Add fetch Instrumentation to Dedupe Fetches (#25516)

* Add fetch instrumentation in cached contexts

* Avoid unhandled rejection errors for Promises that we intentionally ignore

In the final passes, we ignore the newly generated Promises and use
the previous ones. This ensures that if those generate errors, that we
intentionally ignore those.

* Add extra fetch properties if there were any

Author: sebmarkbage

package.json

@@ -77,6 +77,7 @@
     "minimist": "^1.2.3",
     "mkdirp": "^0.5.1",
     "ncp": "^2.0.0",
+    "@actuallyworks/node-fetch": "^2.6.0",
     "pacote": "^10.3.0",
     "prettier": "1.19.1",
     "prop-types": "^15.6.2",

packages/react-reconciler/src/ReactFiberHooks.new.js

@@ -770,6 +770,8 @@ if (enableUseMemoCacheHook) {
   };
 }
 
+function noop(): void {}
+
 function use<T>(usable: Usable<T>): T {
   if (usable !== null && typeof usable === 'object') {
     // $FlowFixMe[method-unbinding]
@@ -795,6 +797,11 @@ function use<T>(usable: Usable<T>): T {
             index,
           );
           if (prevThenableAtIndex !== null) {
+            if (thenable !== prevThenableAtIndex) {
+              // Avoid an unhandled rejection errors for the Promises that we'll
+              // intentionally ignore.
+              thenable.then(noop, noop);
+            }
             switch (prevThenableAtIndex.status) {
               case 'fulfilled': {
                 const fulfilledValue: T = prevThenableAtIndex.value;

packages/react-reconciler/src/ReactFiberHooks.old.js

@@ -770,6 +770,8 @@ if (enableUseMemoCacheHook) {
   };
 }
 
+function noop(): void {}
+
 function use<T>(usable: Usable<T>): T {
   if (usable !== null && typeof usable === 'object') {
     // $FlowFixMe[method-unbinding]
@@ -795,6 +797,11 @@ function use<T>(usable: Usable<T>): T {
             index,
           );
           if (prevThenableAtIndex !== null) {
+            if (thenable !== prevThenableAtIndex) {
+              // Avoid an unhandled rejection errors for the Promises that we'll
+              // intentionally ignore.
+              thenable.then(noop, noop);
+            }
             switch (prevThenableAtIndex.status) {
               case 'fulfilled': {
                 const fulfilledValue: T = prevThenableAtIndex.value;

packages/react-server/src/ReactFizzHooks.js

@@ -608,6 +608,11 @@ function use<T>(usable: Usable<T>): T {
             index,
           );
           if (prevThenableAtIndex !== null) {
+            if (thenable !== prevThenableAtIndex) {
+              // Avoid an unhandled rejection errors for the Promises that we'll
+              // intentionally ignore.
+              thenable.then(noop, noop);
+            }
             switch (prevThenableAtIndex.status) {
               case 'fulfilled': {
                 const fulfilledValue: T = prevThenableAtIndex.value;

packages/react-server/src/ReactFlightCache.js

@@ -9,9 +9,22 @@
 
 import type {CacheDispatcher} from 'react-reconciler/src/ReactInternalTypes';
 
+function createSignal(): AbortSignal {
+  return new AbortController().signal;
+}
+
 export const DefaultCacheDispatcher: CacheDispatcher = {
   getCacheSignal(): AbortSignal {
-    throw new Error('Not implemented.');
+    if (!currentCache) {
+      throw new Error('Reading the cache is only supported while rendering.');
+    }
+    let entry: AbortSignal | void = (currentCache.get(createSignal): any);
+    if (entry === undefined) {
+      entry = createSignal();
+      // $FlowFixMe[incompatible-use] found when upgrading Flow
+      currentCache.set(createSignal, entry);
+    }
+    return entry;
   },
   getCacheForType<T>(resourceType: () => T): T {
     if (!currentCache) {

packages/react-server/src/ReactFlightHooks.js

@@ -121,6 +121,8 @@ function useId(): string {
   return ':' + currentRequest.identifierPrefix + 'S' + id.toString(32) + ':';
 }
 
+function noop(): void {}
+
 function use<T>(usable: Usable<T>): T {
   if (usable !== null && typeof usable === 'object') {
     // $FlowFixMe[method-unbinding]
@@ -147,6 +149,11 @@ function use<T>(usable: Usable<T>): T {
             index,
           );
           if (prevThenableAtIndex !== null) {
+            if (thenable !== prevThenableAtIndex) {
+              // Avoid an unhandled rejection errors for the Promises that we'll
+              // intentionally ignore.
+              thenable.then(noop, noop);
+            }
             switch (prevThenableAtIndex.status) {
               case 'fulfilled': {
                 const fulfilledValue: T = prevThenableAtIndex.value;

packages/react/src/React.js

@@ -71,6 +71,9 @@ import ReactSharedInternals from './ReactSharedInternals';
 import {startTransition} from './ReactStartTransition';
 import {act} from './ReactAct';
 
+// Patch fetch
+import './ReactFetch';
+
 // TODO: Move this branching into the other module instead and just re-export.
 const createElement: any = __DEV__
   ? createElementWithValidation

packages/react/src/ReactFetch.js

@@ -0,0 +1,133 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+import {
+  enableCache,
+  enableFetchInstrumentation,
+} from 'shared/ReactFeatureFlags';
+
+import ReactCurrentCache from './ReactCurrentCache';
+
+function createFetchCache(): Map<string, Array<any>> {
+  return new Map();
+}
+
+const simpleCacheKey = '["GET",[],null,"follow",null,null,null,null]'; // generateCacheKey(new Request('https://blank'));
+
+function generateCacheKey(request: Request): string {
+  // We pick the fields that goes into the key used to dedupe requests.
+  // We don't include the `cache` field, because we end up using whatever
+  // caching resulted from the first request.
+  // Notably we currently don't consider non-standard (or future) options.
+  // This might not be safe. TODO: warn for non-standard extensions differing.
+  // IF YOU CHANGE THIS UPDATE THE simpleCacheKey ABOVE.
+  return JSON.stringify([
+    request.method,
+    Array.from(request.headers.entries()),
+    request.mode,
+    request.redirect,
+    request.credentials,
+    request.referrer,
+    request.referrerPolicy,
+    request.integrity,
+  ]);
+}
+
+if (enableCache && enableFetchInstrumentation) {
+  if (typeof fetch === 'function') {
+    const originalFetch = fetch;
+    try {
+      // eslint-disable-next-line no-native-reassign
+      fetch = function fetch(
+        resource: URL | RequestInfo,
+        options?: RequestOptions,
+      ) {
+        const dispatcher = ReactCurrentCache.current;
+        if (!dispatcher) {
+          // We're outside a cached scope.
+          return originalFetch(resource, options);
+        }
+        if (
+          options &&
+          options.signal &&
+          options.signal !== dispatcher.getCacheSignal()
+        ) {
+          // If we're passed a signal that is not ours, then we assume that
+          // someone else controls the lifetime of this object and opts out of
+          // caching. It's effectively the opt-out mechanism.
+          // Ideally we should be able to check this on the Request but
+          // it always gets initialized with its own signal so we don't
+          // know if it's supposed to override - unless we also override the
+          // Request constructor.
+          return originalFetch(resource, options);
+        }
+        // Normalize the Request
+        let url: string;
+        let cacheKey: string;
+        if (typeof resource === 'string' && !options) {
+          // Fast path.
+          cacheKey = simpleCacheKey;
+          url = resource;
+        } else {
+          // Normalize the request.
+          const request = new Request(resource, options);
+          if (
+            (request.method !== 'GET' && request.method !== 'HEAD') ||
+            // $FlowFixMe: keepalive is real
+            request.keepalive
+          ) {
+            // We currently don't dedupe requests that might have side-effects. Those
+            // have to be explicitly cached. We assume that the request doesn't have a
+            // body if it's GET or HEAD.
+            // keepalive gets treated the same as if you passed a custom cache signal.
+            return originalFetch(resource, options);
+          }
+          cacheKey = generateCacheKey(request);
+          url = request.url;
+        }
+        const cache = dispatcher.getCacheForType(createFetchCache);
+        const cacheEntries = cache.get(url);
+        let match;
+        if (cacheEntries === undefined) {
+          // We pass the original arguments here in case normalizing the Request
+          // doesn't include all the options in this environment.
+          match = originalFetch(resource, options);
+          cache.set(url, [cacheKey, match]);
+        } else {
+          // We use an array as the inner data structure since it's lighter and
+          // we typically only expect to see one or two entries here.
+          for (let i = 0, l = cacheEntries.length; i < l; i += 2) {
+            const key = cacheEntries[i];
+            const value = cacheEntries[i + 1];
+            if (key === cacheKey) {
+              match = value;
+              // I would've preferred a labelled break but lint says no.
+              return match.then(response => response.clone());
+            }
+          }
+          match = originalFetch(resource, options);
+          cacheEntries.push(cacheKey, match);
+        }
+        // We clone the response so that each time you call this you get a new read
+        // of the body so that it can be read multiple times.
+        return match.then(response => response.clone());
+      };
+      // We don't expect to see any extra properties on fetch but if there are any,
+      // copy them over. Useful for extended fetch environments or mocks.
+      Object.assign(fetch, originalFetch);
+    } catch (error) {
+      // Log even in production just to make sure this is seen if only prod is frozen.
+      // eslint-disable-next-line react-internal/no-production-logging
+      console.warn(
+        'React was unable to patch the fetch() function in this environment. ' +
+          'Suspensey APIs might not work correctly as a result.',
+      );
+    }
+  }
+}

packages/react/src/__tests__/ReactFetch-test.js

@@ -0,0 +1,144 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+// Polyfills for test environment
+global.ReadableStream = require('web-streams-polyfill/ponyfill/es6').ReadableStream;
+global.TextEncoder = require('util').TextEncoder;
+global.TextDecoder = require('util').TextDecoder;
+global.Headers = require('node-fetch').Headers;
+global.Request = require('node-fetch').Request;
+global.Response = require('node-fetch').Response;
+
+let fetchCount = 0;
+async function fetchMock(resource, options) {
+  fetchCount++;
+  const request = new Request(resource, options);
+  return new Response(
+    request.method +
+      ' ' +
+      request.url +
+      ' ' +
+      JSON.stringify(Array.from(request.headers.entries())),
+  );
+}
+
+let React;
+let ReactServerDOMServer;
+let ReactServerDOMClient;
+let use;
+
+describe('ReactFetch', () => {
+  beforeEach(() => {
+    jest.resetModules();
+    fetchCount = 0;
+    global.fetch = fetchMock;
+
+    React = require('react');
+    ReactServerDOMServer = require('react-server-dom-webpack/server.browser');
+    ReactServerDOMClient = require('react-server-dom-webpack/client');
+    use = React.experimental_use;
+  });
+
+  async function render(Component) {
+    const stream = ReactServerDOMServer.renderToReadableStream(<Component />);
+    return ReactServerDOMClient.createFromReadableStream(stream);
+  }
+
+  it('can fetch duplicates outside of render', async () => {
+    let response = await fetch('world');
+    let text = await response.text();
+    expect(text).toMatchInlineSnapshot(`"GET world []"`);
+    response = await fetch('world');
+    text = await response.text();
+    expect(text).toMatchInlineSnapshot(`"GET world []"`);
+    expect(fetchCount).toBe(2);
+  });
+
+  // @gate enableFetchInstrumentation && enableCache
+  it('can dedupe fetches inside of render', async () => {
+    function Component() {
+      const response = use(fetch('world'));
+      const text = use(response.text());
+      return text;
+    }
+    expect(await render(Component)).toMatchInlineSnapshot(`"GET world []"`);
+    expect(fetchCount).toBe(1);
+  });
+
+  // @gate enableFetchInstrumentation && enableCache
+  it('can dedupe fetches using Request and not', async () => {
+    function Component() {
+      const response = use(fetch('world'));
+      const text = use(response.text());
+      const sameRequest = new Request('world', {method: 'get'});
+      const response2 = use(fetch(sameRequest));
+      const text2 = use(response2.text());
+      return text + ' ' + text2;
+    }
+    expect(await render(Component)).toMatchInlineSnapshot(
+      `"GET world [] GET world []"`,
+    );
+    expect(fetchCount).toBe(1);
+  });
+
+  // @gate enableUseHook
+  it('can opt-out of deduping fetches inside of render with custom signal', async () => {
+    const controller = new AbortController();
+    function useCustomHook() {
+      return use(
+        fetch('world', {signal: controller.signal}).then(response =>
+          response.text(),
+        ),
+      );
+    }
+    function Component() {
+      return useCustomHook() + ' ' + useCustomHook();
+    }
+    expect(await render(Component)).toMatchInlineSnapshot(
+      `"GET world [] GET world []"`,
+    );
+    expect(fetchCount).not.toBe(1);
+  });
+
+  // @gate enableUseHook
+  it('opts out of deduping for POST requests', async () => {
+    function useCustomHook() {
+      return use(
+        fetch('world', {method: 'POST'}).then(response => response.text()),
+      );
+    }
+    function Component() {
+      return useCustomHook() + ' ' + useCustomHook();
+    }
+    expect(await render(Component)).toMatchInlineSnapshot(
+      `"POST world [] POST world []"`,
+    );
+    expect(fetchCount).not.toBe(1);
+  });
+
+  // @gate enableFetchInstrumentation && enableCache
+  it('can dedupe fetches using same headers but not different', async () => {
+    function Component() {
+      const response = use(fetch('world', {headers: {a: 'A'}}));
+      const text = use(response.text());
+      const sameRequest = new Request('world', {
+        headers: new Headers({b: 'B'}),
+      });
+      const response2 = use(fetch(sameRequest));
+      const text2 = use(response2.text());
+      return text + ' ' + text2;
+    }
+    expect(await render(Component)).toMatchInlineSnapshot(
+      `"GET world [[\\"a\\",\\"A\\"]] GET world [[\\"b\\",\\"B\\"]]"`,
+    );
+    expect(fetchCount).toBe(2);
+  });
+});