c# 下载代码,求注释

string pathfile = 文件的物理路径;
FileStream fs = new FileStream(pathfile, FileMode.Open, FileAccess.Read);
long p = 0;
FileInfo fi = new FileInfo(pathfile);
long l = fi.Length;
if (Request.Headers["Range"] != null)
{
Response.StatusCode = 206;
p = long.Parse(Request.Headers["Range"].Replace("bytes=", "").Replace("-", ""));
}

Response.AddHeader("Content-Length", ((long)(l - p)).ToString());
if (p != 0)
{
Response.AddHeader("Content-Range", "bytes " + p.ToString() + "-" + ((long)(l - p)).ToString() + "/" + l.ToString());
}

Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", "attachment; filena

string pathfile = 文件的物理路径; //指定文件路径
FileStream fs = new FileStream(pathfile, FileMode.Open, FileAccess.Read); //用只读方式打开文件
long p = 0;
FileInfo fi = new FileInfo(pathfile); //得到文件信息
long l = fi.Length; //得到文件大小
if (Request.Headers["Range"] != null)
{
Response.StatusCode = 206;
p = long.Parse(Request.Headers["Range"].Replace("bytes=", "").Replace("-", ""));
}
//根据http请求做出相应的回答
Response.AddHeader("Content-Length", ((long)(l - p)).ToString());
if (p != 0)
{
Response.AddHeader("Content-Range", "bytes " + p.ToString() + "-" + ((long)(l - p)).ToString() + "/" + l.ToString());
}
//返回一些http头信息
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", "attachment; filename=" + System.IO.Path.GetFileName(pathfile));