Request Handlers.md

Fastify decorators

Request handlers

Request handlers is special classes used to handle and proceed single request. For each request new instance of RequestHandler class is instantiated.

Here the list of available HTTP methods decorators:

@GET, @HEAD, @PATCH, @POST, @PUT, @OPTIONS, @DELETE

There's also one special decorator for all methods: @ALL

Limitations:

• Decorators can't be mixed, and you can use only one decorator per class/method.

Signatures:

Decorators have same signature, which consist of two overloads:

First overload:

name	type	required	default	description
url	string	no	/	Route url which will be passed to Fastify
options	RouteShorthandOptions	no	{}	Config for route which will be passed to Fastify

Second overload:

name	type	required	default	description
url	RouteOptions	no	{}	Route url and config to be passed to Fastify

Request handler per class

Every handler should extend base RequestHandler class:

import { GET, RequestHandler } from 'fastify-decorators';

@GET('/')
class MyRequestHandler extends RequestHandler {
  async handler() {} // concrete implementation of abstract method in RequestHandler
}

Creating hooks

There are also decorator which allows using Fastify Hooks:

import { GET, Hook } from 'fastify-decorators';

@GET('/')
export default class Handler extends RequestHandler {
  public handle(): Promise<never> {
    return Promise.reject({ code: 'NOT_IMPLEMENTED' });
  }

  @Hook('onSend')
  async onSend(request, reply) {
    reply.removeHeader('X-Powered-By');
  }
}

Error handling

fastify-decorators provides abilities to handle error with @ErrorHandler decorator.

Decorator may accept error code or type to handle or be empty which means will handle all errors. Let's take a look on example:

import { FastifyReply, FastifyRequest } from 'fastify';
import { ErrorHandler, GET, RequestHandler } from 'fastify-decorators';

@GET('/handler-with-error')
export default class HandlerWithErrorHandler extends RequestHandler {
  public handle(): Promise<never> {
    return Promise.reject({ code: 'NOT_IMPLEMENTED' });
  }

  @ErrorHandler('NOT_IMPLEMENTED')
  handleNotImplemented(error: Error, request: FastifyRequest, reply: FastifyReply): void {
    reply.status(422).send({ message: 'Not implemented' });
  }
}