Imrpove saving request stats for non-persistent background page

Related issue:
https://github.com/uBlockOrigin/uBlock-issues/issues/2969

Related previous commit:
https://github.com/gorhill/uBlock/commit/5a338b7210

The save-to-storage period is back to being around ~4 minutes, but
now browser.storage.session API is used to keep track of request
stats should the extension be suspended before the period elapse.

platform/common/vapi-background.js

@@ -109,9 +109,9 @@ vAPI.generateSecret = (size = 1) => {
  * 
  * */
 
-vAPI.sessionStorage = webext.storage.session || {
+vAPI.sessionStorage = browser.storage.session || {
     get() {
-        return Promise.resolve({});
+        return Promise.resolve();
     },
     set() {
         return Promise.resolve();
@@ -122,6 +122,7 @@ vAPI.sessionStorage = webext.storage.session || {
     clear() {
         return Promise.resolve();
     },
+    unavailable: true,
 };
 
 /*******************************************************************************
@@ -315,10 +316,10 @@ vAPI.Tabs = class {
         });
      }
 
-    async executeScript() {
+    async executeScript(...args) {
         let result;
         try {
-            result = await webext.tabs.executeScript(...arguments);
+            result = await webext.tabs.executeScript(...args);
         }
         catch(reason) {
         }
@@ -543,7 +544,7 @@ vAPI.Tabs = class {
             targetURL = vAPI.getURL(targetURL);
         }
 
-        vAPI.tabs.update(tabId, { url: targetURL });
+        return vAPI.tabs.update(tabId, { url: targetURL });
     }
 
     async remove(tabId) {
@@ -1778,15 +1779,24 @@ vAPI.cloud = (( ) => {
 /******************************************************************************/
 /******************************************************************************/
 
-vAPI.alarms = browser.alarms || {
-    create() {
+vAPI.alarms = {
+    create(...args) {
+        browser.alarms.create(...args);
     },
-    clear() {
+    createIfNotPresent(name, ...args) {
+        browser.alarms.get(name).then(details => {
+            if ( details !== undefined ) { return; }
+            browser.alarms.create(name, ...args);
+        });
+    },
+    async clear(...args) {
+        return browser.alarms.clear(...args);
     },
     onAlarm: {
-        addListener() {
-        }
-    }
+        addListener(...args) {
+            browser.alarms.onAlarm.addListener(...args);
+        },
+    },
 };
 
 /******************************************************************************/

src/js/background.js

@@ -174,11 +174,10 @@ const µBlock = {  // jshint ignore:line
         'moz-extension-scheme',
     ],
 
-    localSettings: {
-        blockedRequestCount: 0,
-        allowedRequestCount: 0,
+    requestStats: {
+        blockedCount: 0,
+        allowedCount: 0,
     },
-    localSettingsLastModified: 0,
 
     // Read-only
     systemSettings: {

src/js/messaging.js

@@ -365,8 +365,8 @@ const popupDataFromTabId = function(tabId, tabTitle) {
         colorBlindFriendly: µbus.colorBlindFriendly,
         cosmeticFilteringSwitch: false,
         firewallPaneMinimized: µbus.firewallPaneMinimized,
-        globalAllowedRequestCount: µb.localSettings.allowedRequestCount,
-        globalBlockedRequestCount: µb.localSettings.blockedRequestCount,
+        globalAllowedRequestCount: µb.requestStats.allowedCount,
+        globalBlockedRequestCount: µb.requestStats.blockedCount,
         fontSize: µbhs.popupFontSize,
         godMode: µbhs.filterAuthorMode,
         netFilteringSwitch: false,

src/js/pagestore.js

@@ -739,10 +739,8 @@ const PageStore = class {
                 aggregateAllowed += 1;
             }
         }
-        if ( aggregateAllowed !== 0 || aggregateBlocked !== 0 ) {
-            µb.localSettings.blockedRequestCount += aggregateBlocked;
-            µb.localSettings.allowedRequestCount += aggregateAllowed;
-            µb.localSettingsLastModified = now;
+        if ( aggregateAllowed || aggregateBlocked ) {
+            µb.incrementRequestStats(aggregateBlocked, aggregateAllowed);
         }
         journal.length = 0;
     }

src/js/start.js

@@ -327,7 +327,6 @@ const onFirstFetchReady = (fetched, adminExtra) => {
     }
 
     // Order is important -- do not change:
-    fromFetch(µb.localSettings, fetched);
     fromFetch(µb.restoreBackupSettings, fetched);
 
     permanentFirewall.fromString(fetched.dynamicFilteringString);
@@ -362,14 +361,9 @@ const createDefaultProps = ( ) => {
         'dynamicFilteringString': µb.dynamicFilteringDefault.join('\n'),
         'urlFilteringString': '',
         'hostnameSwitchesString': µb.hostnameSwitchesDefault.join('\n'),
-        'lastRestoreFile': '',
-        'lastRestoreTime': 0,
-        'lastBackupFile': '',
-        'lastBackupTime': 0,
         'netWhitelist': µb.netWhitelistDefault,
         'version': '0.0.0.0'
     };
-    toFetch(µb.localSettings, fetchableProps);
     toFetch(µb.restoreBackupSettings, fetchableProps);
     return fetchableProps;
 };
@@ -424,6 +418,7 @@ try {
             ubolog(`Cache magic numbers ready ${Date.now()-vAPI.T0} ms after launch`);
             onCacheSettingsReady(bin);
         }),
+        µb.loadLocalSettings(),
     ]);
 
     // https://github.com/uBlockOrigin/uBlock-issues/issues/1547
@@ -523,6 +518,9 @@ while ( µb.alarmQueue.length !== 0 ) {
     case 'createSelfie':
         µb.selfieManager.create();
         break;
+    case 'saveLocalSettings':
+        µb.saveLocalSettings();
+        break;
     }
 }
 

src/js/storage.js

@@ -97,23 +97,51 @@ import {
 /******************************************************************************/
 
 {
-    let localSettingsLastSaved = Date.now();
-
-    const shouldSave = ( ) => {
-        if ( µb.localSettingsLastModified > localSettingsLastSaved ) {
-            µb.saveLocalSettings();
+    µb.loadLocalSettings = ( ) => Promise.all([
+        vAPI.sessionStorage.get('requestStats'),
+        vAPI.storage.get('requestStats'),
+        vAPI.storage.get([ 'blockedRequestCount', 'allowedRequestCount' ]),
+    ]).then(([ a, b, c ]) => {
+        if ( a instanceof Object && a.requestStats ) { return a.requestStats; }
+        if ( b instanceof Object && b.requestStats ) { return b.requestStats; }
+        if ( c instanceof Object && Object.keys(c).length === 2 ) {
+            return {
+                blockedCount: c.blockedRequestCount,
+                allowedCount: c.allowedRequestCount,
+            };
         }
-        saveTimer.on(saveDelay);
+        return { blockedCount: 0, allowedCount: 0 };
+    }).then(({ blockedCount, allowedCount }) => {
+        µb.requestStats.blockedCount += blockedCount;
+        µb.requestStats.allowedCount += allowedCount;
+    });
+
+    const SAVE_DELAY_IN_MINUTES = 3.6;
+    const QUICK_SAVE_DELAY_IN_SECONDS = 23;
+
+    const saveTimer = vAPI.defer.create(( ) => {
+        µb.saveLocalSettings();
+    });
+
+    const quickSaveTimer = vAPI.defer.create(( ) => {
+        saveTimer.on({ min: SAVE_DELAY_IN_MINUTES });
+        if ( vAPI.sessionStorage.unavailable ) { return; }
+        vAPI.sessionStorage.set({ requestStats: µb.requestStats });
+        vAPI.alarms.createIfNotPresent('saveLocalSettings', {
+            delayInMinutes: SAVE_DELAY_IN_MINUTES + 0.5
+        });
+    });
+
+    µb.incrementRequestStats = (blocked, allowed) => {
+        µb.requestStats.blockedCount += blocked;
+        µb.requestStats.allowedCount += allowed;
+        quickSaveTimer.on({ sec: QUICK_SAVE_DELAY_IN_SECONDS });
     };
 
-    const saveTimer = vAPI.defer.create(shouldSave);
-    const saveDelay = { sec: 23 };
-
-    saveTimer.onidle(saveDelay);
-
-    µb.saveLocalSettings = function() {
-        localSettingsLastSaved = Date.now();
-        return vAPI.storage.set(this.localSettings);
+    µb.saveLocalSettings = ( ) => {
+        vAPI.alarms.clear('saveLocalSettings');
+        quickSaveTimer.off(); saveTimer.off();
+        return vAPI.storage.set({ requestStats: µb.requestStats });
     };
 }