防止通过URL下载文件

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Threading;

/// <summary>
/// FileDownload 的摘要说明
/// </summary>
public class FileDownload
{
    /// <summary>
    /// 输出硬盘文件，提供下载 支持大文件、续传、速度限制、资源占用小
    /// </summary>
    /// <param name="_Request">Page.Request对象</param>
    /// <param name="_Response">Page.Response对象</param>
    /// <param name="_fileName">下载文件名</param>
    /// <param name="_fullPath">带文件名下载路径</param>
    /// <param name="_speed">每秒允许下载的字节数</param>
    /// <returns>返回是否成功</returns>
    public static bool ResponseFile(HttpRequest _Request, HttpResponse _Response, string _fileName, string _fullPath, long _speed)
    {
        try
        {
            FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
            BinaryReader br = new BinaryReader(myFile);
            try
            {
                _Response.AddHeader("Accept-Ranges", "bytes");
                _Response.Buffer = false;
                long fileLength = myFile.Length;
                long startBytes = 0;

                int pack = 10240; //10K bytes
                //int sleep = 200;   //每秒5次   即5*10K bytes每秒
                int sleep = (int)Math.Floor((decimal)1000 * pack / _speed) + 1;
                if (_Request.Headers["Range"] != null)
                {
                    _Response.StatusCode = 206;
                    string[] range = _Request.Headers["Range"].Split(new char[] { ‘=‘, ‘-‘ });
                    startBytes = Convert.ToInt64(range[1]);
                }
                _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                if (startBytes != 0)
                {
                    _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                }
                _Response.AddHeader("Connection", "Keep-Alive");
                _Response.ContentType = "application/octet-stream";
                _Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(_fileName, System.Text.Encoding.UTF8));

                br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                int maxCount = (int)Math.Floor((decimal)(fileLength - startBytes) / pack) + 1;

                for (int i = 0; i < maxCount; i++)
                {
                    if (_Response.IsClientConnected)
                    {
                        _Response.BinaryWrite(br.ReadBytes(pack));
                        Thread.Sleep(sleep);
                    }
                    else
                    {
                        i = maxCount;
                    }
                }
            }
            catch
            {
                return false;
            }
            finally
            {
                br.Close();
                myFile.Close();
            }
        }
        catch
        {
            return false;
        }
        return true;
    }

}

using System;
using System.Collections.Generic;
using System.Web;
using Video.Filters;
using VideoLibrary.Model;
using System.Web.SessionState;
namespace Video.AppCode
{
    /// <summary>
    /// download 的摘要说明
    /// </summary>
    public class download : IHttpHandler,IRequiresSessionState
    {

        private UserInformation user = null;
        public void ProcessRequest(HttpContext context)
        {
            if(context.Session["user"]!=null)
                user=(UserInformation)context.Session["user"];
           dowmload(context,user);
           
        }
        public void dowmload(HttpContext context, UserInformation user)
        {
            if (null != user)
            {
                string PPT_Type = context.Request.QueryString["PPT_Type"];
                string id = context.Request.QueryString["id"];
                string file = "";
                switch (PPT_Type)
                {

                    case "SharePoint":
                        file = "SharePoint 2013 Overview.pptx";
                        FileDownload.ResponseFile(context.Request, context.Response, file, "D://document/" + file, 102400);
                        break;
                    case "Office":
                        if (id == "1")
                        {
                            file = "2013 O365 Customer Presentation.pptx";
                            FileDownload.ResponseFile(context.Request, context.Response, file, "D://document/" + file, 102400);
                        }
                        else if (id == "2")
                        {
                            file = "新一代Office，个人和企业生产力提升.pptx";
                            FileDownload.ResponseFile(context.Request, context.Response, file, "D://document/" + file, 102400);
                        }
                        break;
                }
            }
            else
                context.Response.Redirect("/Home/Index");
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}

<a href="download.ashx?PPT_Type=SharePoint&id=0"></a>