feat(跨域): 添加CORS支持以处理OPTIONS请求和响应头

添加跨域资源共享(CORS)支持，包括处理OPTIONS预检请求和在响应头中添加必要的CORS字段
移除不再使用的Cloud-Expiration头

source.js

@@ -215,6 +215,18 @@ async function tryServeFromStaleCacheOrError(uniqidhex, res, errorMessage) {
 }
 
 async function handleMainRequest(req, res) {
+    // 处理OPTIONS请求，支持跨域预检
+    if (req.method === 'OPTIONS') {
+        res.writeHead(200, {
+            'Access-Control-Allow-Origin': req.headers.origin || '*',
+            'Access-Control-Allow-Methods': 'GET, OPTIONS',
+            'Access-Control-Allow-Headers': 'Content-Type',
+            'Access-Control-Max-Age': '86400'
+        });
+        res.end();
+        return;
+    }
+    
     req.url = req.url.replace(/\/{2,}/g, '/');
     const parsedUrl = url.parse(req.url, true);
     const sign = parsedUrl.query.sign || '';
@@ -426,7 +438,6 @@ const fetchAndServe = async (data, tempCacheContentFile, cacheContentFile, cache
 
         const baseHeaders = {
             'Cloud-Type': data.cloudtype,
-            'Cloud-Expiration': data.expiration,
             'ETag': data.uniqid || '',
             'Cache-Control': 'public, max-age=31536000', // 1 year
             'Expires': new Date(Date.now() + 31536000000).toUTCString(),
@@ -434,6 +445,9 @@ const fetchAndServe = async (data, tempCacheContentFile, cacheContentFile, cache
             'Connection': 'keep-alive',
             'Date': new Date().toUTCString(),
             'Last-Modified': data.headers['last-modified'] || new Date().toUTCString(),
+            'Access-Control-Allow-Origin': req.headers.origin || '*',
+            'Access-Control-Allow-Methods': 'GET, OPTIONS',
+            'Access-Control-Allow-Headers': 'Content-Type',
         };
         const responseHeaders = {
             ...baseHeaders,
@@ -566,7 +580,6 @@ async function serveFromCache(cacheData, cacheContentFile, cacheMetaFile, res, r
 
     const baseHeaders = {
         'Cloud-Type': cacheData.cloudtype || 'unknown',
-        'Cloud-Expiration': cacheData.expiration || 'N/A',
         'ETag': etag || '',
         'Cache-Control': 'public, max-age=31536000', // 1 year
         'Expires': new Date(Date.now() + 31536000000).toUTCString(),
@@ -574,6 +587,9 @@ async function serveFromCache(cacheData, cacheContentFile, cacheMetaFile, res, r
         'Connection': 'keep-alive',
         'Date': new Date().toUTCString(),
         'Last-Modified': lastModified || new Date().toUTCString(),
+        'Access-Control-Allow-Origin': req.headers.origin || '*',
+        'Access-Control-Allow-Methods': 'GET, OPTIONS',
+        'Access-Control-Allow-Headers': 'Content-Type',
     };
 
     viewsInfo.increment('cacheCall');