source: imaps-frontend/node_modules/webpack/lib/util/StringXor.js@ 79a0317

/*
        MIT License http://www.opensource.org/licenses/mit-license.php
        Author Tobias Koppers @sokra
*/

"use strict";

/** @typedef {import("../util/Hash")} Hash */

/**
 * StringXor class provides methods for performing
 * [XOR operations](https://en.wikipedia.org/wiki/Exclusive_or) on strings. In this context
 * we operating on the character codes of two strings, which are represented as
 * [Buffer](https://nodejs.org/api/buffer.html) objects.
 *
 * We use [StringXor in webpack](https://github.com/webpack/webpack/commit/41a8e2ea483a544c4ccd3e6217bdfb80daffca39)
 * to create a hash of the current state of the compilation. By XOR'ing the Module hashes, it
 * doesn't matter if the Module hashes are sorted or not. This is useful because it allows us to avoid sorting the
 * Module hashes.
 * @example
 * ```js
 * const xor = new StringXor();
 * xor.add('hello');
 * xor.add('world');
 * console.log(xor.toString());
 * ```
 * @example
 * ```js
 * const xor = new StringXor();
 * xor.add('foo');
 * xor.add('bar');
 * const hash = createHash('sha256');
 * hash.update(xor.toString());
 * console.log(hash.digest('hex'));
 * ```
 */
class StringXor {
        constructor() {
                /** @type {Buffer|undefined} */
                this._value = undefined;
        }

        /**
         * Adds a string to the current StringXor object.
         * @param {string} str string
         * @returns {void}
         */
        add(str) {
                const len = str.length;
                const value = this._value;
                if (value === undefined) {
                        /**
                         * We are choosing to use Buffer.allocUnsafe() because it is often faster than Buffer.alloc() because
                         * it allocates a new buffer of the specified size without initializing the memory.
                         */
                        const newValue = (this._value = Buffer.allocUnsafe(len));
                        for (let i = 0; i < len; i++) {
                                newValue[i] = str.charCodeAt(i);
                        }
                        return;
                }
                const valueLen = value.length;
                if (valueLen < len) {
                        const newValue = (this._value = Buffer.allocUnsafe(len));
                        let i;
                        for (i = 0; i < valueLen; i++) {
                                newValue[i] = value[i] ^ str.charCodeAt(i);
                        }
                        for (; i < len; i++) {
                                newValue[i] = str.charCodeAt(i);
                        }
                } else {
                        for (let i = 0; i < len; i++) {
                                value[i] = value[i] ^ str.charCodeAt(i);
                        }
                }
        }

        /**
         * Returns a string that represents the current state of the StringXor object. We chose to use "latin1" encoding
         * here because "latin1" encoding is a single-byte encoding that can represent all characters in the
         * [ISO-8859-1 character set](https://en.wikipedia.org/wiki/ISO/IEC_8859-1). This is useful when working
         * with binary data that needs to be represented as a string.
         * @returns {string} Returns a string that represents the current state of the StringXor object.
         */
        toString() {
                const value = this._value;
                return value === undefined ? "" : value.toString("latin1");
        }

        /**
         * Updates the hash with the current state of the StringXor object.
         * @param {Hash} hash Hash instance
         */
        updateHash(hash) {
                const value = this._value;
                if (value !== undefined) hash.update(value);
        }
}

module.exports = StringXor;