/** * CDN 智能选择器 - 在主应用加载前运行 * * 功能： * 1. 检测可用的 CDN 源 * 2. 选择最快的 CDN * 3. 将选择结果存储到 localStorage * 4. 供 Service Worker 使用 * * 使用方式： * 在 index.html 的中添加: * */ (function() { var CDN_GLOBAL_KEY = '__OPENTU_CDN__'; var CDN_API_GLOBAL_KEY = '__OPENTU_CDN_API__'; var LEGACY_CDN_GLOBAL_KEY = '__AITU_CDN__'; var LEGACY_CDN_API_GLOBAL_KEY = '__AITU_CDN_API__'; var STORAGE_KEY = 'opentu-cdn-preference'; var LEGACY_STORAGE_KEY = 'aitu-cdn-preference'; function setCDNPreference(value) { window[CDN_GLOBAL_KEY] = value; window[LEGACY_CDN_GLOBAL_KEY] = value; } function getCDNPreference() { return window[CDN_GLOBAL_KEY] || window[LEGACY_CDN_GLOBAL_KEY] || null; } function isSupportedCDNName(name) { for (var i = 0; i < CDN_SOURCES.length; i++) { if (CDN_SOURCES[i].name === name) { return true; } } return name === 'local'; } function setCDNApi(api) { window[CDN_API_GLOBAL_KEY] = api; window[LEGACY_CDN_API_GLOBAL_KEY] = api; } // 开发模式检测 - 本地开发时跳过 CDN 逻辑 var isDevelopment = window.location.hostname === 'localhost' || window.location.hostname === '127.0.0.1' || window.location.hostname.endsWith('.localhost'); if (isDevelopment) { setCDNPreference({ cdn: 'local', latency: 0, timestamp: Date.now(), isDevelopment: true }); setCDNApi({ selectBestCDN: function() { return Promise.resolve(getCDNPreference()); }, getCDNBaseUrl: function() { return null; }, clearCDNCache: function() {}, reselectCDN: function() { return Promise.resolve(getCDNPreference()); }, sources: [], config: {}, isDevelopment: true, }); return; // 直接返回，不执行 CDN 检测 } // 配置 var CONFIG = { packageName: 'aitu-app', storageKey: STORAGE_KEY, testTimeout: 5000, // 测试超时时间（毫秒） cacheExpiry: 3600000, // 缓存过期时间（1小时） }; // 运行时 CDN 候选：主 CDN 优先，备用 CDN 兜底 var CDN_SOURCES = [ { name: 'jsdelivr', baseUrl: 'https://cdn.jsdelivr.net/npm/' + CONFIG.packageName, testPath: '/version.json', }, ]; /** * 测试单个 CDN 的响应时间 */ function testCDN(source) { return new Promise(function(resolve) { var startTime = Date.now(); var testUrl = source.baseUrl + source.testPath + '?t=' + startTime; var xhr = new XMLHttpRequest(); xhr.timeout = CONFIG.testTimeout; xhr.onload = function() { if (xhr.status === 200) { var latency = Date.now() - startTime; resolve({ name: source.name, latency: latency, success: true }); } else { resolve({ name: source.name, latency: Infinity, success: false }); } }; xhr.onerror = function() { resolve({ name: source.name, latency: Infinity, success: false }); }; xhr.ontimeout = function() { resolve({ name: source.name, latency: Infinity, success: false }); }; xhr.open('GET', testUrl, true); xhr.send(); }); } /** * 选择最快的 CDN */ function selectBestCDN() { // 检查缓存 try { var cached = localStorage.getItem(CONFIG.storageKey) || localStorage.getItem(LEGACY_STORAGE_KEY); if (cached) { var data = JSON.parse(cached); if ( Date.now() - data.timestamp < CONFIG.cacheExpiry && isSupportedCDNName(data.cdn) ) { setCDNPreference(data); return Promise.resolve(data); } if (!isSupportedCDNName(data.cdn)) { clearCDNCache(); } } } catch (e) { // 忽略解析错误 } // 并行测试所有 CDN var tests = CDN_SOURCES.map(testCDN); return Promise.all(tests).then(function(results) { // 过滤成功的结果并按延迟排序 var successfulResults = results .filter(function(r) { return r.success; }) .sort(function(a, b) { return a.latency - b.latency; }); if (successfulResults.length === 0) { return { cdn: 'local', latency: 0, timestamp: Date.now(), allResults: results }; } var best = successfulResults[0]; var preference = { cdn: best.name, latency: best.latency, timestamp: Date.now(), allResults: results, }; // 缓存结果 try { localStorage.setItem(CONFIG.storageKey, JSON.stringify(preference)); } catch (e) { // 忽略存储错误 } // 暴露到全局变量供 SW 使用 setCDNPreference(preference); return preference; }); } /** * 获取 CDN 基础 URL */ function getCDNBaseUrl(cdnName, version) { for (var i = 0; i < CDN_SOURCES.length; i++) { if (CDN_SOURCES[i].name === cdnName) { var baseUrl = CDN_SOURCES[i].baseUrl; if (version) { baseUrl = baseUrl.replace(CONFIG.packageName, CONFIG.packageName + '@' + version); } return baseUrl; } } return null; } /** * 清除 CDN 缓存（用于调试） */ function clearCDNCache() { try { localStorage.removeItem(CONFIG.storageKey); localStorage.removeItem(LEGACY_STORAGE_KEY); delete window[CDN_GLOBAL_KEY]; delete window[LEGACY_CDN_GLOBAL_KEY]; } catch (e) { // 忽略 } } /** * 强制重新选择 CDN */ function reselectCDN() { clearCDNCache(); return selectBestCDN(); } // 暴露 API setCDNApi({ selectBestCDN: selectBestCDN, getCDNBaseUrl: getCDNBaseUrl, clearCDNCache: clearCDNCache, reselectCDN: reselectCDN, sources: CDN_SOURCES, config: CONFIG, }); // 页面加载时自动选择 CDN（非阻塞） if (document.readyState === 'loading') { document.addEventListener('DOMContentLoaded', function() { selectBestCDN(); }); } else { // DOM 已加载完成 selectBestCDN(); } })();