@fastify/accepts-serializer

Serialize according to the Accept header.

Install

npm i @fastify/accepts-serializer

Compatibility

Plugin version	Fastify version
>=6.x	^5.x
^5.x	^4.x
>=3.x <5.x	^3.x
^2.x	^2.x
^1.x	^1.x

Please note that if a Fastify version is out of support, then so are the corresponding versions of this plugin in the table above. See Fastify's LTS policy for more details.

Usage

const protobuf = require('protobufjs')
const YAML = require('yamljs')
const msgpack = require('msgpack5')()

const root = protobuf.loadSync('test/awesome.proto')
const AwesomeMessage = root.lookupType('awesomepackage.AwesomeMessage')

const fastify = require('fastify')()

// Global serializers
fastify.register(require('@fastify/accepts-serializer'), {
  serializers: [
    {
      regex: /^application\/yaml$/,
      serializer: body => YAML.stringify(body)
    },
    {
      regex: /^application\/x-msgpack$/,
      serializer: body => msgpack.encode(body)
    }
  ],
  default: 'application/yaml', // MIME type used if Accept header does not match anything
  cacheSize: 100               // max number of Accept header combinations to cache (default: 100)
})

// Per-router serializers
const config = {
  serializers: [
    {
      regex: /^application\/x-protobuf$/,
      serializer: body => AwesomeMessage.encode(AwesomeMessage.create(body)).finish()
    }
  ]
}

fastify.get('/request', { config }, function (req, reply) {
  reply.send({pippo: 'pluto'})
})

Options

Option	Type	Default	Description
serializers	Array	[]	List of serializer definitions, each with a regex and a serializer function
default	string	—	MIME type to use when no serializer matches the Accept header. If omitted, unmatched requests receive a 406 response
cacheSize	number	100	Maximum number of distinct Accept header combinations to cache. Entries are evicted in LRU order once the limit is reached

Behavior

For each route, a SerializerManager is defined, which has both per-route and global serializer definitions.

The MIME type application/json is always handled by fastify if no serializer is registered for that MIME type.

If no default key is specified in configuration, all requests with an unknown Accept header will be replied to with a 406 response (a boom error is used).

Serializer selection results are cached by Accept header value using an LRU cache bounded by cacheSize. This prevents unbounded memory growth from attacker-controlled Accept header variants.

License

Licensed under MIT.