ASP.NET download big file using BinaryWrite

There are situation when you need to provide download option for a big file located somewhere on server or generated at runtime. Below function could be used to download files of any size. Sometimes downloading big file throws exception OutOfMemoryException showing “Insufficient memory to continue execution of the program”. So this function also handle this situation by breaking down file in 1 MB chunks (can be customized by changing bufferSize variable).

Usage:

DownloadLargeFile("A big file.pdf", "D:\\Big Files\\Big File.pdf", "application/pdf", HttpContext.Current.Response);

Download Function

public static void DownloadLargeFile(string DownloadFileName, string FilePath, string ContentType, HttpResponse response)
        {
            Stream stream = null;

            // read buffer in 1 MB chunks
            // change this if you want a different buffer size
            int bufferSize = 1048576;
                        
            byte[] buffer = new Byte[bufferSize];

            // buffer read length
            int length;
            // Total length of file
            long lengthToRead;

            try
            {
                // Open the file in read only mode 
                stream = new FileStream(FilePath, FileMode.Open, FileAccess.Read, FileShare.Read);

                // Total length of file
                lengthToRead = stream.Length;
                response.ContentType = ContentType;
                response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(DownloadFileName, System.Text.Encoding.UTF8));

                while (lengthToRead > 0)
                {
                    // Verify that the client is connected.
                    if (response.IsClientConnected)
                    {
                        // Read the data in buffer
                        length = stream.Read(buffer, 0, bufferSize);

                        // Write the data to output stream.
                        response.OutputStream.Write(buffer, 0, length);

                        // Flush the data 
                        response.Flush();

                        //buffer = new Byte[10000];
                        lengthToRead = lengthToRead - length;
                    }
                    else
                    {
                        // if user disconnects stop the loop
                        lengthToRead = -1;
                    }
                }
            }
            catch (Exception exp)
            {
                // handle exception
                response.ContentType = "text/html";
                response.Write("Error : " + exp.Message);
            }
            finally
            {
                if (stream != null)
                {
                    stream.Close();
                }
                response.End();
                response.Close();
            }
        }