336 lines
8.9 KiB
JavaScript
336 lines
8.9 KiB
JavaScript
import {
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DevalueError,
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enumerable_symbols,
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get_type,
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is_plain_object,
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is_primitive,
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stringify_key,
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stringify_string,
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valid_array_indices
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} from './utils.js';
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import {
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HOLE,
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NAN,
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NEGATIVE_INFINITY,
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NEGATIVE_ZERO,
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POSITIVE_INFINITY,
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SPARSE,
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UNDEFINED
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} from './constants.js';
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import { encode64 } from './base64.js';
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/**
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* Turn a value into a JSON string that can be parsed with `devalue.parse`
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* @param {any} value
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* @param {Record<string, (value: any) => any>} [reducers]
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*/
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export function stringify(value, reducers) {
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/** @type {any[]} */
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const stringified = [];
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/** @type {Map<any, number>} */
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const indexes = new Map();
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/** @type {Array<{ key: string, fn: (value: any) => any }>} */
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const custom = [];
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if (reducers) {
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for (const key of Object.getOwnPropertyNames(reducers)) {
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custom.push({ key, fn: reducers[key] });
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}
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}
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/** @type {string[]} */
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const keys = [];
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let p = 0;
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/** @param {any} thing */
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function flatten(thing) {
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if (thing === undefined) return UNDEFINED;
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if (Number.isNaN(thing)) return NAN;
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if (thing === Infinity) return POSITIVE_INFINITY;
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if (thing === -Infinity) return NEGATIVE_INFINITY;
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if (thing === 0 && 1 / thing < 0) return NEGATIVE_ZERO;
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if (indexes.has(thing)) return /** @type {number} */ (indexes.get(thing));
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const index = p++;
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indexes.set(thing, index);
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for (const { key, fn } of custom) {
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const value = fn(thing);
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if (value) {
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stringified[index] = `["${key}",${flatten(value)}]`;
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return index;
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}
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}
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if (typeof thing === 'function') {
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throw new DevalueError(`Cannot stringify a function`, keys, thing, value);
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} else if (typeof thing === 'symbol') {
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throw new DevalueError(`Cannot stringify a Symbol primitive`, keys, thing, value);
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}
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let str = '';
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if (is_primitive(thing)) {
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str = stringify_primitive(thing);
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} else {
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const type = get_type(thing);
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switch (type) {
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case 'Number':
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case 'String':
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case 'Boolean':
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case 'BigInt':
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str = `["Object",${flatten(thing.valueOf())}]`;
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break;
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case 'Date':
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const valid = !isNaN(thing.getDate());
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str = `["Date","${valid ? thing.toISOString() : ''}"]`;
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break;
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case 'URL':
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str = `["URL",${stringify_string(thing.toString())}]`;
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break;
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case 'URLSearchParams':
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str = `["URLSearchParams",${stringify_string(thing.toString())}]`;
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break;
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case 'RegExp':
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const { source, flags } = thing;
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str = flags
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? `["RegExp",${stringify_string(source)},"${flags}"]`
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: `["RegExp",${stringify_string(source)}]`;
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break;
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case 'Array': {
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// For dense arrays (no holes), we iterate normally.
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// When we encounter the first hole, we call Object.keys
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// to determine the sparseness, then decide between:
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// - HOLE encoding: [-2, val, -2, ...] (default)
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// - Sparse encoding: [-7, length, idx, val, ...] (for very sparse arrays)
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// Only the sparse path avoids iterating every slot, which
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// is what protects against the DoS of e.g. `arr[1000000] = 1`.
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let mostly_dense = false;
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str = '[';
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for (let i = 0; i < thing.length; i += 1) {
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if (i > 0) str += ',';
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if (Object.hasOwn(thing, i)) {
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keys.push(`[${i}]`);
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str += flatten(thing[i]);
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keys.pop();
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} else if (mostly_dense) {
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// Use dense encoding. The heuristic guarantees the
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// array is only mildly sparse, so iterating over every
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// slot is fine.
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str += HOLE;
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} else {
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// Decide between HOLE encoding and sparse encoding.
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//
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// HOLE encoding: each hole is serialized as the HOLE
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// sentinel (-2). For example, [, "a", ,] becomes
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// [-2, 0, -2]. Each hole costs 3 chars ("-2" + comma).
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//
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// Sparse encoding: lists only populated indices.
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// For example, [, "a", ,] becomes [-7, 3, 1, 0] — the
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// -7 sentinel, the array length (3), then index-value
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// pairs. This avoids paying per-hole, but each element
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// costs extra chars to write its index.
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//
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// The values are the same size either way, so the
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// choice comes down to structural overhead:
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//
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// HOLE overhead:
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// 3 chars per hole ("-2" + comma)
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// = (L - P) * 3
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//
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// Sparse overhead:
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// "-7," — 3 chars (sparse sentinel + comma)
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// + length + "," — (d + 1) chars (array length + comma)
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// + per element: index + "," — (d + 1) chars
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// = (4 + d) + P * (d + 1)
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//
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// where L is the array length, P is the number of
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// populated elements, and d is the number of digits
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// in L (an upper bound on the digits in any index).
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//
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// Sparse encoding is cheaper when:
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// (4 + d) + P * (d + 1) < (L - P) * 3
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const populated_keys = valid_array_indices(/** @type {any[]} */ (thing));
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const population = populated_keys.length;
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const d = String(thing.length).length;
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const hole_cost = (thing.length - population) * 3;
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const sparse_cost = 4 + d + population * (d + 1);
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if (hole_cost > sparse_cost) {
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str = '[' + SPARSE + ',' + thing.length;
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for (let j = 0; j < populated_keys.length; j++) {
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const key = populated_keys[j];
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keys.push(`[${key}]`);
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str += ',' + key + ',' + flatten(thing[key]);
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keys.pop();
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}
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break;
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} else {
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mostly_dense = true;
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str += HOLE;
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}
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}
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}
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str += ']';
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break;
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}
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case 'Set':
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str = '["Set"';
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for (const value of thing) {
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str += `,${flatten(value)}`;
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}
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str += ']';
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break;
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case 'Map':
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str = '["Map"';
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for (const [key, value] of thing) {
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keys.push(`.get(${is_primitive(key) ? stringify_primitive(key) : '...'})`);
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str += `,${flatten(key)},${flatten(value)}`;
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keys.pop();
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}
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str += ']';
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break;
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case 'Int8Array':
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case 'Uint8Array':
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case 'Uint8ClampedArray':
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case 'Int16Array':
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case 'Uint16Array':
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case 'Float16Array':
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case 'Int32Array':
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case 'Uint32Array':
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case 'Float32Array':
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case 'Float64Array':
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case 'BigInt64Array':
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case 'BigUint64Array':
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case 'DataView': {
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/** @type {import("./types.js").TypedArray} */
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const typedArray = thing;
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str = '["' + type + '",' + flatten(typedArray.buffer);
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// handle subarrays
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if (typedArray.byteLength !== typedArray.buffer.byteLength) {
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// to be used with `new TypedArray(buffer, byteOffset, length)`
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str += `,${typedArray.byteOffset},${typedArray.length}`;
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}
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str += ']';
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break;
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}
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case 'ArrayBuffer': {
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/** @type {ArrayBuffer} */
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const arraybuffer = thing;
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const base64 = encode64(arraybuffer);
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str = `["ArrayBuffer","${base64}"]`;
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break;
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}
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case 'Temporal.Duration':
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case 'Temporal.Instant':
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case 'Temporal.PlainDate':
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case 'Temporal.PlainTime':
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case 'Temporal.PlainDateTime':
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case 'Temporal.PlainMonthDay':
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case 'Temporal.PlainYearMonth':
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case 'Temporal.ZonedDateTime':
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str = `["${type}",${stringify_string(thing.toString())}]`;
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break;
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default:
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if (!is_plain_object(thing)) {
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throw new DevalueError(`Cannot stringify arbitrary non-POJOs`, keys, thing, value);
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}
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if (enumerable_symbols(thing).length > 0) {
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throw new DevalueError(`Cannot stringify POJOs with symbolic keys`, keys, thing, value);
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}
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if (Object.getPrototypeOf(thing) === null) {
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str = '["null"';
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for (const key of Object.keys(thing)) {
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if (key === '__proto__') {
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throw new DevalueError(
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`Cannot stringify objects with __proto__ keys`,
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keys,
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thing,
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value
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);
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}
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keys.push(stringify_key(key));
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str += `,${stringify_string(key)},${flatten(thing[key])}`;
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keys.pop();
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}
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str += ']';
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} else {
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str = '{';
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let started = false;
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for (const key of Object.keys(thing)) {
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if (key === '__proto__') {
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throw new DevalueError(
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`Cannot stringify objects with __proto__ keys`,
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keys,
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thing,
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value
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);
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}
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if (started) str += ',';
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started = true;
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keys.push(stringify_key(key));
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str += `${stringify_string(key)}:${flatten(thing[key])}`;
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keys.pop();
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}
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str += '}';
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}
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}
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}
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stringified[index] = str;
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return index;
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}
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const index = flatten(value);
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// special case — value is represented as a negative index
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if (index < 0) return `${index}`;
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return `[${stringified.join(',')}]`;
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}
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/**
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* @param {any} thing
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* @returns {string}
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*/
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function stringify_primitive(thing) {
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const type = typeof thing;
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if (type === 'string') return stringify_string(thing);
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if (thing === void 0) return UNDEFINED.toString();
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if (thing === 0 && 1 / thing < 0) return NEGATIVE_ZERO.toString();
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if (type === 'bigint') return `["BigInt","${thing}"]`;
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return String(thing);
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}
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