97 lines
2.4 KiB
TypeScript
97 lines
2.4 KiB
TypeScript
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/**
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* Module dependencies
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*/
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import { LRUCache } from 'lru-cache'
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import { NumberAllocator } from 'number-allocator'
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/**
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* Topic Alias sending manager
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* This holds both topic to alias and alias to topic map
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* @param {Number} [max] - topic alias maximum entries
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*/
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export default class TopicAliasSend {
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private aliasToTopic: LRUCache<number, string>
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private topicToAlias: Record<string, number>
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private max: number
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private numberAllocator: NumberAllocator
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public length: number
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constructor(max: number) {
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if (max > 0) {
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this.aliasToTopic = new LRUCache<number, string>({ max })
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this.topicToAlias = {}
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this.numberAllocator = new NumberAllocator(1, max)
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this.max = max
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this.length = 0
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}
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}
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/**
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* Insert or update topic - alias entry.
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* @param {String} [topic] - topic
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* @param {Number} [alias] - topic alias
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* @returns {Boolean} - if success return true otherwise false
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*/
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put(topic: string, alias: number): boolean {
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if (alias === 0 || alias > this.max) {
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return false
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}
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const entry = this.aliasToTopic.get(alias)
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if (entry) {
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delete this.topicToAlias[entry]
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}
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this.aliasToTopic.set(alias, topic)
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this.topicToAlias[topic] = alias
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this.numberAllocator.use(alias)
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this.length = this.aliasToTopic.size
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return true
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}
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/**
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* Get topic by alias
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* @param {Number} [alias] - topic alias
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* @returns {String} - if mapped topic exists return topic, otherwise return undefined
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*/
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getTopicByAlias(alias: number): string {
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return this.aliasToTopic.get(alias)
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}
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/**
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* Get topic by alias
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* @param {String} [topic] - topic
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* @returns {Number} - if mapped topic exists return topic alias, otherwise return undefined
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*/
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getAliasByTopic(topic: string): number | undefined {
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const alias = this.topicToAlias[topic]
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if (typeof alias !== 'undefined') {
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this.aliasToTopic.get(alias) // LRU update
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}
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return alias
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}
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/**
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* Clear all entries
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*/
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clear() {
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this.aliasToTopic.clear()
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this.topicToAlias = {}
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this.numberAllocator.clear()
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this.length = 0
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}
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/**
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* Get Least Recently Used (LRU) topic alias
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* @returns {Number} - if vacant alias exists then return it, otherwise then return LRU alias
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*/
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getLruAlias(): number {
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const alias = this.numberAllocator.firstVacant()
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if (alias) return alias
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// get last alias (key) from LRU cache
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return [...this.aliasToTopic.keys()][this.aliasToTopic.size - 1]
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}
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}
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