add remote hci android app

docs/mkdocs/mkdocs.yml

@@ -67,6 +67,9 @@ nav:
     - Zephyr: platforms/zephyr.md
   - Examples:
     - Overview: examples/index.md
+  - Extras:
+    - Overview: extras/index.md
+    - Android Remote HCI: extras/android_remote_hci.md
 
 copyright: Copyright 2021-2023 Google LLC
 

docs/mkdocs/src/extras/android_remote_hci.md

@@ -0,0 +1,119 @@
+ANDROID REMOTE HCI APP
+======================
+
+This application allows using an android phone's built-in Bluetooth controller with 
+a Bumble host stack running outside the phone (typically a development laptop or desktop).
+The app runs an HCI proxy between a TCP socket on the "outside" and the Bluetooth HCI HAL
+on the "inside". (See [this page](https://source.android.com/docs/core/connect/bluetooth) for a high level 
+description of the Android Bluetooth HCI HAL).
+The HCI packets received on the TCP socket are forwarded to the phone's controller, and the 
+packets coming from the controller are forwarded to the TCP socket.
+
+
+Building
+--------
+
+You can build the app by running `./gradlew build` (use `gradlew.bat` on Windows) from the `RemoteHCI` top level directory.
+You can also build with Android Studio: open the `RemoteHCI` project. You can build and/or debug from there.
+
+If the build succeeds, you can find the app APKs (debug and release) at:
+
+  * [Release] ``app/build/outputs/apk/release/app-release-unsigned.apk``
+  * [Debug] ``app/build/outputs/apk/debug/app-debug.apk``
+
+
+Running
+-------
+
+### Preconditions
+When the proxy starts (tapping the "Start" button in the app's main activity), it will try to 
+bind to the Bluetooth HAL. This requires disabling SELinux temporarily, and being the only HAL client.
+
+#### Disabling SELinux
+Binding to the Bluetooth HCI HAL requires certain SELinux permissions that can't simply be changed
+on a device without rebuilding its system image. To bypass these restrictions, you will need
+to disable SELinux on your phone (please be aware that this is global, not just for the proxy app,
+so proceed with caution).
+In order to disable SELinux, you need to root the phone (it may be advisable to do this on a
+development phone).
+
+!!! tip "Disabling SELinux Temporarily"
+    Restart `adb` as root:
+    ```bash
+    $ adb root
+    ```
+
+    Then disable SELinux
+    ```bash
+    $ adb shell setenforce 0
+    ```
+
+    Once you're done using the proxy, you can restore SELinux, if you need to, with
+    ```bash
+    $ adb shell setenforce 1
+    ```
+
+    This state will also reset to the normal SELinux enforcement when you reboot.
+
+#### Stopping the bluetooth process
+Since the Bluetooth HAL service can only accept one client, and that in normal conditions 
+that client is the Android's bluetooth stack, it is required to first shut down the 
+Android bluetooth stack process.
+
+!!! tip "Checking if the Bluetooth process is running"
+    ```bash
+    $ adb shell "ps -A | grep com.google.android.bluetooth"
+    ```
+    If the process is running, you will get a line like:
+    ```
+    bluetooth 10759 876 17455796 136620 do_epoll_wait 0 S com.google.android.bluetooth
+    ```
+    If you don't, it means that the process is not running and you are clear to proceed.
+
+Simply turning Bluetooth off from the phone's settings does not ensure that the bluetooth process will exit.
+If the bluetooth process is still running after toggling Bluetooth off from the settings, you may try enabling
+Airplane Mode, then rebooting. The bluetooth process should, in theory, not restart after the reboot.
+
+!!! tip "Stopping the bluetooth process with adb"
+    ```bash
+    $ adb shell cmd bluetooth_manager disable
+    ```
+
+### Selecting a TCP port
+The RemoteHCI app's main activity has a "TCP Port" setting where you can change the port on
+which the proxy is accepting connections. If the default value isn't suitable, you can 
+change it there.
+
+### Connecting to the proxy
+To connect the Bumble stack to the proxy, you need to be able to reach the phone's network 
+stack. This can be done over the phone's WiFi connection, or, alternatively, using an `adb`
+TCP forward (which should be faster than over WiFi).
+
+!!! tip "Forwarding TCP with `adb`"
+    To connect to the proxy via an `adb` TCP forward, use:
+    ```bash
+    $ adb forward tcp:<outside-port> tcp:<inside-port>
+    ```
+    Where ``<outside-port>`` is the port number for a listening socket on your laptop or 
+    desktop machine, and <inside-port> is the TCP port selected in the app's user interface.
+    Those two ports may be the same, of course.
+    For example, with the default TCP port 9993:
+    ```bash
+    $ adb forward tcp:9993 tcp:9993
+    ```
+
+Once you've ensured that you can reach the proxy's TCP port on the phone, either directly or
+via an `adb` forward, you can then use it as a Bumble transport, using the transport name: 
+``tcp-client:<host>:<port>`` syntax.
+
+!!! example "Connecting a Bumble client"
+    Connecting the `bumble-controller-info` app to the phone's controller.
+    Assuming you have set up an `adb` forward on port 9993:
+    ```bash
+    $ bumble-controller-info tcp-client:localhost:9993
+    ```
+
+    Or over WiFi with, in this example, the IP address of the phone being ```192.168.86.27```
+    ```bash
+    $ bumble-controller-info tcp-client:192.168.86.27:9993
+    ```

docs/mkdocs/src/extras/index.md

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+EXTRAS
+======
+
+A collection of add-ons, apps and tools, to the Bumble project.
+
+Android Remote HCI
+------------------
+
+Allows using an Android phone's built-in Bluetooth controller with a Bumble
+stack running on a development machine.
+See [Android Remote HCI](android_remote_hci.md) for details.