frida-hook.py

#python code
import frida
import time

#========= INIT ============
_PACKAGE_ = "owasp.mstg.uncrackable1"
_HOOKINGSCRIPT_ = "hooking_script.js"


def on_message(message, data):
    if message['type'] == 'send':
        print("[%s][%s] => %s" % (message['type'], message, data))
	
    if message['type'] == 'error':
	for k in message.keys():
            print("\t[%s]: %s"%(k, message[k]))

while(True):
  try:
    print("==== Initialing ====")
    device = frida.get_usb_device()
    print("[+] Device: {}".format(device))
    try:
        pid = device.spawn([_PACKAGE_])
    except Exception as ex:
        print ex 
    print("[+] PID: {}".format(pid))
    device.resume(pid)
    time.sleep(1) #Without it Java.perform silently fails
    session = device.attach(pid)
    print("[+] Attaching session")

    # session = frida.get_usb_device().attach(_PACKAGE_)
    
    print("[+] Loading hooking script")
    script = session.create_script(open(_HOOKINGSCRIPT_).read())
    script.on('message', on_message)
    script.load()

    print("[*]    Initialing successful\n")
    break
  except Exception as e:
    print("[-] Error: {}".format(e))
    raw_input("Try again?")
    pass
    
#prevent the python script from terminating
raw_input("[Frida-Hooking]\nContinue?[Enter]\n")

hooking_script.js

console.log("Script loaded successfully ");
Java.perform(function x(){ //Silently fails without the sleep from the python code
    console.log("Inside java perform function");
    
    return 1;
    }});