Shizuku

# Shizuku

## Background

When developing apps that requires root, the most common method is to run some commands in the su shell. For example, there is an app that uses the `pm enable/disable` command to enable/disable components.

This method has very big disadvantages:

1. **Extremely slow** (Multiple process creation)
2. Needs to process texts (**Super unreliable**)
3. The possibility is limited to available commands
4. Even if ADB has sufficient permissions, the app requires root privileges to run

Shizuku uses a completely different way. See detailed description below.

## User guide & Download

<https://shizuku.rikka.app/>

## How does Shizuku work?

First, we need to talk about how app use system APIs. For example, if the app wants to get installed apps, we all know we should use `PackageManager#getInstalledPackages()`. This is actually an interprocess communication (IPC) process of the app process and system server process, just the Android framework did the inner works for us.

Android uses `binder` to do this type of IPC. `Binder` allows the server-side to learn the uid and pid of the client-side, so that the system server can check if the app has the permission to do the operation.

Usually, if there is a "manager" (e.g., `PackageManager`) for apps to use, there should be a "service" (e.g., `PackageManagerService`) in the system server process. We can simply think if the app holds the `binder` of the "service", it can communicate with the "service". The app process will receive binders of system services on start.

Shizuku guides users to run a process, Shizuku server, with root or ADB first. When the app starts, the `binder` to Shizuku server will also be sent to the app.

The most important feature Shizuku provides is something like be a middle man to receive requests from the app, sent them to the system server, and send back the results. You can see the `transactRemote` method in `rikka.shizuku.server.ShizukuService` class, and `moe.shizuku.api.ShizukuBinderWrapper` class for the detail.

So, we reached our goal, to use system APIs with higher permission. And to the app, it is almost identical to the use of system APIs directly.

## Developer guide

### API & sample

https://github.com/RikkaApps/Shizuku-API

### Migrating from pre-v11

> Existing applications still works, of course.

https://github.com/RikkaApps/Shizuku-API#migration-guide-for-existing-applications-use-shizuku-pre-v11

### Attention

1. ADB permissions are limited

   ADB has limited permissions and different on various system versions. You can see permissions granted to ADB [here](https://github.com/aosp-mirror/platform_frameworks_base/blob/master/packages/Shell/AndroidManifest.xml).

   Before calling the API, you can use `ShizukuService#getUid` to check if Shizuku is running user ADB, or use `ShizukuService#checkPermission` to check if the server has sufficient permissions.

2. Hidden API limitation from Android 9

   As of Android 9, the usage of the hidden AP