创建临时下载链接 [英] Create temporary link for download

问题描述

我使用 ASP.NET
我需要为用户提供从服务器下载文件的临时链接.
它应该是一个临时链接(页面)，在短时间内(例如 12 小时)可用.如何生成此链接(或带有链接的临时网页)?

I use ASP.NET
I need to give user temporary link for downloading file from server.
It should be a temporary link (page), which is available for a short time (12 hours for example). How can I generate this link (or temporary web page with link)?

推荐答案

这是一个相当完整的例子.

Here's a reasonably complete example.

首先是一个使用秘密盐和到期时间创建短十六进制字符串的函数:

First a function to create a short hex string using a secret salt plus an expiry time:

public static string MakeExpiryHash(DateTime expiry)
{
    const string salt = "some random bytes";
    byte[] bytes = Encoding.UTF8.GetBytes(salt + expiry.ToString("s"));
    using (var sha = System.Security.Cryptography.SHA1.Create())
        return string.Concat(sha.ComputeHash(bytes).Select(b => b.ToString("x2"))).Substring(8);
}

然后是一个生成一周到期链接的片段:

Then a snippet that generates a link with a one week expiry:

DateTime expires = DateTime.Now + TimeSpan.FromDays(7);
string hash = MakeExpiryHash(expires);
string link = string.Format("http://myhost/Download?exp={0}&k={1}", expires.ToString("s"), hash);

最后是在提供有效链接的情况下发送文件的下载页面:

Finally the download page for sending a file if a valid link was given:

DateTime expires = DateTime.Parse(Request.Params["exp"]);
string hash = MakeExpiryHash(expires);
if (Request.Params["k"] == hash)
{
    if (expires < DateTime.UtcNow)
    {
        // Link has expired
    }
    else
    {
        string filename = "<Path to file>";
        FileInfo fi = new FileInfo(Server.MapPath(filename));
        Response.ContentType = "application/octet-stream";
        Response.AddHeader("Content-Disposition", "attachment;filename=" + filename);
        Response.AddHeader("Content-Length", fi.Length.ToString());
        Response.WriteFile(fi.FullName);
        Response.Flush();
    }
}
else
{
    // Invalid link
}

你当然应该用一些异常处理来捕获错误的请求.

Which you should certainly wrap in some exception handling to catch mangled requests.

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