Download/Stream file from URL - asp.net

In certain scenarios, it may be necessary to stream or download a file from a remote URL and trigger a "Save As" prompt in the browser. However, when the file is located in a virtually mapped directory, accessing its actual location using Server.MapPath can be challenging.

Instead, you can leverage the power of HttpWebRequest to achieve this functionality. Here's an example that allows you to pass a web URL:

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();
                }
            }
        }
    }
}

By using this approach, you can stream files from remote URLs and allow users to save them locally with a dynamically generated file name.

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