frida-java-bridge playground example (also: how to use frida-compile)

README.md

1. Set up a local clone of frida-java-bridge:

$ git clone https://github.com/frida/frida-java-bridge.git
$ cd frida-java-bridge
$ npm install
$ npm link

2. Make a directory someplace outside frida-java-bridge and save the two attached files as package.json and agent/index.js:

$ mkdir frida-java-playground
$ cd frida-java-playground
$ # create the two files
$ npm install
$ npm link frida-java-bridge

3. Run this in a separate terminal to continuously recompile the code:

$ npm run watch

4. Load the generated _agent.js using the Frida REPL:

$ frida -U com.google.android.apps.maps --runtime=v8 -l _agent.js

Enter run() in the REPL to call the function defined in agent/index.js. It is recommended to put your code in a function as exceptions thrown during script load might get swallowed by the REPL (something that should be fixed in the REPL).

5. Edit your local frida-java-bridge and have fun!

agent.js

const Java = require('frida-java-bridge');

globalThis.run = () => {
  Java.perform(() => {
    console.log('Enumerating loaded classes...');
    const classes = Java.enumerateLoadedClassesSync();
    console.log(`Enumerated ${classes.length} classes`);
  });
};

package.json

{
  "name": "frida-java-playground",
  "version": "1.0.0",
  "description": "Playground for frida-java-bridge",
  "private": true,
  "main": "agent/index.js",
  "scripts": {
    "build": "frida-compile agent -o _agent.js",
    "watch": "frida-compile agent -o _agent.js -w"
  },
  "dependencies": {
    "frida-compile": "^9.0.8",
    "frida-java-bridge": "^3.2.0"
  }
}

Note you need to install frida-compile for that:
https://github.com/frida/frida-compile

@cryptax frida-compile should resolve with the npm install step.

@cryptax frida-compile should resolve with the npm install step.

You're right. True.
I had an blocking errors I hadn't seen during npm install. I fixed those by updating nodejs and npm. I still have a warning compiling fsevents@2.0.7, used by frida-compile, but it seems it is optional.

Should global.run work? The code didn't execute for me, until I wrapped it in

setTimeout(function() {
    Java.perform(function() {
        //code
    });
}, 0);

Should global.run work? The code didn't execute for me, until I wrapped it in

The example code isn't meant to auto-run the code. It just makes that function globally visible so you can do run() in the Frida REPL.