func cacheMiddleware(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // 对静态资源设置缓存策略
        if strings.HasPrefix(r.URL.Path, "/static/") {
            w.Header().Set("Cache-Control", "public, max-age=31536000, immutable") // 缓存一年
        }
        h.ServeHTTP(w, r)
    })
}

// 使用
fs := http.FileServer(http.Dir("static/"))
http.Handle("/static/", cacheMiddleware(fs))

http.HandleFunc("/assets/", func(w http.ResponseWriter, r *http.Request) {
    filePath := "./" + r.URL.Path
    file, err := os.Open(filePath)
    if err != nil {
        http.NotFound(w, r)
        return
    }
    defer file.Close()

    info, _ := file.Stat()
    w.Header().Set("Cache-Control", "public, max-age=604800") // 缓存一周

    // 启用 ETag 和条件请求支持
    etag := fmt.Sprintf("%x-%x", info.ModTime().Unix(), info.Size())
    w.Header().Set("ETag", etag)

    if match := r.Header.Get("If-None-Match"); match != "" {
        if match == etag {
            w.WriteHeader(http.StatusNotModified)
            return
        }
    }

    http.ServeContent(w, r, filePath, info.ModTime(), file)
})

location /static/ {
    alias /path/to/static/;
    expires 1y;
    add_header Cache-Control "public, immutable";
}