README (0.5.1)

The LiquidCore Project

LiquidCore provides an environment for developers to create native mobile micro apps in Javascript that can in turn be embedded into other apps. Think: native <iframe> for mobile apps. A LiquidCore micro app is simply a Node.js module that can be served from the cloud, and therefore, like in a webpage, it can be modified server-side and instantly updated on all mobile devices.

LiquidCore also provides a convenient way for Android developers to execute raw JavaScript inside of their apps, as iOS developers can already do natively with JavaScriptCore.

Version

0.5.1 - Get it through JitPack

Javadocs

Version 0.5.1

Use Cases

This section covers the two major intended use cases of LiquidCore, complete with Hello, World! step-by-step examples.

The Micro Service
The Micro App

You can also use LiquidCore as a raw Native Javascript Engine (i.e. as a replacement for AndroidJSCore). That topic is discussed here.

The Micro Service

A micro app is built on a micro service. A micro service is nothing more than an independent Node.js instance whose startup code is referenced by a URI. For example:

MicroService service = new MicroService(androidContext,
    new URI("http://my.server.com/path/to/code.js"));
service.start();

The service URI can either refer to a server URL or a local Android resource. LiquidCore is designed to primarily use remote URLs, as dynamic updates are an important value proposition, but local resources are also supported. For example, android.resource://com.example.myapp/raw/some_js_file, where some_js_file.js resides in res/raw/some_js_file.js (note that the .js is omitted from the URI when using an Android resource).

A micro service can communicate with the host app once the Node.js environment is set up. This can be determined by adding a ServiceStartListener in the MicroService constructor:

MicroService service = new MicroService(
    androidContext,
    new URI("http://my.server.com/path/to/code.js"),
    new MicroService.StartServiceListener() {
        @Override
        public void onStart(MicroService service, Synchronizer synchronizer) {
            // .. The environment is live, but the startup JS code (from the URI)
            // has not been executed yet.
        }
    }
);
service.start();

A micro service communicates with the host through a simple EventEmitter interface, eponymously called LiquidCore. For example, in your JavaScript startup code (code.js in this example):

LiquidCore.emit('my_event', {foo: "hello, world", bar: 5, l337 : ['a', 'b'] })

On the Java side, the host app can listen for events:

// ... in the StartServiceListener.onStart() method:

service.on("my_event", new MicroService.EventListener() {
    @Override
    public void onEvent(MicroService service, String event, JSONObject payload) {
        try {
            android.util.Log.i("Event:" + event, payload.getString("foo"));
            // logs: I/Event:my_event: hello, world
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
});

Similarly, the micro service can listen for events from the host:

JSONObject payload = new JSONObject();
payload.put("hallo", "die Weld");
service.emit("host_event", payload);

Then, in Javascript:

LiquidCore.on('host_event', function(msg) {
   console.log('Hallo, ' + msg.hallo)
})

LiquidCore creates a convenient virtual file system so that instances of micro services do not unintentionally or maliciously interfere with each other or the rest of the Android filesystem. The file system is described in detail here.

The Micro App

Important Notice: The Micro App concept is being completely re-thought. In version 0.6.0, LiquidView will disappear from LiquidCore and be reborn in a separate project built on top of LiquidCore. The goal is to keep LiquidCore focused on just providing a fast, secure Node VM for mobile devices. The UI will reappear in a project called caraml. Stay tuned.

There are many uses for micro services. They are really useful for taking advantage of all the work that has been done by the Node community. But we want to be able to create our own native applications that do not require much, if any, interaction from the host. To achieve this, we will introduce one more term: Surface. A surface is a UI canvas for micro services.

There are two surfaces so far:

ConsoleSurface. A ConsoleSurface is simply a Node.js terminal console that displays anything written to console.log() and console.error(). It also allows injection of Javascript commands, just like a standard Node console. Run the NodeConsole app under the Tests directory to see it in action.
ReactNativeSurface. You can drive native UI elements using the React Native framework from within your micro app.

There are other surfaces under consideration, including:

WebSurface - a WebView front-end where a micro service can write to the DOM
CardSurface - a limited feature set suitable for driving card-like UI elements in a list
OpenGLSurface - an OpenGL canvas

Eventually, we would like to have virtual/augmented reality surfaces, as well as non-graphical canvases such as chat and voice query interfaces.

"Hallo, die Weld!" Micro Service Tutorial

Prerequisites

A recent version of Node.js -- 8.9.3 or newer
Android Studio

(You can find all the code below in a complete example project here if you get stuck).

To use a micro service, you need two things: the micro service code, and a host app.

We will start by creating a very simple micro service, which does nothing more than send a welcome message to the host. This will be served from a machine on our network. Start by installing the command-line interface:

$ npm install -g liquidcore-cli

Next, generate a project called helloworld using the tool:

$ liquidcore init helloworld
$ cd helloworld && npm install

This will generate a small Hello World project for you. We are going to change it a bit, but the important thing is that this sets everything up correctly and provides you with some nice features like a development server and production bundler.

Once installation has completed, edit the file index.js in your helloworld directory and replace its contents with the following:

/* Hello, World! Micro Service */

// A micro service will exit when it has nothing left to do.  So to
// avoid a premature exit, let's set an indefinite timer.  When we
// exit() later, the timer will get invalidated.
setInterval(function() {}, 1000)

// Listen for a request from the host for the 'ping' event
LiquidCore.on( 'ping', function() {
    // When we get the ping from the host, respond with "Hallo, die Weld!"
    // and then exit.
    LiquidCore.emit( 'pong', { message: 'Hallo, die Weld!' } )
    process.exit(0)
})

// Ok, we are all set up.  Let the host know we are ready to talk
LiquidCore.emit( 'ready' )

Finally, you can now run your development server.

$ npm start server

This will fire off a server built on the metro bundler. Metro does everything we need and more, so if you've used the old liquidserver in the past, this replaces that. Anyway, congratulations, you just created a micro service. You can test that it is working correctly by navigating to http://localhost:8082/liquid.bundle?platform=android in your browser. You should be able to find the contents of index.js that you just created with some additional wrapper code. The wrapper is simply to allow multiple Node.js modules to be packed into a single file. If you were to require() some other module, that module and its dependencies would get wrapped into this single file.

You can leave that running or restart it later. Now we need to create a host app.

In Android Studio, create a new project by selecting File -> New Project ...
Fill out the basics and press Next (Application Name: HelloWorld, Company Domain: liquidplayer.org, Package name: org.liquidplayer.examples.helloworld)
Fill in the Target Devices information. The defaults are fine. Click Next
Select Empty Activity and then Next
The default options are ok. Click Finish

You now have a basic app that does very little. Go ahead and run it in your emulator. If you hadn't figured out why we are creating a "Hallo, die Weld!" app, you probably can see why by now. You already get "Hello, World!" from Android Studio. We're going to make it speak German with our micro service.

Next, open the res/layout/activity_main.xml file. We need to make a couple of modifications. Replace the contents with the following:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="org.liquidplayer.examples.helloworld.MainActivity">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="Sprechen Sie Deutsch!"
        />
</RelativeLayout>

All we've changed is that we have given our TextView a name: text, and added a button. Go ahead and run it again. You should now see a big button in the middle.

Now it is time to connect LiquidCore. First, you must add the library. Go to your root-level build.grade file and add the jitpack dependency:

...

allprojects {
    repositories {
        jcenter()
        maven { url 'https://jitpack.io' }
    }
}

...

Then, add the LiquidCore library to your app's build.gradle:

dependencies {
    ...
    implementation 'com.github.LiquidPlayer:LiquidCore:0.5.1'
}

Go ahead and sync to make sure the library downloads and links properly. Run the app again to ensure that all is good.

Now, let's connect our button to the micro service. Edit MainActivity.java in our app, and replace the contents with the following:

package org.liquidplayer.examples.helloworld;

import android.os.Handler;
import android.os.Looper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import org.json.JSONException;
import org.json.JSONObject;
import org.liquidplayer.service.MicroService;
import org.liquidplayer.service.MicroService.ServiceStartListener;
import org.liquidplayer.service.MicroService.EventListener;

import java.net.URI;
import java.net.URISyntaxException;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final TextView textView = (TextView) findViewById(R.id.text);
        final Button button = (Button) findViewById(R.id.button);

        // Our 'ready' listener will wait for a ready event from the micro service.  Once
        // the micro service is ready, we'll ping it by emitting a "ping" event to the
        // service.
        final EventListener readyListener = new EventListener() {
            @Override
            public void onEvent(MicroService service, String event, JSONObject payload) {
                service.emit("ping");
            }
        };

        // Our micro service will respond to us with a "pong" event.  Embedded in that
        // event is our message.  We'll update the textView with the message from the
        // micro service.
        final EventListener pongListener = new EventListener() {
            @Override
            public void onEvent(MicroService service, String event, final JSONObject payload) {
                // NOTE: This event is typically called inside of the micro service's thread, not
                // the main UI thread.  To update the UI, run this on the main thread.
                new Handler(Looper.getMainLooper()).post(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            textView.setText(payload.getString("message"));
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }
                    }
                });
            }
        };

        // Our start listener will set up our event listeners once the micro service Node.js
        // environment is set up
        final ServiceStartListener startListener = new ServiceStartListener() {
            @Override
            public void onStart(MicroService service, Synchronizer synchronizer) {
                service.addEventListener("ready", readyListener);
                service.addEventListener("pong", pongListener);
            }
        };

        // When our button is clicked, we will launch a new instance of our micro service.
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    URI uri = MicroService.DevServer();
                    MicroService service = new MicroService(MainActivity.this, uri, startListener);
                    service.start();
                } catch (URISyntaxException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

Now, restart the app and then click the button. The "Hello World" message should change to German. You have successfully connected a micro service to a host app!

To demonstrate the instant update feature, leave the app and server running. Now, edit index.js on your server machine to respond with a different message and then save:

...
    LiquidCore.emit( 'pong', { message: 'Das ist super!' } )
...

Go back to the app and press the button again. Your message should update.

That's it. That's all there is to it. Of course, this is an overly simplified example. You have all of the capabilities of Node.js at your disposal.

A quick note about the MicroService.DevServer(): this generates convenience URL which points to the loopback address (10.0.2.2) on Android, which is used to serve the emulator from the host machine. This won't work on actual hardware. You would need to replace this with an actual URL. MicroService.DevServer() assumes the entry file is named liquid.js and the server is running on port 8082. Both of these assumptions can be changed by providing arguments, e.g. MicroService.DevServer('another_file.bundle', 8888) would generate a URL to fetch a bundle with an entry point of another_file.js on port 8888.

Building the LiquidCore Android library

If you are interested in building the library directly and possibly contributing, you must do the following:

% git clone https://github.com/liquidplayer/LiquidCore.git
% cd LiquidCore
% echo ndk.dir=$ANDROID_NDK > local.properties
% echo sdk.dir=$ANDROID_SDK >> local.properties
% ./gradlew assembleRelease

Your library now sits in LiquidCoreAndroid/build/outputs/aar/LiquidCore-release.aar. To use it, simply add the following to your app's build.gradle:

repositories {
    flatDir {
        dirs '/path/to/lib'
    }
}

dependencies {
    implementation(name:'LiquidCore-release', ext:'aar')
}

Note

The Node.js library (libnode.so) is pre-compiled and included in binary form in deps/node-8.9.3/prebuilt. All of the modifications required to produce the library are included in deps/node-8.9.3. To build each library (if you so choose), see the instructions here.

License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Provide feedback

Saved searches

Use saved searches to filter your results more quickly