apk: Allow gadget config file customization from CLI

Add a -c/--gadget-config flag, valid when --gadget is also in use, that
adds arbitrary entries to the injected gadget's config file's
"interaction" section[1].

[1]: https://frida.re/docs/gadget/

completions/frida.fish

@@ -184,6 +184,7 @@ complete --command frida-create --no-files --require-parameter --short-option=t
 add_base_arguments frida-apk
 complete --command frida-apk --force-files --short-option=o --long-option=output --description="output path"
 complete --command frida-apk --force-files --short-option=g --long-option=gadget --description="inject the specified gadget library"
+complete --command frida-apk --force-files --short-option=c --long-option=gadget-config --description="set the given key=value gadget interaction config"
 
 
 ######## frida-compile ########

frida_tools/apk.py

@@ -6,7 +6,7 @@
 import struct
 from enum import IntEnum
 from io import BufferedReader
-from typing import BinaryIO, List
+from typing import BinaryIO, Dict, List
 from zipfile import ZipFile
 
 
@@ -16,11 +16,9 @@
 LD_PRELOAD="$(dirname "$0")/{GADGET_NAME}" "$@"
 """
 
-GADGET_CONFIG = {
-    "interaction": {
-        "type": "listen",
-        "on_load": "wait",
-    },
+GADGET_INTERACTION_CONFIG = {
+    "type": "listen",
+    "on_load": "wait",
 }
 
 
@@ -35,6 +33,15 @@ def _add_options(self, parser: argparse.ArgumentParser) -> None:
             parser.add_argument("-o", "--output", help="output path", metavar="OUTPUT")
             parser.add_argument("-g", "--gadget", type=argparse.FileType("rb"),
                 help="inject the specified gadget library", metavar="GADGET")
+
+            def key_val_type(arg: str) -> tuple[str, str]:
+                split = arg.split("=", 1)
+                if len(split) == 1:
+                    raise argparse.ArgumentTypeError("config entry must be of form key=value")
+                return (split[0], split[1])
+            parser.add_argument("-c", "--gadget-config", type=key_val_type, action="append",
+                help="set the given key=value gadget interaction config", metavar="GADGET_CONFIG")
+
             parser.add_argument("apk", help="apk file")
 
         def _needs_device(self) -> bool:
@@ -44,6 +51,10 @@ def _initialize(self, parser: argparse.ArgumentParser, options: argparse.Namespa
             self._output_path = options.output
             self._path = options.apk
             self._gadget = options.gadget
+            self._gadget_config = options.gadget_config
+
+            if self._gadget_config and self._gadget is None:
+                parser.error("cannot configure gadget without injecting gadget")
 
             if not self._path.endswith(".apk"):
                 parser.error("path must end in .apk")
@@ -57,7 +68,15 @@ def _start(self) -> None:
                 if self._gadget is not None:
                     gadget_arch = get_gadget_arch(self._gadget)
                     lib_dir = f"lib/{gadget_arch}/"
-                    inject(self._gadget.name, lib_dir, self._output_path)
+
+                    config = {
+                        "interaction": {
+                            **GADGET_INTERACTION_CONFIG,
+                            **dict(self._gadget_config)
+                        }
+                    }
+
+                    inject(self._gadget.name, lib_dir, config, self._output_path)
             except Exception as e:
                 self._update_status(f"Error: {e}")
                 self._exit(1)
@@ -118,11 +137,11 @@ def debug(path: str, output_path: str) -> None:
                     oz.writestr(info.filename, f.read(), info.compress_type)
 
 
-def inject(gadget_so: str, lib_dir: str, output_apk: str) -> None:
+def inject(gadget_so: str, lib_dir: str, config: Dict[str, Dict[str, str]], output_apk: str) -> None:
     config_name = GADGET_NAME.removesuffix(".so") + ".config.so"
     with ZipFile(output_apk, "a") as oz:
         oz.writestr(lib_dir + "wrap.sh", WRAP_SCRIPT)
-        oz.writestr(lib_dir + config_name, json.dumps(GADGET_CONFIG))
+        oz.writestr(lib_dir + config_name, json.dumps(config))
         oz.write(gadget_so, lib_dir + GADGET_NAME)