RpcContextCreator

Kind: Class

Source: packages/microservices/context/rpc-context-creator.ts

Part of: Microservices

RpcContextCreator builds the executable wrapper for NestJS microservice RPC handlers. It reflects handler parameter metadata, resolves guards, pipes, interceptors, and exception handling, then returns a function that produces an Observable for each incoming RPC request.

Methods

Where it refuses work

• RpcContextCreator stops the work with RpcException when !canActivate.
• RpcContextCreator stops the work with an early return when cacheMetadata.

Diagram

mermaid
graph LR
  A[Incoming RPC message] --> B[RpcContextCreator.create]
  B --> C[Reflect handler parameter metadata]
  C --> D[Create guards, pipes, and interceptors]
  D --> E[Resolve RPC handler arguments]
  E --> F[Invoke controller method]
  F --> G[RpcProxy exception handling]
  G --> H[Observable response]

Usage

ts
import { lastValueFrom } from 'rxjs';
import { RpcContextCreator } from '@nestjs/microservices/context/rpc-context-creator';

class CustomTransportAdapter {
  constructor(
    private readonly rpcContextCreator: RpcContextCreator,
  ) {}

  registerHandler(
    controller: object,
    moduleKey: string,
    methodName: string,
  ) {
    const callback = (controller as any)[methodName];

    // Nest internally creates this wrapper when binding RPC controller methods.
    const execute = this.rpcContextCreator.create(
      controller,
      callback,
      moduleKey,
      methodName,
    );

    return async (payload: unknown, rpcContext: unknown) => {
      const response$ = await execute(payload, rpcContext);

      // Convert the handler Observable when the transport needs a Promise.
      return lastValueFrom(response$);
    };
  }
}

AI Coding Instructions

• Use create() when binding an RPC controller method; it ensures guards, pipes, interceptors, and exception filters are applied consistently.
• Preserve the original controller instance and method name so reflected parameter metadata can be resolved correctly.
• Treat the function returned by create() as asynchronous and expect it to resolve to an Observable.
• Do not invoke private metadata, guard, or pipe helper methods directly; extend integration behavior through NestJS guards, pipes, interceptors, and exception filters.
• Pass the correct module key and request context when integrating custom transports, especially when request-scoped providers are involved.