feature(addon): #1511 persist active experiments in prefs.

addon/ActivityStreams.js

@@ -80,7 +80,6 @@ function ActivityStreams(metadataStore, tabTracker, telemetrySender, options = {
   this._newTabURL = `${this.options.pageURL}#/`;
   Services.prefs.setIntPref("places.favicons.optimizeToDimension", 64);
   this._experimentProvider = new ExperimentProvider(
-    options.clientID,
     options.experiments,
     options.rng
   );
@@ -834,6 +833,7 @@ ActivityStreams.prototype = {
       case "disable":
       case "uninstall":
         this._tabTracker.handleUserEvent({event: reason});
+        this._experimentProvider.clearPrefs();
         this._unsetHomePage();
         defaultUnload();
         break;

addon/ExperimentProvider.js

@@ -1,60 +1,101 @@
-const seedrandom = require("common/vendor")("seedrandom");
-const simplePrefs = require("sdk/simple-prefs");
-const OVERRIDE_PREF = "experimentOverrides";
+const prefService = require("sdk/preferences/service");
+const {PrefsTarget} = require("sdk/preferences/event-target");
+const ss = require("sdk/simple-storage");
+const {preferencesBranch} = require("sdk/self");
+const PREF_PREFIX = `extensions.${preferencesBranch}.`;
 
-exports.OVERRIDE_PREF = OVERRIDE_PREF;
 exports.ExperimentProvider = class ExperimentProvider {
-  constructor(clientID, experiments = require("../experiments.json"), rng) {
-    this._clientID = clientID;
+  constructor(experiments = require("../experiments.json"), rng) {
     this._experiments = experiments;
-    this._rng = rng || seedrandom(clientID);
+    this._rng = rng || Math.random;
     this._data = {};
     this._experimentId = null;
+    this._target = PrefsTarget();
   }
 
   init() {
     this.setValues();
-    this._onPrefChange = () => this.setValues();
-    simplePrefs.on(OVERRIDE_PREF, this._onPrefChange);
+    this._onPrefChange = prefName => this.overrideExperimentPrefs(prefName);
+
+    Object.keys(this._experiments).forEach(experimentName => {
+      this._target.on(PREF_PREFIX + experimentName, this._onPrefChange);
+      Object.defineProperty(this._data, experimentName, {
+        get() {
+          return prefService.get(PREF_PREFIX + experimentName);
+        }
+      });
+    });
+  }
+
+  overrideExperimentPrefs(prefName) {
+    ss.storage.overrideExperimentProvider = true;
+    this._experimentId = null;
   }
 
   setValues() {
-    // Load override pref, if defined
-    const overrides = simplePrefs.prefs[OVERRIDE_PREF] && simplePrefs.prefs[OVERRIDE_PREF].split(/,?\s+/);
+    if (ss.storage.overrideExperimentProvider) {
+      console.log(`The following experiments were turned on via overrides:\n`); // eslint-disable-line no-console
+      for (let experimentName in this._experiments) {
+        if (prefService.has(PREF_PREFIX + experimentName)) {
+          console.log(`- ${experimentName} - \n`); // eslint-disable-line no-console
+        }
+      }
+      return;
+    }
 
     const randomNumber = this._rng();
     let floor = 0;
+    let inExperiment;
 
     Object.keys(this._experiments).forEach(key => {
-      let inExperiment;
       const experiment = this._experiments[key];
-      if (!overrides && experiment.active === false) {
-        return;
-      }
       const {variant, control} = experiment;
 
-      // If an override pref is defined, use it to determine which
-      // experiment values are used. If not, just use our random number generator.
-      // Note that no _experimentId is set for manually overridden prefs.
-      if (overrides) {
-        inExperiment = overrides.includes(key);
-      } else {
-        const ceiling = variant.threshold + floor;
-        if (ceiling > 1) {
-          throw new Error("Your variant cohort sizes should add up to less than 1.");
-        }
-        inExperiment = randomNumber >= floor && randomNumber < ceiling;
-        if (inExperiment) {
+      if (prefService.get(PREF_PREFIX + key) === variant.value) {
+        if (experiment.active) {
+          // If the user is already part of an active experiment, set the experiment id.
           this._experimentId = variant.id;
+        } else {
+          // If the user is part of an inactive experiment,
+          // reset that experiment's pref.
+          prefService.set(PREF_PREFIX + key, control.value);
+          this._experimentId = null;
         }
-        floor = ceiling;
       }
-      this._data[key] = inExperiment ? variant.value : control.value;
     });
 
-    if (overrides) {
-      console.log(`The following experiments were turned on via overrides:\n - ${overrides.join("\n - ")}`); // eslint-disable-line no-console
-    }
+    Object.keys(this._experiments).forEach(key => {
+      const experiment = this._experiments[key];
+      const {variant, control} = experiment;
+      const ceiling = variant.threshold + floor;
+
+      // If the experiment is not new or not active you will not be assigned to it.
+      if (prefService.has(PREF_PREFIX + key) || !experiment.active) {
+        return;
+      }
+
+      // If the experiment pref is undefined, it's a new experiment. Start
+      // by assuming the user will not be in it.
+      prefService.set(PREF_PREFIX + key, control.value);
+
+      if (ceiling > 1) {
+        throw new Error("Your variant cohort sizes should add up to less than 1.");
+      }
+
+      // If you're already in an experiment, you can't be in another one.
+      if (this._experimentId) {
+        return;
+      }
+
+      // If a user is in no experiments and there are new, active experiments,
+      // randomly assign them to a variant (or control)
+      inExperiment = randomNumber >= floor && randomNumber < ceiling;
+      if (inExperiment) {
+        this._experimentId = variant.id;
+        prefService.set(PREF_PREFIX + key, variant.value);
+      }
+      floor = ceiling;
+    });
   }
 
   // This is an object representing all experiments
@@ -69,8 +110,16 @@ exports.ExperimentProvider = class ExperimentProvider {
   }
 
   destroy() {
-    simplePrefs.removeListener(OVERRIDE_PREF, this._onPrefChange);
-    this._data = {};
     this._experimentId = null;
+    Object.keys(this._experiments).forEach(experimentName => {
+      this._target.removeListener(PREF_PREFIX + experimentName, this._onPrefChange);
+    });
+  }
+
+  clearPrefs() {
+    Object.keys(this._experiments).forEach(experimentName => {
+      prefService.reset(PREF_PREFIX + experimentName);
+    });
+    ss.storage.overrideExperimentProvider = false;
   }
 };

common/vendor-src.js

@@ -12,7 +12,6 @@ if (typeof platform_require !== "undefined") {
 const vendorModules = {
   "redux": require("redux"),
   "redux-thunk": require("redux-thunk"),
-  "seedrandom": require("seedrandom"),
   "url-parse": require("url-parse"),
   "PageMetadataParser": require("page-metadata-parser"),
   "redux-watch": require("redux-watch"),