feature: allow custom hook name

README.md

@@ -19,7 +19,7 @@ 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](https://github.com/fastify/fastify/issues/326#issuecomment-411360862).
+Require `@fastify/cors` and register it as any other plugin, it will add a `onRequest` hook and a [wildcard options route](https://github.com/fastify/fastify/issues/326#issuecomment-411360862).
 ```js
 import Fastify from 'fastify'
 import cors from '@fastify/cors'
@@ -97,6 +97,58 @@ fastify.register(async function (fastify) {
 fastify.listen({ port: 3000 })
 ```
 
+### Custom Fastify hook name
+
+By default, `@fastify/cors` adds a `onRequest` hook where the validation and header injection are executed. This can be customized by passing `hookName` in the options.
+
+```js
+import Fastify from 'fastify'
+import cors from '@fastify/cors'
+
+const fastify = Fastify()
+await fastify.register(cors, { 
+  hookName: 'preHandler',
+})
+
+fastify.get('/', (req, reply) => {
+  reply.send({ hello: 'world' })
+})
+
+await fastify.listen({ port: 3000 })
+```
+
+When configuring CORS asynchronously, an object with `delegator` key is expected:
+
+```js
+const fastify = require('fastify')()
+
+fastify.register(require('@fastify/cors'), {
+  hookName: 'preHandler',
+  delegator: (req, callback) => {
+    const corsOptions = {
+      // This is NOT recommended for production as it enables reflection exploits
+      origin: true
+    };
+
+    // do not include CORS headers for requests from localhost
+    if (/^localhost$/m.test(req.headers.origin)) {
+      corsOptions.origin = false
+    }
+
+    // callback expects two parameters: error and options
+    callback(null, corsOptions)
+  },
+})
+
+fastify.register(async function (fastify) {
+  fastify.get('/', (req, reply) => {
+    reply.send({ hello: 'world' })
+  })
+})
+
+fastify.listen({ port: 3000 })
+```
+
 ## Acknowledgements
 
 The code is a port for Fastify of [`expressjs/cors`](https://github.com/expressjs/cors).

index.js

@@ -19,17 +19,22 @@ const defaultOptions = {
   strictPreflight: true
 }
 
+const defaultHookName = 'onRequest'
+
 function fastifyCors (fastify, opts, next) {
   fastify.decorateRequest('corsPreflightEnabled', false)
 
   let hideOptionsRoute = true
   if (typeof opts === 'function') {
     handleCorsOptionsDelegator(opts, fastify)
+  } else if (opts.delegator) {
+    const { delegator, ...options } = opts
+    handleCorsOptionsDelegator(delegator, fastify, options)
   } else {
     if (opts.hideOptionsRoute !== undefined) hideOptionsRoute = opts.hideOptionsRoute
     const corsOptions = Object.assign({}, defaultOptions, opts)
-    fastify.addHook('onRequest', function onRequestCors (req, reply, next) {
-      onRequest(fastify, corsOptions, req, reply, next)
+    fastify.addHook(opts.hookName || defaultHookName, function handleCors (req, reply, next) {
+      handler(fastify, corsOptions, req, reply, next)
     })
   }
 
@@ -52,8 +57,8 @@ function fastifyCors (fastify, opts, next) {
   next()
 }
 
-function handleCorsOptionsDelegator (optionsResolver, fastify) {
-  fastify.addHook('onRequest', function onRequestCors (req, reply, next) {
+function handleCorsOptionsDelegator (optionsResolver, fastify, { hookName } = { hookName: defaultHookName }) {
+  fastify.addHook(hookName, function handleCors (req, reply, next) {
     if (optionsResolver.length === 2) {
       handleCorsOptionsCallbackDelegator(optionsResolver, fastify, req, reply, next)
       return
@@ -62,7 +67,7 @@ function handleCorsOptionsDelegator (optionsResolver, fastify) {
       const ret = optionsResolver(req)
       if (ret && typeof ret.then === 'function') {
         ret.then(options => Object.assign({}, defaultOptions, options))
-          .then(corsOptions => onRequest(fastify, corsOptions, req, reply, next)).catch(next)
+          .then(corsOptions => handler(fastify, corsOptions, req, reply, next)).catch(next)
         return
       }
     }
@@ -76,12 +81,12 @@ function handleCorsOptionsCallbackDelegator (optionsResolver, fastify, req, repl
       next(err)
     } else {
       const corsOptions = Object.assign({}, defaultOptions, options)
-      onRequest(fastify, corsOptions, req, reply, next)
+      handler(fastify, corsOptions, req, reply, next)
     }
   })
 }
 
-function onRequest (fastify, options, req, reply, next) {
+function handler (fastify, options, req, reply, next) {
   // Always set Vary header
   // https://github.com/rs/cors/issues/10
   addOriginToVaryHeader(reply)

test/cors.test.js

@@ -275,6 +275,103 @@ test('Should support dynamic config (Promise)', t => {
   })
 })
 
+test('Should support custom hook with dynamic config', t => {
+  t.plan(16)
+
+  const configs = [{
+    origin: 'example.com',
+    methods: 'GET',
+    credentials: true,
+    exposedHeaders: ['foo', 'bar'],
+    allowedHeaders: ['baz', 'woo'],
+    maxAge: 123
+  }, {
+    origin: 'sample.com',
+    methods: 'GET',
+    credentials: true,
+    exposedHeaders: ['zoo', 'bar'],
+    allowedHeaders: ['baz', 'foo'],
+    maxAge: 321
+  }]
+
+  const fastify = Fastify()
+  let requestId = 0
+  const configDelegation = function (req, cb) {
+    // request should have id
+    t.ok(req.id)
+    // request should not have send
+    t.notOk(req.send)
+    const config = configs[requestId]
+    requestId++
+    if (config) {
+      cb(null, config)
+    } else {
+      cb(new Error('ouch'))
+    }
+  }
+  fastify.register(cors, {
+    hookName: 'preHandler',
+    delegator: configDelegation
+  })
+
+  fastify.get('/', (req, reply) => {
+    reply.send('ok')
+  })
+
+  fastify.inject({
+    method: 'GET',
+    url: '/'
+  }, (err, res) => {
+    t.error(err)
+    delete res.headers.date
+    t.equal(res.statusCode, 200)
+    t.equal(res.payload, 'ok')
+    t.match(res.headers, {
+      'access-control-allow-origin': 'example.com',
+      vary: 'Origin',
+      'access-control-allow-credentials': 'true',
+      'access-control-expose-headers': 'foo, bar',
+      'content-length': '2'
+    })
+  })
+
+  fastify.inject({
+    method: 'OPTIONS',
+    url: '/',
+    headers: {
+      'access-control-request-method': 'GET',
+      origin: 'example.com'
+    }
+  }, (err, res) => {
+    t.error(err)
+    delete res.headers.date
+    t.equal(res.statusCode, 204)
+    t.equal(res.payload, '')
+    t.match(res.headers, {
+      'access-control-allow-origin': 'sample.com',
+      vary: 'Origin',
+      'access-control-allow-credentials': 'true',
+      'access-control-expose-headers': 'zoo, bar',
+      'access-control-allow-methods': 'GET',
+      'access-control-allow-headers': 'baz, foo',
+      'access-control-max-age': '321',
+      'content-length': '0'
+    })
+  })
+
+  fastify.inject({
+    method: 'GET',
+    url: '/',
+    headers: {
+      'access-control-request-method': 'GET',
+      origin: 'example.com'
+    }
+  }, (err, res) => {
+    t.error(err)
+    t.equal(res.statusCode, 500)
+  })
+})
+
 test('Should support dynamic config. (Invalid function)', t => {
   t.plan(2)