fastify-cors

fastify-cors enables the use of CORS in a Fastify application.

Supports Fastify versions 3.x Please refer to this branch and related versions for Fastify ^2.x compatibility. Please refer to this branch and related versions for Fastify ^1.x compatibility.

Install

npm i fastify-cors

Usage

Require fastify-cors and register it as any other plugin, it will add a preHandler hook and a wildcard options route.

const fastify = require('fastify')()

fastify.register(require('fastify-cors'), { 
  // put your options here
})

fastify.get('/', (req, reply) => {
  reply.send({ hello: 'world' })
})

fastify.listen(3000)

You can use it as is without passing any option, or you can configure it as explained below.

Options

• origin: Configures the Access-Control-Allow-Origin CORS header. The value of origin could be of different types:
  • Boolean - set origin to true to reflect the request origin, or set it to false to disable CORS.
  • String - set origin to a specific origin. For example if you set it to "http://example.com" only requests from "http://example.com" will be allowed.
  • RegExp - set origin to a regular expression pattern which will be used to test the request origin. If it's a match, the request origin will be reflected. For example the pattern /example\.com$/ will reflect any request that is coming from an origin ending with "example.com".
  • Array - set origin to an array of valid origins. Each origin can be a String or a RegExp. For example ["http://example1.com", /\.example2\.com$/] will accept any request from "http://example1.com" or from a subdomain of "example2.com".
  • Function - set origin to a function implementing some custom logic. The function takes the request origin as the first parameter and a callback as a second (which expects the signature err [Error | null], origin), where origin is a non function value of the origin option. Async-await and promises are supported as well. The Fastify instance is bound to function call and you may access via this. For example:

  origin: (origin, cb) => {
    if(/localhost/.test(origin)){
      //  Request from localhost will pass
      cb(null, true)
      return
    }
    // Generate an error on other origins, disabling access
    cb(new Error("Not allowed"))
  }

• methods: Configures the Access-Control-Allow-Methods CORS header. Expects a comma-delimited string (ex: 'GET,PUT,POST') or an array (ex: ['GET', 'PUT', 'POST']).
• allowedHeaders: Configures the Access-Control-Allow-Headers CORS header. Expects a comma-delimited string (ex: 'Content-Type,Authorization') or an array (ex: ['Content-Type', 'Authorization']). If not specified, defaults to reflecting the headers specified in the request's Access-Control-Request-Headers header.
• exposedHeaders: Configures the Access-Control-Expose-Headers CORS header. Expects a comma-delimited string (ex: 'Content-Range,X-Content-Range') or an array (ex: ['Content-Range', 'X-Content-Range']). If not specified, no custom headers are exposed.
• credentials: Configures the Access-Control-Allow-Credentials CORS header. Set to true to pass the header, otherwise it is omitted.
• maxAge: Configures the Access-Control-Max-Age CORS header. In seconds. Set to an integer to pass the header, otherwise it is omitted.
• optionsSuccessStatus: Provides a status code to use for successful OPTIONS requests, since some legacy browsers (IE11, various SmartTVs) choke on 204.
• preflight: if needed you can entirely disable preflight by passing false here (default: true).
• strictPreflight: Enforces strict requirement of the CORS preflight request headers (Access-Control-Request-Method and Origin) as defined by the W3C CORS specification (the current fetch living specification does not define server behavior for missing headers). Preflight requests without the required headers will result in 400 errors when set to true (default: true).
• hideOptionsRoute: hide options route from the documentation built using fastify-swagger (default: true).

Preflight Requests

When preflight is enabled (preflight option is true), a * wildcard OPTIONS route is added to the fastify instance. The response behavior can be overridden for individual routes by adding OPTIONS routes to the fastify instance (* wildcard routes are always lowest priority).

This is an important difference between fastify-cors and the express cors middleware preflightContinue option.

const fastify = require('fastify')()

// Fastify-cors handles CORS preflight OPTIONS requests
fastify.register(require('fastify-cors'))

// Except for OPTIONS /not-preflight
fastify.options('/not-preflight', (req, reply) => {
  reply.send({hello: 'world'})
})

Acknowledgements

The code is a port for Fastify of expressjs/cors.

License

Licensed under MIT.
expressjs/cors license