Fix potential subscription leakage in SSR environments

packages/toolkit/src/query/core/buildInitiate.ts

@@ -22,7 +22,7 @@ import {
   type QueryDefinition,
   type ResultTypeFrom,
 } from '../endpointDefinitions'
-import { countObjectKeys, getOrInsert, isNotNullish } from '../utils'
+import { filterNullishValues } from '../utils'
 import type {
   InfiniteData,
   InfiniteQueryConfigOptions,
@@ -271,17 +271,20 @@ export function buildInitiate({
   mutationThunk,
   api,
   context,
-  internalState,
+  getInternalState,
 }: {
   serializeQueryArgs: InternalSerializeQueryArgs
   queryThunk: QueryThunk
   infiniteQueryThunk: InfiniteQueryThunk<any>
   mutationThunk: MutationThunk
   api: Api<any, EndpointDefinitions, any, any>
   context: ApiContext<EndpointDefinitions>
-  internalState: InternalMiddlewareState
+  getInternalState: (dispatch: Dispatch) => InternalMiddlewareState
 }) {
-  const { runningQueries, runningMutations } = internalState
+  const getRunningQueries = (dispatch: Dispatch) =>
+    getInternalState(dispatch)?.runningQueries
+  const getRunningMutations = (dispatch: Dispatch) =>
+    getInternalState(dispatch)?.runningMutations
 
   const {
     unsubscribeQueryResult,
@@ -306,7 +309,7 @@ export function buildInitiate({
         endpointDefinition,
         endpointName,
       })
-      return runningQueries.get(dispatch)?.[queryCacheKey] as
+      return getRunningQueries(dispatch)?.get(queryCacheKey) as
         | QueryActionCreatorResult<never>
         | InfiniteQueryActionCreatorResult<never>
         | undefined
@@ -322,20 +325,20 @@ export function buildInitiate({
     fixedCacheKeyOrRequestId: string,
   ) {
     return (dispatch: Dispatch) => {
-      return runningMutations.get(dispatch)?.[fixedCacheKeyOrRequestId] as
+      return getRunningMutations(dispatch)?.get(fixedCacheKeyOrRequestId) as
         | MutationActionCreatorResult<never>
         | undefined
     }
   }
 
   function getRunningQueriesThunk() {
     return (dispatch: Dispatch) =>
-      Object.values(runningQueries.get(dispatch) || {}).filter(isNotNullish)
+      filterNullishValues(getRunningQueries(dispatch))
   }
 
   function getRunningMutationsThunk() {
     return (dispatch: Dispatch) =>
-      Object.values(runningMutations.get(dispatch) || {}).filter(isNotNullish)
+      filterNullishValues(getRunningMutations(dispatch))
   }
 
   function middlewareWarning(dispatch: Dispatch) {
@@ -429,7 +432,7 @@ You must add the middleware for RTK-Query to function correctly!`,
 
         const skippedSynchronously = stateAfter.requestId !== requestId
 
-        const runningQuery = runningQueries.get(dispatch)?.[queryCacheKey]
+        const runningQuery = getRunningQueries(dispatch)?.get(queryCacheKey)
         const selectFromState = () => selector(getState())
 
         const statePromise: AnyActionCreatorResult = Object.assign(
@@ -489,14 +492,11 @@ You must add the middleware for RTK-Query to function correctly!`,
         )
 
         if (!runningQuery && !skippedSynchronously && !forceQueryFn) {
-          const running = getOrInsert(runningQueries, dispatch, {})
-          running[queryCacheKey] = statePromise
+          const runningQueries = getRunningQueries(dispatch)!
+          runningQueries.set(queryCacheKey, statePromise)
 
           statePromise.then(() => {
-            delete running[queryCacheKey]
-            if (!countObjectKeys(running)) {
-              runningQueries.delete(dispatch)
-            }
+            runningQueries.delete(queryCacheKey)
           })
         }
 
@@ -559,23 +559,17 @@ You must add the middleware for RTK-Query to function correctly!`,
           reset,
         })
 
-        const running = runningMutations.get(dispatch) || {}
-        runningMutations.set(dispatch, running)
-        running[requestId] = ret
+        const runningMutations = getRunningMutations(dispatch)!
+
+        runningMutations.set(requestId, ret)
         ret.then(() => {
-          delete running[requestId]
-          if (!countObjectKeys(running)) {
-            runningMutations.delete(dispatch)
-          }
+          runningMutations.delete(requestId)
         })
         if (fixedCacheKey) {
-          running[fixedCacheKey] = ret
+          runningMutations.set(fixedCacheKey, ret)
           ret.then(() => {
-            if (running[fixedCacheKey] === ret) {
-              delete running[fixedCacheKey]
-              if (!countObjectKeys(running)) {
-                runningMutations.delete(dispatch)
-              }
+            if (runningMutations.get(fixedCacheKey) === ret) {
+              runningMutations.delete(fixedCacheKey)
             }
           })
         }

packages/toolkit/src/query/core/buildMiddleware/cacheCollection.ts

@@ -13,27 +13,27 @@ export type ReferenceCacheCollection = never
 
 /**
  * @example
-   * ```ts
-   * // codeblock-meta title="keepUnusedDataFor example"
-   * import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
-   * interface Post {
-   *   id: number
-   *   name: string
-   * }
-   * type PostsResponse = Post[]
-   *
-   * const api = createApi({
-   *   baseQuery: fetchBaseQuery({ baseUrl: '/' }),
-   *   endpoints: (build) => ({
-   *     getPosts: build.query<PostsResponse, void>({
-   *       query: () => 'posts',
-   *       // highlight-start
-   *       keepUnusedDataFor: 5
-   *       // highlight-end
-   *     })
-   *   })
-   * })
-   * ```
+ * ```ts
+ * // codeblock-meta title="keepUnusedDataFor example"
+ * import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query/react'
+ * interface Post {
+ *   id: number
+ *   name: string
+ * }
+ * type PostsResponse = Post[]
+ *
+ * const api = createApi({
+ *   baseQuery: fetchBaseQuery({ baseUrl: '/' }),
+ *   endpoints: (build) => ({
+ *     getPosts: build.query<PostsResponse, void>({
+ *       query: () => 'posts',
+ *       // highlight-start
+ *       keepUnusedDataFor: 5
+ *       // highlight-end
+ *     })
+ *   })
+ * })
+ * ```
  */
 export type CacheCollectionQueryExtraOptions = {
   /**
@@ -64,8 +64,6 @@ export const buildCacheCollectionHandler: InternalHandlerBuilder = ({
   const { removeQueryResult, unsubscribeQueryResult, cacheEntriesUpserted } =
     api.internalActions
 
-  const runningQueries = internalState.runningQueries.get(mwApi.dispatch)!
-
   const canTriggerUnsubscribe = isAnyOf(
     unsubscribeQueryResult.match,
     queryThunk.fulfilled,
@@ -80,8 +78,7 @@ export const buildCacheCollectionHandler: InternalHandlerBuilder = ({
     }
 
     const hasSubscriptions = subscriptions.size > 0
-    const isRunning = runningQueries?.[queryCacheKey] !== undefined
-    return hasSubscriptions || isRunning
+    return hasSubscriptions
   }
 
   const currentRemovalTimeouts: QueryStateMeta<TimeoutId> = {}

packages/toolkit/src/query/core/buildMiddleware/index.ts

@@ -45,7 +45,7 @@ export function buildMiddleware<
   ReducerPath extends string,
   TagTypes extends string,
 >(input: BuildMiddlewareInput<Definitions, ReducerPath, TagTypes>) {
-  const { reducerPath, queryThunk, api, context, internalState } = input
+  const { reducerPath, queryThunk, api, context, getInternalState } = input
   const { apiUid } = context
 
   const actions = {
@@ -73,6 +73,8 @@ export function buildMiddleware<
   > = (mwApi) => {
     let initialized = false
 
+    const internalState = getInternalState(mwApi.dispatch)
+
     const builderArgs = {
       ...(input as any as BuildMiddlewareInput<
         EndpointDefinitions,

packages/toolkit/src/query/core/buildMiddleware/types.ts

@@ -47,18 +47,12 @@ export interface InternalMiddlewareState {
   currentSubscriptions: SubscriptionInternalState
   currentPolls: Map<string, QueryPollState>
   runningQueries: Map<
-    Dispatch,
-    Record<
-      string,
-      | QueryActionCreatorResult<any>
-      | InfiniteQueryActionCreatorResult<any>
-      | undefined
-    >
-  >
-  runningMutations: Map<
-    Dispatch,
-    Record<string, MutationActionCreatorResult<any> | undefined>
+    string,
+    | QueryActionCreatorResult<any>
+    | InfiniteQueryActionCreatorResult<any>
+    | undefined
   >
+  runningMutations: Map<string, MutationActionCreatorResult<any> | undefined>
 }
 
 export interface SubscriptionSelectors {
@@ -84,7 +78,7 @@ export interface BuildMiddlewareInput<
     endpointName: string,
     queryArgs: any,
   ) => (dispatch: Dispatch) => QueryActionCreatorResult<any> | undefined
-  internalState: InternalMiddlewareState
+  getInternalState: (dispatch: Dispatch) => InternalMiddlewareState
 }
 
 export type SubMiddlewareApi = MiddlewareAPI<

packages/toolkit/src/query/core/module.ts

@@ -3,6 +3,7 @@
  */
 import type {
   ActionCreatorWithPayload,
+  Dispatch,
   Middleware,
   Reducer,
   ThunkAction,
@@ -72,6 +73,7 @@ import { buildThunks } from './buildThunks'
 import { createSelector as _createSelector } from './rtkImports'
 import { onFocus, onFocusLost, onOffline, onOnline } from './setupListeners'
 import type { InternalMiddlewareState } from './buildMiddleware/types'
+import { getOrInsertComputed } from '../utils'
 
 /**
  * `ifOlderThan` - (default: `false` | `number`) - _number is value in seconds_
@@ -619,11 +621,17 @@ export const coreModule = ({
     })
     safeAssign(api.internalActions, sliceActions)
 
-    const internalState: InternalMiddlewareState = {
-      currentSubscriptions: new Map(),
-      currentPolls: new Map(),
-      runningQueries: new Map(),
-      runningMutations: new Map(),
+    const internalStateMap = new WeakMap<Dispatch, InternalMiddlewareState>()
+
+    const getInternalState = (dispatch: Dispatch) => {
+      const state = getOrInsertComputed(internalStateMap, dispatch, () => ({
+        currentSubscriptions: new Map(),
+        currentPolls: new Map(),
+        runningQueries: new Map(),
+        runningMutations: new Map(),
+      }))
+
+      return state
     }
 
     const {
@@ -641,7 +649,7 @@ export const coreModule = ({
       api,
       serializeQueryArgs: serializeQueryArgs as any,
       context,
-      internalState,
+      getInternalState,
     })
 
     safeAssign(api.util, {
@@ -661,7 +669,7 @@ export const coreModule = ({
       assertTagType,
       selectors,
       getRunningQueryThunk,
-      internalState,
+      getInternalState,
     })
     safeAssign(api.util, middlewareActions)
 

packages/toolkit/src/query/tests/buildMiddleware.test.tsx

@@ -1,6 +1,7 @@
 import { createApi } from '@reduxjs/toolkit/query'
 import { delay } from 'msw'
 import { actionsReducer, setupApiStore } from '../../tests/utils/helpers'
+import { vi } from 'vitest'
 
 const baseQuery = (args?: any) => ({ data: args })
 const api = createApi({
@@ -213,3 +214,53 @@ it('correctly stringifies subscription state and dispatches subscriptionsUpdated
     subscriptionState['getBananas(undefined)']?.[subscription3.requestId],
   ).toEqual({})
 })
+
+it('does not leak subscription state between multiple stores using the same API instance (SSR scenario)', async () => {
+  vi.useFakeTimers()
+  // Simulate SSR: create API once at module level
+  const sharedApi = createApi({
+    baseQuery: (args?: any) => ({ data: args }),
+    tagTypes: ['Test'],
+    endpoints: (build) => ({
+      getTest: build.query<unknown, number>({
+        query(id) {
+          return { url: `test/${id}` }
+        },
+      }),
+    }),
+  })
+
+  // Create first store (simulating first SSR request)
+  const store1Ref = setupApiStore(sharedApi, {}, { withoutListeners: true })
+
+  // Add subscription in store1
+  const sub1 = store1Ref.store.dispatch(
+    sharedApi.endpoints.getTest.initiate(1, {
+      subscriptionOptions: { pollingInterval: 1000 },
+    }),
+  )
+  vi.advanceTimersByTime(10)
+  await sub1
+
+  // Wait for subscription sync (500ms + buffer)
+  vi.advanceTimersByTime(600)
+
+  // Verify store1 has the subscription
+  const store1SubscriptionSelectors = store1Ref.store.dispatch(
+    sharedApi.internalActions.internal_getRTKQSubscriptions(),
+  ) as any
+  const store1InternalSubs = store1SubscriptionSelectors.getSubscriptions()
+  expect(store1InternalSubs.size).toBe(1)
+
+  // Create second store (simulating second SSR request)
+  const store2Ref = setupApiStore(sharedApi, {}, { withoutListeners: true })
+
+  // Check subscriptions via internal action
+  const store2SubscriptionSelectors = store2Ref.store.dispatch(
+    sharedApi.internalActions.internal_getRTKQSubscriptions(),
+  ) as any
+
+  const store2InternalSubs = store2SubscriptionSelectors.getSubscriptions()
+
+  expect(store2InternalSubs.size).toBe(0)
+})

packages/toolkit/src/query/utils/isNotNullish.ts

@@ -1,3 +1,7 @@
 export function isNotNullish<T>(v: T | null | undefined): v is T {
   return v != null
 }
+
+export function filterNullishValues<T>(map?: Map<any, T>) {
+  return [...(map?.values() ?? [])].filter(isNotNullish) as NonNullable<T>[]
+}