Recommended way to download SQL Server CE Files Programmatically

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VS2012

I need some advice on best way to programmatically download SQL Server Compact Edition .sdf files from a server. I've tried 2 different ways and I like one way better, but due to security issues with the client once the project is deployed, my boss is asking me to go the other direction that ends up corrupting the .sdf files once they are downloaded.

Method 1 (The way I like):

C#

int bytesRead = 0;
byte[] buffer = new byte[2048];

FtpWebRequest request = (FtpWebRequest)WebRequest.Create(new Uri(FTPLocation + "sdfFile"));

request.Proxy = null;

request.UsePassive = true;
request.UseBinary = true;
request.KeepAlive = true;
request.Credentials = new NetworkCredential(userNameInput, passwordInput);                                                
request.Method = WebRequestMethods.Ftp.DownloadFile;

Stream reader = request.GetResponse().GetResponseStream();
FileStream fileStream = new FileStream("File Location to Store .sdf file", FileMode.Create);

while (true)
{
     bytesRead = reader.Read(buffer, 0, buffer.Length);
     if (bytesRead == 0)
          break;

     fileStream.Write(buffer, 0, bytesRead);
}

fileStream.Close();
fileStream.Dispose();
reader.Close();
reader.Dispose();

Method 2 (This causes the corruption of the files)

C#

WebClient dbClient = new WebClient();
dbClient.DownloadFile(downloadLocation + "sdfFile", "File Location to store .sdf file");

Has anyone gotten the second method to work without any issues? I can't get a clean test using the 2nd method. The security issue is that the client's laptops can't login to FTP server to download files, they can only download from a website.

Posted 23-Sep-13 9:45am

joshrduncan2012

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Matt T Heffron 23-Sep-13 16:01pm

Just a guess but are the Accept header in the request and the server's Content-Type: in the response consistent with transmitting the file unmodified?

joshrduncan2012 23-Sep-13 16:07pm

Are you referring to what is needed for an HTTPWebRequest?

Matt T Heffron 23-Sep-13 16:14pm

Yes, basically.
Just make sure the file is transferred equivalently to a Binary mode FTP.

joshrduncan2012 23-Sep-13 16:22pm

That's essentially what I was describing in Method 1 (which works perfectly). However, Method 2 (shown above) is what my boss wants and I can't convince him otherwise that I can't guarantee that Method 2 works since I can't get a clean test using Method 2.

Matt T Heffron 23-Sep-13 16:28pm

What are the headers the server is providing in the response?
Verify they are reasonable for a binary file download?
The server must believe the file is a binary file and transmit it as such.
(E.g., if the server is saying "Content-type: text/html" you know you've got a problem!)

joshrduncan2012 23-Sep-13 16:42pm

Thanks Matt!

joshrduncan2012 23-Sep-13 16:48pm

Page Info of the server HTTP page shows Type as "text/html". Should I go by that?

Matt T Heffron 23-Sep-13 17:22pm

See the quick app to get all of the headers in my Solution below.

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Matt T Heffron · Answer 1 · 2013-09-23T11:21:00

Solution 1

Try this console app that will show you all of the headers returned by the server.
Url to the SDF file as the command line argument.

C#

using System;
using System.Net;

namespace HttpHeaders
{
  class Program
  {
    static void Main(string[] args)
    {
      if (args.Length < 1)
        return; // just quit. this is a hack tool after all...
      string uri = args[0];
      var request = (HttpWebRequest)WebRequest.Create(uri);
      request.Method = "HEAD";
      var response = request.GetResponse();
      foreach (var key in response.Headers.Keys)
      {
        Console.Write((string)key);
        Console.Write(": ");
        Console.WriteLine(response.Headers[(string)key]);
      }
    }
  }
}

Posted 23-Sep-13 11:21am

Matt T Heffron

Comments

joshrduncan2012 24-Sep-13 9:34am

Matt,

Should I be concerned about the result of what I'm seeing when I run this code? I'm not seeing anything.

if (args.Length < 1)
return;

This line gets executed every time.

Matt T Heffron 24-Sep-13 12:29pm

This is just checking for the url on the command line.
e.g.:
ThisProgram.exe URL-to-sdf-file-here

If you're executing this directly in Visual Studio 2012 (2010 will be similar):
on the Project menu, select the "ProjectName Properties..." entry.
Select the "Debug" item on the left and enter the url in the "Command line arguments" box.

Matt T Heffron 24-Sep-13 17:29pm

Thanks for accepting the answer!
What was the solution to the problem?

joshrduncan2012 26-Sep-13 15:59pm

My boss suggested that I place the .sdf file in a zip file and then try uploading and downloading it and that worked. Btw, it's nice to have a boss who is also a programmer, too. I double checked the server headers with what you presented. No issues there.

joshrduncan2012 1-Oct-13 15:26pm

Matt,

It turns out the method described in my response below doesn't help. I'm still getting corruption issues when I'm trying to download the sdf files using webclient.downloadfile() method.

Matt T Heffron 1-Oct-13 16:10pm

Three things I'd try:

1. Put an HTML test web page on the server that has a link to the SDF file.
Use a browser to "Save Target As..." and see if the file is corrupted.
If so, the problem is likely on the server side; if not, it is likely on the client.

2. Put a small text file (ASCII or UTF8, etc.) on the server AS .SDF
Download it and see if it arrives "intact". If not, what changes have happened.

3. Try using the WebClient.DownloadData(...) method and save the bytes to the file yourself.