() => operation(txn));
        });
      }

      static isAvailable(): boolean {
        return SimpleDb.isAvailable();
      }

      /**
       * Generates a string used as a prefix when storing data in IndexedDB and
       * LocalStorage.
       */
      static buildStoragePrefix(databaseInfo: DatabaseInfo): string {
        // Use two different prefix formats:
        //
        //   * firestore / persistenceKey / projectID . databaseID / ...
        //   * firestore / persistenceKey / projectID / ...
        //
        // projectIDs are DNS-compatible names and cannot contain dots
        // so there's no danger of collisions.
        let database = databaseInfo.databaseId.projectId;
        Iif (!databaseInfo.databaseId.isDefaultDatabase) {
          database += '.' + databaseInfo.databaseId.database;
        }

        return 'firestore/' + databaseInfo.persistenceKey + '/' + database + '/';
      }

      /**
       * Acquires the owner lease if there's no valid owner. Else returns a rejected
       * promise.
       */
      private tryAcquireOwnerLease(): Promise<void> {
        // NOTE: Don't use this.runTransaction, since it requires us to already
        // have the lease.
        return this.simpleDb.runTransaction('readwrite', [DbOwner.store], txn => {
          const store = txn.store<DbOwnerKey, DbOwner>(DbOwner.store);
          return store.get('owner').next(dbOwner => {
            Eif (!this.validOwner(dbOwner)) {
              const newDbOwner = new DbOwner(this.ownerId, Date.now());
              log.debug(
                LOG_TAG,
                'No valid owner. Acquiring owner lease. Current owner:',
                dbOwner,
                'New owner:',
                newDbOwner
              );
              return store.put('owner', newDbOwner);
            } else {
              log.debug(
                LOG_TAG,
                'Valid owner already. Failing. Current owner:',
                dbOwner
              );
              this.persistenceError = new FirestoreError(
                Code.FAILED_PRECONDITION,
                EXISTING_OWNER_ERROR_MSG
              );
              return PersistencePromise.reject<void>(this.persistenceError);
            }
          });
        });
      }

      /** Checks the owner lease and deletes it if we are the current owner. */
      private releaseOwnerLease(): Promise<void> {
        // NOTE: Don't use this.runTransaction, since it requires us to already
        // have the lease.
        return this.simpleDb.runTransaction('readwrite', [DbOwner.store], txn => {
          const store = txn.store<DbOwnerKey, DbOwner>(DbOwner.store);
          return store.get('owner').next(dbOwner => {
            Eif (dbOwner !== null && dbOwner.ownerId === this.ownerId) {
              log.debug(LOG_TAG, 'Releasing owner lease.');
              return store.delete('owner');
            } else {
              return PersistencePromise.resolve();
            }
          });
        });
      }

      /**
       * Checks the owner lease and returns a rejected promise if we are not the
       * current owner. This should be included in every transaction to guard
       * against losing the owner lease.
       */
      private ensureOwnerLease(txn: SimpleDbTransaction): PersistencePromise<void> {
        const store = txn.store<DbOwnerKey, DbOwner>(DbOwner.store);
        return store.get('owner').next(dbOwner => {
          Iif (dbOwner === null || dbOwner.ownerId !== this.ownerId) {
            this.persistenceError = new FirestoreError(
              Code.FAILED_PRECONDITION,
              EXISTING_OWNER_ERROR_MSG
            );
            return PersistencePromise.reject<void>(this.persistenceError);
          } else {
            return PersistencePromise.resolve();
          }
        });
      }

      /**
       * Returns true if the provided owner exists, has a recent timestamp, and
       * isn't zombied.
       *
       * NOTE: To determine if the owner is zombied, this method reads from
       * LocalStorage which could be mildly expensive.
       */
      private validOwner(dbOwner: DbOwner | null): boolean {
        const now = Date.now();
        const minAcceptable = now - OWNER_LEASE_MAX_AGE_MS;
        const maxAcceptable = now;
        Eif (dbOwner === null) {
          return false; // no owner.
        } else if (dbOwner.leaseTimestampMs < minAcceptable) {
          return false; // owner lease has expired.
        } else if (dbOwner.leaseTimestampMs > maxAcceptable) {
          log.error(
            'Persistence owner-lease is in the future. Discarding.',
            dbOwner
          );
          return false;
        } else if (dbOwner.ownerId === this.getZombiedOwnerId()) {
          return false; // owner's tab closed.
        } else {
          return true;
        }
      }

      /**
       * Schedules a recurring timer to update the owner lease timestamp to prevent
       * other tabs from taking the lease.
       */
      private scheduleOwnerLeaseRefreshes(): void {
        // NOTE: This doesn't need to be scheduled on the async queue and doing so
        // would increase the chances of us not refreshing on time if the queue is
        // backed up for some reason.
        this.ownerLeaseRefreshHandle = setInterval(() => {
          const txResult = this.runTransaction('Refresh owner timestamp', txn => {
            // NOTE: We don't need to validate the current owner contents, since
            // runTransaction does that automatically.
            const store = txn.store<DbOwnerKey, DbOwner>(DbOwner.store);
            return store.put('owner', new DbOwner(this.ownerId, Date.now()));
          });

          txResult.catch(reason => {
            // Probably means we lost the lease. Report the error and stop trying to
            // refresh the lease.
            log.error(reason);
            this.stopOwnerLeaseRefreshes();
          });
        }, OWNER_LEASE_REFRESH_INTERVAL_MS);
      }

      private stopOwnerLeaseRefreshes(): void {
        Eif (this.ownerLeaseRefreshHandle) {
          clearInterval(this.ownerLeaseRefreshHandle);
          this.ownerLeaseRefreshHandle = null;
        }
      }

      /**
       * Attaches a window.unload handler that will synchronously write our
       * ownerId to a "zombie owner id" location in localstorage. This can be used
       * by tabs trying to acquire the lease to determine that the lease should be
       * acquired immediately even if the timestamp is recent. This is particularly
       * important for the refresh case (so the tab correctly re-acquires the owner
       * lease). LocalStorage is used for this rather than IndexedDb because it is
       * a synchronous API and so can be used reliably from an unload handler.
       */
      private attachWindowUnloadHook(): void {
        this.windowUnloadHandler = () => {
          // Record that we're zombied.
          this.setZombiedOwnerId(this.ownerId);

          // Attempt graceful shutdown (including releasing our owner lease), but
          // there's no guarantee it will complete.
          this.shutdown();
        };
        window.addEventListener('unload', this.windowUnloadHandler);
      }

      private detachWindowUnloadHook(): void {
        Eif (this.windowUnloadHandler) {
          window.removeEventListener('unload', this.windowUnloadHandler);
          this.windowUnloadHandler = null;
        }
      }

      /**
       * Returns any recorded "zombied owner" (i.e. a previous owner that became
       * zombied due to their tab closing) from LocalStorage, or null if no such
       * record exists.
       */
      private getZombiedOwnerId(): string | null {
        try {
          const zombiedOwnerId = window.localStorage.getItem(
            this.zombiedOwnerLocalStorageKey()
          );
          log.debug(LOG_TAG, 'Zombied ownerID from LocalStorage:', zombiedOwnerId);
          return zombiedOwnerId;
        } catch (e) {
          // Gracefully handle if LocalStorage isn't available / working.
          log.error('Failed to get zombie owner id.', e);
          return null;
        }
      }

      /**
       * Records a zombied owner (an owner that had its tab closed) in LocalStorage
       * or, if passed null, deletes any recorded zombied owner.
       */
      private setZombiedOwnerId(zombieOwnerId: string | null) {
        try {
          if (zombieOwnerId === null) {
            window.localStorage.removeItem(this.zombiedOwnerLocalStorageKey());
          } else {
            window.localStorage.setItem(
              this.zombiedOwnerLocalStorageKey(),
              zombieOwnerId
            );
          }
        } catch (e) {
          // Gracefully handle if LocalStorage isn't available / working.
          log.error('Failed to set zombie owner id.', e);
        }
      }

      private zombiedOwnerLocalStorageKey(): string {
        return this.localStoragePrefix + ZOMBIE_OWNER_LOCALSTORAGE_SUFFIX;
      }

      private generateOwnerId(): string {
        // For convenience, just use an AutoId.
        return AutoId.newId();
      }
    }