# HandlerMetadataStorage

**Kind:** Class

**Source:** [`packages/core/helpers/handler-metadata-storage.ts`](https://github.com/nestjs/nest/blob/master/packages/core/helpers/handler-metadata-storage.ts#L44)

**Part of:** [Core](subsystem-packages-core)

`HandlerMetadataStorage` associates metadata values with handler functions and provides lookup access later in the execution flow. It is useful for preserving handler-specific configuration discovered during registration, decoration, or route setup.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `set` | `set(controller: TKey, methodName: string, metadata: TValue)` | `void` |
| `get` | `get(controller: TKey, methodName: string)` | `TValue | undefined` |

## Diagram

```mermaid
graph LR
  A[Handler function] -->|set(handler, metadata)| B[HandlerMetadataStorage]
  B -->|stores association| C[Metadata value]
  A -->|get(handler)| B
  B -->|returns TValue or undefined| D[Consumer / runtime logic]
```

## Usage

```ts
import { HandlerMetadataStorage } from './helpers/handler-metadata-storage';

type HandlerOptions = {
  requiresAuth: boolean;
  rateLimit?: number;
};

const handlerMetadata = new HandlerMetadataStorage<HandlerOptions>();

function getProfile() {
  return { id: 'user-123' };
}

handlerMetadata.set(getProfile, {
  requiresAuth: true,
  rateLimit: 100,
});

const options = handlerMetadata.get(getProfile);

if (options?.requiresAuth) {
  // Apply authentication middleware or authorization checks.
}

console.log(options);
// { requiresAuth: true, rateLimit: 100 }
```

## AI Coding Instructions

- Use the same handler reference for both `set()` and `get()`; a different function instance will not resolve the stored metadata.
- Treat `get()` results as optional, since it returns `undefined` when no metadata has been registered.
- Store small, immutable configuration objects where possible so handler metadata remains predictable across the application lifecycle.
- Register metadata during handler setup or discovery, then read it from routing, middleware, or invocation logic.

## Used by

2 references from 2 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (2)

- `RpcHandlerMetadata` — `packages/microservices/context/rpc-context-creator.ts`:35
- `WsHandlerMetadata` — `packages/websockets/context/ws-context-creator.ts`:34