this fixes #138, next: thorough code review

12 files changed, 784 insertions, 697 deletions

diff --git a/js/3p-filters.js b/js/3p-filters.js
index ac18763..cb3da21 100644
--- a/js/3p-filters.js
+++ b/js/3p-filters.js
@@ -31,6 +31,7 @@ var userListName = chrome.i18n.getMessage('1pPageName');
 var listDetails = {};
 var externalLists = '';
 var cacheWasPurged = false;
+var needUpdate = false;
 
 /******************************************************************************/
 
@@ -40,7 +41,6 @@ var onMessage = function(msg) {
     switch ( msg.what ) {
         case 'loadUbiquitousBlacklistCompleted':
             renderBlacklists();
-            selectedBlacklistsChanged();
             break;
 
         default:
@@ -109,6 +109,8 @@ var renderBlacklists = function() {
 
     var listStatsTemplate = chrome.i18n.getMessage('3pListsOfBlockedHostsPerListStats');
     var purgeButtontext = chrome.i18n.getMessage('3pExternalListPurge');
+    var updateButtontext = chrome.i18n.getMessage('3pExternalListNew');
+    var obsoleteButtontext = chrome.i18n.getMessage('3pExternalListObsolete');
 
     var htmlFromBranch = function(groupKey, listKeys, lists) {
         var html = [
@@ -134,7 +136,7 @@ var renderBlacklists = function() {
             listStatsTemplate,
             '</span>'
         ].join('');
-        var listKey, list, listEntry;
+        var listKey, list, listEntry, entryDetails;
         for ( var i = 0; i < listKeys.length; i++ ) {
             listKey = listKeys[i];
             list = lists[listKey];
@@ -146,12 +148,27 @@ var renderBlacklists = function() {
                 .replace('{{total}}', !isNaN(+list.entryCount) ? renderNumber(list.entryCount) : '?');
             html.push(listEntry);
             // https://github.com/gorhill/uBlock/issues/104
-            if ( /^https?:\/\/.+/.test(listKey) && listDetails.cache[listKey] ) {
+            entryDetails = listDetails.cache[listKey];
+            if ( entryDetails === undefined ) {
+                continue;
+            }
+            // Update status
+            if ( !list.off && (entryDetails.repoObsolete || entryDetails.cacheObsolete) ) {
+                html.push(
+                    '&ensp;',
+                    '<span class="status obsolete">',
+                    entryDetails.repoObsolete ? updateButtontext : obsoleteButtontext,
+                    '</span>'
+                );
+                needUpdate = true;
+            }
+            // In cache
+            else if ( entryDetails.cached ) {
                 html.push(
                     '&ensp;',
-                    '<button type="button" class="purge">',
+                    '<span class="status purge">',
                     purgeButtontext,
-                    '</button>'
+                    '</span>'
                 );
             }
         }
@@ -159,6 +176,8 @@ var renderBlacklists = function() {
         return html.join('');
     };
 
+    // https://www.youtube.com/watch?v=unCVi4hYRlY#t=30m18s
+
     var groupsFromLists = function(lists) {
         var groups = {};
         var listKeys = Object.keys(lists);
@@ -178,6 +197,7 @@ var renderBlacklists = function() {
 
     var onListsReceived = function(details) {
         listDetails = details;
+        needUpdate = false;
 
         var lists = details.available;
         var html = [];
@@ -208,13 +228,10 @@ var renderBlacklists = function() {
 
         uDom('#lists .listDetails').remove();
         uDom('#lists').html(html.join(''));
-        uDom('#parseAllABPHideFilters').prop('checked', listDetails.cosmetic === true);
-        uDom('#ubiquitousParseAllABPHideFiltersPrompt2').text(
-            chrome.i18n.getMessage("listsParseAllABPHideFiltersPrompt2")
-                .replace('{{abpHideFilterCount}}', renderNumber(µb.abpHideFilters.getFilterCount()))
-        );
+        uDom('#autoUpdate').prop('checked', listDetails.autoUpdate === true);
+        uDom('#parseCosmeticFilters').prop('checked', listDetails.cosmetic === true);
         uDom('a').attr('target', '_blank');
-        selectedBlacklistsChanged();
+        updateApplyButtons();
     };
 
     messaging.ask({ what: 'getLists' }, onListsReceived);
@@ -222,9 +239,9 @@ var renderBlacklists = function() {
 
 /******************************************************************************/
 
-// Check whether lists need reloading.
+// Return whether selection of lists changed.
 
-var needToReload = function() {
+var listsSelectionChanged = function() {
     if ( listDetails.cosmetic !== getµb().userSettings.parseAllABPHideFilters ) {
         return true;
     }
@@ -261,10 +278,19 @@ var needToReload = function() {
 
 /******************************************************************************/
 
+// Return whether content need update.
+
+var listsContentChanged = function() {
+    return needUpdate;
+};
+
+/******************************************************************************/
+
 // This is to give a visual hint that the selection of blacklists has changed.
 
-var selectedBlacklistsChanged = function() {
-    uDom('#blacklistsApply').prop('disabled', !needToReload());
+var updateApplyButtons = function() {
+    uDom('#buttonApply').toggleClass('enabled', listsSelectionChanged());
+    uDom('#buttonUpdate').toggleClass('enabled', listsContentChanged());
 };
 
 /******************************************************************************/
@@ -278,7 +304,7 @@ var onListCheckboxChanged = function() {
         return;
     }
     listDetails.available[href].off = !this.checked;
-    selectedBlacklistsChanged();
+    updateApplyButtons();
 };
 
 /******************************************************************************/
@@ -295,22 +321,22 @@ var onListLinkClicked = function(ev) {
 
 var onPurgeClicked = function(ev) {
     var button = uDom(this);
-    var href = button.parent().find('a').first().attr('href');
+    var li = button.parent();
+    var href = li.find('a').first().attr('href');
     if ( !href ) {
         return;
     }
     messaging.tell({ what: 'purgeCache', path: href });
     button.remove();
-    cacheWasPurged = true;
-    selectedBlacklistsChanged();
+    if ( li.find('input').first().prop('checked') ) {
+        cacheWasPurged = true;
+        updateApplyButtons();
+    }
 };
 
 /******************************************************************************/
 
-var blacklistsApplyHandler = function() {
-    if ( !needToReload() ) {
-        return;
-    }
+var reloadAll = function(update) {
     // Reload blacklists
     messaging.tell({
         what: 'userSettings',
@@ -334,17 +360,40 @@ var blacklistsApplyHandler = function() {
     }
     messaging.tell({
         what: 'reloadAllFilters',
-        switches: switches
+        switches: switches,
+        update: update
     });
     cacheWasPurged = false;
-    uDom('#blacklistsApply').prop('disabled', true);
+};
+
+/******************************************************************************/
+
+var buttonApplyHandler = function() {
+    reloadAll();
+    uDom('#buttonApply').toggleClass('enabled', false);
+};
+
+/******************************************************************************/
+
+var buttonUpdateHandler = function() {
+    reloadAll(true);
+};
+
+/******************************************************************************/
+
+var autoUpdateCheckboxChanged = function() {
+    messaging.tell({
+        what: 'userSettings',
+        name: 'autoUpdate',
+        value: this.checked
+    });
 };
 
 /******************************************************************************/
 
 var abpHideFiltersCheckboxChanged = function() {
     listDetails.cosmetic = this.checked;
-    selectedBlacklistsChanged();
+    updateApplyButtons();
 };
 
 /******************************************************************************/
@@ -383,11 +432,13 @@ var externalListsApplyHandler = function() {
 
 uDom.onLoad(function() {
     // Handle user interaction
-    uDom('#parseAllABPHideFilters').on('change', abpHideFiltersCheckboxChanged);
-    uDom('#blacklistsApply').on('click', blacklistsApplyHandler);
+    uDom('#autoUpdate').on('change', autoUpdateCheckboxChanged);
+    uDom('#parseCosmeticFilters').on('change', abpHideFiltersCheckboxChanged);
+    uDom('#buttonApply').on('click', buttonApplyHandler);
+    uDom('#buttonUpdate').on('click', buttonUpdateHandler);
     uDom('#lists').on('change', '.listDetails > input', onListCheckboxChanged);
     uDom('#lists').on('click', '.listDetails > a:nth-of-type(1)', onListLinkClicked);
-    uDom('#lists').on('click', 'button.purge', onPurgeClicked);
+    uDom('#lists').on('click', 'span.purge', onPurgeClicked);
     uDom('#externalLists').on('input', externalListsChangeHandler);
     uDom('#externalListsApply').on('click', externalListsApplyHandler);
 
diff --git a/js/about.js b/js/about.js
index b27cb7e..3203b98 100644
--- a/js/about.js
+++ b/js/about.js
@@ -27,95 +27,7 @@ uDom.onLoad(function() {
 
 /******************************************************************************/
 
-var updateList = {};
-var assetListSwitches = ['o', 'o', 'o'];
-var commitHistoryURLPrefix = 'https://github.com/gorhill/ublock/commits/master/';
-
-/******************************************************************************/
-
-var setAssetListClassBit = function(bit, state) {
-    assetListSwitches[assetListSwitches.length-1-bit] = !state ? 'o' : 'x';
-    uDom('#assetList')
-        .removeClass()
-        .addClass(assetListSwitches.join(''));
-};
-
-/******************************************************************************/
-
-var renderAssetList = function(details) {
-    var dirty = false;
-    var paths = Object.keys(details.list).sort();
-    if ( paths.length > 0 ) {
-        uDom('#assetList .assetEntry').remove();
-        var i = 0;
-        var path, status, html = [];
-        while ( path = paths[i++] ) {
-            status = details.list[path].status;
-            dirty = dirty || status !== 'Unchanged';
-            html.push(
-                '<tr class="assetEntry ' + status.toLowerCase().replace(/ +/g, '-') + '">',
-                '<td>',
-                '<a href="' + commitHistoryURLPrefix + path + '">',
-                path.replace(/^(assets\/[^/]+\/)(.+)$/, '$1<b>$2</b>'),
-                '</a>',
-                '<td>',
-                chrome.i18n.getMessage('aboutAssetsUpdateStatus' + status)
-            );
-        }
-        uDom('#assetList table tBody').append(html.join(''));
-        uDom('#assetList a').attr('target', '_blank');
-        updateList = details.list;
-    }
-    setAssetListClassBit(0, paths.length !== 0);
-    setAssetListClassBit(1, dirty);
-    setAssetListClassBit(2, false);
-};
-
-/******************************************************************************/
-
-var updateAssets = function() {
-    setAssetListClassBit(2, true);
-    var onDone = function(details) {
-        if ( details.changedCount !== 0 ) {
-            messaging.tell({ what: 'loadUpdatableAssets' });
-        }
-    };
-    messaging.ask({ what: 'launchAssetUpdater', list: updateList }, onDone);
-};
-
-/******************************************************************************/
-
-var updateAssetsList = function() {
-    messaging.ask({ what: 'getAssetUpdaterList' }, renderAssetList);
-};
-
-/******************************************************************************/
-
-// Updating all assets could be done from elsewhere and if so the
-// list here needs to be updated.
-
-var onAnnounce = function(msg) {
-    switch ( msg.what ) {
-        case 'allLocalAssetsUpdated':
-            updateAssetsList();
-            break;
-
-        default:
-            break;
-    }
-};
-
-messaging.start('about.js');
-messaging.listen(onAnnounce);
-
-/******************************************************************************/
-
 uDom('#aboutVersion').html(chrome.runtime.getManifest().version);
-uDom('#aboutAssetsUpdateButton').on('click', updateAssets);
-
-/******************************************************************************/
-
-updateAssetsList();
 
 /******************************************************************************/
 
diff --git a/js/asset-updater.js b/js/asset-updater.js
deleted file mode 100644
index 546682b..0000000
--- a/js/asset-updater.js
+++ /dev/null
@@ -1,227 +0,0 @@
-/*******************************************************************************
-
-    µBlock - a Chromium browser extension to block requests.
-    Copyright (C) 2014 Raymond Hill
-
-    This program is free software: you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program.  If not, see {http://www.gnu.org/licenses/}.
-
-    Home: https://github.com/gorhill/uBlock
-*/
-
-/* global chrome, µBlock */
-
-/******************************************************************************/
-
-// Asset update manager
-
-µBlock.assetUpdater = (function() {
-
-/******************************************************************************/
-
-var getUpdateList = function(callback) {
-    var localChecksumsText = '';
-    var remoteChecksumsText = '';
-
-    var compareChecksums = function() {
-        var parseChecksumsText = function(text) {
-            var result = {};
-            var lines = text.split(/\n+/);
-            var i = lines.length;
-            var fields;
-            while ( i-- ) {
-                fields = lines[i].trim().split(/\s+/);
-                if ( fields.length !== 2 ) {
-                    continue;
-                }
-                result[fields[1]] = fields[0];
-            }
-            return result;
-        };
-        if ( remoteChecksumsText === 'Error' || localChecksumsText === 'Error' ) {
-            remoteChecksumsText = localChecksumsText = '';
-        }
-        var localAssetChecksums = parseChecksumsText(localChecksumsText);
-        var remoteAssetChecksums = parseChecksumsText(remoteChecksumsText);
-
-        var toUpdate = {};
-        var path;
-        for ( path in remoteAssetChecksums ) {
-            if ( !remoteAssetChecksums.hasOwnProperty(path) ) {
-                continue;
-            }
-            if ( localAssetChecksums[path] === undefined ) {
-                toUpdate[path] = {
-                    status: 'Added',
-                    remoteChecksum: remoteAssetChecksums[path],
-                    localChecksum: ''
-                };
-                continue;
-            }
-            if ( localAssetChecksums[path] === remoteAssetChecksums[path] ) {
-                toUpdate[path] = {
-                    status: 'Unchanged',
-                    remoteChecksum: remoteAssetChecksums[path],
-                    localChecksum: localAssetChecksums[path]
-                };
-                continue;
-            }
-            toUpdate[path] = {
-                status: 'Changed',
-                remoteChecksum: remoteAssetChecksums[path],
-                localChecksum: localAssetChecksums[path]
-            };
-        }
-        for ( path in localAssetChecksums ) {
-            if ( !localAssetChecksums.hasOwnProperty(path) ) {
-                continue;
-            }
-            if ( remoteAssetChecksums[path] === undefined ) {
-                toUpdate[path] = {
-                    status: 'Removed',
-                    remoteChecksum: '',
-                    localChecksum: localAssetChecksums[path]
-                };
-            }
-        }
-
-        callback({ 'list': toUpdate });
-    };
-
-    var validateChecksums = function(details) {
-        if ( details.error || details.content === '' ) {
-            return 'Error';
-        }
-        if ( /^(?:[0-9a-f]{32}\s+\S+(\s+|$))+/.test(details.content) ) {
-            return details.content;
-        }
-        return 'Error';
-    };
-
-    var onLocalChecksumsLoaded = function(details) {
-        localChecksumsText = validateChecksums(details);
-        if ( remoteChecksumsText !== '' ) {
-            compareChecksums();
-        }
-    };
-
-    var onRemoteChecksumsLoaded = function(details) {
-        remoteChecksumsText = validateChecksums(details);
-        if ( localChecksumsText !== '' ) {
-            compareChecksums();
-        }
-    };
-
-    µBlock.assets.getRepo('assets/checksums.txt', onRemoteChecksumsLoaded);
-    µBlock.assets.get('assets/checksums.txt', onLocalChecksumsLoaded);
-};
-
-/******************************************************************************/
-
-// If `list` is null, it will be fetched internally.
-
-var update = function(list, callback) {
-    var assetChangedCount = 0;
-    var assetProcessedCount;
-    var updatedAssetChecksums = [];
-
-    var onCompleted = function() {
-        var details = {
-            what: 'allLocalAssetsUpdated',
-            changedCount: assetChangedCount
-        };
-        callback(details);
-        µBlock.messaging.announce(details);
-    };
-
-    var doCountdown = function() {
-        assetProcessedCount -= 1;
-        if ( assetProcessedCount > 0 ) {
-            return;
-        }
-        µBlock.assets.put(
-            'assets/checksums.txt',
-            updatedAssetChecksums.join('\n'),
-            onCompleted
-        );
-        chrome.storage.local.set({ 'assetsUpdateTimestamp': Date.now() });
-    };
-
-    var assetUpdated = function(details) {
-        var path = details.path;
-        var entry = list[path];
-        if ( details.error ) {
-            updatedAssetChecksums.push(entry.localChecksum + ' ' + path);
-        } else {
-            updatedAssetChecksums.push(entry.remoteChecksum + ' ' + path);
-            assetChangedCount += 1;
-        }
-        doCountdown();
-    };
-
-    var processList = function() {
-        assetProcessedCount = Object.keys(list).length;
-        if ( assetProcessedCount === 0 ) {
-            onCompleted();
-            return;
-        }
-        var entry;
-        var details = { path: '', md5: '' };
-        for ( var path in list ) {
-            if ( list.hasOwnProperty(path) === false ) {
-                continue;
-            }
-            entry = list[path];
-            if ( entry.status === 'Added' || entry.status === 'Changed' ) {
-                details.path = path;
-                details.md5 = entry.remoteChecksum;
-                µBlock.assets.update(details, assetUpdated);
-                continue;
-            }
-            if ( entry.status === 'Unchanged' ) {
-                updatedAssetChecksums.push(entry.localChecksum + ' ' + path);
-            }
-            doCountdown();
-        }
-    };
-
-    var listLoaded = function(details) {
-        list = details.list;
-        processList();
-    };
-
-    // Purge obsolete external assets
-    µBlock.assets.purge(/^https?:\/\/.+$/, Date.now() - µBlock.updateAssetsEvery);
-
-    if ( list ) {
-        processList();
-    } else {
-        getUpdateList(listLoaded);
-    }
-};
-
-/******************************************************************************/
-
-// Export API
-
-return {
-    'getList': getUpdateList,
-    'update': update
-};
-
-/******************************************************************************/
-
-})();
-
-/******************************************************************************/
-
diff --git a/js/assets.js b/js/assets.js
index 3f202d1..e57247c 100644
--- a/js/assets.js
+++ b/js/assets.js
@@ -23,20 +23,6 @@
 
 /*******************************************************************************
 
-Assets
-    Read:
-        If in cache
-            Use cache
-        If not in cache
-            Use local
-    Update:
-        Use remote
-        Save in cache
-
-    Import:
-        Use textarea
-        Save in cache [user directory]
-
 File system structure:
     assets
         ublock
@@ -44,14 +30,11 @@ File system structure:
         thirdparties
             ...
         user
-            blacklisted-hosts.txt
-                ...
+            filters.txt
+            ...
 
 */
 
-// Ref: http://www.w3.org/TR/2012/WD-file-system-api-20120417/
-// Ref: http://www.html5rocks.com/en/tutorials/file/filesystem/
-
 /******************************************************************************/
 
 // Low-level asset files manager
@@ -60,11 +43,31 @@ File system structure:
 
 /******************************************************************************/
 
-var fileSystem;
-var fileSystemQuota = 40 * 1024 * 1024;
 var repositoryRoot = µBlock.projectServerRoot;
 var nullFunc = function() {};
-var thirdpartyHomeURLs = null;
+var reIsExternalPath = /^https?:\/\/[a-z0-9]/;
+var reIsUserPath = /^assets\/user\//;
+
+var exports = {
+    autoUpdate: true,
+    autoUpdateDelay: 2 * 24 * 60 * 60 * 1000
+};
+
+/******************************************************************************/
+
+var AssetEntry = function() {
+    this.localChecksum = '';
+    this.repoChecksum = '';
+    this.expireTimestamp = 0;
+    this.homeURL = '';
+};
+
+var RepoMetadata = function() {
+    this.entries = {};
+    this.waiting = [];
+};
+
+var repoMeta = null;
 
 /******************************************************************************/
 
@@ -78,6 +81,18 @@ var cachedAssetsManager = (function() {
             callback(entries);
             return;
         }
+        // Flush cached non-user assets if these are from a prior version.
+        // https://github.com/gorhill/httpswitchboard/issues/212
+        var onLastVersionRead = function(store) {
+            var currentVersion = chrome.runtime.getManifest().version;
+            var lastVersion = store.extensionLastVersion || '0.0.0.0';
+            if ( currentVersion !== lastVersion ) {
+                chrome.storage.local.set({ 'extensionLastVersion': currentVersion });
+                exports.remove(/^assets\/(ublock|thirdparties)\//);
+                exports.remove('assets/checksums.txt');
+            }
+            callback(entries);
+        };
         var onLoaded = function(bin) {
             // https://github.com/gorhill/httpswitchboard/issues/381
             // Maybe the index was requested multiple times and already 
@@ -91,7 +106,7 @@ var cachedAssetsManager = (function() {
                 }
                 entries = bin.cached_asset_entries || {};
             }
-            callback(entries);
+            chrome.storage.local.get('extensionLastVersion', onLastVersionRead);
         };
         chrome.storage.local.get('cached_asset_entries', onLoaded);
     };
@@ -146,10 +161,8 @@ var cachedAssetsManager = (function() {
             }
         };
         var onEntries = function(entries) {
-            if ( entries[path] === undefined ) {
-                entries[path] = Date.now();
-                bin.cached_asset_entries = entries;
-            }
+            entries[path] = Date.now();
+            bin.cached_asset_entries = entries;
             chrome.storage.local.set(bin, onSaved);
         };
         getEntries(onEntries);
@@ -202,173 +215,177 @@ var getTextFileFromURL = function(url, onLoad, onError) {
 
 /******************************************************************************/
 
-// https://github.com/gorhill/uBlock/issues/89
-// Remove when I am confident everybody moved to the new storage
-
-// Useful to avoid having to manage a directory tree
-
-var cachePathFromPath = function(path) {
-    return path.replace(/\//g, '___');
+var updateLocalChecksums = function() {
+    var localChecksums = [];
+    var entries = repoMeta.entries;
+    var entry;
+    for ( var path in entries ) {
+        if ( entries.hasOwnProperty(path) === false ) {
+            continue;
+        }
+        entry = entries[path];
+        if ( entry.localChecksum !== '' ) {
+            localChecksums.push(entry.localChecksum + ' ' + path);
+        }
+    }
+    cachedAssetsManager.save('assets/checksums.txt', localChecksums.join('\n'));
 };
 
 /******************************************************************************/
 
-// https://github.com/gorhill/uBlock/issues/89
-// Remove when I am confident everybody moved to the new storage
+// Gather meta data of all assets.
+
+var getRepoMeta = function(callback, update) {
+    callback = callback || nullFunc;
 
-var requestFileSystem = function(onSuccess, onError) {
-    if ( fileSystem ) {
-        onSuccess(fileSystem);
+    if ( update ) {
+        repoMeta = null;
+    }
+    if ( repoMeta !== null ) {
+        if ( repoMeta.waiting.length !== 0 ) {
+            repoMeta.waiting.push(callback);
+        } else {
+            callback(repoMeta);
+        }
         return;
     }
 
-    var onRequestFileSystem = function(fs) {
-        fileSystem = fs;
-        onSuccess(fs);
-    };
-
-    var onRequestQuota = function(grantedBytes) {
-        window.webkitRequestFileSystem(window.PERSISTENT, grantedBytes, onRequestFileSystem, onError);
-    };
-
-    navigator.webkitPersistentStorage.requestQuota(fileSystemQuota, onRequestQuota, onError);
-};
-
-/******************************************************************************/
-
-// https://github.com/gorhill/uBlock/issues/89
-// Remove when I am confident everybody moved to the new storage
-
-var oldReadCachedFile = function(path, callback) {
-    var reportBack = function(content, err) {
-        var details = {
-            'path': path,
-            'content': content,
-            'error': err
-        };
-        callback(details);
-    };
-
-    var onCacheFileLoaded = function() {
-        // console.log('µBlock> readLocalFile() / onCacheFileLoaded()');
-        reportBack(this.responseText);
-        this.onload = this.onerror = null;
+    // https://github.com/gorhill/uBlock/issues/84
+    // First try to load from the actual home server of a third-party.
+    var parseHomeURLs = function(text) {
+        var entries = repoMeta.entries;
+        var urlPairs = text.split(/\n\n+/);
+        var i = urlPairs.length;
+        var pair, pos, k, v;
+        while ( i-- ) {
+            pair = urlPairs[i];
+            pos = pair.indexOf('\n');
+            if ( pos === -1 ) {
+                continue;
+            }
+            k = 'assets/thirdparties/' + pair.slice(0, pos).trim();
+            v = pair.slice(pos).trim();
+            if ( k === '' || v === '' ) {
+                continue;
+            }
+            if ( entries[k] === undefined ) {
+                entries[k] = new AssetEntry();
+            }
+            entries[k].homeURL = v;
+        }
+        while ( callback = repoMeta.waiting.pop() ) {
+            callback(repoMeta);
+        }
     };
 
-    var onCacheFileError = function(ev) {
-        // This handler may be called under normal circumstances: it appears
-        // the entry may still be present even after the file was removed.
-        // console.error('µBlock> readLocalFile() / onCacheFileError("%s")', path);
-        reportBack('', 'Error');
-        this.onload = this.onerror = null;
-    };
+    var pathToHomeURLs = 'assets/ublock/thirdparty-lists.txt';
 
-    var onCacheEntryFound = function(entry) {
-        // console.log('µBlock> readLocalFile() / onCacheEntryFound():', entry.toURL());
-        // rhill 2014-04-18: `ublock` query parameter is added to ensure
-        // the browser cache is bypassed.
-        getTextFileFromURL(entry.toURL() + '?ublock=' + Date.now(), onCacheFileLoaded, onCacheFileError);
+    var onLocalHomeURLsLoaded = function(details) {
+        parseHomeURLs(details.content);
     };
 
-    var onCacheEntryError = function(err) {
-        if ( err.name !== 'NotFoundError' ) {
-            console.error('µBlock> readLocalFile() / onCacheEntryError("%s"):', path, err.name);
+    var onRepoHomeURLsLoaded = function(details) {
+        var entries = repoMeta.entries;
+        var entry = entries[pathToHomeURLs];
+        if ( YaMD5.hashStr(details.content) !== entry.repoChecksum ) {
+            entry.repoChecksum = entry.localChecksum;
+            readLocalFile(pathToHomeURLs, onLocalHomeURLsLoaded);
+            return;
         }
-        reportBack('', 'Error');
-    };
-
-    var onRequestFileSystemSuccess = function(fs) {
-        fs.root.getFile(cachePathFromPath(path), null, onCacheEntryFound, onCacheEntryError);
+        cachedAssetsManager.save(pathToHomeURLs, details.content, onLocalHomeURLsLoaded);
     };
 
-    var onRequestFileSystemError = function(err) {
-        console.error('µBlock> readLocalFile() / onRequestFileSystemError():', err.name);
-        reportBack('', 'Error');
-    };
-
-    requestFileSystem(onRequestFileSystemSuccess, onRequestFileSystemError);
-};
-
-/******************************************************************************/
-
-// Flush cached non-user assets if these are from a prior version.
-// https://github.com/gorhill/httpswitchboard/issues/212
-
-var cacheSynchronized = false;
-
-var synchronizeCache = function() {
-    if ( cacheSynchronized ) {
-        return;
-    }
-    cacheSynchronized = true;
-
-    // https://github.com/gorhill/uBlock/issues/89
-    // Remove when I am confident everybody moved to the new storage
+    var checksumCountdown = 2;
+    var localChecksums = '';
+    var repoChecksums = '';
 
-    var directoryReader;
-    var done = function() {
-        directoryReader = null;
-    };
-
-    var onReadEntries = function(entries) {
-        var n = entries.length;
-        if ( !n ) {
-            return done();
+    var checksumsReceived = function() {
+        checksumCountdown -= 1;
+        if ( checksumCountdown !== 0 ) {
+            return;
         }
+        // Remove from cache assets which no longer exist
+        var entries = repoMeta.entries;
+        var checksumsChanged = false;
         var entry;
-        for ( var i = 0; i < n; i++ ) {
-            entry = entries[i];
-            entry.remove(nullFunc);
+        for ( var path in entries ) {
+            if ( entries.hasOwnProperty(path) === false ) {
+                continue;
+            }
+            entry = entries[path];
+            // If repo checksums could not be fetched, assume no change
+            if ( repoChecksums === '' ) {
+                entry.repoChecksum = entry.localChecksum;
+            }
+            if ( entry.repoChecksum !== '' || entry.localChecksum === '' ) {
+                continue;
+            }
+            checksumsChanged = true;
+            cachedAssetsManager.remove(path);
+            entry.localChecksum = '';
+        }
+        if ( checksumsChanged ) {
+            updateLocalChecksums();
+        }
+        // Fetch and store homeURL associations
+        entry = entries[pathToHomeURLs];
+        if ( entry.localChecksum !== entry.repoChecksum ) {
+            readRepoFile(pathToHomeURLs, onRepoHomeURLsLoaded);
+        } else {
+            readLocalFile(pathToHomeURLs, onLocalHomeURLsLoaded);
         }
-        // Read entries until none returned.
-        directoryReader.readEntries(onReadEntries, onReadEntriesError);
-    };
-
-    var onReadEntriesError = function(err) {
-        console.error('µBlock> synchronizeCache() / onReadEntriesError("%s"):', err.name);
-        done();
-    };
-
-    var onRequestFileSystemSuccess = function(fs) {
-        directoryReader = fs.root.createReader();
-        directoryReader.readEntries(onReadEntries, onReadEntriesError);
     };
 
-    var onRequestFileSystemError = function(err) {
-        console.error('µBlock> synchronizeCache() / onRequestFileSystemError():', err.name);
-        done();
+    var validateChecksums = function(details) {
+        if ( details.error || details.content === '' ) {
+            return '';
+        }
+        if ( /^(?:[0-9a-f]{32}\s+\S+(?:\s+|$))+/.test(details.content) === false ) {
+            return '';
+        }
+        return details.content;
     };
 
-    var onLastVersionRead = function(store) {
-        var currentVersion = chrome.runtime.getManifest().version;
-        var lastVersion = store.extensionLastVersion || '0.0.0.0';
-        if ( currentVersion === lastVersion ) {
-            return done();
+    var parseChecksums = function(text, which) {
+        var entries = repoMeta.entries;
+        var lines = text.split(/\n+/);
+        var i = lines.length;
+        var fields, assetPath;
+        while ( i-- ) {
+            fields = lines[i].trim().split(/\s+/);
+            if ( fields.length !== 2 ) {
+                continue;
+            }
+            assetPath = fields[1];
+            if ( entries[assetPath] === undefined ) {
+                entries[assetPath] = new AssetEntry();
+            }
+            entries[assetPath][which + 'Checksum'] = fields[0];
         }
-        chrome.storage.local.set({ 'extensionLastVersion': currentVersion });
-        cachedAssetsManager.remove(/^assets\/(ublock|thirdparties)\//);
-        cachedAssetsManager.remove('assets/checksums.txt');
-        requestFileSystem(onRequestFileSystemSuccess, onRequestFileSystemError);
     };
 
-    // https://github.com/gorhill/uBlock/issues/89
-    // Backward compatiblity.
-
-    var onUserFiltersSaved = function() {
-        chrome.storage.local.get('extensionLastVersion', onLastVersionRead);
+    var onLocalChecksumsLoaded = function(details) {
+        if ( localChecksums = validateChecksums(details) ) {
+            parseChecksums(localChecksums, 'local');
+        }
+        checksumsReceived();
     };
 
-    var onUserFiltersLoaded = function(details) {
-        if ( details.content !== '' ) {
-            cachedAssetsManager.save(details.path, details.content, onUserFiltersSaved);
-        } else {
-            chrome.storage.local.get('extensionLastVersion', onLastVersionRead);
+    var onRepoChecksumsLoaded = function(details) {
+        if ( repoChecksums = validateChecksums(details) ) {
+            parseChecksums(repoChecksums, 'repo');
         }
+        checksumsReceived();
     };
 
-    oldReadCachedFile('assets/user/filters.txt', onUserFiltersLoaded);
+    repoMeta = new RepoMetadata();
+    repoMeta.waiting.push(callback);
+    readRepoFile('assets/checksums.txt', onRepoChecksumsLoaded);
+    readLocalFile('assets/checksums.txt', onLocalChecksumsLoaded);
 };
 
+// https://www.youtube.com/watch?v=-t3WYfgM4x8
+
 /******************************************************************************/
 
 var readLocalFile = function(path, callback) {
@@ -389,7 +406,7 @@ var readLocalFile = function(path, callback) {
         this.onload = this.onerror = null;
     };
 
-    var onLocalFileError = function(ev) {
+    var onLocalFileError = function() {
         console.error('µBlock> readLocalFile() / onLocalFileError("%s")', path);
         reportBack('', 'Error');
         this.onload = this.onerror = null;
@@ -423,6 +440,7 @@ var readRepoFile = function(path, callback) {
     };
 
     var onRepoFileLoaded = function() {
+        this.onload = this.onerror = null;
         // console.log('µBlock> readRepoFile() / onRepoFileLoaded()');
         // https://github.com/gorhill/httpswitchboard/issues/263
         if ( this.status === 200 ) {
@@ -430,13 +448,12 @@ var readRepoFile = function(path, callback) {
         } else {
             reportBack('', 'Error ' + this.statusText);
         }
-        this.onload = this.onerror = null;
     };
 
-    var onRepoFileError = function(ev) {
+    var onRepoFileError = function() {
+        this.onload = this.onerror = null;
         console.error('µBlock> readRepoFile() / onRepoFileError("%s")', path);
         reportBack('', 'Error');
-        this.onload = this.onerror = null;
     };
 
     // 'ublock=...' is to skip browser cache
@@ -473,19 +490,19 @@ var readExternalFile = function(path, callback) {
         cachedAssetsManager.save(path, this.responseText, onExternalFileCached);
     };
 
-    var onExternalFileError = function(ev) {
+    var onExternalFileError = function() {
         console.error('µBlock> onExternalFileError() / onLocalFileError("%s")', path);
         reportBack('', 'Error');
         this.onload = this.onerror = null;
     };
 
     var onCachedContentLoaded = function(details) {
-        // console.log('µBlock> readLocalFile() / onCacheFileLoaded()');
+        // console.log('µBlock> readExternalFile() / onCacheFileLoaded()');
         reportBack(details.content);
     };
 
     var onCachedContentError = function(details) {
-        // console.error('µBlock> readLocalFile() / onCacheFileError("%s")', path);
+        // console.error('µBlock> readExternalFile() / onCacheFileError("%s")', path);
         getTextFileFromURL(details.path, onExternalFileLoaded, onExternalFileError);
     };
 
@@ -494,165 +511,521 @@ var readExternalFile = function(path, callback) {
 
 /******************************************************************************/
 
-var purgeCache = function(pattern, before) {
-    cachedAssetsManager.remove(pattern, before);
-};
+// An asset from an external source with a copy shipped with the extension:
+//       Path --> starts with 'assets/(thirdparties|ublock)/', with a home URL
+//   External --> 
+// Repository --> has checksum (to detect need for update only)
+//      Cache --> has expiration timestamp (in cache)
+//      Local --> install time version
 
-/******************************************************************************/
+var readRepoCopyAsset = function(path, callback) {
+    var assetEntry;
 
-var writeLocalFile = function(path, content, callback) {
-    cachedAssetsManager.save(path, content, callback);
-};
+    var reportBack = function(content, err) {
+        var details = {
+            'path': path,
+            'content': content
+        };
+        if ( err ) {
+            details.error = err;
+        }
+        callback(details);
+    };
 
-/******************************************************************************/
+    var updateChecksum = function() {
+        if ( assetEntry !== undefined ) {
+            if ( assetEntry.repoChecksum !== assetEntry.localChecksum ) {
+                assetEntry.localChecksum = assetEntry.repoChecksum;
+                updateLocalChecksums();
+            }
+        }
+    };
 
-var updateFromRemote = function(details, callback) {
-    // 'ublock=...' is to skip browser cache
-    var targetPath = details.path;
-    // https://github.com/gorhill/uBlock/issues/84
-    var homeURL = '';
-    var repositoryURL = repositoryRoot + targetPath + '?ublock=' + Date.now();
-    var targetMd5 = details.md5 || '';
+    var onInstallFileLoaded = function() {
+        this.onload = this.onerror = null;
+        console.log('µBlock> readRepoCopyAsset("%s") / onInstallFileLoaded()', path);
+        reportBack(this.responseText);
+    };
+
+    var onInstallFileError = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readRepoCopyAsset("%s") / onInstallFileError():', path, this.statusText);
+        reportBack('', 'Error');
+    };
+
+    var onCachedContentLoaded = function(details) {
+        console.log('µBlock> readRepoCopyAsset("%s") / onCacheFileLoaded()', path);
+        reportBack(details.content);
+    };
 
-    var reportBackError = function() {
-        callback({
-            'path': targetPath,
-            'error': 'Error'
-        });
+    var onCachedContentError = function(details) {
+        console.log('µBlock> readRepoCopyAsset("%s") / onCacheFileError()', path);
+        getTextFileFromURL(chrome.runtime.getURL(details.path), onInstallFileLoaded, onInstallFileError);
     };
 
+    var repositoryURL = repositoryRoot + path + '?ublock=' + Date.now();
+
     var onRepoFileLoaded = function() {
         this.onload = this.onerror = null;
-        if ( typeof this.responseText !== 'string' ) {
-            console.error('µBlock> updateFromRemote("%s") / onRepoFileLoaded(): no response', repositoryURL);
-            reportBackError();
+        if ( typeof this.responseText !== 'string' || this.responseText === '' ) {
+            console.error('µBlock> readRepoCopyAsset("%s") / onRepoFileLoaded("%s"): no response', path, repositoryURL);
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
             return;
         }
-        if ( targetMd5 !== '' && YaMD5.hashStr(this.responseText) !== targetMd5 ) {
-            console.error('µBlock> updateFromRemote("%s") / onRepoFileLoaded(): bad md5 checksum', repositoryURL);
-            reportBackError();
-            return;
-        }
-        // console.debug('µBlock> updateFromRemote("%s") / onRepoFileLoaded()', repositoryURL);
-        writeLocalFile(targetPath, this.responseText, callback);
+        console.debug('µBlock> readRepoCopyAsset("%s") / onRepoFileLoaded("%s")', path, repositoryURL);
+        updateChecksum();
+        cachedAssetsManager.save(path, this.responseText, callback);
     };
 
-    var onRepoFileError = function(ev) {
+    var onRepoFileError = function() {
         this.onload = this.onerror = null;
-        console.error('µBlock> updateFromRemote() / onRepoFileError("%s"):', repositoryURL, this.statusText);
-        reportBackError();
+        console.error('µBlock> readRepoCopyAsset("%s") / onRepoFileError("%s"):', path, repositoryURL, this.statusText);
+        cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
     };
 
     var onHomeFileLoaded = function() {
         this.onload = this.onerror = null;
-        if ( typeof this.responseText !== 'string' ) {
-            console.error('µBlock> updateFromRemote("%s") / onHomeFileLoaded(): no response', homeURL);
-            getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+        if ( typeof this.responseText !== 'string' || this.responseText === '' ) {
+            console.error('µBlock> readRepoCopyAsset("%s") / onHomeFileLoaded("%s"): no response', path, assetEntry.homeURL);
+            // Fetch from repo only if obsolescence was due to repo checksum
+            if ( assetEntry.localChecksum !== assetEntry.repoChecksum ) {
+                getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+            } else {
+                cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+            }
             return;
         }
-        if ( targetMd5 !== '' && YaMD5.hashStr(this.responseText) !== targetMd5 ) {
-            console.error('µBlock> updateFromRemote("%s") / onHomeFileLoaded(): bad md5 checksum', homeURL);
+        console.debug('µBlock> readRepoCopyAsset("%s") / onHomeFileLoaded("%s")', path, assetEntry.homeURL);
+        updateChecksum();
+        cachedAssetsManager.save(path, this.responseText, callback);
+    };
+
+    var onHomeFileError = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readRepoCopyAsset("%s") / onHomeFileError("%s"):', path, assetEntry.homeURL, this.statusText);
+        // Fetch from repo only if obsolescence was due to repo checksum
+        if ( assetEntry.localChecksum !== assetEntry.repoChecksum ) {
             getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+        } else {
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+        }
+    };
+
+    var onCacheMetaReady = function(entries) {
+        var timestamp = entries[path];
+        // In cache
+        if ( typeof timestamp === 'number' ) {
+            // Verify obsolescence
+            if ( exports.autoUpdate ) {
+                var obsolete = Date.now() - exports.autoUpdateDelay;
+                if ( timestamp <= obsolete ) {
+                    console.log('µBlock> readRepoCopyAsset("%s") / onCacheMetaReady(): cache is obsolete', path);
+                    getTextFileFromURL(assetEntry.homeURL, onHomeFileLoaded, onHomeFileError);
+                    return;
+                }
+            }
+            // Not obsolete
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
             return;
         }
-        // console.debug('µBlock> updateFromRemote("%s") / onHomeFileLoaded()', homeURL);
-        writeLocalFile(targetPath, this.responseText, callback);
+        // Not in cache
+        getTextFileFromURL(chrome.runtime.getURL(path), onInstallFileLoaded, onInstallFileError);
     };
 
-    var onHomeFileError = function(ev) {
+    var onRepoMetaReady = function(meta) {
+        assetEntry = meta.entries[path];
+
+        // Asset doesn't exist
+        if ( assetEntry === undefined ) {
+            reportBack('', 'Error: Asset not found');
+            return;
+        }
+
+        // Repo copy changed: fetch from home URL
+        if ( exports.autoUpdate ) {
+            if ( assetEntry.localChecksum !== assetEntry.repoChecksum ) {
+                console.log('µBlock> readRepoCopyAsset("%s") / onRepoMetaReady(): repo has newer version', path);
+                getTextFileFromURL(assetEntry.homeURL, onHomeFileLoaded, onHomeFileError);
+                return;
+            }
+        }
+
+        // No change, we will inspect the cached version for obsolescence
+        cachedAssetsManager.entries(onCacheMetaReady);
+    };
+
+    getRepoMeta(onRepoMetaReady);
+};
+
+// https://www.youtube.com/watch?v=uvUW4ozs7pY
+
+/******************************************************************************/
+
+// An important asset shipped with the extension -- typically small, or 
+// doesn't change often:
+//       Path --> starts with 'assets/(thirdparties|ublock)/', without a home URL
+// Repository --> has checksum (to detect need for update and corruption)
+//      Cache --> whatever from above
+//      Local --> install time version
+
+var readRepoOnlyAsset = function(path, callback) {
+
+    var assetEntry;
+
+    var reportBack = function(content, err) {
+        var details = {
+            'path': path,
+            'content': content
+        };
+        if ( err ) {
+            details.error = err;
+        }
+        callback(details);
+    };
+
+    var onInstallFileLoaded = function() {
         this.onload = this.onerror = null;
-        console.error('µBlock> updateFromRemote() / onHomeFileError("%s"):', homeURL, this.statusText);
-        getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+        console.log('µBlock> readRepoOnlyAsset("%s") / onInstallFileLoaded()', path);
+        reportBack(this.responseText);
     };
 
-    // https://github.com/gorhill/uBlock/issues/84
-    // Create a URL from where the asset needs to be downloaded. It can be:
-    // - a home server URL
-    // - a github repo URL
-    var getThirdpartyHomeURL = function() {
-        // If it is a 3rd-party, look-up home server URL, if any.
-        if ( thirdpartyHomeURLs && targetPath.indexOf('assets/thirdparties/') === 0 ) {
-            var k = targetPath.replace('assets/thirdparties/', '');
-            if ( thirdpartyHomeURLs[k] ) {
-                homeURL = thirdpartyHomeURLs[k];
-            }
+    var onInstallFileError = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readRepoOnlyAsset("%s") / onInstallFileError()', path);
+        reportBack('', 'Error');
+    };
+
+    var onCachedContentLoaded = function(details) {
+        console.log('µBlock> readRepoOnlyAsset("%s") / onCachedContentLoaded()', path);
+        reportBack(details.content);
+    };
+
+    var onCachedContentError = function() {
+        console.log('µBlock> readRepoOnlyAsset("%s") / onCachedContentError()', path);
+        getTextFileFromURL(chrome.runtime.getURL(path), onInstallFileLoaded, onInstallFileError);
+    };
+
+    var repositoryURL = repositoryRoot + path + '?ublock=' + Date.now();
+
+    var onRepoFileLoaded = function() {
+        this.onload = this.onerror = null;
+        if ( typeof this.responseText !== 'string' ) {
+            console.error('µBlock> readRepoOnlyAsset("%s") / onRepoFileLoaded("%s"): no response', path, repositoryURL);
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+            return;
         }
-        // If there is a home server, disregard checksum: the file is assumed
-        // most up to date at the home server.
-        if ( homeURL !== '' ) {
-            targetMd5 = '';
-            getTextFileFromURL(homeURL, onHomeFileLoaded, onHomeFileError);
+        if ( YaMD5.hashStr(this.responseText) !== assetEntry.repoChecksum ) {
+            console.error('µBlock> readRepoOnlyAsset("%s") / onRepoFileLoaded("%s"): bad md5 checksum', path, repositoryURL);
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
             return;
         }
-        // The resource will be pulled from Github repo. It's reserved for
-        // more important assets, so we keep and use the checksum.
-        getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+        console.debug('µBlock> readRepoOnlyAsset("%s") / onRepoFileLoaded("%s")', path, repositoryURL);
+        assetEntry.localChecksum = assetEntry.repoChecksum;
+        updateLocalChecksums();
+        cachedAssetsManager.save(path, this.responseText, callback);
     };
 
-    // https://github.com/gorhill/uBlock/issues/84
-    // First try to load from the actual home server of a third-party.
-    var onThirdpartyHomeURLsLoaded = function(details) {
-        thirdpartyHomeURLs = {};
-        if ( details.error ) {
-            getThirdpartyHomeURL();
+    var onRepoFileError = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readRepoOnlyAsset("%s") / onRepoFileError("%s"):', path, repositoryURL, this.statusText);
+        cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+    };
+
+    var onRepoMetaReady = function(meta) {
+        assetEntry = meta.entries[path];
+
+        // Asset doesn't exist
+        if ( assetEntry === undefined ) {
+            reportBack('', 'Error: Asset not found');
             return;
         }
-        var urlPairs = details.content.split(/\n\n+/);
-        var i = urlPairs.length;
-        var pair, pos, k, v;
-        while ( i-- ) {
-            pair = urlPairs[i];
-            pos = pair.indexOf('\n');
-            if ( pos === -1 ) {
-                continue;
+
+        // Asset added or changed: load from repo URL and then cache result
+        if ( exports.autoUpdate ) {
+            if ( assetEntry.localChecksum !== assetEntry.repoChecksum ) {
+                console.log('µBlock> readRepoOnlyAsset("%s") / onRepoMetaReady(): repo has newer version', path);
+                getTextFileFromURL(repositoryURL, onRepoFileLoaded, onRepoFileError);
+                return;
             }
-            k = pair.slice(0, pos).trim();
-            v = pair.slice(pos).trim();
-            if ( k === '' || v === '' ) {
-                continue;
+        }
+
+        // Asset unchanged: load from cache
+        cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+    };
+
+    getRepoMeta(onRepoMetaReady);
+};
+
+/******************************************************************************/
+
+// Asset doesn't exist. Just for symmetry purpose.
+
+var readNilAsset = function(path, callback) {
+    callback({
+        'path': path,
+        'content': '',
+        'error': 'Error: asset not found'
+    });
+};
+
+/******************************************************************************/
+
+// An external asset:
+//       Path --> starts with 'http'
+//   External --> https://..., http://...
+//      Cache --> has expiration timestamp (in cache)
+
+var readExternalAsset = function(path, callback) {
+    var reportBack = function(content, err) {
+        var details = {
+            'path': path,
+            'content': content
+        };
+        if ( err ) {
+            details.error = err;
+        }
+        callback(details);
+    };
+
+    var onCachedContentLoaded = function(details) {
+        console.log('µBlock> readExternalAsset("%s") / onCachedContentLoaded()', path);
+        reportBack(details.content);
+    };
+
+    var onCachedContentError = function() {
+        console.error('µBlock> readExternalAsset("%s") / onCachedContentError()', path);
+        reportBack('', 'Error');
+    };
+
+    var onExternalFileLoaded = function() {
+        this.onload = this.onerror = null;
+        console.log('µBlock> readExternalAsset("%s") / onExternalFileLoaded1()', path);
+        cachedAssetsManager.save(path, this.responseText);
+        reportBack(this.responseText);
+    };
+
+    var onExternalFileError2 = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readExternalAsset("%s") / onExternalFileError2()', path);
+        reportBack('', 'Error');
+    };
+
+    var onExternalFileError1 = function() {
+        this.onload = this.onerror = null;
+        console.error('µBlock> readExternalAsset("%s") / onExternalFileError1()', path);
+        cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+    };
+
+    var entriesReady = function(entries) {
+        var timestamp = entries[path];
+        // In cache
+        if ( typeof timestamp === 'number' ) {
+            // Obsolete?
+            if ( exports.autoUpdate ) {
+                var obsolete = Date.now() - exports.autoUpdateDelay;
+                if ( timestamp <= obsolete ) {
+                    getTextFileFromURL(path, onExternalFileLoaded, onExternalFileError1);
+                    return;
+                }
             }
-            thirdpartyHomeURLs[k] = v;
+            // Not obsolete
+            cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+            return;
         }
-        getThirdpartyHomeURL();
+        // Not in cache
+        getTextFileFromURL(path, onExternalFileLoaded, onExternalFileError2);
+    };
+
+    cachedAssetsManager.entries(entriesReady);
+};
+
+/******************************************************************************/
+
+// User data:
+//       Path --> starts with 'assets/user/'
+//      Cache --> whatever user saved
+
+var readUserAsset = function(path, callback) {
+    var onCachedContentLoaded = function(details) {
+        console.log('µBlock> readUserAsset("%s") / onCachedContentLoaded()', path);
+        callback({ 'path': path, 'content': details.content });
+    };
+
+    var onCachedContentError = function() {
+        console.log('µBlock> readUserAsset("%s") / onCachedContentError()', path);
+        callback({ 'path': path, 'content': '' });
     };
 
-    // Get home servers if not done yet.
-    if ( thirdpartyHomeURLs === null ) {
-        readLocalFile('assets/ublock/thirdparty-lists.txt', onThirdpartyHomeURLsLoaded);
-    } else {
-        getThirdpartyHomeURL();
+    cachedAssetsManager.load(path, onCachedContentLoaded, onCachedContentError);
+};
+
+/******************************************************************************/
+
+// Assets
+//
+// A copy of an asset from an external source shipped with the extension:
+//       Path --> starts with 'assets/(thirdparties|ublock)/', with a home URL
+//   External --> 
+// Repository --> has checksum (to detect obsolescence)
+//      Cache --> has expiration timestamp (to detect obsolescence)
+//      Local --> install time version
+//
+// An important asset shipped with the extension (usually small, or doesn't
+// change often):
+//       Path --> starts with 'assets/(thirdparties|ublock)/', without a home URL
+// Repository --> has checksum (to detect obsolescence or data corruption)
+//      Cache --> whatever from above
+//      Local --> install time version
+//
+// An external filter list:
+//       Path --> starts with 'http'
+//   External --> 
+//      Cache --> has expiration timestamp (to detect obsolescence)
+//
+// User data:
+//       Path --> starts with 'assets/user/'
+//      Cache --> whatever user saved
+//
+// When a checksum is present, it is used to determine whether the asset
+// needs to be updated.
+// When an expiration timestamp is present, it is used to determine whether
+// the asset needs to be updated.
+//
+// If no update required, an asset if first fetched from the cache. If the
+// asset is not cached it is fetched from the closest location: local for 
+// an asset shipped with the extension, external for an asset not shipped
+// with the extension.
+
+exports.get = function(path, callback) {
+
+    if ( reIsUserPath.test(path) ) {
+        readUserAsset(path, callback);
+        return;
     }
+
+    if ( reIsExternalPath.test(path) ) {
+        readExternalAsset(path, callback);
+        return;
+    }
+
+    var onRepoMetaReady = function(meta) {
+        var assetEntry = meta.entries[path];
+
+        // Asset doesn't exist
+        if ( assetEntry === undefined ) {
+            readNilAsset(path, callback);
+            return;
+        }
+
+        // Asset is repo copy of external content
+        if ( assetEntry.homeURL !== '' ) {
+            readRepoCopyAsset(path, callback);
+            return;
+        }
+
+        // Asset is repo only
+        readRepoOnlyAsset(path, callback);
+    };
+
+    getRepoMeta(onRepoMetaReady);
 };
 
+// https://www.youtube.com/watch?v=98y0Q7nLGWk
+
 /******************************************************************************/
 
-var cacheEntries = function(callback) {
-    return cachedAssetsManager.entries(callback);
+exports.put = function(path, content, callback) {
+    cachedAssetsManager.save(path, content, callback);
 };
 
 /******************************************************************************/
 
-// Flush cached assets if cache content is from an older version: the extension
-// always ships with the most up-to-date assets.
+exports.purge = function(pattern, before) {
+    cachedAssetsManager.remove(pattern, before);
+};
+
+/******************************************************************************/
+
+exports.metadata = function(callback) {
+    var out = {};
+
+    var onRepoMetaReady = function(meta) {
+        var entries = meta.entries;
+        var entryRepo, entryOut;
+        for ( var path in entries ) {
+            if ( entries.hasOwnProperty(path) === false ) {
+                continue;
+            }
+            entryRepo = entries[path];
+            entryOut = out[path];
+            if ( entryOut === undefined ) {
+                entryOut = out[path] = {};
+            }
+            entryOut.localChecksum = entryRepo.localChecksum;
+            entryOut.repoChecksum = entryRepo.repoChecksum;
+            entryOut.homeURL = entryRepo.homeURL;
+            entryOut.repoObsolete = entryOut.localChecksum !== entryOut.repoChecksum;
+        }
+        callback(out);
+    };
+
+    var onCacheMetaReady = function(entries) {
+        var obsolete = Date.now() - exports.autoUpdateDelay;
+        var entryOut;
+        for ( var path in entries ) {
+            if ( entries.hasOwnProperty(path) === false ) {
+                continue;
+            }
+            entryOut = out[path];
+            if ( entryOut === undefined ) {
+                entryOut = out[path] = {};
+            }
+            entryOut.lastModified = entries[path];
+            // User data is not literally cache data
+            if ( reIsUserPath.test(path) ) {
+                continue;
+            }
+            entryOut.cached = true;
+            entryOut.cacheObsolete = entryOut.lastModified <= obsolete;
+            if ( reIsExternalPath.test(path) ) {
+                entryOut.homeURL = path;
+            }
+        }
+        getRepoMeta(onRepoMetaReady);
+    };
 
-synchronizeCache();
+    cachedAssetsManager.entries(onCacheMetaReady);
+};
 
 /******************************************************************************/
 
-// Export API
+exports.purgeAll = function(callback) {
+    var onMetaDataReady = function(entries) {
+        var out = {};
+        var entry;
+        for ( var path in entries ) {
+            if ( entries.hasOwnProperty(path) === false ) {
+                continue;
+            }
+            entry = entries[path];
+            if ( !entry.cacheObsolete && !entry.repoObsolete ) {
+                continue;
+            }
+            cachedAssetsManager.remove(path);
+            out[path] = true;
+        }
+        callback(out);
+    };
 
-return {
-    'get': readLocalFile,
-    'getExternal': readExternalFile,
-    'getRepo': readRepoFile,
-    'purge': purgeCache,
-    'put': writeLocalFile,
-    'update': updateFromRemote,
-    'entries': cacheEntries
+    exports.metadata(onMetaDataReady);
 };
 
 /******************************************************************************/
 
+return exports;
+
+/******************************************************************************/
+
 })();
 
 /******************************************************************************/
diff --git a/js/background.js b/js/background.js
index 7c966fc..ff72b98 100644
--- a/js/background.js
+++ b/js/background.js
@@ -31,6 +31,7 @@ return {
     manifest: chrome.runtime.getManifest(),
 
     userSettings: {
+        autoUpdate: true,
         collapseBlocked: true,
         externalLists: '',
         logBlockedRequests: false,
diff --git a/js/messaging-handlers.js b/js/messaging-handlers.js
index 3a93f81..460896f 100644
--- a/js/messaging-handlers.js
+++ b/js/messaging-handlers.js
@@ -250,9 +250,10 @@ var getLists = function(callback) {
         available: null,
         current: µb.remoteBlacklists,
         cosmetic: µb.userSettings.parseAllABPHideFilters,
+        autoUpdate: µb.userSettings.autoUpdate,
         cache: null
     };
-    var onEntries = function(entries) {
+    var onMetadataReady = function(entries) {
         r.cache = entries;
         if ( r.available ) {
             callback(r);
@@ -265,7 +266,7 @@ var getLists = function(callback) {
         }
     };
     µb.getAvailableLists(onLists);
-    µb.assets.entries(onEntries);
+    µb.assets.metadata(onMetadataReady);
 };
 
 /******************************************************************************/
@@ -475,20 +476,6 @@ var onMessage = function(request, sender, callback) {
 
     // Async
     switch ( request.what ) {
-        case 'getAssetUpdaterList':
-            return µb.assetUpdater.getList(callback);
-
-        case 'launchAssetUpdater':
-            return µb.assetUpdater.update(request.list, callback);
-
-        case 'readUserSettings':
-            return chrome.storage.local.get(µb.userSettings, callback);
-
-        case 'readUserFilters':
-            return µb.assets.get(µb.userFiltersPath, callback);
-
-        case 'writeUserFilters':
-            return µb.assets.put(µb.userFiltersPath, request.content, callback);
 
         default:
             break;
@@ -498,20 +485,6 @@ var onMessage = function(request, sender, callback) {
     var response;
 
     switch ( request.what ) {
-        case 'loadUpdatableAssets':
-            response = µb.loadUpdatableAssets();
-            break;
-
-        case 'readFilterListSelection':
-            response = µb.remoteBlacklists;
-            break;
-
-        case 'getSomeStats':
-            response = {
-                storageQuota: µb.storageQuota,
-                storageUsed: µb.storageUsed
-            };
-            break;
 
         default:
             return µb.messaging.defaultHandler(request, sender, callback);
@@ -524,4 +497,6 @@ var onMessage = function(request, sender, callback) {
 
 })();
 
+// https://www.youtube.com/watch?v=3_WcygKJP1k
+
 /******************************************************************************/
diff --git a/js/messaging.js b/js/messaging.js
index bc5d4e7..86c2309 100644
--- a/js/messaging.js
+++ b/js/messaging.js
@@ -132,15 +132,12 @@ var onMessage = function(request, port) {
 
 /******************************************************************************/
 
-// Default is for commonly used message.
+// Default is for commonly used messages.
 
 function defaultHandler(request, sender, callback) {
     // Async
     switch ( request.what ) {
         case 'getAssetContent':
-            if ( /^https?:\/\//.test(request.url) ) {
-                return µBlock.assets.getExternal(request.url, callback);
-            }
             return µBlock.assets.get(request.url, callback);
 
         case 'loadUbiquitousAllowRules':
@@ -171,7 +168,7 @@ function defaultHandler(request, sender, callback) {
             break;
 
         case 'reloadAllFilters':
-            µBlock.reloadPresetBlacklists(request.switches);
+            µBlock.reloadPresetBlacklists(request.switches, request.update);
             break;
 
         case 'userSettings':
@@ -186,6 +183,8 @@ function defaultHandler(request, sender, callback) {
     callback(response);
 }
 
+// https://www.youtube.com/watch?v=rrzRgUAHqc8
+
 /******************************************************************************/
 
 // Port disconnected, relay this information to apropriate listener.
diff --git a/js/pagestore.js b/js/pagestore.js
index d541305..1302155 100644
--- a/js/pagestore.js
+++ b/js/pagestore.js
@@ -218,7 +218,7 @@ PageStore.prototype.updateBadgeFromTab = function(tab) {
 
     var iconStr = '';
     if ( µb.userSettings.showIconBadge && netFiltering && this.perLoadBlockedRequestCount ) {
-        iconStr = this.perLoadBlockedRequestCount.toLocaleString();
+        iconStr = µb.utils.formatCount(this.perLoadBlockedRequestCount);
     }
     chrome.browserAction.setBadgeText({ tabId: tab.id, text: iconStr });
 
@@ -234,6 +234,8 @@ PageStore.prototype.updateBadge = function() {
     chrome.tabs.get(this.tabId, this.updateBadgeFromTab.bind(this));
 };
 
+// https://www.youtube.com/watch?v=drW8p_dTLD4
+
 /******************************************************************************/
 
 return {
diff --git a/js/start.js b/js/start.js
index 2ab08ba..aef9f4a 100644
--- a/js/start.js
+++ b/js/start.js
@@ -35,18 +35,17 @@
 (function() {
     var µb = µBlock;
 
-    var jobDone = function(details) {
-        if ( details.changedCount === 0 ) {
+    var jobCallback = function() {
+        if ( µb.userSettings.autoUpdate !== true ) {
             return;
         }
-        µb.loadUpdatableAssets();
-    };
-
-    var jobCallback = function() {
-        µb.assetUpdater.update(null, jobDone);
+        // TODO: need smarter update, currently blindly reloading all.
+        µb.loadUpdatableAssets(true);
     };
 
     µb.asyncJobs.add('autoUpdateAssets', null, jobCallback, µb.updateAssetsEvery, true);
 })();
 
+// https://www.youtube.com/watch?v=cIrGQD84F1g
+
 /******************************************************************************/
diff --git a/js/storage.js b/js/storage.js
index 1073d2c..a8f1840 100644
--- a/js/storage.js
+++ b/js/storage.js
@@ -70,7 +70,7 @@
 
 /******************************************************************************/
 
-µBlock.loadUserSettings = function() {
+µBlock.loadUserSettings = function(callback) {
     var settingsLoaded = function(store) {
         var µb = µBlock;
         // Backward compatibility after fix to #5
@@ -88,6 +88,8 @@
         µb.userSettings = store;
         µb.netWhitelist = µb.whitelistFromString(store.netWhitelist);
         µb.netWhitelistModifyTime = Date.now();
+
+        callback();
     };
 
     chrome.storage.local.get(this.userSettings, settingsLoaded);
@@ -265,11 +267,7 @@
                 blacklistLoadCount -= 1;
                 continue;
             }
-            if ( /^https?:\/\/.+$/.test(location) ) {
-                µb.assets.getExternal(location, mergeBlacklist);
-            } else {
-                µb.assets.get(location, mergeBlacklist);
-            }
+            µb.assets.get(location, mergeBlacklist);
         }
     };
 
@@ -400,7 +398,7 @@
 // `switches` contains the preset blacklists for which the switch must be
 // revisited.
 
-µBlock.reloadPresetBlacklists = function(switches) {
+µBlock.reloadPresetBlacklists = function(switches, update) {
     var presetBlacklists = this.remoteBlacklists;
 
     // Toggle switches, if any
@@ -420,7 +418,7 @@
     }
 
     // Now force reload
-    this.loadUbiquitousBlacklists();
+    this.loadUpdatableAssets(update);
 };
 
 /******************************************************************************/
@@ -443,9 +441,11 @@
 
 // Load updatable assets
 
-µBlock.loadUpdatableAssets = function() {
-    this.loadUbiquitousBlacklists();
+µBlock.loadUpdatableAssets = function(update) {
+    this.assets.autoUpdate = update;
+    this.assets.autoUpdateDelay = this.updateAssetsEvery;
     this.loadPublicSuffixList();
+    this.loadUbiquitousBlacklists();
 };
 
 /******************************************************************************/
@@ -453,11 +453,8 @@
 // Load all
 
 µBlock.load = function() {
-    this.loadLocalSettings();
-    this.loadUserSettings();
-
-    // load updatable assets -- after updating them if needed
-    this.assetUpdater.update(null, this.loadUpdatableAssets.bind(this));
-
+    // User settings need to be available for this because we need
+    // µBlock.userSettings.externalLists
+    this.loadUserSettings(this.loadUpdatableAssets.bind(this, this.userSettings.autoUpdate));
     this.getBytesInUse();
 };
diff --git a/js/ublock.js b/js/ublock.js
index 169efbb..cce9aa5 100644
--- a/js/ublock.js
+++ b/js/ublock.js
@@ -233,24 +233,3 @@
 };
 
 /******************************************************************************/
-
-µBlock.formatCount = function(count) {
-    if ( typeof count !== 'number' ) {
-        return '';
-    }
-    var s = count.toFixed(0);
-    if ( count >= 1000 ) {
-        if ( count < 10000 ) {
-            s = '>' + s.slice(0,1) + 'K';
-        } else if ( count < 100000 ) {
-            s = s.slice(0,2) + 'K';
-        } else if ( count < 1000000 ) {
-            s = s.slice(0,3) + 'K';
-        } else if ( count < 10000000 ) {
-            s = s.slice(0,1) + 'M';
-        } else {
-            s = s.slice(0,-6) + 'M';
-        }
-    }
-    return s;
-};
diff --git a/js/utils.js b/js/utils.js
index 0b534de..65cc997 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -29,7 +29,11 @@
 
 /******************************************************************************/
 
-var gotoURL = function(details) {
+var exports = {};
+
+/******************************************************************************/
+
+exports.gotoURL = function(details) {
     if ( details.tabId ) {
         chrome.tabs.update(details.tabId, { url: details.url });
     } else {
@@ -39,7 +43,7 @@ var gotoURL = function(details) {
 
 /******************************************************************************/
 
-var gotoExtensionURL = function(url) {
+exports.gotoExtensionURL = function(url) {
 
     var hasQuery = function(url) {
         return url.indexOf('?') >= 0;
@@ -98,11 +102,33 @@ var gotoExtensionURL = function(url) {
 
 /******************************************************************************/
 
-return {
-    gotoURL: gotoURL,
-    gotoExtensionURL: gotoExtensionURL
+exports.formatCount = function(count) {
+    if ( typeof count !== 'number' ) {
+        return '';
+    }
+    var s = count.toFixed(0);
+    if ( count >= 1000 ) {
+        if ( count < 10000 ) {
+            s = '>' + s.slice(0,1) + 'K';
+        } else if ( count < 100000 ) {
+            s = s.slice(0,2) + 'K';
+        } else if ( count < 1000000 ) {
+            s = s.slice(0,3) + 'K';
+        } else if ( count < 10000000 ) {
+            s = s.slice(0,1) + 'M';
+        } else {
+            s = s.slice(0,-6) + 'M';
+        }
+    }
+    return s;
 };
 
+// https://www.youtube.com/watch?v=uvUW4ozs7pY
+
+/******************************************************************************/
+
+return exports;
+
 /******************************************************************************/
 
 })();