feat: add option and functionality that allows a user to hook into feature mutations (#457)

* Add option and functionality that allows a user to hook into feature mutations.

* Fix function argument to include the entire event.

docs/getting-started.md

@@ -59,6 +59,7 @@ Available unleash options include:
   - `custom` - use this when you implement your own custom authentication logic.
 - **ui** (object) - Set of UI specific overrides. You may set the following keys: `headerBackground`, `environment`, `slogan`.
 - **getLogger** (function) - Used to register a [custom log provider](#How do I configure the log output).
+- **eventHook** (`function(event, data)`) - If provided, this function will be invoked whenever a feature is mutated. The possible values for `event` are `'feature-created'`, `'feature-updated'`, `'feature-archived'`, `'feature-revived'`. The `data` argument contains information about the mutation. Its fields are `type` (string) - the event type (same as `event`); `createdBy` (string) - the user who performed the mutation; `data` - the contents of the change. The contents in `data` differs based on the event type; For `'feature-archived'` and `'feature-revived'`, the only field will be `name` - the name of the feature. For `'feature-created'` and `'feature-updated'` the data follows a schema defined in the code [here](https://github.com/Unleash/unleash/blob/master/lib/routes/admin-api/feature-schema.js#L38-L59).
 
 ### 3. Docker
 

lib/event-hook.js

@@ -0,0 +1,23 @@
+'use strict';
+
+const {
+    FEATURE_CREATED,
+    FEATURE_UPDATED,
+    FEATURE_ARCHIVED,
+    FEATURE_REVIVED,
+} = require('./event-type');
+
+exports.addEventHook = (eventHook, eventStore) => {
+    eventStore.on(FEATURE_CREATED, data => {
+        eventHook(FEATURE_CREATED, data);
+    });
+    eventStore.on(FEATURE_UPDATED, data => {
+        eventHook(FEATURE_UPDATED, data);
+    });
+    eventStore.on(FEATURE_ARCHIVED, data => {
+        eventHook(FEATURE_ARCHIVED, data);
+    });
+    eventStore.on(FEATURE_REVIVED, data => {
+        eventHook(FEATURE_REVIVED, data);
+    });
+};

lib/event-hook.test.js

@@ -0,0 +1,32 @@
+'use strict';
+
+const test = require('ava');
+const { EventEmitter } = require('events');
+const eventStore = new EventEmitter();
+const { addEventHook } = require('./event-hook');
+const {
+    FEATURE_CREATED,
+    FEATURE_UPDATED,
+    FEATURE_ARCHIVED,
+    FEATURE_REVIVED,
+} = require('./event-type');
+
+const o = {};
+
+function testHook(feature, data) {
+    o[feature] = data;
+}
+
+test.before(() => {
+    addEventHook(testHook, eventStore);
+});
+
+[FEATURE_CREATED, FEATURE_UPDATED, FEATURE_ARCHIVED, FEATURE_REVIVED].forEach(
+    feature => {
+        test(`should invoke hook on ${feature}`, t => {
+            const data = { dataKey: feature };
+            eventStore.emit(feature, data);
+            t.true(o[feature] === data);
+        });
+    }
+);

lib/server-impl.js

@@ -11,6 +11,7 @@ const { createOptions } = require('./options');
 const StateService = require('./state-service');
 const User = require('./user');
 const AuthenticationRequired = require('./authentication-required');
+const { addEventHook } = require('./event-hook');
 
 async function createApp(options) {
     // Database dependencies (stateful)
@@ -35,6 +36,10 @@ async function createApp(options) {
         stores.clientMetricsStore
     );
 
+    if (typeof config.eventHook === 'function') {
+        addEventHook(config.eventHook, stores.eventStore);
+    }
+
     const stateService = new StateService(config);
     config.stateService = stateService;
     if (config.importFile) {