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Fix special values resolved by nested promises #229

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5 changes: 5 additions & 0 deletions .changeset/small-promises-resolve.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'devalue': patch
---

Fix special values resolved by nested promises in `stringifyAsync`.
75 changes: 48 additions & 27 deletions src/stringify.js
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Original file line number Diff line number Diff line change
Expand Up @@ -35,30 +35,43 @@ export async function stringifyAsync(value, reducers, options) {
return stringified;
}

let out = '[';

for (let i = 0; i < stringified.length; i += 1) {
let value = stringified[i];

if (typeof value !== 'string') {
await value;
value = stringified[i];
if (typeof stringified[i] !== 'string') {
await stringified[i];
}
}

if (i === 0 && value < 0) {
return `${value}`;
}
/** @param {number} index */
function resolve_index(index) {
while (index >= 0 && typeof stringified[index] === 'number') {
index = stringified[index];
}
return index;
}

out += value;
const root = resolve_index(0);
if (root < 0) return `${root}`;

if (i < stringified.length - 1) {
out += ',';
// Resolved promises can alias a sentinel or an existing value. Omit those
// slots and remap references only after every promise has settled.
const indexes = new Map();
/** @type {string[]} */
const values = [];
for (let i = 0; i < stringified.length; i += 1) {
if (typeof stringified[i] === 'string') {
indexes.set(i, values.length);
values.push(stringified[i]);
}
}

out += ']';

return out;
return `[${values
.map((value) =>
value.replace(/\0(-?\d+)\0/g, (_, index) => {
const resolved = resolve_index(+index);
return String(resolved < 0 ? resolved : indexes.get(resolved));
})
)
.join(',')}]`;
}

/**
Expand Down Expand Up @@ -91,6 +104,14 @@ function run(async, value, reducers, options) {

let p = 0;

/** @param {any} thing */
function reference(thing) {
const index = flatten(thing);
// JSON strings escape NUL, so these internal tokens cannot collide with
// serialized string values or keys.
return async ? `\0${index}\0` : index;
}

/**
* @param {string} message
* @param {any} thing
Expand Down Expand Up @@ -140,7 +161,7 @@ function run(async, value, reducers, options) {
for (const { key, fn } of custom) {
const value = fn(thing);
if (value) {
stringified[index] = `["${key}",${flatten(value)}]`;
stringified[index] = `[${stringify_string(key)},${reference(value)}]`;
return index;
}
}
Expand Down Expand Up @@ -169,7 +190,7 @@ function run(async, value, reducers, options) {
keys = prev_keys;

const i = flatten(value, index);
if (i < 0) stringified[index] = i;
if (i !== index) stringified[index] = i;
});

// Promises are awaited sequentially, and traversal may throw before
Expand All @@ -184,7 +205,7 @@ function run(async, value, reducers, options) {
case 'String':
case 'Boolean':
case 'BigInt':
str = `["Object",${flatten(ops.unbox(thing))}]`;
str = `["Object",${reference(ops.unbox(thing))}]`;
break;

case 'Date':
Expand Down Expand Up @@ -225,7 +246,7 @@ function run(async, value, reducers, options) {

if (ops.hasOwn(thing, i)) {
keys.push(i);
str += flatten(ops.get(thing, i));
str += reference(ops.get(thing, i));
keys.pop();
} else if (mostly_dense) {
// Use dense encoding. The heuristic guarantees the
Expand Down Expand Up @@ -276,7 +297,7 @@ function run(async, value, reducers, options) {
for (let j = 0; j < populated_keys.length; j++) {
const key = populated_keys[j];
keys.push(+key);
str += ',' + key + ',' + flatten(ops.get(thing, key));
str += ',' + key + ',' + reference(ops.get(thing, key));
keys.pop();
}
break;
Expand All @@ -296,7 +317,7 @@ function run(async, value, reducers, options) {
str = '["Set"';

for (const value of ops.valuesOf(thing)) {
str += `,${flatten(value)}`;
str += `,${reference(value)}`;
}

str += ']';
Expand All @@ -307,7 +328,7 @@ function run(async, value, reducers, options) {

for (const [key, value] of ops.entriesOf(thing)) {
keys.push(MAP_KEY, key);
str += `,${flatten(key)},${flatten(value)}`;
str += `,${reference(key)},${reference(value)}`;
keys.pop();
keys.pop();
}
Expand All @@ -328,7 +349,7 @@ function run(async, value, reducers, options) {
case 'BigInt64Array':
case 'BigUint64Array': {
const info = ops.viewInfo(thing);
str = '["' + tag + '",' + flatten(info.buffer);
str = '["' + tag + '",' + reference(info.buffer);

// handle subarrays
if (info.byteLength !== info.bufferByteLength) {
Expand All @@ -341,7 +362,7 @@ function run(async, value, reducers, options) {

case 'DataView': {
const info = ops.viewInfo(thing);
str = '["' + tag + '",' + flatten(info.buffer);
str = '["' + tag + '",' + reference(info.buffer);

if (info.byteLength !== info.bufferByteLength) {
str += `,${info.byteOffset},${info.byteLength}`;
Expand Down Expand Up @@ -388,7 +409,7 @@ function run(async, value, reducers, options) {
}

keys.push(key);
str += `,${quote_key(key)},${flatten(ops.get(thing, key))}`;
str += `,${quote_key(key)},${reference(ops.get(thing, key))}`;
keys.pop();
}
str += ']';
Expand All @@ -403,7 +424,7 @@ function run(async, value, reducers, options) {
if (started) str += ',';
started = true;
keys.push(key);
str += `${quote_key(key)}:${flatten(ops.get(thing, key))}`;
str += `${quote_key(key)}:${reference(ops.get(thing, key))}`;
keys.pop();
}
str += '}';
Expand Down
119 changes: 118 additions & 1 deletion test/stringify-async.test.js
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Original file line number Diff line number Diff line change
@@ -1,5 +1,122 @@
import { execFileSync } from 'node:child_process';
import { describe, test } from 'vitest';
import { describe, expect, test } from 'vitest';
import { parse, stringify, stringifyAsync, unflatten } from '../src/index.js';

const special_values = [
{ name: 'undefined', value: undefined },
{ name: 'NaN', value: NaN },
{ name: 'negative zero', value: -0 },
{ name: 'positive infinity', value: Infinity },
{ name: 'negative infinity', value: -Infinity }
];

class Wrapped {
constructor(value) {
this.value = value;
}
}

describe.each([
{ name: 'objects', wrap: (value) => ({ value }) },
{ name: 'arrays', wrap: (value) => [value] },
{ name: 'Sets', wrap: (value) => new Set([value]) },
{ name: 'Map keys', wrap: (value) => new Map([[value, 'unchanged']]) },
{ name: 'Map values', wrap: (value) => new Map([['unchanged', value]]) },
{
name: 'null-prototype objects',
wrap: (value) => Object.assign(Object.create(null), { value })
},
{
name: 'sparse arrays',
wrap: (value) => {
const array = Array(1000);
array[999] = value;
return array;
}
},
{
name: 'custom reducer payloads',
wrap: (value) => new Wrapped(value),
reducers: { Wrapped: (value) => value instanceof Wrapped && [value.value] },
revivers: { Wrapped: ([value]) => new Wrapped(value) }
}
])('stringifyAsync: special values in $name', ({ wrap, reducers, revivers }) => {
test.each(special_values)('resolves $name', async ({ value }) => {
const expected = wrap(value);
const serialized = await stringifyAsync(wrap(Promise.resolve(value)), reducers);

expect(parse(serialized, revivers)).toEqual(expected);
expect(unflatten(JSON.parse(serialized), revivers)).toEqual(expected);
});
});

describe('stringifyAsync: resolved references', () => {
test.each(special_values)('resolves repeated promises of $name', async ({ value }) => {
const promise = Promise.resolve(value);
const serialized = await stringifyAsync({ value: promise, array: [promise, promise] });
const expected = { value, array: [value, value] };

expect(serialized).toEqual(stringify(expected));
expect(parse(serialized)).toEqual(expected);
});

test('resolves special values discovered inside a resolved promise', async () => {
const serialized = await stringifyAsync({
value: Promise.resolve({ nested: Promise.resolve(-Infinity) })
});
const expected = { value: { nested: -Infinity } };

expect(serialized).toEqual(stringify(expected));
expect(parse(serialized)).toEqual(expected);
});

test('preserves ordinary negative numbers and strings containing reference-like text', async () => {
const expected = {
'\u0000-1\u0000': '\u00001\u0000',
values: [-1, -3, -4, -5, -6],
value: undefined
};
const serialized = await stringifyAsync({ ...expected, value: Promise.resolve(undefined) });

expect(serialized).toEqual(stringify(expected));
expect(parse(serialized)).toEqual(expected);
});

test('deduplicates promises resolving to an existing value', async () => {
const value = { nested: true };
const serialized = await stringifyAsync([value, Promise.resolve(value)]);
const parsed = parse(serialized);

expect(serialized).toEqual(stringify([value, value]));
expect(parsed[0]).toBe(parsed[1]);
});

test('preserves typed-array offsets when resolved promises remove reference slots', async () => {
const buffer = new Uint8Array([0, 1, 2, 3]).buffer;
const view = new Uint8Array(buffer, 1, 2);
const expected = { value: undefined, view };
const serialized = await stringifyAsync({ value: Promise.resolve(undefined), view });
const parsed = parse(serialized);

expect(serialized).toEqual(stringify(expected));
expect(parsed).toEqual(expected);
expect(parsed.view.byteOffset).toBe(1);
expect(parsed.view.buffer.byteLength).toBe(4);
});

test('preserves custom reducer names containing quotes and reference-like text', async () => {
const key = 'Type"\u00001\u0000';
const reducers = { [key]: (value) => value instanceof Wrapped && [value.value] };
const revivers = { [key]: ([value]) => new Wrapped(value) };
const expected = new Wrapped(undefined);
const sync = stringify(expected, reducers);
const async = await stringifyAsync(new Wrapped(Promise.resolve(undefined)), reducers);

expect(async).toEqual(sync);
expect(parse(sync, revivers)).toEqual(expected);
expect(parse(async, revivers)).toEqual(expected);
});
});

describe('stringifyAsync: rejection handling', () => {
// Run each regression in isolation so an unhandled internal rejection fails the
Expand Down