# All files / remote persistent_stream.ts

96.98% Statements 193/199
86.27% Branches 44/51
95.74% Functions 45/47
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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 * as api from '../protos/firestore_proto_api';
    import { CredentialsProvider, Token } from '../api/credentials';
    import { SnapshotVersion } from '../core/snapshot_version';
    import { ProtoByteString, TargetId } from '../core/types';
    import { QueryData } from '../local/query_data';
    import { Mutation, MutationResult } from '../model/mutation';
    import { assert } from '../util/assert';
    import { AsyncQueue, TimerId } from '../util/async_queue';
    import { Code, FirestoreError } from '../util/error';
    import * as log from '../util/log';

    import { ExponentialBackoff } from './backoff';
    import { Connection, Stream } from './connection';
    import { JsonProtoSerializer } from './serializer';
    import { WatchChange } from './watch_change';
    import { isNullOrUndefined } from '../util/types';
    import { CancelablePromise } from '../util/promise';

    const LOG_TAG = 'PersistentStream';

    // The generated proto interfaces for these class are missing the database
    // field. So we add it here.
    // TODO(b/36015800): Remove this once the api generator is fixed.
    interface ListenRequest extends api.ListenRequest {
      database?: string;
    }
    export interface WriteRequest extends api.WriteRequest {
      database?: string;
    }

    enum PersistentStreamState {
      /**
       * The streaming RPC is not running and there's no error condition.
       * Calling `start` will start the stream immediately without backoff.
       * While in this state isStarted will return false.
       */
      Initial,

      /**
       * The stream is starting, and is waiting for an auth token to attach to
       * the initial request. While in this state, isStarted will return
       * true but isOpen will return false.
       */
      Auth,

      /**
       * The streaming RPC is up and running. Requests and responses can flow
       * freely. Both isStarted and isOpen will return true.
       */
      Open,

      /**
       * The stream encountered an error. The next start attempt will back off.
       * While in this state isStarted() will return false.
       *
       */
      Error,

      /**
       * An in-between state after an error where the stream is waiting before
       * re-starting. After
       * waiting is complete, the stream will try to open. While in this
       * state isStarted() will return YES but isOpen will return false.
       */
      Backoff,

      /**
       * The stream has been explicitly stopped; no further events will be emitted.
       */
      Stopped
    }

    /**
     * Provides a common interface that is shared by the listeners for stream
     * events by the concrete implementation classes.
     */
    export interface PersistentStreamListener {
      /**
       * Called after the stream was established and can accept outgoing
       * messages
       */
      onOpen: () => Promise<void>;
      /**
       * Called after the stream has closed. If there was an error, the
       * FirestoreError will be set.
       */
      onClose: (err?: FirestoreError) => Promise<void>;
    }

    /**
     * Initial backoff time in milliseconds after an error.
     * Set to 1s according to https://cloud.google.com/apis/design/errors.
     */
    const BACKOFF_INITIAL_DELAY_MS = 1000;

    /** Maximum backoff time in milliseconds */
    const BACKOFF_MAX_DELAY_MS = 60 * 1000;

    const BACKOFF_FACTOR = 1.5;

    /** The time a stream stays open after it is marked idle. */
    const IDLE_TIMEOUT_MS = 60 * 1000;

    /**
     * A PersistentStream is an abstract base class that represents a streaming RPC
     * to the Firestore backend. It's built on top of the connections own support
     * for streaming RPCs, and adds several critical features for our clients:
     *
     *   - Exponential backoff on failure
     *   - Authentication via CredentialsProvider
     *   - Dispatching all callbacks into the shared worker queue
     *
     * Subclasses of PersistentStream implement serialization of models to and
     * from the JSON representation of the protocol buffers for a specific
     * streaming RPC.
     *
     * ## Starting and Stopping
     *
     * Streaming RPCs are stateful and need to be `start`ed before messages can
     * be sent and received. The PersistentStream will call the onOpen function
     * of the listener once the stream is ready to accept requests.
     *
     * Should a `start` fail, PersistentStream will call the registered
     * onClose with a FirestoreError indicating what went wrong.
     *
     * A PersistentStream can be started and stopped repeatedly.
     *
     * Generic types:
     *  SendType: The type of the outgoing message of the underlying
     *    connection stream
     *  ReceiveType: The type of the incoming message of the underlying
     *    connection stream
     *  ListenerType: The type of the listener that will be used for callbacks
     */
    export abstract class PersistentStream<
      SendType,
      ReceiveType,
      ListenerType extends PersistentStreamListener
    > {
      private state: PersistentStreamState;
      private inactivityTimerPromise: CancelablePromise<void> | null = null;
      private stream: Stream<SendType, ReceiveType> | null = null;

      protected backoff: ExponentialBackoff;

      protected listener: ListenerType | null = null;

      constructor(
        private queue: AsyncQueue,
        connectionTimerId: TimerId,
        private idleTimerId: TimerId,
        protected connection: Connection,
        private credentialsProvider: CredentialsProvider
      ) {
        this.backoff = new ExponentialBackoff(
          queue,
          connectionTimerId,
          BACKOFF_INITIAL_DELAY_MS,
          BACKOFF_FACTOR,
          BACKOFF_MAX_DELAY_MS
        );
        this.state = PersistentStreamState.Initial;
      }

      /**
       * Returns true if `start` has been called and no error has occurred. True
       * indicates the stream is open or in the process of opening (which
       * encompasses respecting backoff, getting auth tokens, and starting the
       * actual RPC). Use `isOpen` to determine if the stream is open and ready for
       * outbound requests.
       */
      isStarted(): boolean {
        return (
          this.state === PersistentStreamState.Backoff ||
          this.state === PersistentStreamState.Auth ||
          this.state === PersistentStreamState.Open
        );
      }

      /**
       * Returns true if the underlying RPC is open (the openHandler has been
       * called) and the stream is ready for outbound requests.
       */
      isOpen(): boolean {
        return this.state === PersistentStreamState.Open;
      }

      /**
       * Starts the RPC. Only allowed if isStarted returns false. The stream is
       * not immediately ready for use: onOpen will be invoked when the RPC is ready
       * for outbound requests, at which point isOpen will return true.
       *
       *  When start returns, isStarted will return true.
       */
      start(listener: ListenerType): void {
        if (this.state === PersistentStreamState.Error) {
          this.performBackoff(listener);
          return;
        }

        assert(this.state === PersistentStreamState.Initial, 'Already started');
        this.listener = listener;
        this.auth();
      }

      /**
       * Stops the RPC. This call is idempotent and allowed regardless of the
       * current isStarted state.
       *
       * When stop returns, isStarted and isOpen will both return false.
       */
      stop(): void {
        if (this.isStarted()) {
          this.close(PersistentStreamState.Stopped);
        }
      }

      /**
       * After an error the stream will usually back off on the next attempt to
       * start it. If the error warrants an immediate restart of the stream, the
       * sender can use this to indicate that the receiver should not back off.
       *
       * Each error will call the onClose function. That function can decide to
       * inhibit backoff if required.
       */
      inhibitBackoff(): void {
        assert(!this.isStarted(), 'Can only inhibit backoff in a stopped state');

        this.state = PersistentStreamState.Initial;
        this.backoff.reset();
      }

      /**
       * Marks this stream as idle. If no further actions are performed on the
       * stream for one minute, the stream will automatically close itself and
       * notify the stream's onClose() handler with Status.OK. The stream will then
       * be in a !isStarted() state, requiring the caller to start the stream again
       * before further use.
       *
       * Only streams that are in state 'Open' can be marked idle, as all other
       * states imply pending network operations.
       */
      markIdle(): void {
        // Starts the idle time if we are in state 'Open' and are not yet already
        // running a timer (in which case the previous idle timeout still applies).
        if (this.isOpen() && this.inactivityTimerPromise === null) {
          this.inactivityTimerPromise = this.queue.enqueueAfterDelay(
            this.idleTimerId,
            IDLE_TIMEOUT_MS,
            () => this.handleIdleCloseTimer()
          );
        }
      }

      /** Sends a message to the underlying stream. */
      protected sendRequest(msg: SendType): void {
        this.cancelIdleCheck();
        this.stream!.send(msg);
      }

      /** Called by the idle timer when the stream should close due to inactivity. */
      private async handleIdleCloseTimer(): Promise<void> {
        Eif (this.isOpen()) {
          // When timing out an idle stream there's no reason to force the stream into backoff when
          // it restarts so set the stream state to Initial instead of Error.
          return this.close(PersistentStreamState.Initial);
        }
      }

      /** Marks the stream as active again. */
      private cancelIdleCheck() {
        if (this.inactivityTimerPromise) {
          this.inactivityTimerPromise.cancel();
          this.inactivityTimerPromise = null;
        }
      }

      /**
       * Closes the stream and cleans up as necessary:
       *
       * * closes the underlying GRPC stream;
       * * calls the onClose handler with the given 'error';
       * * sets internal stream state to 'finalState';
       * * adjusts the backoff timer based on the error
       *
       * A new stream can be opened by calling `start` unless `finalState` is set to
       * `PersistentStreamState.Stopped`.
       *
       * @param finalState the intended state of the stream after closing.
       * @param error the error the connection was closed with.
       */
      private async close(
        finalState: PersistentStreamState,
        error?: FirestoreError
      ): Promise<void> {
        assert(
          finalState === PersistentStreamState.Error || isNullOrUndefined(error),
          "Can't provide an error when not in an error state."
        );

        // The stream will be closed so we don't need our idle close timer anymore.
        this.cancelIdleCheck();

        // Ensure we don't leave a pending backoff operation queued (in case close()
        // was called while we were waiting to reconnect).
        this.backoff.cancel();

        if (finalState !== PersistentStreamState.Error) {
          // If this is an intentional close ensure we don't delay our next connection attempt.
          this.backoff.reset();
        } else if (error && error.code === Code.RESOURCE_EXHAUSTED) {
          // Log the error. (Probably either 'quota exceeded' or 'max queue length reached'.)
          log.error(error.toString());
          log.error(
            'Using maximum backoff delay to prevent overloading the backend.'
          );
          this.backoff.resetToMax();
        }

        // Clean up the underlying stream because we are no longer interested in events.
        if (this.stream !== null) {
          this.tearDown();
          this.stream.close();
          this.stream = null;
        }

        // This state must be assigned before calling onClose() to allow the callback to
        // inhibit backoff or otherwise manipulate the state in its non-started state.
        this.state = finalState;
        const listener = this.listener!;

        // Clear the listener to avoid bleeding of events from the underlying streams.
        this.listener = null;

        // If the caller explicitly requested a stream stop, don't notify them of a closing stream (it
        // could trigger undesirable recovery logic, etc.).
        if (finalState !== PersistentStreamState.Stopped) {
          return listener.onClose(error);
        }
      }

      /**
       * Can be overridden to perform additional cleanup before the stream is closed.
       * Calling super.tearDown() is not required.
       */
      protected tearDown(): void {}

      /**
       * Used by subclasses to start the concrete RPC and return the underlying
       * connection stream.
       */
      protected abstract startRpc(
        token: Token | null
      ): Stream<SendType, ReceiveType>;

      /**
       * Called after the stream has received a message. The function will be
       * called on the right queue and must return a Promise.
       * @param message The message received from the stream.
       */
      protected abstract onMessage(message: ReceiveType): Promise<void>;

      private auth(): void {
        assert(
          this.state === PersistentStreamState.Initial,
          'Must be in initial state to auth'
        );

        this.state = PersistentStreamState.Auth;

        this.credentialsProvider.getToken(/*forceRefresh=*/ false).then(
          token => {
            // Normally we'd have to schedule the callback on the AsyncQueue.
            // However, the following calls are safe to be called outside the
            // AsyncQueue since they don't chain asynchronous calls
            this.startStream(token);
          },
          (error: Error) => {
            this.queue.enqueue(async () => {
              if (this.state !== PersistentStreamState.Stopped) {
                // Stream can be stopped while waiting for authorization.
                const rpcError = new FirestoreError(
                  Code.UNKNOWN,
                  'Fetching auth token failed: ' + error.message
                );
                return this.handleStreamClose(rpcError);
              }
            });
          }
        );
      }

      private startStream(token: Token | null): void {
        Iif (this.state === PersistentStreamState.Stopped) {
          // Stream can be stopped while waiting for authorization.
          return;
        }

        assert(
          this.state === PersistentStreamState.Auth,
          'Trying to start stream in a non-auth state'
        );
        // Helper function to dispatch to AsyncQueue and make sure that any
        // close will seem instantaneous and events are prevented from being
        // raised after the close call
        const dispatchIfStillActive = (
          stream: Stream<SendType, ReceiveType>,
          fn: () => Promise<void>
        ) => {
          this.queue.enqueue(async () => {
            // Only raise events if the stream instance has not changed
            if (this.stream === stream) {
              return fn();
            }
          });
        };

        // Only start stream if listener has not changed
        Eif (this.listener !== null) {
          const currentStream = this.startRpc(token);
          this.stream = currentStream;
          this.stream.onOpen(() => {
            dispatchIfStillActive(currentStream, () => {
              assert(
                this.state === PersistentStreamState.Auth,
                'Expected stream to be in state auth, but was ' + this.state
              );
              this.state = PersistentStreamState.Open;
              return this.listener!.onOpen();
            });
          });
          this.stream.onClose((error: FirestoreError) => {
            dispatchIfStillActive(currentStream, () => {
              return this.handleStreamClose(error);
            });
          });
          this.stream.onMessage((msg: ReceiveType) => {
            dispatchIfStillActive(currentStream, () => {
              return this.onMessage(msg);
            });
          });
        }
      }

      private performBackoff(listener: ListenerType): void {
        assert(
          this.state === PersistentStreamState.Error,
          'Should only perform backoff in an error case'
        );
        this.state = PersistentStreamState.Backoff;

        this.backoff.backoffAndRun(async () => {
          Iif (this.state === PersistentStreamState.Stopped) {
            // We should have canceled the backoff timer when the stream was
            // closed, but just in case we make this a no-op.
            return;
          }

          this.state = PersistentStreamState.Initial;
          this.start(listener);
          assert(this.isStarted(), 'PersistentStream should have started');
        });
      }

      private handleStreamClose(error?: FirestoreError): Promise<void> {
        assert(this.isStarted(), "Can't handle server close on non-started stream");
        log.debug(LOG_TAG, `close with error: ${error}`);

        this.stream = null;

        // In theory the stream could close cleanly, however, in our current model
        // we never expect this to happen because if we stop a stream ourselves,
        // this callback will never be called. To prevent cases where we retry
        // without a backoff accidentally, we set the stream to error in all cases.
        return this.close(PersistentStreamState.Error, error);
      }
    }

    /** Listener for the PersistentWatchStream */
    export interface WatchStreamListener extends PersistentStreamListener {
      /**
       * Called on a watchChange. The snapshot parameter will be MIN if the watch
       * change did not have a snapshot associated with it.
       */
      onWatchChange: (
        watchChange: WatchChange,
        snapshot: SnapshotVersion
      ) => Promise<void>;
    }

    /**
     * A PersistentStream that implements the Listen RPC.
     *
     * Once the Listen stream has called the openHandler, any number of listen and
     * unlisten calls calls can be sent to control what changes will be sent from
     * the server for ListenResponses.
     */
    export class PersistentListenStream extends PersistentStream<
      api.ListenRequest,
      api.ListenResponse,
      WatchStreamListener
    > {
      constructor(
        queue: AsyncQueue,
        connection: Connection,
        credentials: CredentialsProvider,
        private serializer: JsonProtoSerializer
      ) {
        super(
          queue,
          TimerId.ListenStreamConnectionBackoff,
          TimerId.ListenStreamIdle,
          connection,
          credentials
        );
      }

      protected startRpc(
        token: Token | null
      ): Stream<api.ListenRequest, api.ListenResponse> {
        return this.connection.openStream<api.ListenRequest, api.ListenResponse>(
          'Listen',
          token
        );
      }

      protected onMessage(watchChangeProto: api.ListenResponse): Promise<void> {
        // A successful response means the stream is healthy
        this.backoff.reset();

        const watchChange = this.serializer.fromWatchChange(watchChangeProto);
        const snapshot = this.serializer.versionFromListenResponse(
          watchChangeProto
        );
        return this.listener!.onWatchChange(watchChange, snapshot);
      }

      /**
       * Registers interest in the results of the given query. If the query
       * includes a resumeToken it will be included in the request. Results that
       * affect the query will be streamed back as WatchChange messages that
       * reference the targetId.
       */
      watch(queryData: QueryData): void {
        const request: ListenRequest = {};
        request.database = this.serializer.encodedDatabaseId;
        request.addTarget = this.serializer.toTarget(queryData);

        const labels = this.serializer.toListenRequestLabels(queryData);
        if (labels) {
          request.labels = labels;
        }

        this.sendRequest(request);
      }

      /**
       * Unregisters interest in the results of the query associated with the
       * given targetId.
       */
      unwatch(targetId: TargetId): void {
        const request: ListenRequest = {};
        request.database = this.serializer.encodedDatabaseId;
        request.removeTarget = targetId;
        this.sendRequest(request);
      }
    }

    /** Listener for the PersistentWriteStream */
    export interface WriteStreamListener extends PersistentStreamListener {
      /**
       * Called by the PersistentWriteStream upon a successful handshake response
       * from the server, which is the receiver's cue to send any pending writes.
       */
      onHandshakeComplete: () => Promise<void>;

      /**
       * Called by the PersistentWriteStream upon receiving a StreamingWriteResponse
       * from the server that contains a mutation result.
       */
      onMutationResult: (
        commitVersion: SnapshotVersion,
        results: MutationResult[]
      ) => Promise<void>;
    }

    /**
     * A Stream that implements the Write RPC.
     *
     * The Write RPC requires the caller to maintain special streamToken
     * state in between calls, to help the server understand which responses the
     * client has processed by the time the next request is made. Every response
     * will contain a streamToken; this value must be passed to the next
     * request.
     *
     * After calling start() on this stream, the next request must be a handshake,
     * containing whatever streamToken is on hand. Once a response to this
     * request is received, all pending mutations may be submitted. When
     * submitting multiple batches of mutations at the same time, it's
     * okay to use the same streamToken for the calls to writeMutations.
     *
     * TODO(b/33271235): Use proto types
     */
    export class PersistentWriteStream extends PersistentStream<
      api.WriteRequest,
      api.WriteResponse,
      WriteStreamListener
    > {
      private handshakeComplete_ = false;

      constructor(
        queue: AsyncQueue,
        connection: Connection,
        credentials: CredentialsProvider,
        private serializer: JsonProtoSerializer
      ) {
        super(
          queue,
          TimerId.WriteStreamConnectionBackoff,
          TimerId.WriteStreamIdle,
          connection,
          credentials
        );
      }

      /**
       * The last received stream token from the server, used to acknowledge which
       * responses the client has processed. Stream tokens are opaque checkpoint
       * markers whose only real value is their inclusion in the next request.
       *
       * PersistentWriteStream manages propagating this value from responses to the
       * next request.
       */
      lastStreamToken: ProtoByteString;

      /**
       * Tracks whether or not a handshake has been successfully exchanged and
       * the stream is ready to accept mutations.
       */
      get handshakeComplete(): boolean {
        return this.handshakeComplete_;
      }

      // Override of PersistentStream.start
      start(listener: WriteStreamListener): void {
        this.handshakeComplete_ = false;
        super.start(listener);
      }

      protected tearDown() {
        if (this.handshakeComplete_) {
          this.writeMutations([]);
        }
      }

      protected startRpc(
        token: Token | null
      ): Stream<api.WriteRequest, api.WriteResponse> {
        return this.connection.openStream<api.WriteRequest, api.WriteResponse>(
          'Write',
          token
        );
      }

      protected onMessage(responseProto: api.WriteResponse): Promise<void> {
        // Always capture the last stream token.
        assert(
          !!responseProto.streamToken,
          'Got a write response without a stream token'
        );
        this.lastStreamToken = responseProto.streamToken!;

        if (!this.handshakeComplete_) {
          // The first response is always the handshake response
          assert(
            !responseProto.writeResults || responseProto.writeResults.length === 0,
            'Got mutation results for handshake'
          );
          this.handshakeComplete_ = true;
          return this.listener!.onHandshakeComplete();
        } else {
          // A successful first write response means the stream is healthy,
          // Note, that we could consider a successful handshake healthy, however,
          // the write itself might be causing an error we want to back off from.
          this.backoff.reset();

          const results = this.serializer.fromWriteResults(
            responseProto.writeResults
          );
          const commitVersion = this.serializer.fromVersion(
            responseProto.commitTime!
          );
          return this.listener!.onMutationResult(commitVersion, results);
        }
      }

      /**
       * Sends an initial streamToken to the server, performing the handshake
       * required to make the StreamingWrite RPC work. Subsequent
       * calls should wait until onHandshakeComplete was called.
       */
      writeHandshake(): void {
        assert(this.isOpen(), 'Writing handshake requires an opened stream');
        assert(!this.handshakeComplete_, 'Handshake already completed');
        // TODO(dimond): Support stream resumption. We intentionally do not set the
        // stream token on the handshake, ignoring any stream token we might have.
        const request: WriteRequest = {};
        request.database = this.serializer.encodedDatabaseId;
        this.sendRequest(request);
      }

      /** Sends a group of mutations to the Firestore backend to apply. */
      writeMutations(mutations: Mutation[]): void {
        assert(this.isOpen(), 'Writing mutations requires an opened stream');
        assert(
          this.handshakeComplete_,
          'Handshake must be complete before writing mutations'
        );
        assert(
          this.lastStreamToken.length > 0,
          'Trying to write mutation without a token'
        );

        const request: WriteRequest = {
          // Protos are typed with string, but we support UInt8Array on Node
          // tslint:disable-next-line:no-any
          streamToken: this.lastStreamToken as any,
          writes: mutations.map(mutation => this.serializer.toMutation(mutation))
        };

        this.sendRequest(request);
      }
    }