Fastify Allow Plugin

The HTTP 1.1 specification has an Allow header for resources to include in client responses, indicating all the methods the resource supports. All resource requests return the Allow header so client developers can discover all the allowable methods on the resource. If a resource does not support a method, for instance, DELETE, then the response status will be 405 Not Allowed along with the Allow header.

This plugin adds an Allow header to all responses with routes that have registered handlers, regardless of the method they handle. It returns a 405 Not Allowed response when a route has no supported method handler. This behaviour is different from Fastify's default behaviour, which is to return a 404 Not Found for unhandled methods on a route.

If a route has no registered method handlers, fastify-allow will send the usual 404 Not Found response.

Install

npm install fastify-allow

Usage

To use the plugin, simply register it before adding method handlers to the fastify instance.

const fastify = require('fastify')()

fastify.register(require('fastify-allow'))

/*
  The replies for GET and POST to this endpoint will include the header Allow: GET, POST
  This route will reply 405 on HEAD, OPTIONS, PUT, PATCH and DELETE in addition to the header
  Allow: GET, POST
*/
fastify.get('/foo', (req, reply) => {
  reply.send({ hello: 'world' })
})

fastify.post('/foo', (req, reply) => {
  reply.status(201)
})

fastify.listen(3000, (err) => {
  if (err) throw err
  console.log('Server listening at http://localhost:3000')
})

Options

The plugin can be configured to retain fastify's default behaviour for unsupported methods, which is to respond with 404 Not Found. Configure the plugin at registration with this option:

fastify.register(require('fastify-allow', { send405: false }))

When send405 is true, wildcard path behavior is also configurable. By default, if a path only has wildcard handlers, and not a specific path handler, then 404 will be returned instead of 405. If you wish 405 to be sent for all paths that match, even when only a wildcard path matches, then set the send405ForWildcard to true:

fastify.register(require('fastify-allow', { send405: true, send405ForWildcard: true }))

fastify.options('*', optionsHandler)

// fastify will send 405 for all requests that do not have method handlers as all paths match '*'

if send405 is set to false, then send405ForWildcard is ignored.

Option	Description	Default value
send405	Controls whether or not to send 405 Not Allowed status codes for request that have handlers for other methods, just not the one being sent.	true
send405ForWildcard	Only applies when send405 is true. Wildcard routes that have no non-wildcard route handlers will still return 405 Not Allowed for requests that have a matching wildcard handler.	false

Typescript Support

fastify-allow is written in Typescript and includes type declarations for the options.

import Fastify from "fastify"
import allowPlugin, {AllowOptions} from "fastify-allow"

const fastify = Fastify()
const allowOpts: AllowOptions = { send405: false, send405ForWildcard: true }

fastify.register(allowPlugin, allowOpts)

// now register handlers