从 URL 下载/流式传输文件 - asp.net

Question

我需要流式传输一个文件，这将导致在浏览器中另存为提示。 问题是，文件所在的目录是虚拟映射的，所以我无法使用 Server.MapPath 来确定它的实际位置。该目录与网站不在同一位置（甚至是 Live Box 上的物理服务器）。

我想要类似以下的内容，但这将允许我传递 Web URL，而不是服务器文件路径。

我可能不得不最终从配置基本路径构建我的文件路径，然后附加到路径的其余部分，但希望我可以这样做。

var filePath = Server.MapPath(DOCUMENT_PATH);

if (!File.Exists(filePath))
    return;

var fileInfo = new System.IO.FileInfo(filePath);
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", String.Format("attachment;filename=\"{0}\"", filePath));
Response.AddHeader("Content-Length", fileInfo.Length.ToString());
Response.WriteFile(filePath);
Response.End();

Answer 1

您可以使用 HttpWebRequest 获取文件并将其流式传输回客户端。这使您可以使用 url 获取文件。我发现的一个例子（但不记得在哪里给予信任）是

    //Create a stream for the file
    Stream stream = null;

    //This controls how many bytes to read at a time and send to the client
    int bytesToRead = 10000;

    // Buffer to read bytes in chunk size specified above
    byte[] buffer = new Byte[bytesToRead];

    // The number of bytes read
    try
    {
      //Create a WebRequest to get the file
      HttpWebRequest fileReq = (HttpWebRequest) HttpWebRequest.Create(url);

      //Create a response for this request
      HttpWebResponse fileResp = (HttpWebResponse) fileReq.GetResponse();

      if (fileReq.ContentLength > 0)
        fileResp.ContentLength = fileReq.ContentLength;

        //Get the Stream returned from the response
        stream = fileResp.GetResponseStream();

        // prepare the response to the client. resp is the client Response
        var resp = HttpContext.Current.Response;

        //Indicate the type of data being sent
        resp.ContentType = MediaTypeNames.Application.Octet;
    
        //Name the file 
        resp.AddHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        resp.AddHeader("Content-Length", fileResp.ContentLength.ToString());
    
        int length;
        do
        {
            // Verify that the client is connected.
            if (resp.IsClientConnected)
            {
                // Read data into the buffer.
                length = stream.Read(buffer, 0, bytesToRead);

                // and write it out to the response's output stream
                resp.OutputStream.Write(buffer, 0, length);

                // Flush the data
                resp.Flush();

                //Clear the buffer
                buffer = new Byte[bytesToRead];
            }
            else
            {
                // cancel the download if client has disconnected
                length = -1;
            }
        } while (length > 0); //Repeat until no data is read
    }
    finally
    {
        if (stream != null)
        {
            //Close the input stream
            stream.Close();
        }
    }

Answer 2

将url下载为字节并将字节转换为流：

using (var client = new WebClient())
{
    var content = client.DownloadData(url);
    using (var stream = new MemoryStream(content))
    {
        ...
    }
}   

Answer 3

我经常这样做，并认为我可以添加一个更简单的答案。我在这里将它设置为一个简单的课程，但我每天晚上都运行它来收集我关注的公司的财务数据。

class WebPage
{
    public static string Get(string uri)
    {
        string results = "N/A";

        try
        {
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

            StreamReader sr = new StreamReader(resp.GetResponseStream());
            results = sr.ReadToEnd();
            sr.Close();
        }
        catch (Exception ex)
        {
            results = ex.Message;
        }
        return results;
    }
}

在这种情况下，我传入一个 url，它以 HTML 形式返回页面。如果你想对流做一些不同的事情，你可以很容易地改变它。

你可以这样使用它：

string page = WebPage.Get("http://finance.yahoo.com/q?s=yhoo");

Answer 4

2 年后，我使用了达拉斯的答案，但我不得不将 HttpWebRequest 更改为 FileWebRequest，因为我正在链接到直接文件。不确定是否到处都是这种情况，但我想我会添加它。另外，我删除了

var resp = Http.Current.Resonse

并且在任何引用 resp 的地方都使用了 Http.Current.Response。

Answer 5

如果您正在寻找 @Dallas 答案的 .NET Core 版本，请使用以下内容。

        Stream stream = null;

        //This controls how many bytes to read at a time and send to the client
        int bytesToRead = 10000;

        // Buffer to read bytes in chunk size specified above
        byte[] buffer = new Byte[bytesToRead];

        // The number of bytes read
        try
        {
            //Create a WebRequest to get the file
            HttpWebRequest fileReq = (HttpWebRequest)HttpWebRequest.Create(@"file url");

            //Create a response for this request
            HttpWebResponse fileResp = (HttpWebResponse)fileReq.GetResponse();

            if (fileReq.ContentLength > 0)
                fileResp.ContentLength = fileReq.ContentLength;

            //Get the Stream returned from the response
            stream = fileResp.GetResponseStream();

            // prepare the response to the client. resp is the client Response
            var resp = HttpContext.Response;

            //Indicate the type of data being sent
            resp.ContentType = "application/octet-stream";

            //Name the file 
            resp.Headers.Add("Content-Disposition", "attachment; filename=test.zip");
            resp.Headers.Add("Content-Length", fileResp.ContentLength.ToString());

            int length;
            do
            {
                // Verify that the client is connected.
                if (!HttpContext.RequestAborted.IsCancellationRequested)
                {
                    // Read data into the buffer.
                    length = stream.Read(buffer, 0, bytesToRead);

                    // and write it out to the response's output stream
                    resp.Body.Write(buffer, 0, length);


                    //Clear the buffer
                    buffer = new Byte[bytesToRead];
                }
                else
                {
                    // cancel the download if client has disconnected
                    length = -1;
                }
            } while (length > 0); //Repeat until no data is read
        }
        finally
        {
            if (stream != null)
            {
                //Close the input stream
                stream.Close();
            }
        }

Answer 6

您可以尝试使用带有 IIS 路径前缀的 DirectoryEntry 类：

using(DirectoryEntry de = new DirectoryEntry("IIS://Localhost/w3svc/1/root" + DOCUMENT_PATH))
{
    filePath = de.Properties["Path"].Value;
}

if (!File.Exists(filePath))
        return;

var fileInfo = new System.IO.FileInfo(filePath);
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", String.Format("attachment;filename=\"{0}\"", filePath));
Response.AddHeader("Content-Length", fileInfo.Length.ToString());
Response.WriteFile(filePath);
Response.End();

Answer 7

如果我们在 Citrix Netscaler 上使用负载均衡器（没有 WAF 策略），达拉斯接受的解决方案对我们有用。

当文件与 WAF 关联时，无法通过 Netscaler 的 LB 下载文件，因为当前场景（内容长度不正确）违反了 RFC 并且 AppFW 重置了连接，这不会未关联 WAF 策略时发生。

所以缺少的是：

Response.End();

另请参阅： Trying to stream a PDF file with asp.net is producing a "damaged file"