Bug 1859608 - Change the user's DoH region when that changes r=necko-reviewers,sunil,kershaw

The DoHConfig now listens for region change notification and
saves the new region in a pref. On the next initialization of
the DoH config we will use the saved pref to update the doh
region even if the pref was already set.

This should also work for testing (manually setting the value of the
pref) as long as no region changes happen.

Differential Revision: https://phabricator.services.mozilla.com/D195023

Author: valenting

browser/components/doh/DoHConfig.sys.mjs

@@ -166,6 +166,18 @@ export const DoHConfigController = {
   // until the region is available.
   async loadRegion() {
     await new Promise(resolve => {
+      // If the region has changed since it was last set, update the pref.
+      let homeRegionOverride = lazy.Preferences.get(
+        `${kGlobalPrefBranch}.home-region-override`
+      );
+      if (homeRegionOverride) {
+        lazy.Preferences.set(
+          `${kGlobalPrefBranch}.home-region`,
+          homeRegionOverride
+        );
+        lazy.Preferences.reset(`${kGlobalPrefBranch}.home-region-override`);
+      }
+
       let homeRegion = lazy.Preferences.get(`${kGlobalPrefBranch}.home-region`);
       if (homeRegion) {
         kRegionPrefBranch = `${kGlobalPrefBranch}.${homeRegion.toLowerCase()}`;
@@ -201,6 +213,7 @@ export const DoHConfigController = {
     await this.loadRegion();
 
     Services.prefs.addObserver(`${kGlobalPrefBranch}.`, this, true);
+    Services.obs.addObserver(this, lazy.Region.REGION_TOPIC);
 
     gProvidersCollection.on("sync", this.updateFromRemoteSettings);
     gConfigCollection.on("sync", this.updateFromRemoteSettings);
@@ -213,6 +226,7 @@ export const DoHConfigController = {
     await this.initComplete;
 
     Services.prefs.removeObserver(`${kGlobalPrefBranch}`, this);
+    Services.obs.removeObserver(this, lazy.Region.REGION_TOPIC);
 
     gProvidersCollection.off("sync", this.updateFromRemoteSettings);
     gConfigCollection.off("sync", this.updateFromRemoteSettings);
@@ -240,6 +254,12 @@ export const DoHConfigController = {
         }
         this.notifyNewConfig();
         break;
+      case lazy.Region.REGION_TOPIC:
+        lazy.Preferences.set(
+          `${kGlobalPrefBranch}.home-region-override`,
+          lazy.Region.home
+        );
+        break;
     }
   },
 

browser/components/doh/test/browser/browser.toml

@@ -29,3 +29,5 @@ skip-if = ["os == 'win' && bits == 32"] # Bug 1713464
 ["browser_trrSelection_disable.js"]
 
 ["browser_userInterference.js"]
+
+["browser_doh_region.js"]

browser/components/doh/test/browser/browser_doh_region.js

@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+"use strict";
+
+add_task(setup);
+add_task(setupRegion); // Sets region to DE
+
+add_task(async function testPrefFirstRollout() {
+  registerCleanupFunction(setupRegion); // Reset region
+
+  let defaults = Services.prefs.getDefaultBranch("");
+
+  setPassingHeuristics();
+
+  is(
+    DoHConfigController.currentConfig.enabled,
+    false,
+    "Rollout should not be enabled"
+  );
+
+  let configFlushedPromise = DoHTestUtils.waitForConfigFlush();
+  defaults.setBoolPref(`${kRegionalPrefNamespace}.enabled`, true);
+  await configFlushedPromise;
+
+  is(
+    DoHConfigController.currentConfig.enabled,
+    true,
+    "Rollout should be enabled"
+  );
+  await ensureTRRMode(2);
+
+  is(
+    Preferences.get("doh-rollout.home-region"),
+    "DE",
+    "Initial region should be DE"
+  );
+  Region._setHomeRegion("UK");
+  await ensureTRRMode(2); // Mode shouldn't change.
+
+  is(Preferences.get("doh-rollout.home-region-override"), "UK");
+
+  await DoHController._uninit();
+  await DoHConfigController._uninit();
+
+  // Check after controller gets reinitialized (or restart)
+  // that the region gets set to UK
+  await DoHConfigController.init();
+  await DoHController.init();
+  is(Preferences.get("doh-rollout.home-region"), "UK");
+
+  is(
+    DoHConfigController.currentConfig.enabled,
+    false,
+    "Rollout should not be enabled for new region"
+  );
+  await ensureTRRMode(undefined); // restart of the controller should change the region.
+});