feat: Add StorageService for offloading large controller data (#7192)

# Add StorageService for Large Controller Data

## Explanation

### What is the current state and why does it need to change?

**Current state**: MetaMask Mobile Engine state is 10.79 MB, with 92%
(9.94 MB) concentrated in just 2 controllers:
- **SnapController**: 5.95 MB of snap source code (55% of total state)
- **TokenListController**: 3.99 MB of token metadata cache (37% of
state)

This data is **rarely accessed** after initial load but stays in Redux
state, causing:
- Slow app startup (parsing 10.79 MB on every launch)
- High memory usage (all data loaded even if not needed)
- Slow persist operations (up to 6.26 MB written per controller change)

**Why change**: Controllers need a way to store large,
infrequently-accessed data outside of Redux state while maintaining
platform portability and testability.

### What is the solution and how does it work?

**New package**: `@metamask/storage-service`

A platform-agnostic service that allows controllers to offload large
data from state to persistent storage via messenger actions.

**How it works**:
1. Controllers call `StorageService:setItem` via messenger to store
large data
2. StorageService saves to platform-specific storage (FilesystemStorage
on mobile, IndexedDB on extension)
3. StorageService publishes events
(`StorageService:itemSet:{namespace}`) so other controllers can react
4. Controllers call `StorageService:getItem` to load data lazily (only
when needed)

**Storage adapter pattern**:
```typescript
// Service accepts platform-specific adapter (like ErrorReportingService)
const service = new StorageService({
  messenger,
  storage: filesystemStorageAdapter, // Mobile provides this
});
```

**Example controller usage**:
```typescript
// Store data (out of state)
await this.messenger.call(
  'StorageService:setItem',
  'MyController',
  'dataKey',
  largeData,
);

// Load on demand (lazy loading)
const data = await this.messenger.call(
  'StorageService:getItem',
  'MyController',
  'dataKey',
);

// Subscribe to changes (optional)
this.messenger.subscribe(
  'StorageService:itemSet:MyController',
  (key, value) => {
    // React to storage changes
  },
);
```

### Why this architecture?

**Platform-agnostic**: Service defines `StorageAdapter` interface;
clients provide implementation (mobile: FilesystemStorage, extension:
IndexedDB, tests: in-memory)

**Messenger-integrated**: Controllers access storage via messenger
actions, no direct dependencies

**Event-driven**: Controllers can subscribe to storage changes without
coupling

**Testable**: InMemoryAdapter provides zero-config testing (no mocking
needed)

**Proven pattern**: Follows ErrorReportingService design (accepts
platform-specific function)

### Expected impact?

**With both controllers optimized**:
- State: 10.79 MB → 0.85 MB (**92% reduction**)
- App startup: 92% faster state parsing
- Memory: 9.94 MB freed
- Disk I/O: Up to 9.94 MB less per persist

**This PR adds infrastructure** - Controllers can now use
StorageService. Separate PRs will integrate with SnapController and
TokenListController.

## References

- **ADR**:
[0017-storage-service-large-data.md](https://github.com/MetaMask/decisions/blob/core/0017-storage-service-large-data/decisions/core/0017-storage-service-large-data.md)
- **Mobile PR**: MetaMask/metamask-mobile#22943

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
  - 100% test coverage (44 tests)
- Tests for all storage operations, namespace isolation, events, error
handling
  - Real-world usage test (simulates 6 MB snap source code)
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
  - Complete README with examples
  - JSDoc for all public APIs
  - Architecture documentation in ADR
- [x] I've communicated my changes to consumers by updating changelogs
for packages I've changed, highlighting breaking changes as necessary
  - CHANGELOG.md created for initial release
  - No breaking changes (new package)
- [x] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes
  - N/A - No breaking changes
  - Consumer PRs will be created after this is merged and released



<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Introduces `@metamask/storage-service` with messenger-based APIs and
an in-memory adapter to offload large controller data, plus repo wiring
and ownership updates.
> 
> - **New Package**: `packages/storage-service`
> - `StorageService`: Messenger-exposed methods `setItem`, `getItem`,
`removeItem`, `getAllKeys`, `clear`; publishes
`StorageService:itemSet:{namespace}` events.
> - `InMemoryStorageAdapter`: Default non-persistent adapter
implementing `StorageAdapter` with key prefix `storageService:`.
> - Types/exports: `StorageAdapter`, `StorageGetResult`, messenger
types, action types file, constants `SERVICE_NAME`,
`STORAGE_KEY_PREFIX`.
> - **Tests & Docs**:
> - Comprehensive unit tests for service and adapter (namespace
isolation, events, errors); Jest config with 100% coverage thresholds.
> - `README.md` with usage/examples; `CHANGELOG.md` initialized;
dual-license files.
> - **Repo Wiring**:
> - Add package to `tsconfig.build.json`, `yarn.lock`, exports/index,
and TypeDoc config.
> - Update `.github/CODEOWNERS` and `teams.json` to include
`storage-service` ownership.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
6bf384a. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Mark Stacey <[email protected]>

Author: andrepimenta

.github/CODEOWNERS

@@ -100,6 +100,7 @@
 /packages/permission-controller                 @MetaMask/wallet-integrations @MetaMask/core-platform
 /packages/permission-log-controller             @MetaMask/wallet-integrations @MetaMask/core-platform
 /packages/remote-feature-flag-controller        @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
+/packages/storage-service                       @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
 
 ## Package Release related
 /packages/account-tree-controller/package.json  @MetaMask/accounts-engineers @MetaMask/core-platform
@@ -168,6 +169,8 @@
 /packages/bridge-controller/CHANGELOG.md                 @MetaMask/swaps-engineers @MetaMask/core-platform
 /packages/remote-feature-flag-controller/package.json @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
 /packages/remote-feature-flag-controller/CHANGELOG.md @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
+/packages/storage-service/package.json @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
+/packages/storage-service/CHANGELOG.md @MetaMask/extension-platform @MetaMask/mobile-platform @MetaMask/core-platform
 /packages/bridge-status-controller/package.json         @MetaMask/swaps-engineers @MetaMask/core-platform
 /packages/bridge-status-controller/CHANGELOG.md         @MetaMask/swaps-engineers @MetaMask/core-platform
 /packages/app-metadata-controller/package.json        @MetaMask/mobile-platform @MetaMask/core-platform

packages/storage-service/CHANGELOG.md

@@ -0,0 +1,14 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- Initial release of `@metamask/storage-service` ([#7192](https://github.com/MetaMask/core/pull/7192))
+
+[Unreleased]: https://github.com/MetaMask/core/

packages/storage-service/LICENSE

@@ -0,0 +1,6 @@
+This project is licensed under either of
+
+ * MIT license ([LICENSE.MIT](LICENSE.MIT))
+ * Apache License, Version 2.0 ([LICENSE.APACHE2](LICENSE.APACHE2))
+
+at your option. 

packages/storage-service/LICENSE.APACHE2

@@ -0,0 +1,201 @@
+ Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright 2025 MetaMask
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

packages/storage-service/LICENSE.MIT

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025 MetaMask
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

packages/storage-service/README.md

@@ -0,0 +1,131 @@
+# `@metamask/storage-service`
+
+A platform-agnostic service for storing large, infrequently accessed controller data outside of memory.
+
+## When to Use
+
+✅ **Use StorageService for:**
+
+- Large data (> 100 KB)
+- Infrequently accessed data
+- Data that doesn't need to be in Redux state
+- Examples: Snap source code, cached API responses
+
+❌ **Don't use for:**
+
+- Frequently accessed data (use controller state)
+- Small data (< 10 KB - overhead not worth it)
+- Data needed for UI rendering
+
+## Installation
+
+`yarn add @metamask/storage-service`
+
+or
+
+`npm install @metamask/storage-service`
+
+## Usage
+
+### Controller Setup
+
+```typescript
+import type {
+  StorageServiceSetItemAction,
+  StorageServiceGetItemAction,
+} from '@metamask/storage-service';
+
+// Grant access to storage actions
+type AllowedActions =
+  | StorageServiceSetItemAction
+  | StorageServiceGetItemAction;
+
+class MyController extends BaseController<...> {
+  async storeData(id: string, data: string) {
+    await this.messenger.call(
+      'StorageService:setItem',
+      'MyController',
+      `${id}:data`,
+      data,
+    );
+  }
+
+  async getData(id: string): Promise<string | undefined> {
+    const { result, error } = await this.messenger.call(
+      'StorageService:getItem',
+      'MyController',
+      `${id}:data`,
+    );
+    if (error) {
+      throw error;
+    }
+    // result is undefined if key doesn't exist
+    return result as string | undefined;
+  }
+}
+```
+
+### Service Initialization
+
+The service accepts an optional `StorageAdapter` for platform-specific storage:
+
+```typescript
+import { StorageService, type StorageAdapter } from '@metamask/storage-service';
+
+// Production: Provide a platform-specific adapter
+const service = new StorageService({
+  messenger: storageServiceMessenger,
+  storage: myPlatformAdapter, // FilesystemStorage, IndexedDB, etc.
+});
+
+// Testing: Uses in-memory storage by default
+const testService = new StorageService({
+  messenger: testMessenger,
+  // No adapter needed - data isolated per test
+});
+```
+
+### Events
+
+Subscribe to storage changes:
+
+```typescript
+this.messenger.subscribe(
+  'StorageService:itemSet:MyController',
+  (key, value) => {
+    console.log(`Data stored: ${key}`);
+  },
+);
+```
+
+## StorageAdapter Interface
+
+Implement this interface to provide platform-specific storage:
+
+```typescript
+import type { Json } from '@metamask/utils';
+
+// Response type for getItem - distinguishes found, not found, and error
+type StorageGetResult =
+  | { result: Json; error?: never } // Data found
+  | { result?: never; error: Error } // Error occurred
+  | Record<string, never>; // Key doesn't exist (empty object)
+
+export type StorageAdapter = {
+  getItem(namespace: string, key: string): Promise<StorageGetResult>;
+  setItem(namespace: string, key: string, value: Json): Promise<void>;
+  removeItem(namespace: string, key: string): Promise<void>;
+  getAllKeys(namespace: string): Promise<string[]>;
+  clear(namespace: string): Promise<void>;
+};
+```
+
+Adapters are responsible for:
+
+- Building the full storage key (e.g., `storageService:namespace:key`)
+- Serializing/deserializing JSON data
+- Returning the correct response format for getItem
+
+## Contributing
+
+This package is part of a monorepo. Instructions for contributing can be found in the [monorepo README](https://github.com/MetaMask/core#readme).