CODEWITHSUNDEEP
javajavacardjcop
Jean
Jean

Reputation: 697

How to use JCOP proprietary method to return available memory?

Below, you see a program that is written to return the EEPROM available memory on reception of any APDU command :

public class HelloWorld extends Applet {
    public static void install(byte[] bArray, short bOffset, byte bLength) {
        new helloWorld.HelloWorld().register(bArray, (short) (bOffset + 1),
                bArray[bOffset]);
    }

    public void process(APDU apdu) {
        if (selectingApplet()) {
            return;
        }

        getAvailableMem(apdu);

    }

    public void getAvailableMem(APDU apdu){
        byte[] buffer = apdu.getBuffer();
        short[] AvailableMem = {};

        UtilX.getAvailableMemoryInfo(AvailableMem, (short) 0,
                UtilX.MEMORY_TYPE_PERSISTENT);

        for(short i=0;i<(short)AvailableMem.length;i++){
            buffer[i]=(byte)AvailableMem[i];
        }

        apdu.setOutgoingAndSend((short)0, (short)(2*AvailableMem.length));
    }
}

But when I send an APDU command to the applet, it returns 0x6F00:

OSC: opensc-tool -s 00a4040006010203040506 -s 00000000
Using reader with a card: ACS CCID USB Reader 0

Sending: 00 A4 04 00 06 01 02 03 04 05 06
Received (SW1=0x90, SW2=0x00)

Sending: 00 00 00 00
Received (SW1=0x6F, SW2=0x00)

Note that I tried the above program with the below loop also : 

for(byte i=0;i<(byte)AvailableMem.length;i++){
                buffer[i]=(byte)AvailableMem[i];
            }

It compiled successfully also! Shouldn't the compiler restrict the type of array indexes to byte only or short only? Why it accepts both types for indexes?

-This second program has the same output in OpenSCTool. What's wrong?

Upvotes: 2

Views: 314

Answers (2)

Paul Bastian
Paul Bastian

Reputation: 2647

Example code taken out of one of my applets:

Declarations in the beginning of my class

    short[] mem = new short[2];

From inside the process tree:

case Cmd.GET_FREE_MEM:
                UtilX.getAvailableMemoryInfo(mem, (short) 0, UtilX.MEMORY_TYPE_PERSISTENT);
                Util.setShort(apdu.getBuffer(), (short) 0, mem[0]);
                Util.setShort(apdu.getBuffer(), (short) 2, mem[1]);
                UtilX.getAvailableMemoryInfo(mem, (short) 0, UtilX.MEMORY_TYPE_TRANSIENT_RESET);
                Util.setShort(apdu.getBuffer(), (short) 4, mem[0]);
                Util.setShort(apdu.getBuffer(), (short) 6, mem[1]);
                apdu.setOutgoingAndSend((short) 0, (short) 8);
                break;

Upvotes: 0

vojta
vojta

Reputation: 5651

You have to store the result into an existing array of non-zero length:

class MyApplet extends Applet {

short[] shorts = JCSystem.makeTransientShortArray((short)2, JCSystem.CLEAR_ON_RESET);

public void process(APDU apdu) {
    //...
    UtilX.getAvailableMemoryInfo(shorts, (short)0, UtilX.MEMORY_TYPE_PERSISTENT);
    //...
}

Your status code 6F00 is an uncaught instance of ArrayIndexOutOfBoundsException.

You can use both integer types as an index: byte or short, there is no real difference (for arrays not longer than 0x7F, of course).

Upvotes: 2

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