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Merge pull request davidyaha#65 from AlexLeung/master
Implemented Generic AsyncIterator
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,111 @@ | ||
| import { $$asyncIterator } from 'iterall'; | ||
| import {PubSubEngine} from 'graphql-subscriptions/dist/pubsub-engine'; | ||
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| /** | ||
| * A class for digesting PubSubEngine events via the new AsyncIterator interface. | ||
| * This implementation is a generic version of the one located at | ||
| * https://github.com/apollographql/graphql-subscriptions/blob/master/src/event-emitter-to-async-iterator.ts | ||
| * @class | ||
| * | ||
| * @constructor | ||
| * | ||
| * @property pullQueue @type {Function[]} | ||
| * A queue of resolve functions waiting for an incoming event which has not yet arrived. | ||
| * This queue expands as next() calls are made without PubSubEngine events occurring in between. | ||
| * | ||
| * @property pushQueue @type {any[]} | ||
| * A queue of PubSubEngine events waiting for next() calls to be made. | ||
| * This queue expands as PubSubEngine events arrice without next() calls occurring in between. | ||
| * | ||
| * @property eventsArray @type {string[]} | ||
| * An array of PubSubEngine event names which this PubSubAsyncIterator should watch. | ||
| * | ||
| * @property allSubscribed @type {Promise<number[]>} | ||
| * A promise of a list of all subscription ids to the passed PubSubEngine. | ||
| * | ||
| * @property listening @type {boolean} | ||
| * Whether or not the PubSubAsynIterator is in listening mode (responding to incoming PubSubEngine events and next() calls). | ||
| * Listening begins as true and turns to false once the return method is called. | ||
| * | ||
| * @property pubsub @type {PubSubEngine} | ||
| * The PubSubEngine whose events will be observed. | ||
| */ | ||
| export class PubSubAsyncIterator<T> implements AsyncIterator<T> { | ||
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| constructor(pubsub: PubSubEngine, eventNames: string | string[]) { | ||
| this.pubsub = pubsub; | ||
| this.pullQueue = []; | ||
| this.pushQueue = []; | ||
| this.listening = true; | ||
| this.eventsArray = typeof eventNames === 'string' ? [eventNames] : eventNames; | ||
| this.allSubscribed = this.subscribeAll(); | ||
| } | ||
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| public async next() { | ||
| await this.allSubscribed; | ||
| return this.listening ? this.pullValue() : this.return(); | ||
| } | ||
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| public async return() { | ||
| this.emptyQueue(await this.allSubscribed); | ||
| return { value: undefined, done: true }; | ||
| } | ||
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| public async throw(error) { | ||
| this.emptyQueue(await this.allSubscribed); | ||
| return Promise.reject(error); | ||
| } | ||
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| public [$$asyncIterator]() { | ||
| return this; | ||
| } | ||
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| private pullQueue: Function[]; | ||
| private pushQueue: any[]; | ||
| private eventsArray: string[]; | ||
| private allSubscribed: Promise<number[]>; | ||
| private listening: boolean; | ||
| private pubsub: PubSubEngine; | ||
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| private async pushValue(event) { | ||
| await this.allSubscribed; | ||
| if (this.pullQueue.length !== 0) { | ||
| this.pullQueue.shift()({ value: event, done: false }); | ||
| } else { | ||
| this.pushQueue.push(event); | ||
| } | ||
| } | ||
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| private pullValue() { | ||
| return new Promise((resolve => { | ||
| if (this.pushQueue.length !== 0) { | ||
| resolve({ value: this.pushQueue.shift(), done: false }); | ||
| } else { | ||
| this.pullQueue.push(resolve); | ||
| } | ||
| }).bind(this)); | ||
| } | ||
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| private emptyQueue(subscriptionIds: number[]) { | ||
| if (this.listening) { | ||
| this.listening = false; | ||
| this.unsubscribeAll(subscriptionIds); | ||
| this.pullQueue.forEach(resolve => resolve({ value: undefined, done: true })); | ||
| this.pullQueue.length = 0; | ||
| this.pushQueue.length = 0; | ||
| } | ||
| } | ||
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| private subscribeAll() { | ||
| return Promise.all(this.eventsArray.map( | ||
| eventName => this.pubsub.subscribe(eventName, this.pushValue.bind(this), {}), | ||
| )); | ||
| } | ||
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| private unsubscribeAll(subscriptionIds: number[]) { | ||
| for (const subscriptionId of subscriptionIds) { | ||
| this.pubsub.unsubscribe(subscriptionId); | ||
| } | ||
| } | ||
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|
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| } |
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