WebSocket guards and pipes in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a WebSocket guard in NestJS?

A WebSocket guard controls access to WebSocket events by checking conditions like user authentication before allowing the event handler to run.

beginner

How do pipes work in NestJS WebSocket gateways?

Pipes transform or validate incoming data before it reaches the event handler, ensuring data is correct and safe to use.

intermediate

Where do you apply a guard in a NestJS WebSocket gateway?

You apply guards using the @UseGuards() decorator on the gateway class or on specific event handler methods.

beginner

What happens if a WebSocket guard returns false?

If a guard returns false, the WebSocket event handler does not run, effectively blocking the event for that client.

intermediate

Can pipes modify the data sent to WebSocket event handlers?

Yes, pipes can transform the incoming data before it reaches the handler, for example, converting strings to numbers or trimming text.

What decorator is used to apply a guard in a NestJS WebSocket gateway?

A @UseGuards()

B @UsePipes()

C @SubscribeMessage()

D @WebSocketGateway()

The @UseGuards() decorator applies guards to control access to WebSocket events.

What is the main role of a pipe in a WebSocket gateway?

A To send messages to clients

B To authenticate users

C To transform or validate incoming data

D To close WebSocket connections

Pipes transform or validate data before it reaches the event handler.

If a guard denies access, what happens to the WebSocket event handler?

A It does not run

B It runs twice

C It runs normally

D It sends an error message automatically

When a guard returns false, the event handler is blocked and does not execute.

Which of these is NOT a use case for pipes in WebSocket gateways?

A Validating data format

B Sanitizing input

C Transforming data types

D Checking user permissions

Checking user permissions is the job of guards, not pipes.

Where can you apply pipes in a NestJS WebSocket gateway?

A Only on the gateway class

B On both the gateway class and event handler methods

C Only on event handler methods

D Pipes cannot be applied in WebSocket gateways

Pipes can be applied at the class level or on individual event handlers.

Explain how WebSocket guards and pipes work together in a NestJS gateway to secure and validate incoming events.

Think about the order: first guard checks, then pipe processes data.

Describe how to apply a guard and a pipe to a specific WebSocket event handler in NestJS.

Remember decorators go right above the method.