How to handle RpcException in NestJS

Question

I am trying to build a NestJS backend with multiple microservices and one REST API as a Gateway which communicates with the microservices. For communication between the Gateway and Microservices I am using gRPC. Simple communication is already working, but now I wanted to implement Error Handling in the Microservices. The NestJS Documentation states that this is possible with the RpcException class.https://docs.nestjs.com/microservices/exception-filters But if I try to catch the Exception in the Gateway API I only get "ERROR [ExceptionsHandler] 2 UNKNOWN: ..." followed by the Exceptions error message.

Gateway API: user.controller.ts

import { Controller, Get, Param } from '@nestjs/common';
import { ApiTags } from '@nestjs/swagger';
import { UserViewModel } from '../../proto/build/service-name/user';
import { UserService } from './user.service';

@Controller('user')
export class UserController {
  constructor(private readonly userService: UserService) {}

  @Get(':id')
  async getUserById(@Param('id') id: number): Promise<UserViewModel> {
    try {
      return await this.userService.getUserById(id);
    } catch (error) {
      return error;
    }
  }
}

Gateway API: user.service.ts

import { Inject, Injectable, OnModuleInit } from '@nestjs/common';
import { ClientGrpc } from '@nestjs/microservices';
import {
  IUserService,
  UserViewModel,
} from '../../proto/build/service-name/user';

@Injectable()
export class UserService implements OnModuleInit {
  private grpcService: IUserService;

  constructor(@Inject('USER_PACKAGE') private client: ClientGrpc) {}

  onModuleInit() {
    this.grpcService = this.client.getService<IUserService>('IUserService');
  }

  async getUserById(id: number): Promise<UserViewModel> {
    return this.grpcService.getUserById({ id });
  }
}

Microservice: user.controller.ts

import { Metadata } from '@grpc/grpc-js';
import { Controller } from '@nestjs/common';
import { GrpcMethod, RpcException } from '@nestjs/microservices';
import { User } from './../../node_modules/.prisma/client/index.d';
import { PrismaService } from '../prisma/prisma.service';
import { UserViewModel, GetUserById } from '../proto/build/service-name/user';

@Controller()
export class UserController {
  constructor(private readonly prisma: PrismaService) {}

  @GrpcMethod('IUserService', 'getUserById')
  async getUserById(
    data: GetUserById,
    metadata: Metadata,
  ): Promise<UserViewModel> {
    const user: User = await this.prisma.user.findFirst({
      where: { id: { equals: data.id } },
    });

    if (!user) {
      throw new RpcException('User not found');
    }

    return { name: user.name, email: user.email };
  }
}

Answer 1

I ran into this issue as well when building microservices with an API gateway. The solution I came up with is a combination of the answers I've found here but allows you to use the build in NestJS exceptions.

So basically I wrap the built in NestJS HTTP exception with the RpcException in the microservice. Then you can catch the execption in your api gateway and handle it with a filter. The RcpException message can be either a string or object, this allows you to pass the built in HTTP exceptions (NotFoundException, UnauthorizedException, etc) as a message so you don't have to deal with status codes.

Microservice

// Some service method to fetch a product by id
public async findById(id: number): Promise<Product> {
  // ...
  if (!product) {
    throw new RpcException(
      new NotFoundException("Product was not found!");
    );
  }
  //...
}

Gateway Controller

@Get(':productId')
public getProductById(@Param('productId') productId: number): Observable<any> {
  return this._productsServiceClient
    .send({ cmd: 'find-by-id' }, { productId })
    .pipe(catchError(error => throwError(() => new RpcException(error.response))))
}

Exception Filter

import { ArgumentsHost, Catch, ExceptionFilter } from '@nestjs/common';
import { RpcException } from '@nestjs/microservices';
import { Response } from 'express';

@Catch(RpcException)
export class RpcExceptionFilter implements ExceptionFilter {
  catch(exception: RpcException, host: ArgumentsHost) {
    const error: any = exception.getError();
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    
    response
      .status(error.statusCode)
      .json(error);
  }
}

Register Filter

// main.ts
app.useGlobalFilters(new RpcExceptionFilter());

Answer 2

1. Extend the RpcException and use in the microservice.
2. Create AllGlobalExceptionsFilter in the gateway(the sender)
3. Use in gateway(sender) controller

export interface IRpcException {
  message: string;
  status: number;
}

export class FitRpcException extends RpcException implements IRpcException {
  constructor(message: string, statusCode: HttpStatus) {
    super(message);
    this.initStatusCode(statusCode);
  }
  public status: number;

  private initStatusCode(statusCode) {
    this.status = statusCode;
  }
}

@Catch()
export class AllGlobalExceptionsFilter implements ExceptionFilter {
  constructor(private readonly httpAdapterHost: HttpAdapterHost) {}

  catch(exception: IRpcException, host: ArgumentsHost): void {
    const { httpAdapter } = this.httpAdapterHost;
    const ctx = host.switchToHttp();

    const httpStatus = exception.status
      ? exception.status
      : HttpStatus.INTERNAL_SERVER_ERROR;

    const responseBody = {
      statusCode: httpStatus,
      timestamp: new Date().toISOString(),
      path: httpAdapter.getRequestUrl(ctx.getRequest()),
      message: exception.message,
    };

    httpAdapter.reply(ctx.getResponse(), responseBody, httpStatus);
  }
}

@UseFilters(AllGlobalExceptionsFilter)

Answer 3

i have tried on nestjs 9. just only

throw new RpcException({ code: grpc.status.UNAVAILABLE, message: 'error' })

ps: grpc need import like that

import * as grpc from '@grpc/grpc-js'.