[IGSTK-Developers] Make SM even safer? Request Validation

[Patrick Cheng]

Hi all,

As you all know, for SM warped class, we are using the request methods 
in the API to talk or command the SM. The request method is basically 
generating some inputs to the SM, and let the SM do the remaining job, 
which is pretty safe.

But I think, every time before we generating all the inputs and push 
them back to the SM, we should do a request validation check, to see if 
current state is good for this kind of request or not.

My reason is: For some complex state machine, ( eg. SM for 
LandmarkRegistration and SM for my demo applications), there are 
multiple inputs and request, and there are certain call sequence for the 
request methods to make things happen.  In the application, some of the 
inputs are taken from the user inputs, like a confirm dialog or open a 
file chooser. But I don’t want the application to take those actions if 
this request is invalid for right now. Say, trying to load an image, but 
the patient hasn’t been registered.

So I propose add a request validation to the state machine. I have 
implemented in the application class. In the 
Sandbox/Example/FourViewsTrackingWithCT

Basically, at the beginning of all the request method, I will do a 
requestvalidation check, if it’s invalid, it will return. The data 
structure is pretty simple. I add an enumeration of all the request 
methods in head file. And create a vector with all valid states that can 
perform this kind of request for each request method. Those are being 
done at the contractor, below the state machine initialization. 
Currently I didn’t implement any action for invalid request, but that 
could be easily added.

.h--------------------------------
typedef enum
     {
     SetPatientNameRequest,
     LoadImageRequest			// There are some other requests
     } RequestType;

   const static int NumberOfRequest = 9;

   typedef std::vector < StateMachineType::StateIdentifierType > 
RequestToStateMapType;

   std::vector < RequestToStateMapType > m_RequestValidationMap;

   bool RequestValidation( RequestType request );
-----------------------------------

.cxx------------------------------

In constructor
RequestToStateMapType rtsm;
   for( unsigned int i = 0; i < NumberOfRequest; i++)
     m_RequestValidationMap.push_back( rtsm );

   rtsm.clear();
   rtsm.push_back( m_InitialState.GetIdentifier() );
   rtsm.push_back( m_PatientNameReadyState.GetIdentifier() );
   m_RequestValidationMap[ SetPatientNameRequest ] = rtsm;
   rtsm.clear();
   rtsm.push_back( m_PatientNameReadyState.GetIdentifier() );
   rtsm.push_back( m_ImageReadyState.GetIdentifier() );
   rtsm.push_back( m_PatientNameVerifiedState.GetIdentifier() );
   m_RequestValidationMap[ LoadImageRequest ] = rtsm;

bool FourViewsTrackingWithCT::RequestValidation( 
FourViewsTrackingWithCT::RequestType request)
{
   RequestToStateMapType::iterator it;
   for ( it = m_RequestValidationMap[request].begin(); it 
!=m_RequestValidationMap[request].end(); it++ )
   {
     if ( *it == m_StateMachine.GetCurrentStateIdentifier() )
       return true;
   }
   return false;
}

In request method add:
void FourViewsTrackingWithCT::RequestLoadImage()
{
   if( !RequestValidation( LoadImageRequest ) ) return;
…………………………….
}



So I think this should work, and pretty simple.

Further more, we can even expose the request enum in API, and only put 
a generic Request( RequestType request) method in API for all the class.

If the implementation of that Request method. We can do sth like

Request( RequestType request)
{
   If( ! RequestValidation( request ) ) return;     // we could also add 
some invalid request action before return.

Case request
………. Call the actual Request Method.
}

Thanks for reading this long email.
Please let me know your thoughts

Patrick

-- 
Peng (Patrick) Cheng
Research Engineer
cheng at isis.georgetown.edu

Imaging Science and Information Systems (ISIS) Center
Department of Radiology, Georgetown University Medical Center
2115 Wisconsin Avenue, Suite 603
Washington, DC, 20007

Work phone: 202-687-2902
Work fax:   202-784-3479
Cell phone: 202-674-5626