153 lines
3.4 KiB
JavaScript
153 lines
3.4 KiB
JavaScript
'use strict'
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const {
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wellknownHeaderNames,
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headerNameLowerCasedRecord
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} = require('./constants')
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class TstNode {
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/** @type {any} */
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value = null
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/** @type {null | TstNode} */
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left = null
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/** @type {null | TstNode} */
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middle = null
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/** @type {null | TstNode} */
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right = null
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/** @type {number} */
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code
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/**
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* @param {string} key
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* @param {any} value
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* @param {number} index
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*/
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constructor (key, value, index) {
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if (index === undefined || index >= key.length) {
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throw new TypeError('Unreachable')
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}
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const code = this.code = key.charCodeAt(index)
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// check code is ascii string
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if (code > 0x7F) {
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throw new TypeError('key must be ascii string')
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}
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if (key.length !== ++index) {
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this.middle = new TstNode(key, value, index)
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} else {
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this.value = value
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}
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}
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/**
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* @param {string} key
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* @param {any} value
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*/
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add (key, value) {
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const length = key.length
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if (length === 0) {
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throw new TypeError('Unreachable')
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}
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let index = 0
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let node = this
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while (true) {
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const code = key.charCodeAt(index)
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// check code is ascii string
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if (code > 0x7F) {
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throw new TypeError('key must be ascii string')
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}
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if (node.code === code) {
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if (length === ++index) {
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node.value = value
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break
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} else if (node.middle !== null) {
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node = node.middle
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} else {
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node.middle = new TstNode(key, value, index)
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break
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}
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} else if (node.code < code) {
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if (node.left !== null) {
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node = node.left
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} else {
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node.left = new TstNode(key, value, index)
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break
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}
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} else if (node.right !== null) {
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node = node.right
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} else {
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node.right = new TstNode(key, value, index)
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break
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}
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}
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}
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/**
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* @param {Uint8Array} key
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* @return {TstNode | null}
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*/
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search (key) {
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const keylength = key.length
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let index = 0
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let node = this
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while (node !== null && index < keylength) {
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let code = key[index]
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// A-Z
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// First check if it is bigger than 0x5a.
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// Lowercase letters have higher char codes than uppercase ones.
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// Also we assume that headers will mostly contain lowercase characters.
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if (code <= 0x5a && code >= 0x41) {
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// Lowercase for uppercase.
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code |= 32
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}
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while (node !== null) {
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if (code === node.code) {
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if (keylength === ++index) {
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// Returns Node since it is the last key.
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return node
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}
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node = node.middle
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break
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}
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node = node.code < code ? node.left : node.right
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}
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}
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return null
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}
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}
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class TernarySearchTree {
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/** @type {TstNode | null} */
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node = null
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/**
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* @param {string} key
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* @param {any} value
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* */
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insert (key, value) {
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if (this.node === null) {
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this.node = new TstNode(key, value, 0)
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} else {
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this.node.add(key, value)
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}
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}
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/**
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* @param {Uint8Array} key
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* @return {any}
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*/
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lookup (key) {
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return this.node?.search(key)?.value ?? null
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}
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}
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const tree = new TernarySearchTree()
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for (let i = 0; i < wellknownHeaderNames.length; ++i) {
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const key = headerNameLowerCasedRecord[wellknownHeaderNames[i]]
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tree.insert(key, key)
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}
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module.exports = {
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TernarySearchTree,
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tree
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}
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