Question

i have been looking for a way to update my application for ages, and still haven’t found a solution. (Please don’t say ClickOnce, it isn’t suitable for this app).

Years ago i used to use MCadmin to run a Minecraft server, and i remembered that when it started, sometimes it would just say “Update downloaded, please restart!”. I have tried to find out how this was done, so i have been looking in the source code and found some things.

Here is some code that i found:

private void CheckUpdateThread()
    {
        Program.AddRTLine(Color.Green, "Verifying existence of essential files...\r\n", false);

        if (!File.Exists("ICSharpCode.SharpZipLib.dll"))
            Util.DownloadURLToFile("https://internal.mcadmin.eu/ICSharpCode.SharpZipLib.dll", "ICSharpCode.SharpZipLib.dll");
        if (!File.Exists("LICENSE.txt"))
            Util.DownloadURLToFile("https://internal.mcadmin.eu/LICENSE.txt", "LICENSE.txt");

        Program.AddRTLine(Color.Green, "Essential file validation completed!\r\n", false);

        if (Program.dontUpdate)
        {
            Program.AddRTLine(Color.Green, "Update checking disabled!!!\r\n", false); 
            return;
        }

        UpdateRunning = true;

        Program.AddRTLine(Color.Green, "Checking for updates...\r\n", false);

        bool isUpdate;

        if (Program.dontUpdateMCAdmin || 1 == 1)
        {
            Program.AddRTLine(Color.Green, "MCAdmin update checking disabled.\r\n", false);
        }
        else
        {
            isUpdate = Util.DownloadURLToAndDiff("https://internal.mcadmin.eu/MCAdmin.exe", "MCAdmin.exe.new", "MCAdmin.exe");
            if (!isUpdate)
            {
                if (OutOfDateMCA)
                {
                    Program.AddRTLine(Color.Orange, "MCAdmin update downloaded! Restart MCAdmin to apply update!\r\n", false);
                    SendAdminMessage("MCAdmin update downloaded, consider restarting.", 4);
                }
                else
                {
                    Program.AddRTLine(Color.Green, "MCAdmin already up to date!\r\n", false);
                }
            }
            else
            {
                try
                {
                    if (File.Exists("MCAdmin.exe.old"))
                        File.Delete("MCAdmin.exe.old");
                }
                catch { }
                try
                {
                    if (File.Exists("MCAdmin.exe"))
                        File.Delete("MCAdmin.exe");
                }
                catch { }

                if (File.Exists("MCAdmin.exe")) 
                    File.Move("MCAdmin.exe", "MCAdmin.exe.old");
                File.Move("MCAdmin.exe.new", "MCAdmin.exe");

                OutOfDateMCA = true;
                Program.AddRTLine(Color.Orange, "MCAdmin update downloaded! Restart MCAdmin to apply update!\r\n", false);

                SendAdminMessage("MCAdmin update downloaded, consider restarting.", 4);
            }

        }

This code is from a single void in a class called “UpdateManager”.

See how it does the whole “MCadmin.exe.old” and “MCadmin.exe.new” files, a bit like shadow copying.

There is more to the updater code, but i don’t quite understand.

Here is the SVN:
https://code.google.com/p/mcadminfork/source/browse/

Could anybody help me find out how this updater was acheived?

Thanks.

Answer 1

Util.DownloadURLToAndDiff() does the actual downloading and file comparison. So you probably want to look at that.

Otherwise, it’s pretty simple:

1. Download MCAdmin.exe.new
2. Delete MCAdmin.exe.old (leftover from previous update)
3. Try to delete current MCAdmin.exe
4. If delete fails (file in use probably), rename MCAdmin.exe MCAdmin.exe.old
5. Rename MCAdmin.exe.new MCAdmin.exe