如何在 ASP.NET 中从远程 URL 流式传输或下载文件？

从 ASP.NET 中的远程 URL 流式传输或下载文件

问题：

您需要从远程 URL 流式传输或下载文件并将其显示为浏览器中的另存为对话框。然而，该文件的目录是虚拟的，无法通过 Server.MapPath 等传统方法访问它。

解决方案：

利用 HttpWebRequest 从 URL 和流中检索文件它返回给客户端。这种方法允许您处理只能通过 URL 访问的文件。

下面是一个代码示例：

    //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();
        }
    }

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