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import {delay, filter, map, skip, switchMap, take, takeUntil, tap} from 'rxjs/operators';
import {ChannelState} from './constants';
import type {PhysicalChannel} from './types';
export interface PersistentChannelParams<T extends string | Uint8Array = string | Uint8Array> {
/**
* New `Channel` factory.
*/
newChannel: () => PhysicalChannel<T>;
/**
* Minimum amount of time in ms to wait before attempting to reconnect.
* Defaults to 1,500 +/- 500 milliseconds.
*/
minReconnectionDelay?: number;
/**
* Maximum amount of time in ms to wait before attempting to reconnect.
* Defaults to 10,000 milliseconds.
*/
maxReconnectionDelay?: number;
/**
* Factor which is raised to the power of number of retry attempts and
* subsequently multiplied the `minReconnectionDelay` to get to current
* reconnection delay.
*/
reconnectionDelayGrowFactor?: number;
/**
* Minimum time the WebSocket should be open to reset retry counter.
* Defaults to 5,000 milliseconds.
*/
minUptime?: number;
}
/**
* Channel which automatically reconnects if disconnected. Once stopped via
* `.stop()`, the instance is fully disposed and cannot be restarted.
*/
export class PersistentChannel<T extends string | Uint8Array = string | Uint8Array> {
/**
* Whether the service is "active". The service becomes active when it is
* started using the ".start()" method. When service is "active" it will
* attempt to always keep an open channel connected.
*/
public readonly active$ = new BehaviorSubject(false);
/**
* Currently used channel, if any. When service is "active" it attempts to
* create and open a channel.
*/
public readonly channel$ = new BehaviorSubject<undefined | PhysicalChannel<T>>(undefined);
/**
* Whether the currently active channel (if any) is "open". An open channel
* is one where communication can happen, where a message can be sent to the
* other side.
*/
public readonly open$ = new BehaviorSubject<boolean>(false);
/** Emits incoming messages. */
public readonly message$ = this.channel$.pipe(
filter((channel) => !!channel),
switchMap((channel) => channel!.message$),
);
/** Emits errors from channel factory or underlying channels. */
public readonly error$ = new Subject<Error>();
/** Number of times we have attempted to reconnect. */
protected retries = 0;
private readonly subs: Subscription[] = [];
private readonly stop$ = new Subject<void>();
constructor(public readonly params: PersistentChannelParams<T>) {
const start$ = new Subject<void>();
this.subs.push(
this.active$
.pipe(
skip(1),
filter((active) => active),
)
.subscribe(() => {
start$.next(undefined);
}),
);
this.subs.push(
this.active$
.pipe(
skip(1),
filter((active) => !active),
)
.subscribe(() => {
this.stop$.next(undefined);
}),
);
// Create new channel when service starts.
this.subs.push(
start$.subscribe(() => {
this.createChannel();
}),
);
// Re-connect, when channel closes.
this.subs.push(
start$
.pipe(
switchMap(() => this.channel$),
filter((channel) => !!channel),
takeUntil(this.stop$),
switchMap((channel) => channel!.close$),
takeUntil(this.stop$),
switchMap(() =>
from(
(async () => {
const timeout = this.reconnectDelay();
this.retries++;
await new Promise((resolve) => setTimeout(resolve, timeout));
})(),
),
),
takeUntil(this.stop$),
tap(() => this.createChannel()),
delay(params.minUptime || 5_000),
takeUntil(this.stop$),
tap(() => {
const isOpen = this.channel$.getValue()?.isOpen();
if (isOpen) {
this.retries = 0;
}
}),
)
.subscribe(),
);
// Track if channel is connected.
this.subs.push(
start$
.pipe(
switchMap(() => this.channel$),
filter((channel) => !!channel),
switchMap((channel) => channel!.state$),
map((state) => state === ChannelState.OPEN),
)
.subscribe((open) => {
if (open !== this.open$.getValue()) this.open$.next(open);
}),
);
// Reset re-try counter when service stops.
this.subs.push(
this.stop$.subscribe(() => {
this.retries = 0;
}),
);
}
private createChannel(): void {
try {
this.channel$.next(this.params.newChannel());
} catch (error) {
this.error$.next(error instanceof Error ? error : new Error(String(error)));
}
}
public start(): void {
if (this.active$.getValue()) return;
this.active$.next(true);
}
public stop(): void {
if (!this.active$.getValue()) return;
this.active$.next(false);
const channel = this.channel$.getValue();
Eif (channel) {
channel.close();
this.channel$.next(undefined);
}
this.open$.next(false);
for (const sub of this.subs) sub.unsubscribe();
this.subs.length = 0;
this.stop$.complete();
this.error$.complete();
this.active$.complete();
this.channel$.complete();
this.open$.complete();
}
public reconnectDelay(): number {
if (this.retries <= 0) return 0;
const minReconnectionDelay = this.params.minReconnectionDelay || Math.round(1_000 + Math.random() * 1_000);
const maxReconnectionDelay = this.params.maxReconnectionDelay || 10_000;
const reconnectionDelayGrowFactor = this.params.reconnectionDelayGrowFactor || 1.3;
const delay = Math.min(
maxReconnectionDelay,
minReconnectionDelay * reconnectionDelayGrowFactor ** (this.retries - 1),
);
return delay;
}
public send$(data: T): Observable<number> {
return this.channel$.pipe(
filter((channel) => !!channel),
switchMap((channel) => channel!.open$),
filter((channel) => channel.isOpen()),
take(1),
map((channel) => {
const canSend = this.active$.getValue() && this.open$.getValue();
return canSend ? channel.send(data) : -1;
}),
);
}
}
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