timeout.ts

import { asyncScheduler } from '../scheduler/async';
import { MonoTypeOperatorFunction, SchedulerLike, OperatorFunction, ObservableInput, ObservedValueOf } from '../types';
import { isValidDate } from '../util/isDate';
import { Subscription } from '../Subscription';
import { operate } from '../util/lift';
import { Observable } from '../Observable';
import { innerFrom } from '../observable/from';
import { createErrorClass } from '../util/createErrorClass';
import { caughtSchedule } from '../util/caughtSchedule';
import { OperatorSubscriber } from './OperatorSubscriber';

export interface TimeoutConfig<T, O extends ObservableInput<unknown> = ObservableInput<T>, M = unknown> {
  /**
   * The time allowed between values from the source before timeout is triggered.
   */
  each?: number;

  /**
   * The relative time as a `number` in milliseconds, or a specific time as a `Date` object,
   * by which the first value must arrive from the source before timeout is triggered.
   */
  first?: number | Date;

  /**
   * The scheduler to use with time-related operations within this operator. Defaults to {@link asyncScheduler}
   */
  scheduler?: SchedulerLike;

  /**
   * A factory used to create observable to switch to when timeout occurs. Provides
   * some information about the source observable's emissions and what delay or
   * exact time triggered the timeout.
   */
  with?: (info: TimeoutInfo<T, M>) => O;

  /**
   * Optional additional metadata you can provide to code that handles
   * the timeout, will be provided through the {@link TimeoutError}.
   * This can be used to help identify the source of a timeout or pass along
   * other information related to the timeout.
   */
  meta?: M;
}

export interface TimeoutInfo<T, M = unknown> {
  /** Optional metadata that was provided to the timeout configuration. */
  readonly meta: M;
  /** The number of messages seen before the timeout */
  readonly seen: number;
  /** The last message seen */
  readonly lastValue: T | null;
}

/**
 * An error emitted when a timeout occurs.
 */
export interface TimeoutError<T = unknown, M = unknown> extends Error {
  /**
   * The information provided to the error by the timeout
   * operation that created the error. Will be `null` if
   * used directly in non-RxJS code with an empty constructor.
   * (Note that using this constructor directly is not recommended,
   * you should create your own errors)
   */
  info: TimeoutInfo<T, M> | null;
}

export interface TimeoutErrorCtor {
  /**
   * @deprecated Internal implementation detail. Do not construct error instances.
   * Cannot be tagged as internal: https://github.com/ReactiveX/rxjs/issues/6269
   */
  new <T = unknown, M = unknown>(info?: TimeoutInfo<T, M>): TimeoutError<T, M>;
}

/**
 * An error thrown by the {@link operators/timeout} operator.
 *
 * Provided so users can use as a type and do quality comparisons.
 * We recommend you do not subclass this or create instances of this class directly.
 * If you have need of a error representing a timeout, you should
 * create your own error class and use that.
 *
 * @see {@link operators/timeout}
 *
 * @class TimeoutError
 */
export const TimeoutError: TimeoutErrorCtor = createErrorClass(
  (_super) =>
    function TimeoutErrorImpl(this: any, info: TimeoutInfo<any> | null = null) {
      _super(this);
      this.message = 'Timeout has occurred';
      this.name = 'TimeoutError';
      this.info = info;
    }
);

/**
 * If `with` is provided, this will return an observable that will switch to a different observable if the source
 * does not push values within the specified time parameters.
 *
 * <span class="informal">The most flexible option for creating a timeout behavior.</span>
 *
 * The first thing to know about the configuration is if you do not provide a `with` property to the configuration,
 * when timeout conditions are met, this operator will emit a {@link TimeoutError}. Otherwise, it will use the factory
 * function provided by `with`, and switch your subscription to the result of that. Timeout conditions are provided by
 * the settings in `first` and `each`.
 *
 * The `first` property can be either a `Date` for a specific time, a `number` for a time period relative to the
 * point of subscription, or it can be skipped. This property is to check timeout conditions for the arrival of
 * the first value from the source _only_. The timings of all subsequent values  from the source will be checked
 * against the time period provided by `each`, if it was provided.
 *
 * The `each` property can be either a `number` or skipped. If a value for `each` is provided, it represents the amount of
 * time the resulting observable will wait between the arrival of values from the source before timing out. Note that if
 * `first` is _not_ provided, the value from `each` will be used to check timeout conditions for the arrival of the first
 * value and all subsequent values. If `first` _is_ provided, `each` will only be use to check all values after the first.
 *
 * ### Example
 *
 * Emit a custom error if there is too much time between values
 *
 * ```ts
 * import { interval, throwError } from 'rxjs';
 * import { timeout } from 'rxjs/operators';
 *
 * class CustomTimeoutError extends Error {
 *   constructor() {
 *      super('It was too slow');
 *      this.name = 'CustomTimeoutError';
 *   }
 * }
 *
 * const slow$ = interval(900);
 *
 * slow$.pipe(
 *    timeout({
 *      each: 1000,
 *      with: () => throwError(new CustomTimeoutError())
 *    })
 * )
 * .subscribe({
 *    error: console.error
 * })
 * ```
 *
 * ### Example
 *
 * Switch to a faster observable if your source is slow.
 *
 * ```ts
 * import { interval, throwError } from 'rxjs';
 * import { timeout } from 'rxjs/operators';
 *
 * const slow$ = interval(900);
 * const fast$ = interval(500);
 *
 * slow$.pipe(
 *    timeout({
 *      each: 1000,
 *      with: () => fast$,
 *    })
 * )
 * .subscribe(console.log)
 * ```
 * @param config The configuration for the timeout.
 */
export function timeout<T, O extends ObservableInput<unknown>, M = unknown>(
  config: TimeoutConfig<T, O, M> & { with: (info: TimeoutInfo<T, M>) => O }
): OperatorFunction<T, T | ObservedValueOf<O>>;

/**
 * Returns an observable that will error or switch to a different observable if the source does not push values
 * within the specified time parameters.
 *
 * <span class="informal">The most flexible option for creating a timeout behavior.</span>
 *
 * The first thing to know about the configuration is if you do not provide a `with` property to the configuration,
 * when timeout conditions are met, this operator will emit a {@link TimeoutError}. Otherwise, it will use the factory
 * function provided by `with`, and switch your subscription to the result of that. Timeout conditions are provided by
 * the settings in `first` and `each`.
 *
 * The `first` property can be either a `Date` for a specific time, a `number` for a time period relative to the
 * point of subscription, or it can be skipped. This property is to check timeout conditions for the arrival of
 * the first value from the source _only_. The timings of all subsequent values  from the source will be checked
 * against the time period provided by `each`, if it was provided.
 *
 * The `each` property can be either a `number` or skipped. If a value for `each` is provided, it represents the amount of
 * time the resulting observable will wait between the arrival of values from the source before timing out. Note that if
 * `first` is _not_ provided, the value from `each` will be used to check timeout conditions for the arrival of the first
 * value and all subsequent values. If `first` _is_ provided, `each` will only be use to check all values after the first.
 *
 * ### Handling TimeoutErrors
 *
 * If no `with` property was provided, subscriptions to the resulting observable may emit an error of {@link TimeoutError}.
 * The timeout error provides useful information you can examine when you're handling the error. The most common way to handle
 * the error would be with {@link catchError}, although you could use {@link tap} or just the error handler in your `subscribe` call
 * directly, if your error handling is only a side effect (such as notifying the user, or logging).
 *
 * In this case, you would check the error for `instanceof TimeoutError` to validate that the error was indeed from `timeout`, and
 * not from some other source. If it's not from `timeout`, you should probably rethrow it if you're in a `catchError`.
 *
 *
 * ### Example
 *
 * Emit a {@link TimeoutError} if the first value, and _only_ the first value, does not arrive within 5 seconds
 *
 * ```ts
 * import { interval } from 'rxjs';
 * import { timeout } from 'rxjs/operators';
 *
 * // A random interval that lasts between 0 and 10 seconds per tick
 * const source$ = interval(Math.round(Math.random() * 10000));
 *
 * source$.pipe(
 *    timeout({ first: 5000 })
 * )
 * .subscribe(console.log);
 * ```
 *
 * ### Example
 *
 * Emit a {@link TimeoutError} if the source waits longer than 5 seconds between any two values or the first value
 * and subscription.
 *
 * ```ts
 * import { timer } from 'rxjs';
 * import { timeout, expand } from 'rxjs/operators';
 *
 * const getRandomTime = () => Math.round(Math.random() * 10000);
 *
 * // An observable that waits a random amount of time between each delivered value
 * const source$ = timer(getRandomTime()).pipe(
 *  expand(() => timer(getRandomTime()))
 * )
 *
 * source$.pipe(
 *    timeout({ each: 5000 })
 * )
 * .subscribe(console.log);
 * ```
 *
 * ### Example
 *
 * Emit a {@link TimeoutError} if the the source does not emit before 7 seconds, _or_ if the source waits longer than
 * 5 seconds between any two values after the first.
 *
 * ```ts
 * import { timer } from 'rxjs';
 * import { timeout, expand } from 'rxjs/operators';
 *
 * const getRandomTime = () => Math.round(Math.random() * 10000);
 *
 * // An observable that waits a random amount of time between each delivered value
 * const source$ = timer(getRandomTime()).pipe(
 *  expand(() => timer(getRandomTime()))
 * )
 *
 * source$.pipe(
 *    timeout({ first: 7000, each: 5000 })
 * )
 * .subscribe(console.log);
 * ```
 */
export function timeout<T, M = unknown>(config: Omit<TimeoutConfig<T, any, M>, 'with'>): OperatorFunction<T, T>;

/**
 * Returns an observable that will error if the source does not push its first value before the specified time passed as a `Date`.
 * This is functionally the same as `timeout({ first: someDate })`.
 *
 * <span class="informal">Errors if the first value doesn't show up before the given date and time</span>
 *
 * ![](timeout.png)
 *
 * @param first The date to at which the resulting observable will timeout if the source observable
 * does not emit at least one value.
 * @param scheduler The scheduler to use. Defaults to {@link asyncScheduler}.
 */
export function timeout<T>(first: Date, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;

/**
 * Returns an observable that will error if the source does not push a value within the specified time in milliseconds.
 * This is functionally the same as `timeout({ each: milliseconds })`.
 *
 * <span class="informal">Errors if it waits too long between any value</span>
 *
 * ![](timeout.png)
 *
 * @param each The time allowed between each pushed value from the source before the resulting observable
 * will timeout.
 * @param scheduler The scheduler to use. Defaults to {@link asyncScheduler}.
 */
export function timeout<T>(each: number, scheduler?: SchedulerLike): MonoTypeOperatorFunction<T>;

/**
 *
 * Errors if Observable does not emit a value in given time span.
 *
 * <span class="informal">Timeouts on Observable that doesn't emit values fast enough.</span>
 *
 * ![](timeout.png)
 *
 * @return A function that returns an Observable that mirrors behaviour of the
 * source Observable, unless timeout happens when it throws an error.
 */
export function timeout<T, O extends ObservableInput<any>, M>(
  config: number | Date | TimeoutConfig<T, O, M>,
  schedulerArg?: SchedulerLike
): OperatorFunction<T, T | ObservedValueOf<O>> {
  // Intentionally terse code.
  // If the first argument is a valid `Date`, then we use it as the `first` config.
  // Otherwise, if the first argument is a `number`, then we use it as the `each` config.
  // Otherwise, it can be assumed the first argument is the configuration object itself, and
  // we destructure that into what we're going to use, setting important defaults as we do.
  // NOTE: The default for `scheduler` will be the `scheduler` argument if it exists, or
  // it will default to the `asyncScheduler`.
  const { first, each, with: _with = timeoutErrorFactory, scheduler = schedulerArg ?? asyncScheduler, meta = null! } = (isValidDate(config)
    ? { first: config }
    : typeof config === 'number'
    ? { each: config }
    : config) as TimeoutConfig<T, O, M>;

  if (first == null && each == null) {
    // Ensure timeout was provided at runtime.
    throw new TypeError('No timeout provided.');
  }

  return operate((source, subscriber) => {
    // This subscription encapsulates our subscription to the
    // source for this operator. We're capturing it separately,
    // because if there is a `with` observable to fail over to,
    // we want to unsubscribe from our original subscription, and
    // hand of the subscription to that one.
    let originalSourceSubscription: Subscription;
    // The subscription for our timeout timer. This changes
    // every time get get a new value.
    let timerSubscription: Subscription;
    // A bit of state we pass to our with and error factories to
    // tell what the last value we saw was.
    let lastValue: T | null = null;
    // A bit of state we pass to the with and error factories to
    // tell how many values we have seen so far.
    let seen = 0;
    const startTimer = (delay: number) => {
      timerSubscription = caughtSchedule(
        subscriber,
        scheduler,
        () => {
          originalSourceSubscription.unsubscribe();
          innerFrom(
            _with!({
              meta,
              lastValue,
              seen,
            })
          ).subscribe(subscriber);
        },
        delay
      );
    };

    originalSourceSubscription = source.subscribe(
      new OperatorSubscriber(
        subscriber,
        (value: T) => {
          // clear the timer so we can emit and start another one.
          timerSubscription?.unsubscribe();
          seen++;
          // Emit
          subscriber.next((lastValue = value));
          // null | undefined are both < 0. Thanks, JavaScript.
          each! > 0 && startTimer(each!);
        },
        undefined,
        undefined,
        () => {
          if (!timerSubscription?.closed) {
            timerSubscription?.unsubscribe();
          }
          // Be sure not to hold the last value in memory after unsubscription
          // it could be quite large.
          lastValue = null;
        }
      )
    );

    // Intentionally terse code.
    // If `first` was provided, and it's a number, then use it.
    // If `first` was provided and it's not a number, it's a Date, and we get the difference between it and "now".
    // If `first` was not provided at all, then our first timer will be the value from `each`.
    startTimer(first != null ? (typeof first === 'number' ? first : +first - scheduler!.now()) : each!);
  });
}

/**
 * The default function to use to emit an error when timeout occurs and a `with` function
 * is not specified.
 * @param info The information about the timeout to pass along to the error
 */
function timeoutErrorFactory(info: TimeoutInfo<any>): Observable<never> {
  throw new TimeoutError(info);
}