Encode server rendered host components as array tuples (#18273)

This replaces the HTML renderer with instead resolving host elements into arrays tagged with the react.element symbol. These turn into proper React Elements on the client. The symbol is encoded as the magical value "$". This has security implications so this special value needs to remain escaped for other strings. We could just encode the element as {$$typeof: "$", key: key props: props} but that's a lot more bytes. So instead I encode it as: ["$", key, props] and then convert it back. It would be nicer if React's reconciler could just accept these tuples.
facebook · Mar 11, 2020 · dc7eeda · dc7eeda
1 parent bf35108
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diff --git a/fixtures/flight-browser/index.html b/fixtures/flight-browser/index.html
@@ -57,9 +57,7 @@ <h1>Flight Example</h1>
 
  let model = {
  title: <Title />,
- content: {
- __html: <HTML />,
- }
+ content: <HTML />,
  };
 
  let stream = ReactFlightDOMServer.renderToReadableStream(model);
@@ -90,7 +88,7 @@ <h1>Flight Example</h1>
  <Suspense fallback="...">
  <h1>{model.title}</h1>
  </Suspense>
- <div dangerouslySetInnerHTML={model.content} />
+ {model.content}
  </div>;
  }
 

diff --git a/fixtures/flight/server/handler.js b/fixtures/flight/server/handler.js
@@ -20,9 +20,7 @@ function HTML() {
 module.exports = function(req, res) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  let model = {
- content: {
- __html: <HTML />,
- },
+ content: <HTML />,
  };
  ReactFlightDOMServer.pipeToNodeWritable(model, res);
 };
diff --git a/fixtures/flight/src/App.js b/fixtures/flight/src/App.js
@@ -1,7 +1,7 @@
 import React, {Suspense} from 'react';
 
 function Content({data}) {
- return <p dangerouslySetInnerHTML={data.model.content} />;
+ return data.model.content;
 }
 
 function App({data}) {

diff --git a/packages/react-client/src/ReactFlightClient.js b/packages/react-client/src/ReactFlightClient.js
@@ -7,6 +7,8 @@
  * @flow
  */
 
+import {REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
+
 export type ReactModelRoot<T> = {|
  model: T,
 |};
@@ -19,6 +21,8 @@ export type JSONValue =
  | {[key: string]: JSONValue}
  | Array<JSONValue>;
 
+const isArray = Array.isArray;
+
 const PENDING = 0;
 const RESOLVED = 1;
 const ERRORED = 2;
@@ -141,28 +145,81 @@ function definePendingProperty(
  });
 }
 
+function createElement(type, key, props): React$Element<any> {
+ const element: any = {
+ // This tag allows us to uniquely identify this as a React Element
+ $$typeof: REACT_ELEMENT_TYPE,
+
+ // Built-in properties that belong on the element
+ type: type,
+ key: key,
+ ref: null,
+ props: props,
+
+ // Record the component responsible for creating this element.
+ _owner: null,
+ };
+ if (__DEV__) {
+ // We don't really need to add any of these but keeping them for good measure.
+ // Unfortunately, _store is enumerable in jest matchers so for equality to
+ // work, I need to keep it or make _store non-enumerable in the other file.
+ element._store = {};
+ Object.defineProperty(element._store, 'validated', {
+ configurable: false,
+ enumerable: false,
+ writable: true,
+ value: true, // This element has already been validated on the server.
+ });
+ Object.defineProperty(element, '_self', {
+ configurable: false,
+ enumerable: false,
+ writable: false,
+ value: null,
+ });
+ Object.defineProperty(element, '_source', {
+ configurable: false,
+ enumerable: false,
+ writable: false,
+ value: null,
+ });
+ }
+ return element;
+}
+
 export function parseModelFromJSON(
  response: Response,
  targetObj: Object,
  key: string,
  value: JSONValue,
-): any {
- if (typeof value === 'string' && value[0] === '$') {
- if (value[1] === '$') {
- // This was an escaped string value.
- return value.substring(1);
- } else {
- let id = parseInt(value.substring(1), 16);
- let chunks = response.chunks;
- let chunk = chunks.get(id);
- if (!chunk) {
- chunk = createPendingChunk();
- chunks.set(id, chunk);
- } else if (chunk.status === RESOLVED) {
- return chunk.value;
+): mixed {
+ if (typeof value === 'string') {
+ if (value[0] === '$') {
+ if (value === '$') {
+ return REACT_ELEMENT_TYPE;
+ } else if (value[1] === '$' || value[1] === '@') {
+ // This was an escaped string value.
+ return value.substring(1);
+ } else {
+ let id = parseInt(value.substring(1), 16);
+ let chunks = response.chunks;
+ let chunk = chunks.get(id);
+ if (!chunk) {
+ chunk = createPendingChunk();
+ chunks.set(id, chunk);
+ } else if (chunk.status === RESOLVED) {
+ return chunk.value;
+ }
+ definePendingProperty(targetObj, key, chunk);
+ return undefined;
  }
- definePendingProperty(targetObj, key, chunk);
- return undefined;
+ }
+ }
+ if (isArray(value)) {
+ let tuple: [mixed, mixed, mixed, mixed] = (value: any);
+ if (tuple[0] === REACT_ELEMENT_TYPE) {
+ // TODO: Consider having React just directly accept these arrays as elements.
+ // Or even change the ReactElement type to be an array.
+ return createElement(tuple[1], tuple[2], tuple[3]);
  }
  }
  return value;

diff --git a/packages/react-flight-dom-relay/src/ReactFlightDOMRelayClient.js b/packages/react-flight-dom-relay/src/ReactFlightDOMRelayClient.js
@@ -22,11 +22,11 @@ function parseModel(response, targetObj, key, value) {
  if (typeof value === 'object' && value !== null) {
  if (Array.isArray(value)) {
  for (let i = 0; i < value.length; i++) {
- value[i] = parseModel(response, value, '' + i, value[i]);
+ (value: any)[i] = parseModel(response, value, '' + i, value[i]);
  }
  } else {
  for (let innerKey in value) {
- value[innerKey] = parseModel(
+ (value: any)[innerKey] = parseModel(
  response,
  value,
  innerKey,

diff --git a/packages/react-flight-dom-webpack/src/__tests__/ReactFlightDOM-test.js b/packages/react-flight-dom-webpack/src/__tests__/ReactFlightDOM-test.js
@@ -92,7 +92,12 @@ describe('ReactFlightDOM', () => {
  let result = ReactFlightDOMClient.readFromReadableStream(readable);
  await waitForSuspense(() => {
  expect(result.model).toEqual({
- html: '<div><span>hello</span><span>world</span></div>',
+ html: (
+ <div>
+ <span>hello</span>
+ <span>world</span>
+ </div>
+ ),
  });
  });
  });
@@ -120,7 +125,7 @@ describe('ReactFlightDOM', () => {
 
  // View
  function Message({result}) {
- return <p dangerouslySetInnerHTML={{__html: result.model.html}} />;
+ return <section>{result.model.html}</section>;
  }
  function App({result}) {
  return (
@@ -140,7 +145,7 @@ describe('ReactFlightDOM', () => {
  root.render(<App result={result} />);
  });
  expect(container.innerHTML).toBe(
- '<p><div><span>hello</span><span>world</span></div></p>',
+ '<section><div><span>hello</span><span>world</span></div></section>',
  );
  });
 
@@ -176,6 +181,38 @@ describe('ReactFlightDOM', () => {
  expect(container.innerHTML).toBe('<p>$1</p>');
  });
 
+ it.experimental('should not get confused by @', async () => {
+ let {Suspense} = React;
+
+ // Model
+ function RootModel() {
+ return {text: '@div'};
+ }
+
+ // View
+ function Message({result}) {
+ return <p>{result.model.text}</p>;
+ }
+ function App({result}) {
+ return (
+ <Suspense fallback={<h1>Loading...</h1>}>
+ <Message result={result} />
+ </Suspense>
+ );
+ }
+
+ let {writable, readable} = getTestStream();
+ ReactFlightDOMServer.pipeToNodeWritable(<RootModel />, writable);
+ let result = ReactFlightDOMClient.readFromReadableStream(readable);
+
+ let container = document.createElement('div');
+ let root = ReactDOM.createRoot(container);
+ await act(async () => {
+ root.render(<App result={result} />);
+ });
+ expect(container.innerHTML).toBe('<p>@div</p>');
+ });
+
  it.experimental('should progressively reveal chunks', async () => {
  let {Suspense} = React;
 

diff --git a/packages/react-flight-dom-webpack/src/__tests__/ReactFlightDOMBrowser-test.js b/packages/react-flight-dom-webpack/src/__tests__/ReactFlightDOMBrowser-test.js
@@ -65,7 +65,12 @@ describe('ReactFlightDOMBrowser', () => {
  let result = ReactFlightDOMClient.readFromReadableStream(stream);
  await waitForSuspense(() => {
  expect(result.model).toEqual({
- html: '<div><span>hello</span><span>world</span></div>',
+ html: (
+ <div>
+ <span>hello</span>
+ <span>world</span>
+ </div>
+ ),
  });
  });
  });

diff --git a/packages/react-server/src/ReactDOMServerFormatConfig.js b/packages/react-server/src/ReactDOMServerFormatConfig.js
@@ -9,8 +9,6 @@
 
 import {convertStringToBuffer} from 'react-server/src/ReactServerStreamConfig';
 
-import {renderToStaticMarkup} from 'react-dom/server';
-
 export function formatChunkAsString(type: string, props: Object): string {
  let str = '<' + type + '>';
  if (typeof props.children === 'string') {
@@ -23,13 +21,3 @@ export function formatChunkAsString(type: string, props: Object): string {
 export function formatChunk(type: string, props: Object): Uint8Array {
  return convertStringToBuffer(formatChunkAsString(type, props));
 }
-
-export function renderHostChildrenToString(
- children: React$Element<any>,
-): string {
- // TODO: This file is used to actually implement a server renderer
- // so we can't actually reference the renderer here. Instead, we
- // should replace this method with a reference to Fizz which
- // then uses this file to implement the server renderer.
- return renderToStaticMarkup(children);
-}
diff --git a/packages/react-server/src/ReactFlightServer.js b/packages/react-server/src/ReactFlightServer.js
@@ -19,7 +19,7 @@ import {
  processModelChunk,
  processErrorChunk,
 } from './ReactFlightServerConfig';
-import {renderHostChildrenToString} from './ReactServerFormatConfig';
+
 import {REACT_ELEMENT_TYPE} from 'shared/ReactSymbols';
 
 type ReactJSONValue =
@@ -88,7 +88,7 @@ function attemptResolveModelComponent(element: React$Element<any>): ReactModel {
  return type(props);
  } else if (typeof type === 'string') {
  // This is a host element. E.g. HTML.
- return renderHostChildrenToString(element);
+ return [REACT_ELEMENT_TYPE, type, element.key, element.props];
  } else {
  throw new Error('Unsupported type.');
  }
@@ -119,7 +119,7 @@ function serializeIDRef(id: number): string {
 function escapeStringValue(value: string): string {
  if (value[0] === '$') {
  // We need to escape $ prefixed strings since we use that to encode
- // references to IDs.
+ // references to IDs and as a special symbol value.
  return '$' + value;
  } else {
  return value;
@@ -134,6 +134,10 @@ export function resolveModelToJSON(
  return escapeStringValue(value);
  }
 
+ if (value === REACT_ELEMENT_TYPE) {
+ return '$';
+ }
+
  while (
  typeof value === 'object' &&
  value !== null &&

diff --git a/packages/react-server/src/forks/ReactServerFormatConfig.custom.js b/packages/react-server/src/forks/ReactServerFormatConfig.custom.js
@@ -28,5 +28,3 @@ export opaque type Destination = mixed; // eslint-disable-line no-undef
 
 export const formatChunkAsString = $$$hostConfig.formatChunkAsString;
 export const formatChunk = $$$hostConfig.formatChunk;
-export const renderHostChildrenToString =
- $$$hostConfig.renderHostChildrenToString;