如何在 ASP.NET 中從遠端 URL 下載和串流檔案？

從URL 下載/串流檔案- asp.net

在某些情況下，可能需要從遠端URL 串流或下載檔案並觸發「另存為”瀏覽器中的提示。但是，當檔案位於虛擬映射目錄中時，使用 Server.MapPath 存取其實際位置可能會很困難。

相反，您可以利用 HttpWebRequest 的強大功能來實現此功能。以下是一個允許您傳遞 Web URL 的範例：

using System.IO;
using System.Net;

namespace FileDownloader
{
    public static class FileDownloader
    {
        public static void DownloadFile(string url, string fileName)
        {
            // Create a stream for the file
            Stream stream = null;

            // Configure streaming chunk size
            int bytesToRead = 10000;

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

            // Initialize response
            HttpWebResponse fileResp = null;

            try
            {
                // Create a WebRequest to get the file
                HttpWebRequest fileReq = (HttpWebRequest)HttpWebRequest.Create(url);

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

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

                // Prepare the response to the client
                HttpResponse resp = HttpContext.Current.Response;

                // Set response type and add headers
                resp.ContentType = MediaTypeNames.Application.Octet;
                resp.AddHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
                resp.AddHeader("Content-Length", fileResp.ContentLength.ToString());

                int length;
                do
                {
                    // Verify client connection
                    if (resp.IsClientConnected)
                    {
                        // Read data into the buffer
                        length = stream.Read(buffer, 0, bytesToRead);

                        // Write data 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 download if client disconnects
                        length = -1;
                    }
                } while (length > 0); // Repeat until no data remains
            }
            finally
            {
                // Close the input stream
                if (stream != null)
                {
                    stream.Close();
                }

                // Dispose the response
                if (fileResp != null)
                {
                    fileResp.Close();
                }
            }
        }
    }
}

透過使用此方法，您可以從遠端 URL 串流文件，並允許使用者使用動態產生的文件名稱將它們保存在本地。

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