Why applet conversion failed in case of using Shareable interface? (How to use Export files in such cases)

问题

I wrote two java card applet named MasterApp and SlaveApp that are in two different packages named masterPack and slavePack :

Master AIDs :

Package : 01 02 03 04 01
Applet : 01 02 03 04 01 01

Slave AIDs :

Package : 01 02 03 04 02
Applet : 01 02 03 04 02 02

As you see below I want to call SharedMethod() of the MasterApp in the Process() method of my SlaveApp :

Master Program :

package masterPack;

import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISOException;
import javacard.framework.Shareable;
import javacard.framework.Util;
public class MasterApp extends Applet implements Shareable {
    // goodNews = "Shared Method Called Successful"
    byte[] goodNews = { (byte) 'S', (byte) 'h', (byte) 'a', (byte) 'r',
            (byte) 'e', (byte) 'd', (byte) ' ', (byte) 'M', (byte) 'e',
            (byte) 't', (byte) 'h', (byte) 'o', (byte) 'd', (byte) ' ',
            (byte) 'C', (byte) 'a', (byte) 'l', (byte) 'l', (byte) 'e',
            (byte) 'd', (byte) ' ', (byte) 'S', (byte) 'u', (byte) 'c',
            (byte) 'c', (byte) 'e', (byte) 's', (byte) 's', (byte) 'f',
            (byte) 'u', (byte) 'l' };

    private MasterApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength)
            throws ISOException {
        new MasterApp().register();
    }

    public void process(APDU arg0) throws ISOException {
        if (selectingApplet()) {
            return;
        }

    }

    public void SharedMethod(APDU apdu) {
        byte[] buffer = apdu.getBuffer();
        Util.arrayCopyNonAtomic(goodNews, (short) 0, buffer, (short) 0,
                (short) goodNews.length);
        apdu.setOutgoingAndSend((short) 0, (short) goodNews.length);
    }

}

Slave Program :

package slavePack;

import masterPack.MasterApp;
import javacard.framework.AID;
import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISOException;
import javacard.framework.JCSystem;

public class SlaveApp extends Applet {

    byte[] masterAppletAID={(byte)0x01,(byte)0x02,(byte)0x03,(byte)0x04,(byte)0x01,(byte)0x01};
    AID aid = JCSystem.lookupAID(masterAppletAID, (short)0, (byte)masterAppletAID.length);
    MasterApp MasterAppInstance = (MasterApp)JCSystem.getAppletShareableInterfaceObject(aid, (byte)0);

    private SlaveApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength)
            throws ISOException {
        new SlaveApp().register();
    }

    public void process(APDU apdu) throws ISOException {
        if(selectingApplet()){
            return;
        }
        MasterAppInstance.SharedMethod(apdu);

    }

}

In the first step I convert the MasterApp to .cap file successfully and now I have its .exp file in the same directory of its .cap file.

As the second step I wanted to convert SlaveApp to .cap file, but I failed. I guessed that I need to the previous .exp file in the directory of SlaveApp for conversion, so I move it to the directory of SlaveApp.class and tried again, but nothing changed and I received the same below errors again :

Questions :

1- What's the origin of the error?

2- How can I restrict this sharedMethod only for one applet? I mean, in this situation all the other applets can call it, is there any way to limit this accessibility?

3- In cases that we don't have the .exp file of MasterApp, what we must do?

Note that I appreciate any other comment to make my program more efficient (For example the type of variables and their declaration's points).

Update :

Based on @Paul-Bastin answer, I added an interface named MyShareableInterface to my the MasterApp package and this interface implements the Shareable interface. In this Interface I declared the same SharedMethod method that I used in MasterApp as interface. After that I implement this Interface using MasterApp applet. All the other are the same, but nothing changed.

MyShareableInterface.java :

package masterPack;

import javacard.framework.APDU;
import javacard.framework.Shareable;

public interface MyShareableInterface extends Shareable {
    public void SharedMethod(APDU apdu);

}

MasterApp.java :

public class MasterApp extends Applet implements MyShareableInterface {
//Same Body
}

SlaveApp.java :

It is exactly the same as before.

Problem : Nothing changed. I had the same error.

Update 2:

APDU object removed from input arguments of SharedMethod in all three files. It's body replaced with ISOException.throwIt((short)0x9100) also (In the MasterApp.java). I have the same errors againg.

After the above changes I recreate the project from the beginning and now I am dealing with three .java file in two packages as follow :

MyShareableInterface.java :

package masterPack;

import javacard.framework.Shareable;

public interface MyShareableInterface extends Shareable{
    public void SharedMthod();
}

MasterApp.java :

package masterPack;

import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISOException;

public class MasterApp extends Applet implements MyShareableInterface {

    private MasterApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength)
            throws ISOException {
        new MasterApp().register();
    }

    public void process(APDU arg0) throws ISOException {
        // TODO Auto-generated method stub

    }

    public void SharedMthod() {
        // TODO Auto-generated method stub
        ISOException.throwIt((short)0x9100);

    }

}

SlaveApp.java :

package slavePack;

import masterPack.MasterApp;
import javacard.framework.AID;
import javacard.framework.APDU;
import javacard.framework.Applet;
import javacard.framework.ISOException;
import javacard.framework.JCSystem;

public class SlaveApp extends Applet {

    byte[] masterAppletAID={(byte)0x01,(byte)0x02,(byte)0x03,(byte)0x04,(byte)0x01,(byte)0x01};
    AID aid = JCSystem.lookupAID(masterAppletAID, (short)0, (byte)masterAppletAID.length);
    MasterApp MasterAppInstance = (MasterApp)JCSystem.getAppletShareableInterfaceObject(aid, (byte)0);

    private SlaveApp() {
    }

    public static void install(byte bArray[], short bOffset, byte bLength)
            throws ISOException {
        new SlaveApp().register();
    }

    public void process(APDU apdu) throws ISOException {
        if(selectingApplet()){
            return;
        }
        MasterAppInstance.SharedMthod();

    }

}

There is no error in the code. I can even convert the MasterApp.java to .cap file successfully. There problem is failure in SlaveApp.java conversion procedure. I failed in this step.

Note that : AID-s are the same as first version of question. Two first file are in masterPack and the latter is in slavePack.

回答1:

You must create an interface that extends Shareable.
Then your applet must implement that interface
You get this interface in your slave applet yb calling JCSystem.getAppletShareableInterfaceObject
You call the public method of your interface over this object
Do not share the apdu object!

I highly recommend Zhiqun Chen - Java Card Technology Book

来源：https://stackoverflow.com/questions/29339911/why-applet-conversion-failed-in-case-of-using-shareable-interface-how-to-use-e

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javacard