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on this file since 8d391a1 was 6a3a178, checked in by Ema <ema_spirova@…>, 3 years ago |
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1 | /*
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2 | MIT License http://www.opensource.org/licenses/mit-license.php
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3 | Author Tobias Koppers @sokra
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4 | */
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5 |
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6 | "use strict";
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7 |
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8 | const createHash = require("../util/createHash");
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9 |
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10 | /** @typedef {import("../util/Hash")} Hash */
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11 |
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12 | /**
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13 | * @typedef {Object} HashableObject
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14 | * @property {function(Hash): void} updateHash
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15 | */
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16 |
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17 | class LazyHashedEtag {
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18 | /**
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19 | * @param {HashableObject} obj object with updateHash method
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20 | */
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21 | constructor(obj) {
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22 | this._obj = obj;
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23 | this._hash = undefined;
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24 | }
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25 |
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26 | /**
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27 | * @returns {string} hash of object
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28 | */
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29 | toString() {
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30 | if (this._hash === undefined) {
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31 | const hash = createHash("md4");
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32 | this._obj.updateHash(hash);
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33 | this._hash = /** @type {string} */ (hash.digest("base64"));
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34 | }
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35 | return this._hash;
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36 | }
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37 | }
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38 |
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39 | /** @type {WeakMap<HashableObject, LazyHashedEtag>} */
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40 | const map = new WeakMap();
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41 |
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42 | /**
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43 | * @param {HashableObject} obj object with updateHash method
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44 | * @returns {LazyHashedEtag} etag
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45 | */
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46 | const getter = obj => {
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47 | const hash = map.get(obj);
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48 | if (hash !== undefined) return hash;
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49 | const newHash = new LazyHashedEtag(obj);
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50 | map.set(obj, newHash);
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51 | return newHash;
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52 | };
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53 |
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54 | module.exports = getter;
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