Exchange out-of-band data

The exchange of out-of-band data transmission between Android and Anbox (WebRTC platform) enables Android application developers to trigger an action from an Android application and forward it to Anbox(WebRTC platform). Once Anbox receives the action, as one peer of WebRTC platform, the action will be propagated from the Anbox to the remote peer(WebRTC client) through WebRTC data channel so that client can react to the action received from the remote peer and respond accordingly on the UI.

This document will walk you through how to send a message from an Android application
running in the container to the client application developed with the Anbox Streaming

Android Application

Add Required Permissions

For the Android application running in the container, you need to add the
following required permission to the AndroidManifest.xml to allow the
application to send messages to the Anbox runtime:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android=""

    <uses-permission android:name="android.permission.ANBOX_SEND_MESSAGE" />

Any attempt of an application which lacks the android.permission.ANBOX_SEND_MESSAGE
permission to invoke APIs that are provided by the Anbox Platform Library will
be disallowed and a security exception will be raised.

Import Java Library

Check out the Anbox Streaming SDK from Github

$ git clone

To import the com.canonical.anbox.platform_api_skeleton.jar library into your
Android project, please refer to the official documentation
on how to import an external library into an Android application project.

Alternatively, you can follow the steps below:

Copy the com.canonical.anbox.platform_api_skeleton.jar to project_root/app/libs
directory (If the folder doesn’t exist, just create it).

Edit the build.gradle under the app folder by adding the following line
under the dependencies scope.

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation files('libs/com.canonical.anbox.platform_api_skeleton.jar')

Send Message from Android

The following example demonstrates how to send a message with the Anbox
Platform API to a remote client:

import com.canonical.anbox.PlatformAPISkeleton;

public class FakeCameraActivity extends AppCompatActivity {
     public void onResume() {

        String type = “message-type”;
        String data = ”message-data”;
        PlatformAPISkeleton api_skeleton = new PlatformAPISkeleton();
        if (!api_skeleton.sendMessage(type, data)) {
            Log.e(TAG, "Failed to send a message type " + type + " to Anbox session");

NOTE: The length for message type is limited to 256KB and the length of data is limited to 1MB.

Receive Message on the Client

A client application that receives a message from the Android application can be written
in JavaScript, C or C++ by using the Anbox Streaming SDK.

Web Application

For a web based application you can use the JavaScript SDK which you can find at To receive the data sent from the Android application
running in the Anbox container you need to implement the messageReceived callback
of the AnboxStream object:

    let stream = new AnboxStream({
      callbacks: {
        messageReceived: (type, data) => {
          console.log("type: ", type, "  data: ", data);

Native Application

For a native application you can use the native SDK from
To receive the data sent from the Android application running in the Anbox
container you need to register a callback via the anbox_stream_set_message_received_callback method:

    anbox_stream_set_message_received_callback(, [](
        const char* type, size_t type_size,
        const char* data, size_t data_size, void *user_data){
      std::cout << "Received message from container type: '"<< std::string(type, type_size) << "'" << std::endl;
    }, nullptr));

With those, whenever a message is sent from an Android application, the
native application will receive the message and print it to its standard output.