add ability to get response time on reply

docs/Reply.md

@@ -10,6 +10,7 @@
   - [.hasHeader(key)](#hasheaderkey)
   - [.redirect(dest)](#redirectdest)
   - [.callNotFound()](#callnotfound)
+  - [.getResponseTime()](#getresponsetime)
   - [.type(contentType)](#typecontenttype)
   - [.serializer(func)](#serializerfunc)
   - [.sent](#sent)
@@ -109,6 +110,14 @@ Invokes the custom not found handler.
 reply.callNotFound()
 ```
 
+<a name="getResponseTime"></a>
+### .getResponseTime()
+Invokes the custom response time getter to calculate the amount of time passed since the request was started.
+
+```js
+const milliseconds = reply.getResponseTime()
+```
+
 <a name="type"></a>
 ### .type(contentType)
 Sets the content type for the response.

fastify.d.ts

@@ -166,6 +166,7 @@ declare namespace fastify {
     getHeader(name: string): string | undefined
     hasHeader(name: string): boolean
     callNotFound(): void
+    getResponseTime(): number
     type(contentType: string): FastifyReply<HttpResponse>
     redirect(url: string): FastifyReply<HttpResponse>
     redirect(statusCode: number, url: string): FastifyReply<HttpResponse>

lib/reply.js

@@ -222,6 +222,16 @@ Reply.prototype.callNotFound = function () {
   notFound(this)
 }
 
+Reply.prototype.getResponseTime = function () {
+  var responseTime = 0
+
+  if (this[kReplyStartTime] !== undefined) {
+    responseTime = now() - this[kReplyStartTime]
+  }
+
+  return responseTime
+}
+
 function preserializeHook (reply, payload) {
   if (reply.context.preSerialization !== null) {
     onSendHookRunner(
@@ -460,11 +470,8 @@ function onResponseCallback (err, request, reply) {
   if (reply.log[kDisableRequestLogging]) {
     return
   }
-  var responseTime = 0
 
-  if (reply[kReplyStartTime] !== undefined) {
-    responseTime = now() - reply[kReplyStartTime]
-  }
+  var responseTime = reply.getResponseTime()
 
   if (err != null) {
     reply.log.error({

test/internals/reply.test.js

@@ -14,7 +14,7 @@ const {
 } = require('../../lib/symbols')
 
 test('Once called, Reply should return an object with methods', t => {
-  t.plan(12)
+  t.plan(13)
   const response = { res: 'res' }
   function context () {}
   function request () {}
@@ -27,6 +27,7 @@ test('Once called, Reply should return an object with methods', t => {
   t.is(typeof reply.status, 'function')
   t.is(typeof reply.header, 'function')
   t.is(typeof reply.serialize, 'function')
+  t.is(typeof reply.getResponseTime, 'function')
   t.is(typeof reply[kReplyHeaders], 'object')
   t.strictEqual(reply.res, response)
   t.strictEqual(reply.context, context)
@@ -977,3 +978,30 @@ test('should throw error when attempting to set reply.sent more than once', t =>
     t.pass()
   })
 })
+
+test('reply.getResponseTime() should return 0 before the timer is initialised on the reply by setting up response listeners', t => {
+  t.plan(1)
+  const response = { statusCode: 200 }
+  const context = {}
+  const reply = new Reply(response, context, null)
+  t.equal(reply.getResponseTime(), 0)
+})
+
+test('reply.getResponseTime() should return a number greater than 0 after the timer is initialised on the reply by setting up response listeners', t => {
+  t.plan(1)
+  const fastify = require('../..')()
+  fastify.route({
+    method: 'GET',
+    url: '/',
+    handler: (req, reply) => {
+      reply.send('hello world')
+    }
+  })
+
+  fastify.addHook('onResponse', (req, reply) => {
+    t.true(reply.getResponseTime() > 0)
+    t.end()
+  })
+
+  fastify.inject({ method: 'GET', url: '/' })
+})

test/types/index.ts

@@ -345,6 +345,10 @@ server
   .get('/deprecatedpath/*', (req, reply) => {
     reply.callNotFound()
   })
+  .get('/getResponseTime', function (req, reply) {
+    const milliseconds : number = reply.getResponseTime()
+    reply.send({ milliseconds })
+  })
 
 // Generics example
 interface Query {