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fix: round-trip special values from nested stringifyAsync promises #214

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fix: round-trip special values from nested stringifyAsync promises #214

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5 changes: 5 additions & 0 deletions .changeset/nested-stringify-async-sentinels.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'devalue': patch
---

fix: round-trip special values from nested stringifyAsync promises
167 changes: 136 additions & 31 deletions src/stringify.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,43 +29,50 @@ export function stringify(value, reducers, options) {
* @param {import('./types.js').StringifyOptions} [options]
*/
export async function stringifyAsync(value, reducers, options) {
const stringified = run(true, value, reducers, options);
const result = run(true, value, reducers, options);

if (typeof stringified === 'string') {
return stringified;
if (typeof result === 'string') {
return result;
}

let out = '[';
const { stringified, spans } = result;

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

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

if (i === 0 && value < 0) {
return `${value}`;
}
}

out += value;

if (i < stringified.length - 1) {
out += ',';
const slot = stringified[i];
if (slot && typeof slot.then === 'function') {
await slot;
}
}

out += ']';
if (typeof stringified[0] === 'number' && stringified[0] < 0) {
return `${stringified[0]}`;
}

return out;
return `[${materialize(stringified, spans).join(',')}]`;
}

/**
* @overload
* @param {false} async
* @param {any} value
* @param {Record<string, (value: any) => any>} [reducers]
* @param {import('./types.js').StringifyOptions} [options]
* @returns {string | any[]}
*/
/**
* @overload
* @param {true} async
* @param {any} value
* @param {Record<string, (value: any) => any>} [reducers]
* @param {import('./types.js').StringifyOptions} [options]
* @returns {string | { stringified: any[], spans: Array<Array<{ start: number, length: number, target: number }> | undefined> }}
*/
/**
* @param {boolean} async
* @param {any} value
* @param {Record<string, (value: any) => any>} [reducers]
* @param {import('./types.js').StringifyOptions} [options]
* @returns {string | any[] | { stringified: any[], spans: Array<Array<{ start: number, length: number, target: number }> | undefined> }}
*/
function run(async, value, reducers, options) {
const ops = merge_operations(default_stringify_operations, options?.operations);
Expand All @@ -91,6 +98,28 @@ function run(async, value, reducers, options) {

let p = 0;

/** @type {Array<Array<{ start: number, length: number, target: number }> | undefined>} */
const spans = [];

/**
* @param {number} parent
* @param {string} str
* @param {number} ref
*/
function embed(parent, str, ref) {
const token = String(ref);

if (async && ref >= 0) {
(spans[parent] ??= []).push({
start: str.length,
length: token.length,
target: ref
});
}

return str + token;
}

/**
* @param {string} message
* @param {any} thing
Expand Down Expand Up @@ -140,7 +169,9 @@ function run(async, value, reducers, options) {
for (const { key, fn } of custom) {
const value = fn(thing);
if (value) {
stringified[index] = `["${key}",${flatten(value)}]`;
let encoded = `["${key}",`;
encoded = embed(index, encoded, flatten(value));
stringified[index] = encoded + ']';
return index;
}
}
Expand Down Expand Up @@ -184,7 +215,9 @@ function run(async, value, reducers, options) {
case 'String':
case 'Boolean':
case 'BigInt':
str = `["Object",${flatten(ops.unbox(thing))}]`;
str = '["Object",';
str = embed(index, str, flatten(ops.unbox(thing)));
str += ']';
break;

case 'Date':
Expand Down Expand Up @@ -225,7 +258,7 @@ function run(async, value, reducers, options) {

if (ops.hasOwn(thing, i)) {
keys.push(i);
str += flatten(ops.get(thing, i));
str = embed(index, str, flatten(ops.get(thing, i)));
keys.pop();
} else if (mostly_dense) {
// Use dense encoding. The heuristic guarantees the
Expand Down Expand Up @@ -272,11 +305,13 @@ function run(async, value, reducers, options) {
const sparse_cost = 4 + d + population * (d + 1);

if (hole_cost > sparse_cost) {
spans[index] = undefined;
str = '[' + SPARSE + ',' + length;
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 + ',';
str = embed(index, str, flatten(ops.get(thing, key)));
keys.pop();
}
break;
Expand All @@ -296,7 +331,8 @@ function run(async, value, reducers, options) {
str = '["Set"';

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

str += ']';
Expand All @@ -307,7 +343,10 @@ 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 += ',';
str = embed(index, str, flatten(key));
str += ',';
str = embed(index, str, flatten(value));
keys.pop();
keys.pop();
}
Expand All @@ -328,7 +367,8 @@ function run(async, value, reducers, options) {
case 'BigInt64Array':
case 'BigUint64Array': {
const info = ops.viewInfo(thing);
str = '["' + tag + '",' + flatten(info.buffer);
str = '["' + tag + '",';
str = embed(index, str, flatten(info.buffer));

// handle subarrays
if (info.byteLength !== info.bufferByteLength) {
Expand All @@ -341,7 +381,8 @@ function run(async, value, reducers, options) {

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

if (info.byteLength !== info.bufferByteLength) {
str += `,${info.byteOffset},${info.byteLength}`;
Expand Down Expand Up @@ -388,7 +429,8 @@ function run(async, value, reducers, options) {
}

keys.push(key);
str += `,${quote_key(key)},${flatten(ops.get(thing, key))}`;
str += `,${quote_key(key)},`;
str = embed(index, str, flatten(ops.get(thing, key)));
keys.pop();
}
str += ']';
Expand All @@ -403,7 +445,8 @@ function run(async, value, reducers, options) {
if (started) str += ',';
started = true;
keys.push(key);
str += `${quote_key(key)}:${flatten(ops.get(thing, key))}`;
str += `${quote_key(key)}:`;
str = embed(index, str, flatten(ops.get(thing, key)));
keys.pop();
}
str += '}';
Expand All @@ -421,9 +464,71 @@ function run(async, value, reducers, options) {
// special case — value is represented as a negative index
if (index < 0) return `${index}`;

if (async) return { stringified, spans };

return stringified;
}

/**
* @param {any[]} stringified
* @param {Array<Array<{ start: number, length: number, target: number }> | undefined>} spans
*/
function materialize(stringified, spans) {
/** @type {Map<number, number>} */
const sentinel_of = new Map();

/** @type {number[]} */
const kept = [];

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

if (typeof slot === 'number' && slot < 0) {
sentinel_of.set(i, slot);
} else {
kept.push(i);
}
}

if (sentinel_of.size === 0) {
return stringified;
}

/** @type {Map<number, number>} */
const remap = new Map();

for (let i = 0; i < kept.length; i += 1) {
remap.set(kept[i], i);
}

return kept.map((old) => {
const slot = stringified[old];
const slot_spans = spans[old];

if (typeof slot !== 'string' || !slot_spans || slot_spans.length === 0) {
return slot;
}

let out = '';
let cursor = 0;

for (const span of slot_spans) {
out += slot.slice(cursor, span.start);

if (sentinel_of.has(span.target)) {
out += String(sentinel_of.get(span.target));
} else {
out += String(remap.get(span.target));
}

cursor = span.start + span.length;
}

out += slot.slice(cursor);
return out;
});
}

/**
* @param {any} thing
* @returns {string}
Expand Down
32 changes: 32 additions & 0 deletions test/index.test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2555,6 +2555,38 @@ describe('stringifyAsync: promises', () => {
expect(result).toEqual(stringify(NaN));
});

test('round-trips special values from nested promises', async () => {
const plain = { a: undefined, b: [NaN, -0, Infinity, -Infinity], c: 1 };
const promised = {
a: Promise.resolve(undefined),
b: [
Promise.resolve(NaN),
Promise.resolve(-0),
Promise.resolve(Infinity),
Promise.resolve(-Infinity)
],
c: Promise.resolve(1)
};

const result = await stringifyAsync(promised);

expect(result).toEqual(stringify(plain));

const parsed = parse(result);
expect(parsed.a).toBeUndefined();
expect(Number.isNaN(parsed.b[0])).toBeTruthy();
expect(Object.is(parsed.b[1], -0)).toBeTruthy();
expect(parsed.b[2]).toBe(Infinity);
expect(parsed.b[3]).toBe(-Infinity);
expect(parsed.c).toBe(1);

const nested = await stringifyAsync({
a: Promise.resolve({ b: Promise.resolve(undefined) })
});
expect(nested).toEqual(stringify({ a: { b: undefined } }));
expect(parse(nested).a.b).toBeUndefined();
});

test('resolves nested promises in objects', async () => {
const result = await stringifyAsync({
a: Promise.resolve(1),
Expand Down