ASP.NET - ASP.NET 2.0 文件下载（支持大文件、防盗链）

1.文件下载
HTTP 文件下载主要有两种方式：
URL方式直接下载，优点是：占用服务器资源少，速度快；缺点是： 不能准确计量下载次数，无法防止盗链，保存在数据库中的文件无法下载，常见格式的文件如.html 直接在浏览器中打开，不能直接下载。
二进制数据流输出方式，优点是：准确计量下载次数、能防盗链、所有文件格式都能直接下载而不是打开、保存在数据库中等非文件数据能以文件方式下载等；缺点是占用服务器资源多。
大文件下载原理是把文件切成小段数据流下载，微软msdn给出了大文件下载的示例，但存在中文文件名乱码问题，稍加改动即可。代码为：

protected void ResponseFile(string path) {    
        System.IO.Stream iStream = null;    
        byte[] buffer = new Byte[10000];    
        int length;    
        long dataToRead;    
        string filename = System.IO.Path.GetFileName(path);    
    
        try {    
                iStream = new System.IO.FileStream(path, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read);    
                dataToRead = iStream.Length;    
                Response.ContentType = "application/octet-stream";    
                Response.AddHeader("Content-Disposition", "p_w_upload; filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8));    
                while (dataToRead > 0) {    
                        if (Response.IsClientConnected) {    
                                length = iStream.Read(buffer, 0, 10000);    
                                Response.OutputStream.Write(buffer, 0, length);    
                                Response.Flush();    
                                buffer = new Byte[10000];    
                                dataToRead = dataToRead - length;    
                                }    
                        else {    
                                dataToRead = -1;    
                                }    
                        }    
                }    
        catch (Exception ex) {    
                Response.Write("文件下载时出现错误!");    
                }    
                finally {    
                        if (iStream != null) {    
                                iStream.Close();    
                                }    
                        }    
                }

2.防止盗链

protected void Page_Load(object sender, EventArgs e) {    
        /*-------------大文件下载，防盗链------------------*/
        if (Request.QueryString["FileName"] == null) { InvalidRedirect(); }    
        string fileName = Request.QueryString["FileName"];    
        if (fileName == string.Empty) { InvalidRedirect(); }    
        //判断配置文件是否直接下载    
        string downDirect = ConfigurationManager.AppSettings["Down"].ToLower();    
        if (downDirect == "true") { UpdateHits(fileName);    
        //更新下载次数 Response.Redirect("Upload/" + fileName);    return; }    
        string path = Server.MapPath(Request.ApplicationPath + "/Upload/" + fileName);    
        string referrer = string.Empty;    
        if (Request.UrlReferrer != null) { referrer = Request.UrlReferrer.ToString().ToLower(); }    
        string d = ConfigurationManager.AppSettings["Valid"].ToLower();    
        string[] domainName = ConfigurationManager.AppSettings["Refers"].ToLower().Split(new char[] { ',' });    
        // 如果设置为防止盗链，判断访问来源是否合法    
        if (d == "false") {    
                foreach (string s in domainName) {    
                        if (referrer.IndexOf(s.ToLower()) > 0) { UpdateHits(fileName);    
                        //更新下载次数    
                        ResponseFile(path);    
                        return;    
                        }    
                        }    
                InvalidRedirect();    
                }    
                else {    
                        ResponseFile(path);    
                        }    
                }    
        protected void UpdateHits(string fileName) {    
                //更新文件下载次数的代码    
                }    
        protected void InvalidRedirect() {    
                string defaultPage = ConfigurationManager.AppSettings["DefaultRedirect"];    
                Response.Redirect(defaultPage, true);    
                }

3.配置文件
配置文件中配置下载方式、盗链功能是否开启及盗链默认转向的页面地址：

<appSettings>    
        <add key="Down" value="false"/>    
        <!--是否直接下载-->    
        <add key="Valid" value="false"/>    
        <!--是否允许盗链-->    
        <add key="Refers" value="localhost,google.cn"/>    
        <!--多个允许的访问来源用半角的","分割-->    
        <add key="DefaultRedirect" value="Error.htm"/>    
        <!--默认转向的页面-->    
</appSettings>