path: root/src/js/assets.js

/*******************************************************************************

    uBlock Origin - a comprehensive, efficient content blocker
    Copyright (C) 2014-present 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
*/

'use strict';

/******************************************************************************/

import µb from './background.js';
import { broadcast } from './broadcast.js';
import cacheStorage from './cachestorage.js';
import { ubolog } from './console.js';
import { i18n$ } from './i18n.js';
import logger from './logger.js';
import * as sfp from './static-filtering-parser.js';
import { orphanizeString, } from './text-utils.js';

/******************************************************************************/

const reIsExternalPath = /^(?:[a-z-]+):\/\//;
const reIsUserAsset = /^user-/;
const errorCantConnectTo = i18n$('errorCantConnectTo');
const MS_PER_HOUR = 60 * 60 * 1000;
const MS_PER_DAY = 24 * MS_PER_HOUR;
const MINUTES_PER_DAY = 24 * 60;
const EXPIRES_DEFAULT = 7;

const assets = {};

// A hint for various pieces of code to take measures if possible to save
// bandwidth of remote servers.
let remoteServerFriendly = false;

/******************************************************************************/

const stringIsNotEmpty = s => typeof s === 'string' && s !== '';

const parseExpires = s => {
    const matches = s.match(/(\d+)\s*([dhm]?)/i);
    if ( matches === null ) { return; }
    let updateAfter = parseInt(matches[1], 10);
    if ( matches[2] === 'h' ) {
        updateAfter = Math.max(updateAfter, 4) / 24;
    } else if ( matches[2] === 'm' ) {
        updateAfter = Math.max(updateAfter, 240) / 1440;
    }
    return updateAfter;
};

const extractMetadataFromList = (content, fields) => {
    const out = {};
    const head = content.slice(0, 1024);
    for ( let field of fields ) {
        field = field.replace(/\s+/g, '-');
        const re = new RegExp(`^(?:! *|# +)${field.replace(/-/g, '(?: +|-)')}: *(.+)$`, 'im');
        const match = re.exec(head);
        let value = match && match[1].trim() || undefined;
        if ( value !== undefined && value.startsWith('%') ) {
            value = undefined;
        }
        field = field.toLowerCase().replace(
            /-[a-z]/g, s => s.charAt(1).toUpperCase()
        );
        out[field] = value && orphanizeString(value);
    }
    // Pre-process known fields
    if ( out.lastModified ) {
        out.lastModified = (new Date(out.lastModified)).getTime() || 0;
    }
    if ( out.expires ) {
        out.expires = parseExpires(out.expires);
    }
    if ( out.diffExpires ) {
        out.diffExpires = parseExpires(out.diffExpires);
    }
    return out;
};
assets.extractMetadataFromList = extractMetadataFromList;

const resourceTimeFromXhr = xhr => {
    if ( typeof xhr.response !== 'string' ) {  return 0; }
    const metadata = extractMetadataFromList(xhr.response, [
        'Last-Modified'
    ]);
    return metadata.lastModified || 0;
};

const resourceTimeFromParts = (parts, time) => {
    const goodParts = parts.filter(part => typeof part === 'object');
    return goodParts.reduce((acc, part) =>
        ((part.resourceTime || 0) > acc ? part.resourceTime : acc),
        time
    );
};

const resourceIsStale = (networkDetails, cacheDetails) => {
    if ( typeof networkDetails.resourceTime !== 'number' ) { return false; }
    if ( networkDetails.resourceTime === 0 ) { return false; }
    if ( typeof cacheDetails.resourceTime !== 'number' ) { return false; }
    if ( cacheDetails.resourceTime === 0 ) { return false; }
    if ( networkDetails.resourceTime < cacheDetails.resourceTime ) {
        ubolog(`Skip ${networkDetails.url}\n\tolder than ${cacheDetails.remoteURL}`);
        return true;
    }
    return false;
};

const getUpdateAfterTime = (assetKey, diff = false) => {
    const entry = assetCacheRegistry[assetKey];
    if ( entry ) {
        if ( diff && typeof entry.diffExpires === 'number' ) {
            return entry.diffExpires * MS_PER_DAY;
        }
        if ( typeof entry.expires === 'number' ) {
            return entry.expires * MS_PER_DAY;
        }
    }
    if ( assetSourceRegistry ) {
        const entry = assetSourceRegistry[assetKey];
        if ( entry && typeof entry.updateAfter === 'number' ) {
            return entry.updateAfter * MS_PER_DAY;
        }
    }
    return EXPIRES_DEFAULT * MS_PER_DAY; // default to 7-day
};

const getWriteTime = assetKey => {
    const entry = assetCacheRegistry[assetKey];
    if ( entry ) { return entry.writeTime || 0; }
    return 0;
};

const isDiffUpdatableAsset = content => {
    if ( typeof content !== 'string' ) { return false; }
    const data = extractMetadataFromList(content, [
        'Diff-Path',
    ]);
    return typeof data.diffPath === 'string' &&
        data.diffPath.startsWith('%') === false;
};

const computedPatchUpdateTime = assetKey => {
    const entry = assetCacheRegistry[assetKey];
    if ( entry === undefined ) { return 0; }
    if ( typeof entry.diffPath !== 'string' ) { return 0; }
    if ( typeof entry.diffExpires !== 'number' ) { return 0; }
    const match = /(\d+)\.(\d+)\.(\d+)\.(\d+)/.exec(entry.diffPath);
    if ( match === null ) { return getWriteTime(); }
    const date = new Date();
    date.setUTCFullYear(
        parseInt(match[1], 10),
        parseInt(match[2], 10) - 1,
        parseInt(match[3], 10)
    );
    date.setUTCHours(0, parseInt(match[4], 10) + entry.diffExpires * MINUTES_PER_DAY, 0, 0);
    return date.getTime();
};

/******************************************************************************/

// favorLocal: avoid making network requests whenever possible
// favorOrigin: avoid using CDN URLs whenever possible

const getContentURLs = (assetKey, options = {}) => {
    const contentURLs = [];
    const entry = assetSourceRegistry[assetKey];
    if ( entry instanceof Object === false ) { return contentURLs; }
    if ( typeof entry.contentURL === 'string' ) {
        contentURLs.push(entry.contentURL);
    } else if ( Array.isArray(entry.contentURL) ) {
        contentURLs.push(...entry.contentURL);
    } else if ( reIsExternalPath.test(assetKey) ) {
        contentURLs.push(assetKey);
    }
    if ( options.favorLocal ) {
        contentURLs.sort((a, b) => {
            if ( reIsExternalPath.test(a) ) { return 1; }
            if ( reIsExternalPath.test(b) ) { return -1; }
            return 0;
        });
    }
    if ( options.favorOrigin !== true && Array.isArray(entry.cdnURLs) ) {
        const cdnURLs = entry.cdnURLs.slice();
        for ( let i = 0, n = cdnURLs.length; i < n; i++ ) {
            const j = Math.floor(Math.random() * n);
            if ( j === i ) { continue; }
            [ cdnURLs[j], cdnURLs[i] ] = [ cdnURLs[i], cdnURLs[j] ];
        }
        if ( options.favorLocal ) {
            contentURLs.push(...cdnURLs);
        } else {
            contentURLs.unshift(...cdnURLs);
        }
    }
    return contentURLs;
};

/******************************************************************************/

const observers = [];

assets.addObserver = function(observer) {
    if ( observers.indexOf(observer) === -1 ) {
        observers.push(observer);
    }
};

assets.removeObserver = function(observer) {
    let pos;
    while ( (pos = observers.indexOf(observer)) !== -1 ) {
        observers.splice(pos, 1);
    }
};

const fireNotification = function(topic, details) {
    let result;
    for ( const observer of observers ) {
        const r = observer(topic, details);
        if ( r !== undefined ) { result = r; }
    }
    return result;
};

/******************************************************************************/

assets.fetch = function(url, options = {}) {
    return new Promise((resolve, reject) => {
    // Start of executor

    const timeoutAfter = µb.hiddenSettings.assetFetchTimeout || 30;
    const xhr = new XMLHttpRequest();
    let contentLoaded = 0;

    const cleanup = function() {
        xhr.removeEventListener('load', onLoadEvent);
        xhr.removeEventListener('error', onErrorEvent);
        xhr.removeEventListener('abort', onErrorEvent);
        xhr.removeEventListener('progress', onProgressEvent);
        timeoutTimer.off();
    };

    const fail = function(details, msg) {
        logger.writeOne({
            realm: 'message',
            type: 'error',
            text: msg,
        });
        details.content = '';
        details.error = msg;
        reject(details);
    };

    // https://github.com/gorhill/uMatrix/issues/15
    const onLoadEvent = function() {
        cleanup();
        // xhr for local files gives status 0, but actually succeeds
        const details = {
            url,
            statusCode: this.status || 200,
            statusText: this.statusText || ''
        };
        if ( details.statusCode < 200 || details.statusCode >= 300 ) {
            return fail(details, `${url}: ${details.statusCode} ${details.statusText}`);
        }
        details.content = this.response;
        details.resourceTime = resourceTimeFromXhr(this);
        resolve(details);
    };

    const onErrorEvent = function() {
        cleanup();
        fail({ url }, errorCantConnectTo.replace('{{msg}}', url));
    };

    const onTimeout = function() {
        xhr.abort();
    };

    // https://github.com/gorhill/uBlock/issues/2526
    // - Timeout only when there is no progress.
    const onProgressEvent = function(ev) {
        if ( ev.loaded === contentLoaded ) { return; }
        contentLoaded = ev.loaded;
        timeoutTimer.offon({ sec: timeoutAfter });
    };

    const timeoutTimer = vAPI.defer.create(onTimeout);

    // Be ready for thrown exceptions:
    // I am pretty sure it used to work, but now using a URL such as
    // `file:///` on Chromium 40 results in an exception being thrown.
    try {
        xhr.open('get', url, true);
        xhr.addEventListener('load', onLoadEvent);
        xhr.addEventListener('error', onErrorEvent);
        xhr.addEventListener('abort', onErrorEvent);
        xhr.addEventListener('progress', onProgressEvent);
        xhr.responseType = options.responseType || 'text';
        xhr.send();
        timeoutTimer.on({ sec: timeoutAfter });
    } catch (e) {
        onErrorEvent.call(xhr);
    }

    // End of executor
    });
};

/******************************************************************************/

assets.fetchText = async function(url) {
    const isExternal = reIsExternalPath.test(url);
    let actualUrl = isExternal ? url : vAPI.getURL(url);

    // https://github.com/gorhill/uBlock/issues/2592
    //   Force browser cache to be bypassed, but only for resources which have
    //   been fetched more than one hour ago.
    // https://github.com/uBlockOrigin/uBlock-issues/issues/682#issuecomment-515197130
    //   Provide filter list authors a way to completely bypass
    //   the browser cache.
    // https://github.com/gorhill/uBlock/commit/048bfd251c9b#r37972005
    //   Use modulo prime numbers to avoid generating the same token at the
    //   same time across different days.
    // Do not bypass browser cache if we are asked to be gentle on remote
    // servers.
    if ( isExternal && remoteServerFriendly !== true ) {
        const cacheBypassToken =
            µb.hiddenSettings.updateAssetBypassBrowserCache
                ? Math.floor(Date.now() /    1000) % 86413
                : Math.floor(Date.now() / 3600000) %    13;
        const queryValue = `_=${cacheBypassToken}`;
        if ( actualUrl.indexOf('?') === -1 ) {
            actualUrl += '?';
        } else {
            actualUrl += '&';
        }
        actualUrl += queryValue;
    }

    let details = { content: '' };
    try {
        details = await assets.fetch(actualUrl);

        // Consider an empty result to be an error
        if ( stringIsNotEmpty(details.content) === false ) {
            details.content = '';
        }

        // We never download anything else than plain text: discard if
        // response appears to be a HTML document: could happen when server
        // serves some kind of error page for example.
        const text = details.content.trim();
        if ( text.startsWith('<') && text.endsWith('>') ) {
            details.content = '';
            details.error = 'assets.fetchText(): Not a text file';
        }
    } catch(ex) {
        details = ex;
    }

    // We want to return the caller's URL, not our internal one which may
    // differ from the caller's one.
    details.url = url;

    return details;
};

/******************************************************************************/

// https://github.com/gorhill/uBlock/issues/3331
//   Support the seamless loading of sublists.

assets.fetchFilterList = async function(mainlistURL) {
    const toParsedURL = url => {
        try {
            return new URL(url.trim());
        } catch (ex) {
        }
    };

    // https://github.com/NanoAdblocker/NanoCore/issues/239
    //   Anything under URL's root directory is allowed to be fetched. The
    //   URL of a sublist will always be relative to the URL of the parent
    //   list (instead of the URL of the root list).
    let rootDirectoryURL = toParsedURL(
        reIsExternalPath.test(mainlistURL)
            ? mainlistURL
            : vAPI.getURL(mainlistURL)
    );
    if ( rootDirectoryURL !== undefined ) {
        const pos = rootDirectoryURL.pathname.lastIndexOf('/');
        if ( pos !== -1 ) {
            rootDirectoryURL.pathname =
                rootDirectoryURL.pathname.slice(0, pos + 1);
        } else {
            rootDirectoryURL = undefined;
        }
    }

    const sublistURLs = new Set();

    // https://github.com/uBlockOrigin/uBlock-issues/issues/1113
    //   Process only `!#include` directives which are not excluded by an
    //   `!#if` directive.
    const processIncludeDirectives = function(results) {
        const out = [];
        const reInclude = /^!#include +(\S+)[^\n\r]*(?:[\n\r]+|$)/gm;
        for ( const result of results ) {
            if ( typeof result === 'string' ) {
                out.push(result);
                continue;
            }
            if ( result instanceof Object === false ) { continue; }
            const content = result.content;
            const slices = sfp.utils.preparser.splitter(
                content,
                vAPI.webextFlavor.env
            );
            for ( let i = 0, n = slices.length - 1; i < n; i++ ) {
                const slice = content.slice(slices[i+0], slices[i+1]);
                if ( (i & 1) !== 0 ) {
                    out.push(slice);
                    continue;
                }
                let lastIndex = 0;
                for (;;) {
                    if ( rootDirectoryURL === undefined ) { break; }
                    const match = reInclude.exec(slice);
                    if ( match === null ) { break; }
                    if ( toParsedURL(match[1]) !== undefined ) { continue; }
                    if ( match[1].indexOf('..') !== -1 ) { continue; }
                    // Compute nested list path relative to parent list path
                    const pos = result.url.lastIndexOf('/');
                    if ( pos === -1 ) { continue; }
                    const subURL = result.url.slice(0, pos + 1) + match[1].trim();
                    if ( sublistURLs.has(subURL) ) { continue; }
                    sublistURLs.add(subURL);
                    out.push(
                        slice.slice(lastIndex, match.index + match[0].length),
                        `! >>>>>>>> ${subURL}\n`,
                        assets.fetchText(subURL),
                        `! <<<<<<<< ${subURL}\n`
                    );
                    lastIndex = reInclude.lastIndex;
                }
                out.push(lastIndex === 0 ? slice : slice.slice(lastIndex));
            }
        }
        return out;
    };

    // https://github.com/AdguardTeam/FiltersRegistry/issues/82
    //   Not checking for `errored` status was causing repeated notifications
    //   to the caller. This can happen when more than one out of multiple
    //   sublists can't be fetched.

    let allParts = [
        this.fetchText(mainlistURL)
    ];
    // Abort processing `include` directives if at least one included sublist
    // can't be fetched.
    let resourceTime = 0;
    do {
        allParts = await Promise.all(allParts);
        const part = allParts
            .find(part => typeof part === 'object' && part.error !== undefined);
        if ( part !== undefined ) {
            return { url: mainlistURL, content: '', error: part.error };
        }
        resourceTime = resourceTimeFromParts(allParts, resourceTime);
        // Skip pre-parser directives for diff-updatable assets
        if ( allParts.length === 1 && allParts[0] instanceof Object ) {
            if ( isDiffUpdatableAsset(allParts[0].content) ) {
                allParts[0] = allParts[0].content;
                break;
            }
        }
        allParts = processIncludeDirectives(allParts);
    } while ( allParts.some(part => typeof part !== 'string') );
    // If we reach this point, this means all fetches were successful.
    return {
        url: mainlistURL,
        resourceTime,
        content: allParts.length === 1
            ? allParts[0]
            : allParts.join('') + '\n'
    };
};

/*******************************************************************************

    The purpose of the asset source registry is to keep key detail information
    about an asset:
    - Where to load it from: this may consist of one or more URLs, either local
      or remote.
    - After how many days an asset should be deemed obsolete -- i.e. in need of
      an update.
    - The origin and type of an asset.
    - The last time an asset was registered.

**/

let assetSourceRegistryPromise;
let assetSourceRegistry = Object.create(null);

function getAssetSourceRegistry() {
    if ( assetSourceRegistryPromise === undefined ) {
        assetSourceRegistryPromise = cacheStorage.get(
            'assetSourceRegistry'
        ).then(bin => {
            if (
                bin instanceof Object &&
                bin.assetSourceRegistry instanceof Object
            ) {
                assetSourceRegistry = bin.assetSourceRegistry;
                return assetSourceRegistry;
            }
            return assets.fetchText(
                µb.assetsBootstrapLocation || µb.assetsJsonPath
            ).then(details => {
                return details.content !== ''
                    ? details
                    : assets.fetchText(µb.assetsJsonPath);
            }).then(details => {
                updateAssetSourceRegistry(details.content, true);
                return assetSourceRegistry;
            });
        });
    }

    return assetSourceRegistryPromise;
}

function registerAssetSource(assetKey, newDict) {
    const currentDict = assetSourceRegistry[assetKey] || {};
    for ( const [ k, v ] of Object.entries(newDict) ) {
        if ( v === undefined || v === null ) {
            delete currentDict[k];
        } else {
            currentDict[k] = newDict[k];
        }
    }
    let contentURL = newDict.contentURL;
    if ( contentURL !== undefined ) {
        if ( typeof contentURL === 'string' ) {
            contentURL = currentDict.contentURL = [ contentURL ];
        } else if ( Array.isArray(contentURL) === false ) {
            contentURL = currentDict.contentURL = [];
        }
        let remoteURLCount = 0;
        for ( let i = 0; i < contentURL.length; i++ ) {
            if ( reIsExternalPath.test(contentURL[i]) ) {
                remoteURLCount += 1;
            }
        }
        currentDict.hasLocalURL = remoteURLCount !== contentURL.length;
        currentDict.hasRemoteURL = remoteURLCount !== 0;
    } else if ( currentDict.contentURL === undefined ) {
        currentDict.contentURL = [];
    }
    if ( currentDict.submitter ) {
        currentDict.submitTime = Date.now(); // To detect stale entries
    }
    assetSourceRegistry[assetKey] = currentDict;
}

function unregisterAssetSource(assetKey) {
    assetCacheRemove(assetKey);
    delete assetSourceRegistry[assetKey];
}

const saveAssetSourceRegistry = (( ) => {
    const save = ( ) => {
        timer.off();
        cacheStorage.set({ assetSourceRegistry });
    };
    const timer = vAPI.defer.create(save);
    return function(lazily) {
        if ( lazily ) {
            timer.offon(500);
        } else {
            save();
        }
    };
})();

async function assetSourceGetDetails(assetKey) {
    await getAssetSourceRegistry();
    const entry = assetSourceRegistry[assetKey];
    if ( entry === undefined ) { return; }
    return entry;
}

function updateAssetSourceRegistry(json, silent = false) {
    let newDict;
    try {
        newDict = JSON.parse(json);
        newDict['assets.json'].defaultListset =
            Array.from(Object.entries(newDict))
                .filter(a => a[1].content === 'filters' && a[1].off === undefined)
                .map(a => a[0]);
    } catch (ex) {
    }
    if ( newDict instanceof Object === false ) { return; }

    const oldDict = assetSourceRegistry;

    fireNotification('assets.json-updated', { newDict, oldDict });

    // Remove obsolete entries (only those which were built-in).
    for ( const assetKey in oldDict ) {
        if (
            newDict[assetKey] === undefined &&
            oldDict[assetKey].submitter === undefined
        ) {
            unregisterAssetSource(assetKey);
        }
    }
    // Add/update existing entries. Notify of new asset sources.
    for ( const assetKey in newDict ) {
        if ( oldDict[assetKey] === undefined && !silent ) {
            fireNotification(
                'builtin-asset-source-added',
                { assetKey: assetKey, entry: newDict[assetKey] }
            );
        }
        registerAssetSource(assetKey, newDict[assetKey]);
    }
    saveAssetSourceRegistry();
}

assets.registerAssetSource = async function(assetKey, details) {
    await getAssetSourceRegistry();
    registerAssetSource(assetKey, details);
    saveAssetSourceRegistry(true);
};

assets.unregisterAssetSource = async function(assetKey) {
    await getAssetSourceRegistry();
    unregisterAssetSource(assetKey);
    saveAssetSourceRegistry(true);
};

/*******************************************************************************

    The purpose of the asset cache registry is to keep track of all assets
    which have been persisted into the local cache.

**/

const assetCacheRegistryStartTime = Date.now();
let assetCacheRegistryPromise;
let assetCacheRegistry = {};

function getAssetCacheRegistry() {
    if ( assetCacheRegistryPromise === undefined ) {
        assetCacheRegistryPromise = cacheStorage.get(
            'assetCacheRegistry'
        ).then(bin => {
            if (
                bin instanceof Object &&
                bin.assetCacheRegistry instanceof Object
            ) {
                if ( Object.keys(assetCacheRegistry).length === 0 ) {
                    assetCacheRegistry = bin.assetCacheRegistry;
                } else {
                    console.error(
                        'getAssetCacheRegistry(): assetCacheRegistry reassigned!'
                    );
                    if (
                        Object.keys(bin.assetCacheRegistry).sort().join() !==
                        Object.keys(assetCacheRegistry).sort().join()
                    ) {
                        console.error(
                            'getAssetCacheRegistry(): assetCacheRegistry changes overwritten!'
                        );
                    }
                }
            }
            return assetCacheRegistry;
        });
    }

    return assetCacheRegistryPromise;
}

const saveAssetCacheRegistry = (( ) => {
    const save = function() {
        timer.off();
        cacheStorage.set({ assetCacheRegistry });
    };
    const timer = vAPI.defer.create(save);
    return function(lazily) {
        if ( lazily ) {
            timer.offon({ sec: 30 });
        } else {
            save();
        }
    };
})();

async function assetCacheRead(assetKey, updateReadTime = false) {
    const t0 = Date.now();
    const internalKey = `cache/${assetKey}`;

    const reportBack = function(content) {
        if ( content instanceof Blob ) { content = ''; }
        const details = { assetKey, content };
        if ( content === '' ) { details.error = 'ENOTFOUND'; }
        return details;
    };

    const [ , bin ] = await Promise.all([
        getAssetCacheRegistry(),
        cacheStorage.get(internalKey),
    ]);

    if ( µb.readyToFilter !== true ) {
        µb.supportStats.maxAssetCacheWait = Math.max(
            Date.now() - t0,
            parseInt(µb.supportStats.maxAssetCacheWait, 10) || 0
        ) + ' ms';
    }

    if (
        bin instanceof Object === false ||
        bin.hasOwnProperty(internalKey) === false
    ) {
        return reportBack('');
    }

    const entry = assetCacheRegistry[assetKey];
    if ( entry === undefined ) {
        return reportBack('');
    }

    entry.readTime = Date.now();
    if ( updateReadTime ) {
        saveAssetCacheRegistry(true);
    }

    return reportBack(bin[internalKey]);
}

async function assetCacheWrite(assetKey, details) {
    let content = '';
    let options = {};
    if ( typeof details === 'string' ) {
        content = details;
    } else if ( details instanceof Object ) {
        content = details.content || '';
        options = details;
    }

    if ( content === '' ) {
        return assetCacheRemove(assetKey);
    }

    const cacheDict = await getAssetCacheRegistry();

    let entry = cacheDict[assetKey];
    if ( entry === undefined ) {
        entry = cacheDict[assetKey] = {};
    }
    entry.writeTime = entry.readTime = Date.now();
    entry.resourceTime = options.resourceTime || 0;
    if ( typeof options.url === 'string' ) {
        entry.remoteURL = options.url;
    }
    cacheStorage.set({
        assetCacheRegistry,
        [`cache/${assetKey}`]: content
    });

    const result = { assetKey, content };
    // https://github.com/uBlockOrigin/uBlock-issues/issues/248
    if ( options.silent !== true ) {
        fireNotification('after-asset-updated', result);
    }
    return result;
}

async function assetCacheRemove(pattern) {
    const cacheDict = await getAssetCacheRegistry();
    const removedEntries = [];
    const removedContent = [];
    for ( const assetKey in cacheDict ) {
        if ( pattern instanceof RegExp && !pattern.test(assetKey) ) {
            continue;
        }
        if ( typeof pattern === 'string' && assetKey !== pattern ) {
            continue;
        }
        removedEntries.push(assetKey);
        removedContent.push('cache/' + assetKey);
        delete cacheDict[assetKey];
    }
    if ( removedContent.length !== 0 ) {
        await Promise.all([
            cacheStorage.remove(removedContent),
            cacheStorage.set({ assetCacheRegistry }),
        ]);
    }
    for ( let i = 0; i < removedEntries.length; i++ ) {
        fireNotification('after-asset-updated', {
            assetKey: removedEntries[i]
        });
    }
}

async function assetCacheGetDetails(assetKey) {
    const cacheDict = await getAssetCacheRegistry();
    const entry = cacheDict[assetKey];
    if ( entry === undefined ) { return; }
    return entry;
}

async function assetCacheSetDetails(assetKey, details) {
    const cacheDict = await getAssetCacheRegistry();
    const entry = cacheDict[assetKey];
    if ( entry === undefined ) { return; }
    let modified = false;
    for ( const [ k, v ] of Object.entries(details) ) {
        if ( v === undefined ) {
            if ( entry[k] !== undefined ) {
                delete entry[k];
                modified = true;
                continue;
            }
        }
        if ( v !== entry[k] ) {
            entry[k] = v;
            modified = true;
        }
    }
    if ( modified ) {
        saveAssetCacheRegistry();
    }
}

async function assetCacheMarkAsDirty(pattern, exclude) {
    const cacheDict = await getAssetCacheRegistry();
    let mustSave = false;
    for ( const assetKey in cacheDict ) {
        if ( pattern instanceof RegExp ) {
            if ( pattern.test(assetKey) === false ) { continue; }
        } else if ( typeof pattern === 'string' ) {
            if ( assetKey !== pattern ) { continue; }
        } else if ( Array.isArray(pattern) ) {
            if ( pattern.indexOf(assetKey) === -1 ) { continue; }
        }
        if ( exclude instanceof RegExp ) {
            if ( exclude.test(assetKey) ) { continue; }
        } else if ( typeof exclude === 'string' ) {
            if ( assetKey === exclude ) { continue; }
        } else if ( Array.isArray(exclude) ) {
            if ( exclude.indexOf(assetKey) !== -1 ) { continue; }
        }
        const cacheEntry = cacheDict[assetKey];
        if ( !cacheEntry.writeTime ) { continue; }
        cacheDict[assetKey].writeTime = 0;
        mustSave = true;
    }
    if ( mustSave ) {
        cacheStorage.set({ assetCacheRegistry });
    }
}

/*******************************************************************************

    User assets are NOT persisted in the cache storage. User assets are
    recognized by the asset key which always starts with 'user-'.

    TODO(seamless migration):
    Can remove instances of old user asset keys when I am confident all users
    are using uBO v1.11 and beyond.

**/

/*******************************************************************************

    User assets are NOT persisted in the cache storage. User assets are
    recognized by the asset key which always starts with 'user-'.

**/

const readUserAsset = async function(assetKey) {
    const bin = await vAPI.storage.get(assetKey);
    const content =
        bin instanceof Object && typeof bin[assetKey] === 'string'
            ? bin[assetKey]
            : '';
    return { assetKey, content };
};

const saveUserAsset = function(assetKey, content) {
    return vAPI.storage.set({ [assetKey]: content }).then(( ) => {
        return { assetKey, content };
    });
};

/******************************************************************************/

assets.get = async function(assetKey, options = {}) {
    if ( assetKey === µb.userFiltersPath ) {
        return readUserAsset(assetKey);
    }

    let assetDetails = {};

    const reportBack = (content, url = '', err = undefined) => {
        const details = { assetKey, content };
        if ( err !== undefined ) {
            details.error = assetDetails.lastError = err;
        } else {
            assetDetails.lastError = undefined;
        }
        if ( options.needSourceURL ) {
            if (
                url === '' &&
                assetCacheRegistry instanceof Object &&
                assetCacheRegistry[assetKey] instanceof Object
            ) {
                details.sourceURL = assetCacheRegistry[assetKey].remoteURL;
            }
            if ( reIsExternalPath.test(url) ) {
                details.sourceURL = url;
            }
        }
        return details;
    };

    // Skip read-time property for non-updatable assets: the property is
    // completely unused for such assets and thus there is no point incurring
    // storage write overhead at launch when reading compiled or selfie assets.
    const updateReadTime = /^(?:compiled|selfie)\//.test(assetKey) === false;

    const details = await assetCacheRead(assetKey, updateReadTime);
    if ( details.content !== '' ) {
        return reportBack(details.content);
    }

    const assetRegistry = await getAssetSourceRegistry();

    assetDetails = assetRegistry[assetKey] || {};

    const contentURLs = getContentURLs(assetKey, options);
    if ( contentURLs.length === 0 && reIsExternalPath.test(assetKey) ) {
        assetDetails.content = 'filters';
        contentURLs.push(assetKey);
    }

    let error = 'ENOTFOUND';
    for ( const contentURL of contentURLs ) {
        const details = assetDetails.content === 'filters'
            ? await assets.fetchFilterList(contentURL)
            : await assets.fetchText(contentURL);
        if ( details.error !== undefined ) {
            error = details.error;
        }
        if ( details.content === '' ) { continue; }
        if ( reIsExternalPath.test(contentURL) && options.dontCache !== true ) {
            assetCacheWrite(assetKey, {
                content: details.content,
                url: contentURL,
                silent: options.silent === true,
            });
            registerAssetSource(assetKey, { error: undefined });
            if ( assetDetails.content === 'filters' ) {
                const metadata = extractMetadataFromList(details.content, [
                    'Last-Modified',
                    'Expires',
                    'Diff-Name',
                    'Diff-Path',
                    'Diff-Expires',
                ]);
                metadata.diffUpdated = undefined;
                assetCacheSetDetails(assetKey, metadata);
            }
        }
        return reportBack(details.content, contentURL);
    }
    if ( assetRegistry[assetKey] !== undefined ) {
        registerAssetSource(assetKey, {
            error: { time: Date.now(), error }
        });
    }
    return reportBack('', '', error);
};

/******************************************************************************/

async function getRemote(assetKey, options = {}) {
    const [
        assetDetails = {},
        cacheDetails = {},
    ] = await Promise.all([
        assetSourceGetDetails(assetKey),
        assetCacheGetDetails(assetKey),
    ]);

    let error;
    let stale = false;

    const reportBack = function(content, url = '', err = '') {
        const details = { assetKey, content, url };
        if ( err !== '') {
            details.error = assetDetails.lastError = err;
        } else {
            assetDetails.lastError = undefined;
        }
        return details;
    };

    for ( const contentURL of getContentURLs(assetKey, options) ) {
        if ( reIsExternalPath.test(contentURL) === false ) { continue; }

        const result = assetDetails.content === 'filters'
            ? await assets.fetchFilterList(contentURL)
            : await assets.fetchText(contentURL);

        // Failure
        if ( stringIsNotEmpty(result.content) === false ) {
            error = result.statusText;
            if ( result.statusCode === 0 ) {
                error = 'network error';
            }
            continue;
        }

        error = undefined;

        // If fetched resource is older than cached one, ignore
        if ( options.favorOrigin !== true ) {
            stale = resourceIsStale(result, cacheDetails);
            if ( stale ) { continue; }
        }

        // Success
        assetCacheWrite(assetKey, {
            content: result.content,
            url: contentURL,
            resourceTime: result.resourceTime || 0,
        });

        if ( assetDetails.content === 'filters' ) {
            const metadata = extractMetadataFromList(result.content, [
                'Last-Modified',
                'Expires',
                'Diff-Name',
                'Diff-Path',
                'Diff-Expires',
            ]);
            metadata.diffUpdated = undefined;
            assetCacheSetDetails(assetKey, metadata);
        }

        registerAssetSource(assetKey, { birthtime: undefined, error: undefined });
        return reportBack(result.content, contentURL);
    }

    if ( error !== undefined ) {
        registerAssetSource(assetKey, { error: { time: Date.now(), error } });
        return reportBack('', '', 'ENOTFOUND');
    }

    if ( stale ) {
        assetCacheSetDetails(assetKey, { writeTime: cacheDetails.resourceTime });
    }

    return reportBack('');
}

/******************************************************************************/

assets.put = async function(assetKey, content) {
    return reIsUserAsset.test(assetKey)
        ? await saveUserAsset(assetKey, content)
        : await assetCacheWrite(assetKey, content);
};

/******************************************************************************/

assets.metadata = async function() {
    await Promise.all([
        getAssetSourceRegistry(),
        getAssetCacheRegistry(),
    ]);

    const assetDict = JSON.parse(JSON.stringify(assetSourceRegistry));
    const cacheDict = assetCacheRegistry;
    const now = Date.now();
    for ( const assetKey in assetDict ) {
        const assetEntry = assetDict[assetKey];
        const cacheEntry = cacheDict[assetKey];
        if (
            assetEntry.content === 'filters' &&
            assetEntry.external !== true
        ) {
            assetEntry.isDefault =
                assetEntry.off === undefined ||
                assetEntry.off === true &&
                    µb.listMatchesEnvironment(assetEntry);
        }
        if ( cacheEntry ) {
            assetEntry.cached = true;
            assetEntry.writeTime = cacheEntry.writeTime;
            const obsoleteAfter = cacheEntry.writeTime + getUpdateAfterTime(assetKey);
            assetEntry.obsolete = obsoleteAfter < now;
            assetEntry.remoteURL = cacheEntry.remoteURL;
            if ( cacheEntry.diffUpdated ) {
                assetEntry.diffUpdated = cacheEntry.diffUpdated;
            }
        } else if (
            assetEntry.contentURL &&
            assetEntry.contentURL.length !== 0
        ) {
            assetEntry.writeTime = 0;
            assetEntry.obsolete = true;
        }
    }

    return assetDict;
};

/******************************************************************************/

assets.purge = assetCacheMarkAsDirty;

assets.remove = function(pattern) {
    return assetCacheRemove(pattern);
};

assets.rmrf = function() {
    return assetCacheRemove(/./);
};

/******************************************************************************/

assets.getUpdateAges = async function(conditions = {}) {
    const assetDict = await assets.metadata();
    const now = Date.now();
    const out = [];
    for ( const [ assetKey, asset ] of Object.entries(assetDict) ) {
        if ( asset.hasRemoteURL !== true ) { continue; }
        const tokens = conditions[asset.content];
        if ( Array.isArray(tokens) === false ) { continue; }
        if ( tokens.includes('*') === false ) {
            if ( tokens.includes(assetKey) === false ) { continue; }
        }
        const age = now  - (asset.writeTime || 0);
        out.push({
            assetKey,
            age,
            ageNormalized: age / Math.max(1, getUpdateAfterTime(assetKey)),
        });
    }
    return out;
};

/******************************************************************************/

// Asset updater area.
const updaterAssetDelayDefault = 120000;
const updaterUpdated = [];
const updaterFetched = new Set();

let updaterStatus;
let updaterAssetDelay = updaterAssetDelayDefault;
let updaterAuto = false;

const getAssetDiffDetails = assetKey => {
    const out = { assetKey };
    const cacheEntry = assetCacheRegistry[assetKey];
    if ( cacheEntry === undefined ) { return; }
    out.patchPath = cacheEntry.diffPath;
    if ( out.patchPath === undefined ) { return; }
    const match = /#.+$/.exec(out.patchPath);
    if ( match !== null ) {
        out.diffName = match[0].slice(1);
    } else {
        out.diffName = cacheEntry.diffName;
    }
    if ( out.diffName === undefined ) { return; }
    out.diffExpires = getUpdateAfterTime(assetKey, true);
    out.lastModified = cacheEntry.lastModified;
    out.writeTime = cacheEntry.writeTime;
    const assetEntry = assetSourceRegistry[assetKey];
    if ( assetEntry === undefined ) { return; }
    if ( assetEntry.content !== 'filters' ) { return; }
    if ( Array.isArray(assetEntry.cdnURLs) ) {
        out.cdnURLs = assetEntry.cdnURLs.slice();
    } else if ( reIsExternalPath.test(assetKey) ) {
        out.cdnURLs = [ assetKey ];
    } else if ( typeof assetEntry.contentURL === 'string' ) {
        out.cdnURLs = [ assetEntry.contentURL ];
    } else if ( Array.isArray(assetEntry.contentURL) ) {
        out.cdnURLs = assetEntry.contentURL.slice(0).filter(url =>
            reIsExternalPath.test(url)
        );
    }
    if ( Array.isArray(out.cdnURLs) === false ) { return; }
    if ( out.cdnURLs.length === 0 ) { return; }
    return out;
};

async function diffUpdater() {
    if ( updaterAuto === false ) { return; }
    if ( µb.hiddenSettings.differentialUpdate === false ) { return; }
    const toUpdate = await getUpdateCandidates();
    const now = Date.now();
    const toHardUpdate = [];
    const toSoftUpdate = [];
    while ( toUpdate.length !== 0 ) {
        const assetKey = toUpdate.shift();
        const assetDetails = getAssetDiffDetails(assetKey);
        if ( assetDetails === undefined ) { continue; }
        assetDetails.what = 'update';
        const computedUpdateTime = computedPatchUpdateTime(assetKey);
        if ( computedUpdateTime !== 0 && computedUpdateTime <= now ) {
            assetDetails.fetch = true;
            toHardUpdate.push(assetDetails);
        } else {
            assetDetails.fetch = false;
            toSoftUpdate.push(assetDetails);
        }
    }
    if ( toHardUpdate.length === 0 ) { return; }
    ubolog('Diff updater: cycle start');
    return new Promise(resolve => {
        let pendingOps = 0;
        const bc = new globalThis.BroadcastChannel('diffUpdater');
        const terminate = error => {
            worker.terminate();
            bc.close();
            resolve();
            if ( typeof error !== 'string' ) { return; }
            ubolog(`Diff updater: terminate because ${error}`);
        };
        const checkAndCorrectDiffPath = data => {
            if ( typeof data.text !== 'string' ) { return; }
            if ( data.text === '' ) { return; }
            const metadata = extractMetadataFromList(data.text, [ 'Diff-Path' ]);
            if ( metadata instanceof Object === false ) { return; }
            if ( metadata.diffPath === data.patchPath ) { return; }
            assetCacheSetDetails(data.assetKey, metadata);
        };
        bc.onmessage = ev => {
            const data = ev.data || {};
            if ( data.what === 'ready' ) {
                ubolog('Diff updater: hard updating', toHardUpdate.map(v => v.assetKey).join());
                while ( toHardUpdate.length !== 0 ) {
                    const assetDetails = toHardUpdate.shift();
                    assetDetails.fetch = true;
                    bc.postMessage(assetDetails);
                    pendingOps += 1;
                }
                return;
            }
            if ( data.what === 'broken' ) {
                terminate(data.error);
                return;
            }
            if ( data.status === 'needtext' ) {
                ubolog('Diff updater: need text for', data.assetKey);
                assetCacheRead(data.assetKey).then(result => {
                    data.text = result.content;
                    data.status = undefined;
                    checkAndCorrectDiffPath(data);
                    bc.postMessage(data);
                });
                return;
            }
            if ( data.status === 'updated' ) {
                ubolog(`Diff updater: successfully patched ${data.assetKey} using ${data.patchURL} (${data.patchSize})`);
                const metadata = extractMetadataFromList(data.text, [
                    'Last-Modified',
                    'Expires',
                    'Diff-Name',
                    'Diff-Path',
                    'Diff-Expires',
                ]);
                assetCacheWrite(data.assetKey, {
                    content: data.text,
                    resourceTime: metadata.lastModified || 0,
                });
                metadata.diffUpdated = true;
                assetCacheSetDetails(data.assetKey, metadata);
                updaterUpdated.push(data.assetKey);
            } else if ( data.error ) {
                ubolog(`Diff updater: failed to update ${data.assetKey} using ${data.patchPath}\n\treason: ${data.error}`);
            } else if ( data.status === 'nopatch-yet' || data.status === 'nodiff' ) {
                ubolog(`Diff updater: skip update of ${data.assetKey} using ${data.patchPath}\n\treason: ${data.status}`);
                assetCacheSetDetails(data.assetKey, { writeTime: data.writeTime });
                broadcast({
                    what: 'assetUpdated',
                    key: data.assetKey,
                    cached: true,
                });
            } else {
                ubolog(`Diff updater: ${data.assetKey} / ${data.patchPath} / ${data.status}`);
            }
            pendingOps -= 1;
            if ( pendingOps === 0 && toSoftUpdate.length !== 0 ) {
                ubolog('Diff updater: soft updating', toSoftUpdate.map(v => v.assetKey).join());
                while ( toSoftUpdate.length !== 0 ) {
                    bc.postMessage(toSoftUpdate.shift());
                    pendingOps += 1;
                }
            }
            if ( pendingOps !== 0 ) { return; }
            ubolog('Diff updater: cycle complete');
            terminate();
        };
        const worker = new Worker('js/diff-updater.js');
    });
}

function updateFirst() {
    ubolog('Updater: cycle start');
    ubolog('Updater: prefer', updaterAuto ? 'CDNs' : 'origin');
    updaterStatus = 'updating';
    updaterFetched.clear();
    updaterUpdated.length = 0;
    diffUpdater().catch(reason => {
        ubolog(reason);
    }).finally(( ) => {
        updateNext();
    });
}

async function getUpdateCandidates() {
    const [ assetDict, cacheDict ] = await Promise.all([
        getAssetSourceRegistry(),
        getAssetCacheRegistry(),
    ]);
    const toUpdate = [];
    for ( const assetKey in assetDict ) {
        const assetEntry = assetDict[assetKey];
        if ( assetEntry.hasRemoteURL !== true ) { continue; }
        if ( updaterFetched.has(assetKey) ) { continue; }
        const cacheEntry = cacheDict[assetKey];
        if (
            fireNotification('before-asset-updated', {
                assetKey,
                type: assetEntry.content
            }) === true
        ) {
            toUpdate.push(assetKey);
            continue;
        }
        // This will remove a cached asset when it's no longer in use.
        if ( cacheEntry && cacheEntry.readTime < assetCacheRegistryStartTime ) {
            assetCacheRemove(assetKey);
        }
    }
    // https://github.com/uBlockOrigin/uBlock-issues/issues/1165
    //   Update most obsolete asset first.
    toUpdate.sort((a, b) => {
        const ta = cacheDict[a] !== undefined ? cacheDict[a].writeTime : 0;
        const tb = cacheDict[b] !== undefined ? cacheDict[b].writeTime : 0;
        return ta - tb;
    });
    return toUpdate;
}

async function updateNext() {
    const toUpdate = await getUpdateCandidates();
    const now = Date.now();
    const toHardUpdate = [];

    while ( toUpdate.length !== 0 ) {
        const assetKey = toUpdate.shift();
        const writeTime = getWriteTime(assetKey);
        const updateDelay = getUpdateAfterTime(assetKey);
        if ( (writeTime + updateDelay) > now ) { continue; }
        toHardUpdate.push(assetKey);
    }
    if ( toHardUpdate.length === 0 ) {
        return updateDone();
    }

    const assetKey = toHardUpdate.pop();
    updaterFetched.add(assetKey);

    // In auto-update context, be gentle on remote servers.
    remoteServerFriendly = updaterAuto;

    let result;
    if ( assetKey !== 'assets.json' || µb.hiddenSettings.debugAssetsJson !== true ) {
        result = await getRemote(assetKey, { favorOrigin: updaterAuto === false });
    } else {
        result = await assets.fetchText(µb.assetsJsonPath);
        result.assetKey = 'assets.json';
    }

    remoteServerFriendly = false;

    if ( result.error ) {
        ubolog(`Full updater: failed to update ${assetKey}`);
        fireNotification('asset-update-failed', { assetKey: result.assetKey });
    } else {
        ubolog(`Full updater: successfully updated ${assetKey}`);
        updaterUpdated.push(result.assetKey);
        if ( result.assetKey === 'assets.json' && result.content !== '' ) {
            updateAssetSourceRegistry(result.content);
        }
    }

    updaterTimer.on(updaterAssetDelay);
}

const updaterTimer = vAPI.defer.create(updateNext);

function updateDone() {
    const assetKeys = updaterUpdated.slice(0);
    updaterFetched.clear();
    updaterUpdated.length = 0;
    updaterStatus = undefined;
    updaterAuto = false;
    updaterAssetDelay = updaterAssetDelayDefault;
    ubolog('Updater: cycle end');
    if ( assetKeys.length ) {
        ubolog(`Updater: ${assetKeys.join()} were updated`);
    }
    fireNotification('after-assets-updated', { assetKeys });
}

assets.updateStart = function(details) {
    const oldUpdateDelay = updaterAssetDelay;
    const newUpdateDelay = typeof details.fetchDelay === 'number'
        ? details.fetchDelay
        : updaterAssetDelayDefault;
    updaterAssetDelay = Math.min(oldUpdateDelay, newUpdateDelay);
    updaterAuto = details.auto === true;
    if ( updaterStatus !== undefined ) {
        if ( newUpdateDelay < oldUpdateDelay ) {
            updaterTimer.offon(updaterAssetDelay);
        }
        return;
    }
    updateFirst();
};

assets.updateStop = function() {
    updaterTimer.off();
    if ( updaterStatus !== undefined ) {
        updateDone();
    }
};

assets.isUpdating = function() {
    return updaterStatus === 'updating' &&
           updaterAssetDelay <= µb.hiddenSettings.manualUpdateAssetFetchPeriod;
};

/******************************************************************************/

export default assets;

/******************************************************************************/