@samitouri / QOS-React-1 / commits / f247ebaf44

[Flight] Walk parsed JSON instead of using reviver for parsing RSC payload (#35776)

## Summary Follow-up to https://github.com/vercel/next.js/pull/89823 with the actual changes to React. Replaces the `JSON.parse` reviver callback in `initializeModelChunk` with a two-step approach: plain `JSON.parse()` followed by a recursive `reviveModel()` post-process (same as in Flight Reply Server). This yields a **~75% speedup** in RSC chunk deserialization. | Payload | Original (ms) | Walk (ms) | Speedup | |---------|---------------|-----------|---------| | Small (2 elements, 142B) | 0.0024 | 0.0007 | **+72%** | | Medium (~12 elements, 914B) | 0.0116 | 0.0031 | **+73%** | | Large (~90 elements, 16.7KB) | 0.1836 | 0.0451 | **+75%** | | XL (~200 elements, 25.7KB) | 0.3742 | 0.0913 | **+76%** | | Table (1000 rows, 110KB) | 3.0862 | 0.6887 | **+78%** | ## Problem `createFromJSONCallback` returns a reviver function passed as the second argument to `JSON.parse()`. This reviver is called for **every key-value pair** in the parsed JSON. While the logic inside the reviver is lightweight, the dominant cost is the **C++ → JavaScript boundary crossing** — V8's `JSON.parse` is implemented in C++, and calling back into JavaScript for every node incurs significant overhead. Even a trivial no-op reviver `(k, v) => v` makes `JSON.parse` **~4x slower** than bare `JSON.parse` without a reviver: ``` 108 KB payload: Bare JSON.parse: 0.60 ms Trivial reviver: 2.95 ms (+391%) ``` ## Change Replace the reviver with a two-step process: 1. `JSON.parse(resolvedModel)` — parse the entire payload in C++ with no callbacks 2. `reviveModel` — recursively walk the resulting object in pure JavaScript to apply RSC transformations The `reviveModel` function includes additional optimizations over the original reviver: - **Short-circuits plain strings**: only calls `parseModelString` when the string starts with `$`, skipping the vast majority of strings (class names, text content, etc.) - **Stays entirely in JavaScript** — no C++ boundary crossings during the walk ## Results You can find the related applications in the [Next.js PR ](https://github.com/vercel/next.js/pull/89823)as I've been testing this on Next.js applications. ### Table as Server Component with 1000 items Before: ``` "min": 13.782875000000786, "max": 22.23400000000038, "avg": 17.116868530000083, "p50": 17.10766700000022, "p75": 18.50787499999933, "p95": 20.426249999998618, "p99": 21.814125000000786 ``` After: ``` "min": 10.963916999999128, "max": 18.096083000000363, "avg": 13.543286884999988, "p50": 13.58350000000064, "p75": 14.871791999999914, "p95": 16.08429099999921, "p99": 17.591458000000785 ``` ### Table as Client Component with 1000 items Before: ``` "min": 3.888875000000553, "max": 9.044959000000745, "avg": 4.651271475000067, "p50": 4.555749999999534, "p75": 4.966624999999112, "p95": 5.47754200000054, "p99": 6.109499999998661 ```` After: ``` "min": 3.5986250000005384, "max": 5.374291000000085, "avg": 4.142990245000046, "p50": 4.10570799999914, "p75": 4.392041999999492, "p95": 4.740084000000934, "p99": 5.1652500000000146 ``` ### Nested Suspense Before: ``` Requests: 200 Min: 73ms Max: 106ms Avg: 78ms P50: 77ms P75: 80ms P95: 85ms P99: 94ms ``` After: ``` Requests: 200 Min: 56ms Max: 67ms Avg: 59ms P50: 58ms P75: 60ms P95: 65ms P99: 66ms ``` ### Even more nested Suspense (double-level Suspense) Before: ``` Requests: 200 Min: 159ms Max: 208ms Avg: 169ms P50: 167ms P75: 173ms P95: 183ms P99: 188ms ``` After: ``` Requests: 200 Min: 125ms Max: 170ms Avg: 134ms P50: 132ms P75: 138ms P95: 148ms P99: 160ms ``` ## How did you test this change? Ran it across many Next.js benchmark applications. The entire Next.js test suite passes with this change. --------- Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>

Tim Neutkens committed Feb 19, 2026 at 17:37 UTC f247ebaf44317ac6648b62f99ceaed1e4fc4dc01

2 files changed +49 -19

packages/react-client/src/ReactFlightClient.js

+49 -16

@@ -355,7 +355,6 @@ type Response = {

355 _encodeFormAction: void | EncodeFormActionCallback,

356 _nonce: ?string,

357 _chunks: Map<number, SomeChunk<any>>,

358 - _fromJSON: (key: string, value: JSONValue) => any,

358 _stringDecoder: StringDecoder,

359 _closed: boolean,

360 _closedReason: mixed,

@@ -2302,6 +2301,11 @@ function defineLazyGetter<T>(

2301 // TODO: We should ideally throw here to indicate a difference.

2302 return OMITTED_PROP_ERROR;

2303 },

2304 + // no-op: the walk function may try to reassign this property after

2305 + // parseModelString returns. With the JSON.parse reviver, the engine's

2306 + // internal CreateDataProperty silently failed. We use a no-op setter

2307 + // to match that behavior in strict mode.

2308 + set: function () {},

2309 enumerable: true,

2310 configurable: false,

2311 });

@@ -2622,6 +2626,11 @@ function parseModelString(

2626 // TODO: We should ideally throw here to indicate a difference.

2627 return OMITTED_PROP_ERROR;

2628 },

2629 + // no-op: the walk function may try to reassign this property

2630 + // after parseModelString returns. With the JSON.parse reviver,

2631 + // the engine's internal CreateDataProperty silently failed.

2632 + // We use a no-op setter to match that behavior in strict mode.

2633 + set: function () {},

2634 enumerable: true,

2635 configurable: false,

2636 });

@@ -2699,7 +2708,6 @@ function ResponseInstance(

2708 this._nonce = nonce;

2709 this._chunks = chunks;

2710 this._stringDecoder = createStringDecoder();

2702 - this._fromJSON = (null: any);

2711 this._closed = false;

2712 this._closedReason = null;

2713 this._allowPartialStream = allowPartialStream;

@@ -2783,9 +2791,6 @@ function ResponseInstance(

2791 markAllTracksInOrder();

2792 }

2793 }

2786 -

2787 - // Don't inline this call because it causes closure to outline the call above.

2788 - this._fromJSON = createFromJSONCallback(this);

2794 }

2795

2796 export function createResponse(

@@ -5259,24 +5264,52 @@ export function processStringChunk(

5264 }

5265

5266 function parseModel<T>(response: Response, json: UninitializedModel): T {

5262 - return JSON.parse(json, response._fromJSON);

5267 + const rawModel = JSON.parse(json);

5268 + // Pass a wrapper object as parentObject to match the original JSON.parse

5269 + // reviver behavior, where the root value's reviver receives {"": rootValue}

5270 + // as `this`. This ensures parentObject is never null when accessed downstream.

5271 + return reviveModel(response, rawModel, {'': rawModel}, '');

5272 }

5273

5265 -function createFromJSONCallback(response: Response) {

5266 - // $FlowFixMe[missing-this-annot]

5267 - return function (key: string, value: JSONValue) {

5268 - if (key === __PROTO__) {

5269 - return undefined;

5274 +function reviveModel(

5275 + response: Response,

5276 + value: JSONValue,

5277 + parentObject: Object,

5278 + key: string,

5279 +): any {

5280 + if (typeof value === 'string') {

5281 + if (value[0] === '$') {

5282 + return parseModelString(response, parentObject, key, value);

5283 }

5271 - if (typeof value === 'string') {

5272 - // We can't use .bind here because we need the "this" value.

5273 - return parseModelString(response, this, key, value);

5284 + return value;

5285 + }

5286 + if (typeof value !== 'object' || value === null) {

5287 + return value;

5288 + }

5289 + if (isArray(value)) {

5290 + for (let i = 0; i < value.length; i++) {

5291 + (value: any)[i] = reviveModel(response, value[i], value, '' + i);

5292 }

5275 - if (typeof value === 'object' && value !== null) {

5293 + if (value[0] === REACT_ELEMENT_TYPE) {

5294 + // React element tuple

5295 return parseModelTuple(response, value);

5296 }

5297 return value;

5279 - };

5298 + }

5299 + // Plain object

5300 + for (const k in value) {

5301 + if (k === __PROTO__) {

5302 + delete (value: any)[k];

5303 + } else {

5304 + const walked = reviveModel(response, (value: any)[k], value, k);

5305 + if (walked !== undefined) {

5306 + (value: any)[k] = walked;

5307 + } else {

5308 + delete (value: any)[k];

5309 + }

5310 + }

5311 + }

5312 + return value;

5313 }

5314

5315 export function close(weakResponse: WeakResponse): void {

packages/react-noop-renderer/src/ReactNoopFlightClient.js

-3

@@ -43,9 +43,6 @@ const {createResponse, createStreamState, processBinaryChunk, getRoot, close} =

43 requireModule(idx: string) {

44 return readModule(idx);

45 },

46 - parseModel(response: Response, json) {

47 - return JSON.parse(json, response._fromJSON);

48 - },

46 bindToConsole(methodName, args, badgeName) {

47 return Function.prototype.bind.apply(

48 // eslint-disable-next-line react-internal/no-production-logging