Read bytearray from retval on onLeave event

Question

I'm trying to get the return value of a android native function call using Frida but with no success:

Interceptor.attach(Module.getExportByName('lib.so', 'Token'), {
    onEnter: function(args) {
    },
    onLeave: function(retval) {
      console.log(retval);
    }
});

I know that the value is a bytearray but I can't find a way to read it from the native pointer.

Can anyone point me in the right direction? What should I do the get the value from retval? I already tried to use cast, but it didn't work.

thanks

Answer 1

I just needed to cast to array buffer:

        var b = Java.use('[B')
        var buffer = Java.cast(retval, b);
        var result = Java.array('byte', buffer);

        var str_ = "";
        for (var i=0; i < result.length; i++) {
            str_ += String.fromCharCode(result[i]);     

        }
        console.log("String: " + str_)

     }```