The Anti-Service, Persistence sans System.ServiceModel

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Introduction

I was asked to create a small reminder application for an organization I belong to. Ever hour it would prompt with a quote. My "work" answer for something like this would be to create a Windows service, make it self installing, easy peazy. But I wanted to be adventurous, because this is mostly U/I and I didn't want to mess with the service user account, how could this be done without a service? This article outlines this adventure...

Background

The basic components to this project are:

• Windows (WinForms in this case, but WPF will work too), OnClose and Timers
• Sockets/Listeners for forcing single instance and "killing" the application
• InnoSetup Script

Using the Code

• Create a new Windows project (New Project... Windows)
• Create a timer. Drag and drop a timer object, set the parameters, create a timer handler. Your project may not be on a timer, that's ok, if an event triggers the window to show/hide, that's all you want
• Create a "Force Close" mechanism, I created a checkbox called "CanClose"
• Override FormClosing

  private void TheMessage_FormClosing(object sender, FormClosingEventArgs e)
  {
      e.Cancel = !CanClose.Checked;
      this.Hide();
  }

• Create a separate ForceClose() method which sets CanClose and calls "Close"

  public void ForceClose()
  {
     CanClose.Checked = true;
     Close();
  }

• Sockets and threading. This is where it gets interesting. So I wanted the behavior that the application should be single instance. There are several good ways to do that, the mutex here on CodeProject is great. But, I also needed it to install/uninstall cleanly, which means it needs to force itself closed. To do that, I used sockets listener/client on a dedicated port. It sounds counter intuitive, but I created the client first (is that the chicken or the egg?!)

  public void Main(string[] args){
      ...
  
      bool killStream = args.Length > 0 && args[0] == "-kill";
      try
      {
          using (TcpClient clnt = new TcpClient())
          {
              clnt.Connect("localhost", 7231);
              if (clnt.Connected)
              {
                  clnt.GetStream().Write(new byte[] 
  		{ (byte)(killStream ? 0 : 1) }, 0, 1); // 0 - kill or 1 - show
                  clnt.Close();
                  return;
              }
          }
      }
      // I really hate catching an exception as logic, but there's no other way
      catch (SocketException) { } // nothing listening, not already running
  
      if (killStream) // if it's a kill... don't start
          return; 

  Finally the listener...

      TcpListener lstn = new TcpListener
  			(System.Net.IPAddress.Parse("127.0.0.1"), 7231);
      lstn.Start();
  
      // So, we start a long loop listening for incoming messages
      while (true)
      {
          using (TcpClient clnt = lstn.AcceptTcpClient())
          {
              byte[] buff = new byte[1];
  
              if (1 == clnt.GetStream().Read(buff, 0, 1))
              {
                  switch (buff[0])
                  {
                      case 0: // Kill request
                          msgWindow.ForceClose();
                          return;
                      case 1: // Show request
                          msgWindow.Show();
                          continue;
                  }
              }
          }
      }

• And finally, you need an InnoSetup Script that will invoke this before attempting to re-install/uninstall, that looks like this...

  [Files]
  Source: "{Your Project}\bin\Release\AntiService.exe"; DestDir: "{app}"; 
  	Flags: ignoreversion; BeforeInstall: StopLBApp
  ...
  
  [Code]
  procedure StopLBApp();
  var
    FileName : String;
    ResultCode: Integer;
  begin
    Log('Asking any existing processes to stop now');
    FileName := ExpandConstant('{app}\AntiService.exe');
    if FileExists(FileName) then
    begin
      if not ShellExec('', FileName, '-kill', '', 
  	SW_SHOWNORMAL, ewNoWait, ResultCode) then
        MsgBox('DeinitializeSetup:' #13#13 'Execution of ''' + 
  	FileName + ''' failed. ' + SysErrorMessage(ResultCode) + '.', 
  		mbError, MB_OK);
    end;
  end;

Summary

So what you have is an application that once it's started, will stay running, and will attempt to show a window every time it's launched or on some event. Timer in my case. I hope you have enjoyed!

History

• 9^th September, 2010: Initial post