Zip Folder is always corrupted after downloaded

Question

Hi,

For some reason when I download a zip folder from my server's folder it is always corrupted. Here is the code:

  protected void gvFiles_RowCommand(object sender, System.Web.UI.WebControls.GridViewCommandEventArgs e)
        {
            string fileUrl = String.Empty; 

            if(e.CommandName.Equals("DownloadFile"))
            {
                fileUrl = e.CommandArgument as String;
                string fileName = Path.GetFileName(fileUrl);

                Response.AppendHeader("content-disposition",
        "attachment; filename=" + fileName);
                Response.ContentType = "application/zip";

                Response.WriteFile(fileUrl);
                Response.End();  



            }
        }

And here is how the GridView is populated:

private void BindData()
        {
            List<SampleFile> files = new List<SampleFile>(); 

            for(int i=1;i<=3;i++)
            {
                SampleFile sampleFile = new SampleFile();
                sampleFile.Name = "File " + i;
                sampleFile.Url = Server.MapPath("~/Files/File"+i+".txt");
                files.Add(sampleFile);
            }

            SampleFile file = new SampleFile();
            file.Name = "Zip File";
            file.Url = Server.MapPath("~/Files/WebSiteNestedMasters.zip");
            files.Add(file);
            gvFiles.DataSource = files;
            gvFiles.DataBind(); 
        }

Answer 1

I don't know asp.net at all, but this is pretty commonly a result of doing the download in a text mode instead of binary mode. Line ending characters get converted from \r\n to \n or vice versa, and everything goes nuts.

Answer 2

First, verify that the contents of the file actually looks like a zip file. You can do that simply by dropping the file into notepad, and looking at the contents. If the file starts with PK and some funny characters, it might be a zip file. If it contains HTML, that might be a clue as to why it is going wrong.

Looking at your code, it struck me that you're passing the url to the file to Response.WriteFile. Does Response.WriteFile handle url's or does it use local filenames? Perhaps everything up to Response.WriteFile works, and thus the right headers are sent, etc. but then the code crashes with an exception, which might make your "zip file" contain a HTML error message.

---

Edit: Ok, first problem-solving step completed. File looks like a zip file in notepad, not a HTML error message.

Next step, since the file resides on the server, try writing an url directly to the file, instead of going through your application. Does that work?

If not, try a different zip program (which one are you using by the way?).

As an example of why you should try the file directly and different unzipping programs. FinalBuilder produces zip files that PowerArchiver complains about, but 7zip does not, so there might be something wrong with either the file or your program, or possibly even both.

But verify that the files are correct, can be opened, both if you don't download them at all, and check what happens if you download them directly outside of your application.

---

Edit: Ok, you've verified that the file won't open even if you download it directly from your server.

How about opening the file in just explorer, bypassing the web server altogether? For instance, since it looks like you have the file locally, try just navigating to the right folder and opening the file directly. Does that work?

Answer 3

As @lassevk suggested you should download the corrupted zip file and compare it with the original file on the server. Are both the same length? Use a hex editor to inspect the contents of the file. In this related thread you are saying that if you point the browser directly to the zip file it is also corrupted, meaning that the problem is probably not related to the headers but something wrong with IIS. Are you using some third party ISAPI extensions that could modify the file?

Answer 4

Here is the updated code:

fileUrl = e.CommandArgument as String;
                string fileName = Path.GetFileName(fileUrl);

                FileStream fs = new FileStream(fileUrl, FileMode.Open);
                byte[] buffer = new byte[fs.Length];
                fs.Read(buffer, 0, (int) fs.Length);
                fs.Close(); 

                Response.Clear(); 
                Response.AppendHeader("content-disposition",
        "attachment; filename=" + fileName);
                Response.ContentType = "application/octet-stream";
                Response.AppendHeader("content-length", buffer.Length.ToString());

                Response.BinaryWrite(buffer); 
                Response.Flush(); 
                Response.End();

Answer 5

Here is the fiddler stats:

HTTP/1.1 200 OK Server: ASP.NET Development Server/8.0.0.0 Date: Wed, 17 Dec 2008 22:22:05 GMT X-AspNet-Version: 2.0.50727 Content-Disposition: attachment; filename=MyZipFolder.zip Content-Length: 148 Cache-Control: private Content-Type: application/x-zip-compressed Connection: Close

Answer 6

What exactly is in this test zip file?

Answer 7

Assuming that you need to do this: (e.g. you are unable to provide a direct link)

<a href='<% Eval("Url")) %>'>download</a>

I'll first make an observation that having a RowCommand handler start to return a file isn't the way to do this. Create some sort of download link to a different page. Separate file downloading from the rest of the page containing the grid.

now ...

You've got the basics about right, but like a comment in this CodeProject tutorial you're soon going to run into issues.

Where the above code sample falls down:

• not responsive to user
• the code will keep going and you'll have no idea if the user actually downloaded the file (it may not matter to you)
• won't work with all browsers
• cannot resume a download
• doesn't show progress
• larger files will use more server memory and take longer to stream
• and a lot of downloads will mean the server is going to take a resource hit

whereas you might want ..

• works just like a clicked download (ie using get, not post)
• works in all browsers on all platforms in the way the user expects (ie filename hint works on things like IE for Mac or Netscape 4.1).
• show download progress
• resumable downloads
• tracking all downloads and knowing when downloads complete
• looks like a file, even if it isn't
• expiration on url.
• allows for high concurrent # of downloads for any size of file

Although written in VB .net1.1 the article Tracking and Resuming Large File Downloads in ASP.NET [devx] is far better at explaining how to do it correctly.

Easy code is easy but doesn't always work, and efficiently streaming files to users 100% of the time takes a little more effort than setting a content header and shoveling some bits down the wire.

Answer 8

I just tried the same code with the .docx file and same result (The file is corrupted): Here is the code:

if(e.CommandName.Equals("DownloadFile"))
            {
                fileUrl = e.CommandArgument as String;
                string fileName = Path.GetFileName(fileUrl);

                FileInfo info = new FileInfo(fileUrl);

                Response.Clear();
                Response.ClearContent();
                Response.ClearHeaders();
                Response.Buffer = true;

                Response.AppendHeader("Content-Length",info.Length.ToString());
                Response.ContentType = GetContentType(fileUrl);
                Response.AppendHeader("Content-Disposition:", "attachment; filename=" + fileName);
                Response.TransmitFile(fileUrl);
                Response.Flush(); 
                Response.End();
            }