Digital Logic µFR NFC Card Reader - part 5: refactor, look back at initial design

Follow up on my project to create an object oriented framework for smart card use. In this article I want to add vendor-specific card functionality. That is when I I find out that I'd better relocate some functions away from the Reader classes, to avoid that I have to adapt that family for any card I want to support.

In my original design, the Reader created the Card objects.

Depending on the card standard, it would create the appropriate object.

But now, I want to add a special card, the Infineon Security2Go card. It's a ISO14443 card, but it runs a custom application.

There are (as always) several way to model this.

In this post, I choose to create a new class that inherits from the ClassISO14443, and add behaviour for the Infineon card.

What I learned while extending the card class for the Infineon card, I'd also had to extend the Reader class to.

To make it recognise Infineon cards and learn how to create an object of the custom class for them.

But the Reader doesn't change. It uses the same protocols, functions, .... . So that's unfortunate, that it has this binding with any possible card.

The Reader class was intended to deal with the NFC hardware. So I should not contaminate it with non-reader related tasks.

So I moved the createCard() family of functions out of the Reader family, and moved it (for now) to the Factory family.

From:

Card* UfrReader::getCard() {
  //...
  // if DL_MIFARE_MINI, the ID is to be ignored.
  // Create an ISO14443_4 card
  Card *card = NULL;
  if (lpucSak == DL_MIFARE_MINI) {
    card = new CardISO14443(this, lpucSak, id, lpucUidSize);
  } else {
    std::copy(std::begin(aucUid), std::end(aucUid), id.begin());
    card = new Card(this, lpucSak, id, lpucUidSize);
  }
  return card;
}

To:

Card* UfrFactory::getCard(Reader *reader) {
  //...
  // if DL_MIFARE_MINI, the ID is to be ignored.
  // Create an ISO14443_4 card
  Card *card = NULL;
  if (lpucSak == DL_MIFARE_MINI) {
    card = new CardISO14443(reader, lpucSak, id, lpucUidSize);
  } else {
    std::copy(std::begin(aucUid), std::end(aucUid), id.begin());
    card = new Card(reader, lpucSak, id, lpucUidSize);
  }
  return card;
}

So it's out of the Reader family. That one can concentrate on standard functionality again.

For programs that need to work with an Infineon card, I created a dedicated factory:

class S2GoFactory: public UfrFactory {
public:
  static CardS2Go * getCard(Reader *reader) {
     //...
    CardS2Go *card = NULL;
    card = new CardS2Go(reader, lpucSak, id, lpucUidSize);
     return card;
  }
};

As with the previous posts, the current version of the app is attached. It checks the ID of a Security2Go card.

int main() {
  Reader *reader = NULL;
  try {
    reader = S2GoFactory::getReader();
    while (!reader->hasCard()) {
      usleep(500);
    }
    CardS2Go *crd = S2GoFactory::getCard(reader);
    std::cout << "this is an ISO14443 capable card" << std::endl;
    crd->setISO14443_4();
    crd->selectApp();
    crd->unsetISO14443_4();

    S2GoFactory::releaseCard(crd, reader);
    crd = NULL;
  } catch (const UrfException &e) {
    std::cerr << e.what() << ": 0x" << std::hex << e.getError() << std::dec
        << std::endl;
  }
  S2GoFactory::releaseReader(reader);
  reader = NULL;
  return 0;
}