ValidationPipe in WebsocketGateway returns Internal Server Error

Bug Report

Note: I created an issue because I experience this issue, but it was already properly described by someone else on StackOverflow, see here.

I’m trying to add some validation to my WebSocketGateway in NestJS. Here’s the code:

// MessageDTO

import { IsNotEmpty, MinLength } from 'class-validator';

export class MessageDTO {
  @IsNotEmpty()
  username: string;

  @IsNotEmpty()
  @MinLength(10)
  text: string;
}

// Gateway

import { ValidationPipe, UsePipes } from '@nestjs/common';
import { MessageBody, SubscribeMessage, WebSocketGateway, WsResponse } from '@nestjs/websockets';
import { MessageService } from './message/message.service';
import { MessageDTO } from './message/message.dto';
import { Message } from './message/message.entity';

@WebSocketGateway()
export class AppGateway {
  constructor(private readonly messageService: MessageService) {}

  @UsePipes(new ValidationPipe())
  @SubscribeMessage('message')
  async handleMessage(@MessageBody() dto: MessageDTO): Promise<WsResponse<Message>> {
    const message = await this.messageService.saveMessage(dto);
    return { event: 'message', data: message };
  }
}

Now, when I try to send a message that doesn’t meet validation rules, it errors out, but the client always receives { status: 'error', message: 'Internal server error'}. Also, Nest logs the error to the console which should not happen:

Error: Bad Request Exception
    at ValidationPipe.exceptionFactory (/usr/src/app/node_modules/@nestjs/common/pipes/validation.pipe.js:78:20)
    at ValidationPipe.transform (/usr/src/app/node_modules/@nestjs/common/pipes/validation.pipe.js:50:24)
    at processTicksAndRejections (internal/process/task_queues.js:89:5)
    at async resolveParamValue (/usr/src/app/node_modules/@nestjs/websockets/context/ws-context-creator.js:104:31)
    at async Promise.all (index 0)
    at async pipesFn (/usr/src/app/node_modules/@nestjs/websockets/context/ws-context-creator.js:106:13)
    at async /usr/src/app/node_modules/@nestjs/websockets/context/ws-context-creator.js:41:17
    at async AppGateway.<anonymous> (/usr/src/app/node_modules/@nestjs/websockets/context/ws-proxy.js:11:32)
    at async WebSocketsController.pickResult (/usr/src/app/node_modules/@nestjs/websockets/web-sockets-controller.js:85:24)

Current behavior

Throws an error service and client-side, but incorrectly.

Expected behavior

Front-end should have the error returned in the ack callback.

Environment

Nest version: 7.4.2
Platform: MacOS

[kkoomen]

But… is this what we want? Is the current logic normal? because it seems odd to me.

[jmcdo29]

The documentation still needs to be updated to mention that this is the error thrown by default. You can change the error type though by making use of the exceptionFactory property of the ValidationPipe, or you can follow the advice of my comment above