frida-utils/apk-injector/patch-main.py

#!/usr/bin/python3
import os
import xml.etree.ElementTree as ET

def get_main_activity() -> str:
    root = ET.parse("app/AndroidManifest.xml").getroot()
    for activity in root.iter("activity"):
        for action in activity.iter("action"):
            if action.attrib.get("{http://schemas.android.com/apk/res/android}name") == "android.intent.action.MAIN":
                return str(activity.attrib.get("{http://schemas.android.com/apk/res/android}name"))
    raise Exception("No main activity found")

def find_main_activity(classname: str) -> str:
    classname = classname.replace(".", "/") + ".smali"
    if classname.startswith("/"):
        raise Exception("Invalid classname")
    for path, _, files in os.walk("."):
        for file in files:
            result = os.path.join(path,file)
            if result.endswith(classname):
                return result
    raise Exception("No file with classname found")

def patch_class(path: str) -> None:
    with open(path, "r") as file:
        lines = file.readlines()
    patched = False
    with open(path, "w") as file:
        matched = False
        for line in lines:
            if ".method public constructor <init>()V" in line:
                matched = True
            if matched and "return-void" in line:
                file.write("const-string v0, \"frida-gadget\"\n")
                file.write("invoke-static {v0}, Ljava/lang/System;->loadLibrary(Ljava/lang/String;)V\n")
                matched = False
                patched = True
            file.write(line)
    if not patched:
        raise Exception("Failed to patch class")

main_activity = get_main_activity()
path = find_main_activity(main_activity)
patch_class(path)