# WsContextCreator

**Kind:** Class

**Source:** [`packages/websockets/context/ws-context-creator.ts`](https://github.com/nestjs/nest/blob/master/packages/websockets/context/ws-context-creator.ts#L40)

**Part of:** [Websockets](subsystem-packages-websockets)

`WsContextCreator` builds the executable wrapper for WebSocket gateway handlers. It resolves handler metadata, parameter values, guards, pipes, interceptors, and exception filters before delegating execution through the WebSocket proxy layer.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `create` | `create(instance: Controller, callback: (...args: unknown[]) => void, moduleKey: string, methodName: string)` | `(...args: any[]) => Promise<void>` |
| `reflectCallbackParamtypes` | `reflectCallbackParamtypes(instance: Controller, callback: (...args: any[]) => any)` | `any[]` |
| `reflectCallbackPattern` | `reflectCallbackPattern(callback: (...args: any[]) => any)` | `string` |
| `createGuardsFn` | `createGuardsFn(guards: any[], instance: Controller, callback: (...args: unknown[]) => any, contextType: TContext)` | `Function | null` |
| `getMetadata` | `getMetadata(instance: Controller, methodName: string, contextType: TContext)` | `WsHandlerMetadata` |
| `exchangeKeysForValues` | `exchangeKeysForValues(keys: string[], metadata: TMetadata, moduleContext: string, paramsFactory: WsParamsFactory, contextFactory: (args: unknown[]) => ExecutionContextHost)` | `ParamProperties[]` |
| `createPipesFn` | `createPipesFn(pipes: PipeTransform[], paramsOptions: (ParamProperties & { metatype?: unknown })[])` | `void` |
| `getParamValue` | `getParamValue(value: T, { metatype, type, data }: { metatype: any; type: any; data: any }, pipes: PipeTransform[])` | `Promise<any>` |

## Where it refuses work

- `WsContextCreator` stops the work with `WsException` when `!canActivate`.
- `WsContextCreator` stops the work with an early return when `cacheMetadata`.

## Diagram

```mermaid
graph LR
  A[Incoming WebSocket event] --> B[WsContextCreator.create]
  B --> C[Reflect handler metadata and pattern]
  C --> D[Create guards]
  C --> E[Create pipes]
  C --> F[Create interceptors]
  C --> G[Create exception filter handler]
  D --> H[Validate execution]
  E --> I[Transform handler parameters]
  F --> J[Invoke gateway callback]
  G --> K[Handle WebSocket exceptions]
  H --> I
  I --> F
  J --> K
```

## Usage

```ts
import { WsContextCreator } from '@nestjs/websockets';

class ChatGateway {
  async handleMessage(client: unknown, payload: { text: string }) {
    console.log(`Received: ${payload.text}`);
  }
}

// WsContextCreator is typically created and injected by Nest's WebSocket
// runtime rather than instantiated directly.
class GatewayHandlerBinder {
  constructor(private readonly wsContextCreator: WsContextCreator) {}

  bind(gateway: ChatGateway, server: { on(event: string, handler: Function): void }) {
    const handler = this.wsContextCreator.create(
      gateway,
      gateway.handleMessage,
      'ChatModule',
      'handleMessage',
    );

    server.on('message', handler);
  }
}
```

## AI Coding Instructions

- Treat `WsContextCreator` as framework infrastructure; prefer gateway decorators and Nest module configuration over manually constructing it.
- Preserve the handler creation flow: metadata reflection, guards, pipes, interceptors, and exception filters must all be included in wrapped handlers.
- Ensure parameter metadata matches the gateway callback signature, since `getParamValue()` and pipe execution depend on reflected parameter configuration.
- Do not invoke gateway callbacks directly when framework behavior is required; use the function returned by `create()` so guards, pipes, and exception handling run.
- Keep WebSocket message patterns stable, as `reflectCallbackPattern()` is used to associate handlers with incoming events.

## How it works

## `WsContextCreator`

`WsContextCreator` builds the executable wrapper for a WebSocket gateway callback. Its constructor receives the WebSocket proxy plus contexts/consumers for exception filters, pipes, guards, and interceptors; it also creates its own context utility, WebSocket parameter factory, and per-handler metadata cache. [packages/websockets/context/ws-context-creator.ts:40-55]