# All files / remote remote_store.ts

96.25% Statements 231/240
85.06% Branches 74/87
97.96% Functions 48/49
96.14% Lines 224/233

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61
    62
    63
    64
    65
    66
    67
    68
    69
    70
    71
    72
    73
    74
    75
    76
    77
    78
    79
    80
    81
    82
    83
    84
    85
    86
    87
    88
    89
    90
    91
    92
    93
    94
    95
    96
    97
    98
    99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416
    417
    418
    419
    420
    421
    422
    423
    424
    425
    426
    427
    428
    429
    430
    431
    432
    433
    434
    435
    436
    437
    438
    439
    440
    441
    442
    443
    444
    445
    446
    447
    448
    449
    450
    451
    452
    453
    454
    455
    456
    457
    458
    459
    460
    461
    462
    463
    464
    465
    466
    467
    468
    469
    470
    471
    472
    473
    474
    475
    476
    477
    478
    479
    480
    481
    482
    483
    484
    485
    486
    487
    488
    489
    490
    491
    492
    493
    494
    495
    496
    497
    498
    499
    500
    501
    502
    503
    504
    505
    506
    507
    508
    509
    510
    511
    512
    513
    514
    515
    516
    517
    518
    519
    520
    521
    522
    523
    524
    525
    526
    527
    528
    529
    530
    531
    532
    533
    534
    535
    536
    537
    538
    539
    540
    541
    542
    543
    544
    545
    546
    547
    548
    549
    550
    551
    552
    553
    554
    555
    556
    557
    558
    559
    560
    561
    562
    563
    564
    565
    566
    567
    568
    569
    570
    571
    572
    573
    574
    575
    576
    577
    578
    579
    580
    581
    582
    583
    584
    585
    586
    587
    588
    589
    590
    591
    592
    593
    594
    595
    596
    597
    598
    599
    600
    601
    602
    603
    604
    605
    606
    607
    608
    609
    610
    611
    612
    613
    614
    615
    616
    617
    618
    619
    620
    621
    622
    623
    624
    625
    626
    627
    628
    629
    630
    631
    632
    633
    634
    635
    636
    637
    638
    639
    640
    641
    642
    643
    644
    645
    646
    647
    648
    649
    650
    651
    652
    653
    654
    655
    656
    657
    658
    659
    660
    661
    662
    663
    664
    665
    666
    667
    668
    669
    670
    671
    672
    673
    674
    675
    676
    677
    678
    679
    680
    681
    682
    683
    684
    685
    686
    687
    688
    689
    690
    691
    692
    693
    694
    695
    696
    697
    698
    699
    700
    701
    702
    703
    704
    705
    706
    707
    708
    709
    710
    711
    712
    713
    714
    715
    716
    717
    718
    719
    720
    721
    722
    723
    724
    725
    726
    727
    728
    729
    730
    731
    732
    733
    734
    735
    736
    737
    738
    739
    740
    741
    742
    743
    744
    745
    746
    747
    748
    749
    750
    751
    752
    753
    754
    755
    756
    757
    758
    759
    760

    2x
    2x
    2x

    2x
    2x
    2x

    2x

    2x
    2x
    2x
    2x
    2x

    2x

    2x
    2x

    2x

    2x

    2x

    2x
    619x
    619x

    619x

    619x

    619x

    619x
    619x

    619x

    619x

    619x

    2x
    619x

    2x
    8077x

    8077x

    657x
    657x
    4x

    653x
    653x

    653x
    653x

    653x
    14x

    639x

    653x

    2x
    18x

    18x

    2x
    654x

    652x
    652x

    652x
    652x

    652x
    652x

    2x
    618x
    618x

    618x
    618x

    2x
    480x

    480x

    480x

    360x
    120x
    116x

    2x
    314x

    314x
    314x
    312x
    312x
    266x

    2x
    558x
    558x

    2x
    318x
    318x

    2x

    876x

    2x
    432x

    432x

    432x

    2x
    1627x

    2x

    714x
    714x

    2x

    428x
    436x

    2x

    62x

    62x
    62x

    62x
    58x

    4x

    2x

    2454x

    2454x

    6x

    2448x
    2448x

    779x
    779x
    779x

    779x

    779x

    779x
    779x

    779x

    779x

    779x

    8x
    8x

    8x
    8x
    2x

    2x
    2x
    2x

    6x

    6x
    2x
    2x
    2x
    2x

    6x

    6x

    6x

    6x

    6x

    6x

    6x

    6x

    779x

    779x
    589x
    476x

    476x
    476x

    779x

    6x
    6x
    6x
    6x
    6x
    6x

    6x
    6x
    6x

    6x

    2x
    652x
    652x

    652x

    2x
    2507x
    2457x

    2457x
    1809x
    971x

    648x
    648x

    2x
    3155x

    2x
    28x

    2x
    648x

    648x

    648x

    648x
    322x
    326x
    136x

    2x
    1072x

    2x
    354x

    354x

    2x
    348x

    344x

    344x

    693x
    693x

    526x

    526x

    526x
    526x

    526x

    526x

    2x
    72x

    72x
    70x

    70x
    70x

    70x

    70x

    70x
    32x

    2x

    2x
    70x

    56x

    56x

    56x

    56x

    2x
    192x

    2x
    18x

    18x

    18x
    18x
    18x

    2x
     /**
     * 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 { SnapshotVersion } from '../core/snapshot_version';
    import { Transaction } from '../core/transaction';
    import { BatchId, OnlineState, TargetId } from '../core/types';
    import { LocalStore } from '../local/local_store';
    import { QueryData, QueryPurpose } from '../local/query_data';
    import { NoDocument } from '../model/document';
    import { DocumentKey } from '../model/document_key';
    import { MutationResult } from '../model/mutation';
    import {
      BATCHID_UNKNOWN,
      MutationBatch,
      MutationBatchResult
    } from '../model/mutation_batch';
    import { emptyByteString } from '../platform/platform';
    import { assert } from '../util/assert';
    import { Code, FirestoreError } from '../util/error';
    import * as log from '../util/log';
    import * as objUtils from '../util/obj';

    import { Datastore } from './datastore';
    import { ExistenceFilter } from './existence_filter';
    import {
      PersistentListenStream,
      PersistentWriteStream
    } from './persistent_stream';
    import { ResetMapping, UpdateMapping } from './remote_event';
    import { RemoteSyncer } from './remote_syncer';
    import { isPermanentError } from './rpc_error';
    import {
      WatchChange,
      WatchChangeAggregator,
      WatchTargetChange,
      WatchTargetChangeState
    } from './watch_change';
    import { OnlineStateTracker } from './online_state_tracker';
    import { AsyncQueue } from '../util/async_queue';

    const LOG_TAG = 'RemoteStore';

    // TODO(b/35853402): Negotiate this with the stream.
    const MAX_PENDING_WRITES = 10;

    /**
     * RemoteStore - An interface to remotely stored data, basically providing a
     * wrapper around the Datastore that is more reliable for the rest of the
     * system.
     *
     * RemoteStore is responsible for maintaining the connection to the server.
     * - maintaining a list of active listens.
     * - reconnecting when the connection is dropped.
     * - resuming all the active listens on reconnect.
     *
     * RemoteStore handles all incoming events from the Datastore.
     * - listening to the watch stream and repackaging the events as RemoteEvents
     * - notifying SyncEngine of any changes to the active listens.
     *
     * RemoteStore takes writes from other components and handles them reliably.
     * - pulling pending mutations from LocalStore and sending them to Datastore.
     * - retrying mutations that failed because of network problems.
     * - acking mutations to the SyncEngine once they are accepted or rejected.
     */
    export class RemoteStore {
      private pendingWrites: MutationBatch[] = [];
      private lastBatchSeen: BatchId = BATCHID_UNKNOWN;

      /**
       * A mapping of watched targets that the client cares about tracking and the
       * user has explicitly called a 'listen' for this target.
       *
       * These targets may or may not have been sent to or acknowledged by the
       * server. On re-establishing the listen stream, these targets should be sent
       * to the server. The targets removed with unlistens are removed eagerly
       * without waiting for confirmation from the listen stream.
       */
      private listenTargets: { [targetId: number]: QueryData } = {};

      /**
       * A mapping of targetId to pending acks needed.
       *
       * If a targetId is present in this map, then we're waiting for watch to
       * acknowledge a removal or addition of the target. If a target is not in this
       * mapping, and it's in the listenTargets map, then we consider the target to
       * be active.
       *
       * We increment the count here every time we issue a request over the stream
       * to watch or unwatch. We then decrement the count every time we get a target
       * added or target removed message from the server. Once the count is equal to
       * 0 we know that the client and server are in the same state (once this state
       * is reached the targetId is removed from the map to free the memory).
       */
      private pendingTargetResponses: { [targetId: number]: number } = {};

      private accumulatedWatchChanges: WatchChange[] = [];

      private watchStream: PersistentListenStream = null;
      private writeStream: PersistentWriteStream = null;

      private onlineStateTracker: OnlineStateTracker;

      constructor(
        /**
         * The local store, used to fill the write pipeline with outbound
         * mutations and resolve existence filter mismatches.
         */
        private localStore: LocalStore,
        /** The client-side proxy for interacting with the backend. */
        private datastore: Datastore,
        asyncQueue: AsyncQueue,
        onlineStateHandler: (onlineState: OnlineState) => void
      ) {
        this.onlineStateTracker = new OnlineStateTracker(
          asyncQueue,
          onlineStateHandler
        );
      }

      /** SyncEngine to notify of watch and write events. */
      syncEngine: RemoteSyncer;

      /**
       * Starts up the remote store, creating streams, restoring state from
       * LocalStore, etc.
       */
      start(): Promise<void> {
        return this.enableNetwork();
      }

      private isNetworkEnabled(): boolean {
        assert(
          (this.watchStream == null) === (this.writeStream == null),
          'WatchStream and WriteStream should both be null or non-null'
        );
        return this.watchStream != null;
      }

      /** Re-enables the network. Idempotent. */
      enableNetwork(): Promise<void> {
        if (this.isNetworkEnabled()) {
          return Promise.resolve();
        }

        // Create new streams (but note they're not started yet).
        this.watchStream = this.datastore.newPersistentWatchStream();
        this.writeStream = this.datastore.newPersistentWriteStream();

        // Load any saved stream token from persistent storage
        return this.localStore.getLastStreamToken().then(token => {
          this.writeStream.lastStreamToken = token;

          if (this.shouldStartWatchStream()) {
            this.startWatchStream();
          } else {
            this.onlineStateTracker.set(OnlineState.Unknown);
          }

          return this.fillWritePipeline(); // This may start the writeStream.
        });
      }

      /**
       * Temporarily disables the network. The network can be re-enabled using
       * enableNetwork().
       */
      async disableNetwork(): Promise<void> {
        this.disableNetworkInternal();
        // Set the OnlineState to Offline so get()s return from cache, etc.
        this.onlineStateTracker.set(OnlineState.Offline);
      }

      /**
       * Disables the network, if it is currently enabled.
       */
      private disableNetworkInternal(): void {
        if (this.isNetworkEnabled()) {
          // NOTE: We're guaranteed not to get any further events from these streams (not even a close
          // event).
          this.watchStream.stop();
          this.writeStream.stop();

          this.cleanUpWatchStreamState();
          this.cleanUpWriteStreamState();

          this.writeStream = null;
          this.watchStream = null;
        }
      }

      shutdown(): Promise<void> {
        log.debug(LOG_TAG, 'RemoteStore shutting down.');
        this.disableNetworkInternal();
        // Set the OnlineState to Unknown (rather than Offline) to avoid potentially
        // triggering spurious listener events with cached data, etc.
        this.onlineStateTracker.set(OnlineState.Unknown);
        return Promise.resolve();
      }

      /** Starts new listen for the given query. Uses resume token if provided */
      listen(queryData: QueryData): void {
        assert(
          !objUtils.contains(this.listenTargets, queryData.targetId),
          'listen called with duplicate targetId!'
        );
        // Mark this as something the client is currently listening for.
        this.listenTargets[queryData.targetId] = queryData;

        if (this.shouldStartWatchStream()) {
          // The listen will be sent in onWatchStreamOpen
          this.startWatchStream();
        } else if (this.isNetworkEnabled() && this.watchStream.isOpen()) {
          this.sendWatchRequest(queryData);
        }
      }

      /** Removes the listen from server */
      unlisten(targetId: TargetId): void {
        assert(
          objUtils.contains(this.listenTargets, targetId),
          'unlisten called without assigned target ID!'
        );
        delete this.listenTargets[targetId];
        if (this.isNetworkEnabled() && this.watchStream.isOpen()) {
          this.sendUnwatchRequest(targetId);
          if (objUtils.isEmpty(this.listenTargets)) {
            this.watchStream.markIdle();
          }
        }
      }

      /**
       * We need to increment the the expected number of pending responses we're due
       * from watch so we wait for the ack to process any messages from this target.
       */
      private sendWatchRequest(queryData: QueryData): void {
        this.recordPendingTargetRequest(queryData.targetId);
        this.watchStream.watch(queryData);
      }

      /**
       * We need to increment the expected number of pending responses we're due
       * from watch so we wait for the removal on the server before we process any
       * messages from this target.
       */
      private sendUnwatchRequest(targetId: TargetId): void {
        this.recordPendingTargetRequest(targetId);
        this.watchStream.unwatch(targetId);
      }

      /**
       * Increment the mapping of how many acks are needed from watch before we can
       * consider the server to be 'in-sync' with the client's active targets.
       */
      private recordPendingTargetRequest(targetId: TargetId): void {
        // For each request we get we need to record we need a response for it.
        this.pendingTargetResponses[targetId] =
          (this.pendingTargetResponses[targetId] || 0) + 1;
      }

      private startWatchStream(): void {
        assert(
          this.shouldStartWatchStream(),
          'startWriteStream() called when shouldStartWatchStream() is false.'
        );
        this.watchStream.start({
          onOpen: this.onWatchStreamOpen.bind(this),
          onClose: this.onWatchStreamClose.bind(this),
          onWatchChange: this.onWatchStreamChange.bind(this)
        });

        this.onlineStateTracker.handleWatchStreamStart();
      }

      /**
       * Returns whether the watch stream should be started because it's necessary
       * and has not yet been started.
       */
      private shouldStartWatchStream(): boolean {
        return (
          this.isNetworkEnabled() &&
          !this.watchStream.isStarted() &&
          !objUtils.isEmpty(this.listenTargets)
        );
      }

      private cleanUpWatchStreamState(): void {
        // If the connection is closed then we'll never get a snapshot version for
        // the accumulated changes and so we'll never be able to complete the batch.
        // When we start up again the server is going to resend these changes
        // anyway, so just toss the accumulated state.
        this.accumulatedWatchChanges = [];
        this.pendingTargetResponses = {};
      }

      private async onWatchStreamOpen(): Promise<void> {
        // TODO(b/35852690): close the stream again (with some timeout?) if no watch
        // targets are active
        objUtils.forEachNumber(this.listenTargets, (targetId, queryData) => {
          this.sendWatchRequest(queryData);
        });
      }

      private async onWatchStreamClose(
        error: FirestoreError | null
      ): Promise<void> {
        assert(
          this.isNetworkEnabled(),
          'onWatchStreamClose() should only be called when the network is enabled'
        );

        this.cleanUpWatchStreamState();
        this.onlineStateTracker.handleWatchStreamFailure();

        // If there was an error, retry the connection.
        if (this.shouldStartWatchStream()) {
          this.startWatchStream();
        } else {
          // No need to restart watch stream because there are no active targets.
          // The online state is set to unknown because there is no active attempt
          // at establishing a connection
          this.onlineStateTracker.set(OnlineState.Unknown);
        }
      }

      private async onWatchStreamChange(
        watchChange: WatchChange,
        snapshotVersion: SnapshotVersion
      ): Promise<void> {
        // Mark the client as online since we got a message from the server
        this.onlineStateTracker.set(OnlineState.Online);

        if (
          watchChange instanceof WatchTargetChange &&
          watchChange.state === WatchTargetChangeState.Removed &&
          watchChange.cause
        ) {
          // There was an error on a target, don't wait for a consistent snapshot
          // to raise events
          return this.handleTargetError(watchChange);
        }
        // Accumulate watch changes but don't process them if there's no
        // snapshotVersion or it's older than a previous snapshot we've processed
        // (can happen after we resume a target using a resume token).
        this.accumulatedWatchChanges.push(watchChange);
        if (
          !snapshotVersion.isEqual(SnapshotVersion.MIN) &&
          snapshotVersion.compareTo(
            this.localStore.getLastRemoteSnapshotVersion()
          ) >= 0
        ) {
          const changes = this.accumulatedWatchChanges;
          this.accumulatedWatchChanges = [];
          return this.handleWatchChangeBatch(snapshotVersion, changes);
        }
      }

      /**
       * Takes a batch of changes from the Datastore, repackages them as a
       * RemoteEvent, and passes that on to the listener, which is typically the
       * SyncEngine.
       */
      private handleWatchChangeBatch(
        snapshotVersion: SnapshotVersion,
        changes: WatchChange[]
      ): Promise<void> {
        const aggregator = new WatchChangeAggregator(
          snapshotVersion,
          this.listenTargets,
          this.pendingTargetResponses
        );
        aggregator.addChanges(changes);
        const remoteEvent = aggregator.createRemoteEvent();
        // Get the new response counts from the aggregator
        this.pendingTargetResponses = aggregator.pendingTargetResponses;

        const promises: Array<Promise<void>> = [];
        // Handle existence filters and existence filter mismatches.
        objUtils.forEachNumber(
          aggregator.existenceFilters,
          (targetId: TargetId, filter: ExistenceFilter) => {
            const queryData = this.listenTargets[targetId];
            Iif (!queryData) {
              // A watched target might have been removed already.
              return;
            }
            const query = queryData.query;
            if (query.isDocumentQuery()) {
              Eif (filter.count === 0) {
                // The existence filter told us the document does not exist.
                // We need to deduce that this document does not exist and apply
                // a deleted document to our updates. Without applying a deleted
                // document there might be another query that will raise this
                // document as part of a snapshot until it is resolved,
                // essentially exposing inconsistency between queries.
                const key = new DocumentKey(query.path);
                const deletedDoc = new NoDocument(key, snapshotVersion);
                remoteEvent.addDocumentUpdate(deletedDoc);
              } else {
                assert(
                  filter.count === 1,
                  'Single document existence filter with count: ' + filter.count
                );
              }
            } else {
              // Not a document query.
              const promise = this.localStore
                .remoteDocumentKeys(targetId)
                .then(trackedRemote => {
                  if (remoteEvent.targetChanges[targetId]) {
                    const mapping = remoteEvent.targetChanges[targetId].mapping;
                    Eif (mapping !== null) {
                      Eif (mapping instanceof UpdateMapping) {
                        trackedRemote = mapping.applyToKeySet(trackedRemote);
                      } else {
                        assert(
                          mapping instanceof ResetMapping,
                          'Expected either reset or update mapping but got something else: ' +
                            mapping
                        );
                        trackedRemote = mapping.documents;
                      }
                    }
                  }

                  Eif (trackedRemote.size !== filter.count) {
                    // Existence filter mismatch, resetting mapping.

                    // Make sure the mismatch is exposed in the remote event.
                    remoteEvent.handleExistenceFilterMismatch(targetId);

                    // Clear the resume token for the query, since we're in a
                    // known mismatch state.
                    const newQueryData = new QueryData(
                      query,
                      targetId,
                      queryData.purpose
                    );
                    this.listenTargets[targetId] = newQueryData;

                    // Cause a hard reset by unwatching and rewatching
                    // immediately, but deliberately don't send a resume token
                    // so that we get a full update.
                    // Make sure we expect that this acks are going to happen.
                    this.sendUnwatchRequest(targetId);

                    // Mark the query we send as being on behalf of an existence
                    // filter mismatch, but don't actually retain that in
                    // listenTargets. This ensures that we flag the first
                    // re-listen this way without impacting future listens of
                    // this target (that might happen e.g. on reconnect).
                    const requestQueryData = new QueryData(
                      query,
                      targetId,
                      QueryPurpose.ExistenceFilterMismatch
                    );
                    this.sendWatchRequest(requestQueryData);
                  }
                });
              promises.push(promise);
            }
          }
        );

        return Promise.all(promises).then(() => {
          // Update in-memory resume tokens. LocalStore will update the
          // persistent view of these when applying the completed RemoteEvent.
          objUtils.forEachNumber(remoteEvent.targetChanges, (targetId, change) => {
            if (change.resumeToken.length > 0) {
              const queryData = this.listenTargets[targetId];
              // A watched target might have been removed already.
              Eif (queryData) {
                this.listenTargets[targetId] = queryData.update({
                  resumeToken: change.resumeToken,
                  snapshotVersion: change.snapshotVersion
                });
              }
            }
          });

          // Finally handle remote event
          return this.syncEngine.applyRemoteEvent(remoteEvent);
        });
      }

      /** Handles an error on a target */
      private handleTargetError(watchChange: WatchTargetChange): Promise<void> {
        assert(!!watchChange.cause, 'Handling target error without a cause');
        const error = watchChange.cause!;
        let promiseChain = Promise.resolve();
        watchChange.targetIds.forEach(targetId => {
          promiseChain = promiseChain.then(async () => {
            // A watched target might have been removed already.
            Eif (objUtils.contains(this.listenTargets, targetId)) {
              delete this.listenTargets[targetId];
              return this.syncEngine.rejectListen(targetId, error);
            }
          });
        });
        return promiseChain;
      }

      cleanUpWriteStreamState() {
        this.lastBatchSeen = BATCHID_UNKNOWN;
        log.debug(
          LOG_TAG,
          'Stopping write stream with ' +
            this.pendingWrites.length +
            ' pending writes'
        );
        this.pendingWrites = [];
      }

      /**
       * Notifies that there are new mutations to process in the queue. This is
       * typically called by SyncEngine after it has sent mutations to LocalStore.
       */
      async fillWritePipeline(): Promise<void> {
        if (this.canWriteMutations()) {
          return this.localStore
            .nextMutationBatch(this.lastBatchSeen)
            .then(batch => {
              if (batch === null) {
                if (this.pendingWrites.length === 0) {
                  this.writeStream.markIdle();
                }
              } else {
                this.commit(batch);
                return this.fillWritePipeline();
              }
            });
        }
      }

      /**
       * Returns true if the backend can accept additional write requests.
       *
       * When sending mutations to the write stream (e.g. in fillWritePipeline),
       * call this method first to check if more mutations can be sent.
       *
       * Currently the only thing that can prevent the backend from accepting
       * write requests is if there are too many requests already outstanding. As
       * writes complete the backend will be able to accept more.
       */
      canWriteMutations(): boolean {
        return (
          this.isNetworkEnabled() && this.pendingWrites.length < MAX_PENDING_WRITES
        );
      }

      // For testing
      outstandingWrites(): number {
        return this.pendingWrites.length;
      }

      /**
       * Given mutations to commit, actually commits them to the Datastore. Note
       * that this does *not* return a Promise specifically because the AsyncQueue
       * should not block operations for this.
       */
      private commit(batch: MutationBatch): void {
        assert(
          this.canWriteMutations(),
          "commit called when batches can't be written"
        );
        this.lastBatchSeen = batch.batchId;

        this.pendingWrites.push(batch);

        if (this.shouldStartWriteStream()) {
          this.startWriteStream();
        } else if (this.isNetworkEnabled() && this.writeStream.handshakeComplete) {
          this.writeStream.writeMutations(batch.mutations);
        }
      }

      private shouldStartWriteStream(): boolean {
        return (
          this.isNetworkEnabled() &&
          !this.writeStream.isStarted() &&
          this.pendingWrites.length > 0
        );
      }

      private startWriteStream(): void {
        assert(
          this.shouldStartWriteStream(),
          'startWriteStream() called when shouldStartWriteStream() is false.'
        );
        this.writeStream.start({
          onOpen: this.onWriteStreamOpen.bind(this),
          onClose: this.onWriteStreamClose.bind(this),
          onHandshakeComplete: this.onWriteHandshakeComplete.bind(this),
          onMutationResult: this.onMutationResult.bind(this)
        });
      }

      private async onWriteStreamOpen(): Promise<void> {
        this.writeStream.writeHandshake();
      }

      private onWriteHandshakeComplete(): Promise<void> {
        // Record the stream token.
        return this.localStore
          .setLastStreamToken(this.writeStream.lastStreamToken)
          .then(() => {
            // Drain any pending writes.
            //
            // Note that at this point pendingWrites contains mutations that
            // have already been accepted by fillWritePipeline/commitBatch. If
            // the pipeline is full, canWriteMutations will be false, despite
            // the fact that we actually need to send mutations over.
            //
            // This also means that this method indirectly respects the limits
            // imposed by canWriteMutations since writes can't be added to the
            // pendingWrites array when canWriteMutations is false. If the
            // limits imposed by canWriteMutations actually protect us from
            // DOSing ourselves then those limits won't be exceeded here and
            // we'll continue to make progress.
            for (const batch of this.pendingWrites) {
              this.writeStream.writeMutations(batch.mutations);
            }
          });
      }

      private onMutationResult(
        commitVersion: SnapshotVersion,
        results: MutationResult[]
      ): Promise<void> {
        // This is a response to a write containing mutations and should be
        // correlated to the first pending write.
        assert(
          this.pendingWrites.length > 0,
          'Got result for empty pending writes'
        );
        const batch = this.pendingWrites.shift()!;
        const success = MutationBatchResult.from(
          batch,
          commitVersion,
          results,
          this.writeStream.lastStreamToken
        );
        return this.syncEngine.applySuccessfulWrite(success).then(() => {
          // It's possible that with the completion of this mutation another
          // slot has freed up.
          return this.fillWritePipeline();
        });
      }

      private async onWriteStreamClose(error?: FirestoreError): Promise<void> {
        assert(
          this.isNetworkEnabled(),
          'onWriteStreamClose() should only be called when the network is enabled'
        );

        // If the write stream closed due to an error, invoke the error callbacks if
        // there are pending writes.
        if (error && this.pendingWrites.length > 0) {
          assert(
            !!error,
            'We have pending writes, but the write stream closed without an error'
          );
          // A promise that is resolved after we processed the error
          let errorHandling: Promise<void>;
          Eif (this.writeStream.handshakeComplete) {
            // This error affects the actual write.
            errorHandling = this.handleWriteError(error!);
          } else {
            // If there was an error before the handshake has finished, it's
            // possible that the server is unable to process the stream token
            // we're sending. (Perhaps it's too old?)
            errorHandling = this.handleHandshakeError(error!);
          }

          return errorHandling.then(() => {
            // The write stream might have been started by refilling the write
            // pipeline for failed writes
            if (this.shouldStartWriteStream()) {
              this.startWriteStream();
            }
          });
        }
        // No pending writes, nothing to do
      }

      private async handleHandshakeError(error: FirestoreError): Promise<void> {
        // Reset the token if it's a permanent error or the error code is
        // ABORTED, signaling the write stream is no longer valid.
        if (isPermanentError(error.code) || error.code === Code.ABORTED) {
          log.debug(
            LOG_TAG,
            'RemoteStore error before completed handshake; resetting stream token: ',
            this.writeStream.lastStreamToken
          );
          this.writeStream.lastStreamToken = emptyByteString();

          return this.localStore.setLastStreamToken(emptyByteString());
        } else {
          // Some other error, don't reset stream token. Our stream logic will
          // just retry with exponential backoff.
        }
      }

      private async handleWriteError(error: FirestoreError): Promise<void> {
        if (isPermanentError(error.code)) {
          // This was a permanent error, the request itself was the problem
          // so it's not going to succeed if we resend it.
          const batch = this.pendingWrites.shift()!;

          // In this case it's also unlikely that the server itself is melting
          // down -- this was just a bad request so inhibit backoff on the next
          // restart.
          this.writeStream.inhibitBackoff();

          return this.syncEngine
            .rejectFailedWrite(batch.batchId, error)
            .then(() => {
              // It's possible that with the completion of this mutation
              // another slot has freed up.
              return this.fillWritePipeline();
            });
        } else {
          // Transient error, just let the retry logic kick in.
        }
      }

      createTransaction(): Transaction {
        return new Transaction(this.datastore);
      }

      handleUserChange(user: User): Promise<void> {
        log.debug(LOG_TAG, 'RemoteStore changing users: uid=', user.uid);

        // If the network has been explicitly disabled, make sure we don't
        // accidentally re-enable it.
        Eif (this.isNetworkEnabled()) {
          // Tear down and re-create our network streams. This will ensure we get a fresh auth token
          // for the new user and re-fill the write pipeline with new mutations from the LocalStore
          // (since mutations are per-user).
          this.disableNetworkInternal();
          this.onlineStateTracker.set(OnlineState.Unknown);
          return this.enableNetwork();
        }
      }
    }