add logResponsePayload option to log response returned value

README.md

@@ -120,6 +120,12 @@ events"](#hapievents) section.
 
   When enabled, responses with status codes in the 400-500 range will have the value returned by the hapi lifecycle method added to the `response` event log as `err`.
 
+### `options.logResponsePayload: boolean`
+
+  **Default**: `false`
+
+  When enabled, add the response returned value (Hapi `request.response.source`) as `responsePayload` to the `response` event log.
+
 ### `options.logRequestStart: boolean | (Request) => boolean`
 
   **Default**: false

index.js

@@ -191,6 +191,7 @@ async function register (server, options) {
           tags: options.logRouteTags ? request.route.settings.tags : undefined,
           err: options.log4xxResponseErrors && (statusCode >= 400 && statusCode < 500) ? request.response.source : undefined,
           res: request.raw.res,
+          responsePayload: options.logResponsePayload && request.response && request.response.source !== undefined ? request.response.source : undefined,
           responseTime
         },
         requestCompleteMessage(request, responseTime)

test.js

@@ -1587,6 +1587,60 @@ experiment('options.logRequestComplete', () => {
   })
 })
 
+experiment('options.logResponsePayload', () => {
+  test('when options.logResponsePayload is true, the response returned value should be added to the log as "responsePayload"', async () => {
+    const server = getServer()
+
+    let done
+
+    const finish = new Promise(function (resolve, reject) {
+      done = resolve
+    })
+
+    server.route({
+      path: '/',
+      method: 'GET',
+      handler: async (req, h) => {
+        return { foo: 100 }
+      }
+    })
+
+    await registerWithOptionsSink(server, { level: 'info', logResponsePayload: true }, data => {
+      expect(data.responsePayload).to.be.equals({ foo: 100 })
+      done()
+    })
+
+    await server.inject('/')
+    await finish
+  })
+
+  test('when options.logResponsePayload is omitted, "responsePayload" should not be added to the response event log', async () => {
+    const server = getServer()
+
+    let done
+
+    const finish = new Promise(function (resolve, reject) {
+      done = resolve
+    })
+
+    server.route({
+      path: '/',
+      method: 'GET',
+      handler: async (req, h) => {
+        return { foo: 101 }
+      }
+    })
+
+    await registerWithOptionsSink(server, { level: 'info' }, data => {
+      expect(data.responsePayload).to.be.undefined()
+      done()
+    })
+
+    await server.inject('/')
+    await finish
+  })
+})
+
 experiment('logging with mergeHapiLogData option enabled', () => {
   test("log event data is merged into pino's log object", async () => {
     const server = getServer()