comparing le + offset to file size in processReadBinary

[hfmanson]

The comparison should use normal integers since le+offset can be greater than 32767. The difference can be cast back to a short.

[philipWendland]

Hi,
all smart cards that I know of only support 16 bit integers (signed, because of Java). You can not have files larger than 16 KiB.

Your pull request does not compile:

[cap] error: line 704: net.pwendland.javacard.pki.isoapplet.IsoFileSystem: unsupported int type of intermediate value, must cast intermediate value to type short or byte.

[hfmanson]

Dear philip,

le will be 0x7FFF because the applet implements the ExtendedLength interface

        short le = apdu.setOutgoing();

The problem occurs when reading with a non 0 offset, e.g. 0x100, :
in the comparison:

if (le+offset >= fileData.length) {
    le = (short)(fileData.length - offset);
}

Then le+offset is 0x7fff + 0x100 == 0x80FF. When this result is cast to a short it results in a negative number.

Which javac are you using in your project? I converted IsoApplet to Netbeans 8.2 where I don't get a compile error.

[hfmanson]

With this updated code the intermediate value will always be short

[philipWendland]

Squashed, rebased, reworded and applied in 4ec7308.

Can I ask what the real-word use case for this was? I cannot imagine why this change is relevant in practice.