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In memory multiple files downloaded as a in memory zip

By Sudeep on 1/2/2019

This problem is pretty hard to explain until one faces it for the first time.
My environment is Azure web app.
My code downloads multiple files using a third party REST endpoint on the server side.
My ASP.NET UI then downloads it to the client.
I don't have the luxury of a server folder aka Server.MapPath

So here is the piece of code which does it. Keep in mind that the third party API returns this for each GET call, which is pretty much similar to the out of box Response object of C#.

So what my code does is to get all the IRestResponse and stores them in list using this piece of code. "envId" is the id of the file and "access_token" is self explanatory both are specific to the third party API(Portal)

So this function is called multiple times and the result is stored in a List called "filesToDownload"

Next comes the difficult part, how to create a zip of these files, keeping in mind I cannot download them on server then use those files to send it across to the client

protected void btnDownload_Click(object sender, EventArgs e)
    {
        string operation = "download";
        //this is the function which gets the content for each file and populates the same 
        //in the list
        RetreiveSelectedRecords(operation);
        if (filesToDownload != null && filesToDownload.Count > 1)
        {
            using (var zMemoryStream = new MemoryStream())
            {
                using (var archive = new System.IO.Compression.ZipArchive(zMemoryStream, ZipArchiveMode.Create, true))
                {
                    int i = 0;
                    foreach (var dFile in filesToDownload)
                    {
                        i++;
                        var contentHeader = dFile.Headers.FirstOrDefault(x => x.Name == "Content-Disposition");
                        string fileName = "foo" + i.ToString().Trim() + ".txt";
                        if (contentHeader != null)
                        {
                            string temp = contentHeader.Value.ToString();
                            fileName = temp.Split(';')[1].Replace("filename", "").Replace("=", "").Replace("\"", "").Replace("\"", "").Trim();
                        }
                        var demoFile = archive.CreateEntry(fileName);
                        using (var entryStream = demoFile.Open())
                        {
                            using (var compressStreamWriter = new MemoryStream(dFile.RawBytes))
                            {

                                compressStreamWriter.CopyTo(entryStream);

                            }
                        }
                    }
                }
                Response.ClearContent();
                Response.Clear();
                Response.ContentType = "application/zip";
                Response.AddHeader("Content-Disposition", "attachment; filename=ndDownload.zip");
                Response.BinaryWrite(zMemoryStream.ToArray());
                Response.Flush();
                Response.Close();
                Response.End();
            }
        }
        else if(filesToDownload!=null && filesToDownload.Count == 1)
        {
            Response.ClearContent();
            Response.Clear();
            Response.ContentType = filesToDownload[0].ContentType;
            
            var contentHeader = filesToDownload[0].Headers.FirstOrDefault(x => x.Name == "Content-Disposition");
            if (contentHeader != null)
            {
                Response.AddHeader("Content-Disposition", contentHeader.Value.ToString());
            }
            Response.BufferOutput = true;
            byte[] Content = filesToDownload[0].RawBytes;
            Response.OutputStream.Write(Content, 0, Content.Length);
            
            Response.Flush();
            Response.Close();           
            Response.End();
        }
    }

I hope this helps you to work with multiple files on Azure. 

 

 

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