Introduction

A Windows service is an EXE specially designed to communicate with the SCM (Service Control Manager) of Windows NT/2000. The Service Control Manager (SCM) maintains a database of installed services and driver services, and provides a unified and secure means of controlling them. SCM is started at system boot and it is a remote procedure call (RPC) server. As a developer to try a simple service, we can divide the program into four parts.

1. Main program of Win32 / Console Application.
2. A so called ServiceMain(), main program of Service. Entry point of a service.
3. A Service Control Handler, a function to communicate with SCM.
4. A Service Installer/ Uninstaller, to register an EXE as a Service.

Firstly, let us take a look at the Main program of the Console application (it can also be a WinMain()).

 #include  " Winsvc.h "   // Header file for Services. 
 main()
 {
  SERVICE_TABLE_ENTRY Table[] = { { " Service1 " ,ServiceMain} , {NULL,NULL} } ;
  StartServiceCtrlDispatcher(Table);
}

The only thing done by the main() is to fill a SERVICE_TABLE_ENTRY array. The position [0][0] contains the name of the Service (any string you like). Position [0][1] contains the name of the Service Main function, I specified in the list earlier. It actually is a function pointer to the Service main function. The name can be any thing. Now we start the first step to a service by calling StartServiceCtrlDispatcher() with the SERVICE_TABLE_ENTRY array. Note that the function signature should be of the form. The [1][0] and [1][1] positions are NULL, just to say the end of the array (not a must). We can add more entries to the list if we have more than one service running from the same EXE.

The declaration of a typical ServiceMain():

   void  WINAPI ServiceMain(DWORD argc, LPTSTR  * argv) </ PRE >

Now, let us analyze our ServiceMain function.

The main steps of this function are:

1. Fill the SERVICE_STATUS structure with appropriate values to communicate with the SCM.
2. Register the Service Control Handler function said earlier in the list.
3. Call the actual processing functions.

For proceeding, we need two global variables here:

• SERVICE_STATUS m_ServiceStatus;
• SERVICE_STATUS_HANDLE m_ServiceStatusHandle;

The ServiceMain() can accept command line arguments just as any C++ main() function. The first parameter contains the number of arguments being passed to the service. There will always be at least one argument. The second parameter is a pointer to an array of string pointers. The first item in the array always points to the service name. The SERVICE_STATUS data structure is used to fill the current state of the Service and notify it to the SCM. We use an API function SetServiceStatus() for the purpose. The data members of SERVICE_STATUS to look for are:

 < PRE > dwServiceType  =  SERVICE_WIN32; 
dwCurrentState  =  SERVICE_START_PENDING;  // Means Trying To Start(Initially)</PRE>

dwControlsAccepted = SERVICE_ACCEPT_STOP; accepts Stop/Start only in Service control program, usually in the Control Panel (NT) / Administrative tools (2000). We can also set our service to accept PAUSE and CONTINUE functionality.

In the beginning of the ServiceMain(), we should set the dwCurrentState of SERVICE_STATUS to SERVICE_START_PENDING. This signals the SCM that the service is starting. If any error occurs in the way, we should notify the SCM by passing SERVICE_STOPPED. By default, the SCM will look for an activity from the service and if it fails to show any progress within 2 minutes, SCM kills that service.

The API function RegisterServiceCtrlHandler() is used to set the Service Control Handler Function of the Service with the SCM. The function takes two parameters as earlier, one service name (string) and the pointer to the Service Control Handler Function. That function should be with the signature.

Once we get till here, we now set dwCurrentState as SERVICE_RUNNING to notify that the service has started to function. The next step is to call the actual processing steps.

Now, let us analyze our Service Control Handler function:

The Service Control Handler function is used by the SCM to communicate to the Service program about a user action on the service, like a start, stop, pause or continue. It basically contains a switch statement to deal with each case. Here, we will call appropriate steps to clean up and terminate the process. This function receives an opcode which can have values like SERVICE_CONTROL_PAUSE, SERVICE_CONTROL_CONTINUE, SERVICE_CONTROL_STOP, SERVICE_CONTROL_INTERROGATE etc. We have to write appropriate steps on each.

Now Service Installer/ Uninstaller

For installing a service, we need to make some entries in the system registry. Windows has some APIs to do these steps, instead of using the registry functions. They are CreateService() and DeleteService(). For both these functions, we need to open the SCM database with appropriate rights. I prefer SC_MANAGER_ALL_ACCESS. For installing a service, first open the SCM by OpenSCManager(NULL,NULL,SC_MANAGER_ALL_ACCESS). Then invoke the CreateService() with appropriate binary file path of our service. Here also, we have to give the name of our service. We need this name if we want to delete a particular service. In deleting a service, we need to open the specific service first by its name and then invoke the DeleteService() on it. That’s all what we need. Take a look at the code given with it for more details.

Thank You

Anish C.V.

The Code Goes Here:

   #include  " stdafx.h " 
#include  " Windows.h " 
#include  " Winsvc.h " 
#include  " time.h " 
 
SERVICE_STATUS m_ServiceStatus;
SERVICE_STATUS_HANDLE m_ServiceStatusHandle;
BOOL bRunning = true ;
 void  WINAPI ServiceMain(DWORD argc, LPTSTR  * argv);
 void  WINAPI ServiceCtrlHandler(DWORD Opcode);
BOOL InstallService();
BOOL DeleteService();
 int  main( int  argc,  char *  argv[])
 {
   if (argc > 1 )
   {
     if (strcmp(argv[ 1 ], " -i " ) == 0 )
     {
       if (InstallService())
        printf( " \n\nService Installed Sucessfully\n " );
       else 
        printf( " \n\nError Installing Service\n " );
    } 
     if (strcmp(argv[ 1 ], " -d " ) == 0 )
     {
       if (DeleteService())
        printf( " \n\nService UnInstalled Sucessfully\n " );
       else 
        printf( " \n\nError UnInstalling Service\n " );
    } 
     else 
      {
      printf( " \n\nUnknown Switch Usage\n\nFor Install  
            use Srv1  - i\n\nFor UnInstall use Srv1  - d\n " ); 
     } 
  } 
   else 
    {
    SERVICE_TABLE_ENTRY DispatchTable[] = 
                  { { " Service1 " ,ServiceMain} , {NULL,NULL} } ;
    StartServiceCtrlDispatcher(DispatchTable);
  } 
   return   0 ;
} 
 
 void  WINAPI ServiceMain(DWORD argc, LPTSTR  * argv)
 {
  DWORD status;
  DWORD specificError;
  m_ServiceStatus.dwServiceType  =  SERVICE_WIN32;
  m_ServiceStatus.dwCurrentState  =  SERVICE_START_PENDING;
  m_ServiceStatus.dwControlsAccepted  =  SERVICE_ACCEPT_STOP;
  m_ServiceStatus.dwWin32ExitCode  =   0 ;
  m_ServiceStatus.dwServiceSpecificExitCode  =   0 ;
  m_ServiceStatus.dwCheckPoint  =   0 ;
  m_ServiceStatus.dwWaitHint  =   0 ;

  m_ServiceStatusHandle  =  RegisterServiceCtrlHandler( " Service1 " , 
                                            ServiceCtrlHandler); 
   if  (m_ServiceStatusHandle  ==  (SERVICE_STATUS_HANDLE) 0 )
   {
     return ;
  } 
  m_ServiceStatus.dwCurrentState  =  SERVICE_RUNNING;
  m_ServiceStatus.dwCheckPoint  =   0 ;
  m_ServiceStatus.dwWaitHint  =   0 ;
   if  ( ! SetServiceStatus (m_ServiceStatusHandle,  & m_ServiceStatus))
   {
  } 
 
  bRunning = true ;
   while (bRunning)
   {
    Sleep( 3000 );
     // Place Your Code for processing here. 
   } 
   return ;
} 
 
 void  WINAPI ServiceCtrlHandler(DWORD Opcode)
 {
   switch (Opcode)
   {
     case  SERVICE_CONTROL_PAUSE: 
      m_ServiceStatus.dwCurrentState  =  SERVICE_PAUSED;
       break ;
     case  SERVICE_CONTROL_CONTINUE:
      m_ServiceStatus.dwCurrentState  =  SERVICE_RUNNING;
       break ;
     case  SERVICE_CONTROL_STOP:
      m_ServiceStatus.dwWin32ExitCode  =   0 ;
      m_ServiceStatus.dwCurrentState  =  SERVICE_STOPPED;
      m_ServiceStatus.dwCheckPoint  =   0 ;
      m_ServiceStatus.dwWaitHint  =   0 ;

      SetServiceStatus (m_ServiceStatusHandle, & m_ServiceStatus);
      bRunning = false ;
       break ;
     case  SERVICE_CONTROL_INTERROGATE:
       break ; 
  } 
   return ;
} 
 
BOOL InstallService()
 {
   char  strDir[ 1024 ];
  HANDLE schSCManager,schService;
  GetCurrentDirectory( 1024 ,strDir);
  strcat(strDir, " \\Srv1.exe " ); 
  schSCManager  =  OpenSCManager(NULL,NULL,SC_MANAGER_ALL_ACCESS);

   if  (schSCManager  ==  NULL) 
     return   false ;
  LPCTSTR lpszBinaryPathName = strDir;

  schService  =  CreateService(schSCManager, " Service1 " , 
         " The Display Name Needed " ,  //  service name to display 
      SERVICE_ALL_ACCESS,  //  desired access  
      SERVICE_WIN32_OWN_PROCESS,  //  service type  
      SERVICE_DEMAND_START,  //  start type  
      SERVICE_ERROR_NORMAL,  //  error control type  
      lpszBinaryPathName,  //  service's binary  
      NULL,  //  no load ordering group  
      NULL,  //  no tag identifier  
      NULL,  //  no dependencies 
      NULL,  //  LocalSystem account 
      NULL);  //  no password 
 
   if  (schService  ==  NULL)
     return   false ; 

  CloseServiceHandle(schService);
   return   true ;
} 
 
BOOL DeleteService()
 {
  HANDLE schSCManager;
  SC_HANDLE hService;
  schSCManager  =  OpenSCManager(NULL,NULL,SC_MANAGER_ALL_ACCESS);

   if  (schSCManager  ==  NULL)
     return   false ;
  hService = OpenService(schSCManager, " Service1 " ,SERVICE_ALL_ACCESS);
   if  (hService  ==  NULL)
     return   false ;
   if (DeleteService(hService) == 0 )
     return   false ;
   if (CloseServiceHandle(hService) == 0 )
     return   false ;

 return   true ;
}

About C.V Anish

A Developer from India. Concentrating on the Microsoft Technologies. VC++ and VB. Click here to view C.V Anish's