Create your Windows Service

I decided to conduct one experiment, I can’t disclose the essence of it yet, but I’ll definitely describe it according to the results))) For this experiment, I need to write an application that works as a service on Windows.

I’m thinking of describing how to create a normal Win32 Console Application project in Visual Studio there is no need)))

Where does the service begin?

Of course, with the _tmain function :

int _tmain(int argc, _TCHAR* argv[]) {
  SERVICE_TABLE_ENTRY ServiceTable[1];
  ServiceTable[0].lpServiceName = serviceName;
  ServiceTable[0].lpServiceProc = (LPSERVICE_MAIN_FUNCTION)ServiceMain;

  StartServiceCtrlDispatcher(ServiceTable); 
}


SERVICE_TABLE_ENTRY is a structure that describes the entry point for the service manager, in this case, the entry will occur through the ServiceMain function . The StartServiceCtrlDispatcher function actually connects our service with SCM (Service Control Manager)

Service Entry Point

Before describing the function, we need two global variables:

SERVICE_STATUS ServiceStatus;
SERVICE_STATUS_HANDLE hStatus;


The SERVICE_STATUS structure is used to notify SCM of the current status of the service. Read more about the fields and their values ​​on MSDN.
Below is the full text of the ServiceMain function:

void ServiceMain(int argc, char** argv) {
  int error;
  int i = 0;

  serviceStatus.dwServiceType    = SERVICE_WIN32_OWN_PROCESS;
  serviceStatus.dwCurrentState    = SERVICE_START_PENDING;
  serviceStatus.dwControlsAccepted  = SERVICE_ACCEPT_STOP | SERVICE_ACCEPT_SHUTDOWN;
  serviceStatus.dwWin32ExitCode   = 0;
  serviceStatus.dwServiceSpecificExitCode = 0;
  serviceStatus.dwCheckPoint     = 0;
  serviceStatus.dwWaitHint      = 0;

  serviceStatusHandle = RegisterServiceCtrlHandler(serviceName, (LPHANDLER_FUNCTION)ControlHandler);
  if (serviceStatusHandle == (SERVICE_STATUS_HANDLE)0) {
    return;
  } 

  error = InitService();
  if (error) {
    serviceStatus.dwCurrentState    = SERVICE_STOPPED;
    serviceStatus.dwWin32ExitCode   = -1;
    SetServiceStatus(serviceStatusHandle, &serviceStatus);
    return;
  }
  
  serviceStatus.dwCurrentState = SERVICE_RUNNING;
  SetServiceStatus (serviceStatusHandle, &serviceStatus);

  while (serviceStatus.dwCurrentState == SERVICE_RUNNING)
  {
    char buffer[255];
    sprintf_s(buffer, "%u", i);
    int result = addLogMessage(buffer);
    if (result)  {
      serviceStatus.dwCurrentState    = SERVICE_STOPPED;
      serviceStatus.dwWin32ExitCode   = -1;
      SetServiceStatus(serviceStatusHandle, &serviceStatus);
      return;
    }
    i++;
  }

  return;
}


The logic of this function is simple. First, register a function that will process control requests from SCM, for example, a stop request. Registration is performed using the RegisterServiceCtrlHandler function . And when the service starts correctly, we write values ​​to the file with the i variable .
To change the status of the service, the SetServiceStatus function is used .
Now we describe the query processing function:

void ControlHandler(DWORD request) {
  switch(request)
  {
    case SERVICE_CONTROL_STOP:
      addLogMessage("Stopped.");

      serviceStatus.dwWin32ExitCode = 0;
      serviceStatus.dwCurrentState = SERVICE_STOPPED;
      SetServiceStatus (serviceStatusHandle, &serviceStatus);
      return;

    case SERVICE_CONTROL_SHUTDOWN:
      addLogMessage("Shutdown.");

      serviceStatus.dwWin32ExitCode = 0;
      serviceStatus.dwCurrentState = SERVICE_STOPPED;
      SetServiceStatus (serviceStatusHandle, &serviceStatus);
      return;
    
    default:
      break;
  }

  SetServiceStatus (serviceStatusHandle, &serviceStatus);

  return;
}


The ControlHandler is called every time SCM sends requests for changes to the state of the service. It is mainly used to describe the correct completion of a service.

Service Installation

There are several options, one of them using the sc utility . Installation is done with the following command:

sc create SampleService binpath= c:\SampleService.exe


Removing a service:

sc delete SampleService


This method, as for me, is not very programmer because we will describe the installation of the service in code. Let's change a little logic of function _tmain :

int _tmain(int argc, _TCHAR* argv[]) {

  servicePath = LPTSTR(argv[0]);

  if(argc - 1 == 0) {
    SERVICE_TABLE_ENTRY ServiceTable[1];
    ServiceTable[0].lpServiceName = serviceName;
    ServiceTable[0].lpServiceProc = (LPSERVICE_MAIN_FUNCTION)ServiceMain;

    if(!StartServiceCtrlDispatcher(ServiceTable)) {
      addLogMessage("Error: StartServiceCtrlDispatcher");
    }
  } else if( wcscmp(argv[argc-1], _T("install")) == 0) {
    InstallService();
  } else if( wcscmp(argv[argc-1], _T("remove")) == 0) {
    RemoveService();
  } else if( wcscmp(argv[argc-1], _T("start")) == 0 ){
    StartService();
  }
}


We now have three more functions:

int InstallService() {
  SC_HANDLE hSCManager = OpenSCManager(NULL, NULL, SC_MANAGER_CREATE_SERVICE);
  if(!hSCManager) {
    addLogMessage("Error: Can't open Service Control Manager");
    return -1;
  }
  
  SC_HANDLE hService = CreateService(
     hSCManager,
     serviceName,
     serviceName,
     SERVICE_ALL_ACCESS,
     SERVICE_WIN32_OWN_PROCESS,
     SERVICE_DEMAND_START,
     SERVICE_ERROR_NORMAL,
     servicePath,
     NULL, NULL, NULL, NULL, NULL
  );

  if(!hService) {
    int err = GetLastError();
    switch(err) {
      case ERROR_ACCESS_DENIED:
        addLogMessage("Error: ERROR_ACCESS_DENIED");
        break;
      case ERROR_CIRCULAR_DEPENDENCY:
        addLogMessage("Error: ERROR_CIRCULAR_DEPENDENCY");
        break;
      case ERROR_DUPLICATE_SERVICE_NAME:
        addLogMessage("Error: ERROR_DUPLICATE_SERVICE_NAME");
        break;
      case ERROR_INVALID_HANDLE:
        addLogMessage("Error: ERROR_INVALID_HANDLE");
        break;
      case ERROR_INVALID_NAME:
        addLogMessage("Error: ERROR_INVALID_NAME");
        break;
      case ERROR_INVALID_PARAMETER:
        addLogMessage("Error: ERROR_INVALID_PARAMETER");
        break;
      case ERROR_INVALID_SERVICE_ACCOUNT:
        addLogMessage("Error: ERROR_INVALID_SERVICE_ACCOUNT");
        break;
      case ERROR_SERVICE_EXISTS:
        addLogMessage("Error: ERROR_SERVICE_EXISTS");
        break;
      default:
        addLogMessage("Error: Undefined");
    }
    CloseServiceHandle(hSCManager);
    return -1;
  }
  CloseServiceHandle(hService);
  
  CloseServiceHandle(hSCManager);
  addLogMessage("Success install service!");
  return 0;
}

int RemoveService() {
  SC_HANDLE hSCManager = OpenSCManager(NULL, NULL, SC_MANAGER_ALL_ACCESS);
  if(!hSCManager) {
     addLogMessage("Error: Can't open Service Control Manager");
     return -1;
  }
  SC_HANDLE hService = OpenService(hSCManager, serviceName, SERVICE_STOP | DELETE);
  if(!hService) {
     addLogMessage("Error: Can't remove service");
     CloseServiceHandle(hSCManager);
     return -1;
  }
  
  DeleteService(hService);
  CloseServiceHandle(hService);
  CloseServiceHandle(hSCManager);
  addLogMessage("Success remove service!");
  return 0;
}

int StartService() {
  SC_HANDLE hSCManager = OpenSCManager(NULL, NULL, SC_MANAGER_CREATE_SERVICE);
  SC_HANDLE hService = OpenService(hSCManager, serviceName, SERVICE_START);
  if(!StartService(hService, 0, NULL)) {
    CloseServiceHandle(hSCManager);
    addLogMessage("Error: Can't start service");
    return -1;
  }
  
  CloseServiceHandle(hService);
  CloseServiceHandle(hSCManager);
  return 0;
}


Now we can install, remove and start the service without resorting to various utilities:

SampleService.exe install
SampleService.exe remove
SampleService.exe start


Sources

To be continued if everyone does not reject :)