mirror of https://github.com/webpack/webpack.git
107 lines
3.0 KiB
JavaScript
107 lines
3.0 KiB
JavaScript
/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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/** @typedef {import("../util/Hash")} Hash */
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/**
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* StringXor class provides methods for performing
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* [XOR operations](https://en.wikipedia.org/wiki/Exclusive_or) on strings. In this context
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* we operating on the character codes of two strings, which are represented as
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* [Buffer](https://nodejs.org/api/buffer.html) objects.
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*
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* We use [StringXor in webpack](https://github.com/webpack/webpack/commit/41a8e2ea483a544c4ccd3e6217bdfb80daffca39)
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* to create a hash of the current state of the compilation. By XOR'ing the Module hashes, it
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* doesn't matter if the Module hashes are sorted or not. This is useful because it allows us to avoid sorting the
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* Module hashes.
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*
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* @example
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* ```js
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* const xor = new StringXor();
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* xor.add('hello');
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* xor.add('world');
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* console.log(xor.toString());
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* ```
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*
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* @example
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* ```js
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* const xor = new StringXor();
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* xor.add('foo');
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* xor.add('bar');
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* const hash = createHash('sha256');
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* hash.update(xor.toString());
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* console.log(hash.digest('hex'));
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* ```
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*/
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class StringXor {
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constructor() {
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/** @type {Buffer|undefined} */
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this._value = undefined;
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}
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/**
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* Adds a string to the current StringXor object.
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*
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* @param {string} str string
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* @returns {void}
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*/
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add(str) {
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const len = str.length;
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const value = this._value;
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if (value === undefined) {
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/**
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* We are choosing to use Buffer.allocUnsafe() because it is often faster than Buffer.alloc() because
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* it allocates a new buffer of the specified size without initializing the memory.
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*/
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const newValue = (this._value = Buffer.allocUnsafe(len));
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for (let i = 0; i < len; i++) {
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newValue[i] = str.charCodeAt(i);
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}
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return;
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}
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const valueLen = value.length;
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if (valueLen < len) {
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const newValue = (this._value = Buffer.allocUnsafe(len));
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let i;
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for (i = 0; i < valueLen; i++) {
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newValue[i] = value[i] ^ str.charCodeAt(i);
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}
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for (; i < len; i++) {
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newValue[i] = str.charCodeAt(i);
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}
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} else {
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for (let i = 0; i < len; i++) {
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value[i] = value[i] ^ str.charCodeAt(i);
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}
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}
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}
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/**
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* Returns a string that represents the current state of the StringXor object. We chose to use "latin1" encoding
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* here because "latin1" encoding is a single-byte encoding that can represent all characters in the
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* [ISO-8859-1 character set](https://en.wikipedia.org/wiki/ISO/IEC_8859-1). This is useful when working
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* with binary data that needs to be represented as a string.
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*
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* @returns {string} Returns a string that represents the current state of the StringXor object.
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*/
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toString() {
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const value = this._value;
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return value === undefined ? "" : value.toString("latin1");
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}
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/**
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* Updates the hash with the current state of the StringXor object.
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*
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* @param {Hash} hash Hash instance
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*/
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updateHash(hash) {
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const value = this._value;
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if (value !== undefined) hash.update(value);
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}
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}
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module.exports = StringXor;
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