Servo for Cordova

[!WARNING]
This plugin is built to demonstrate the usage of Servo in Cordova. Due to some workarounds that involve an embedded web server and WebSockets it's not secure and SHOULD NOT BE USED IN PRODUCTION apps. Read more under Limitations

With this plugin for Apache Cordova you can try Servo as an alternative engine on Android (for now).

Why?

Servo aims to empower developers with a lightweight, high-performance alternative for embedding web technologies in applications.

From servo.org

Servo looks promising as a new engine to power Cordova and other WebView uses cases independently of the WebView the host operating system provides.

How to use

You can add this to any Cordova project with:

cordova plugin add cordova-plugin-servo-webview

Because app assets are served with a local web server you need to adjust this in config.xml:

<content src="http://localhost:5000" />

Status

This is the first stage of development. Which means this plugin uses a build from Servos main branch without any modifications and just the current APIs. It works with some workarounds.

When Servo adds two important features 1. Custom URL scheme handler & 2. evaluateJavaScript to their Java API this plugin can get rid of limitations as outlined below and work pretty similar to AndroidWebView without adding insecure hacks to Cordova.

%%{init: {
  "theme": "base",
  "themeVariables": {
    "cScale0": "#22c55e",
    "cScale1": "#ef4444",
    "cScale2": "#ef4444",
    "cScaleLabel0": "#052e16",
    "cScaleLabel1": "#450a0a",
    "cScaleLabel2": "#450a0a"
  }
}}%%
timeline
    title Maturity
    Servo TODAY: Legacy bridge mode with WebSocket workarounds
        : Local webserver for assets
    ServoView adds Custom ProtocolHandlers : Use custom scheme API for local file loading
        : Remove webserver for file serving
    ServoView adds evaluateJavascript: Replace WebSocket bridge mode
        : Leverage two-way JavaScript bridge
        : Remove web server entirely

Limitations & Workarounds

Servo and it's ServoView Java implementation allow embedding Servo in Android apps pretty neatly. Servo lacks some APIs that make it a perfect replacement for Android WebView today. Therefore, some workarounds are part of this version that have some serious drawbacks:

1. The Cordova ↔ Native bridge uses a legacy bridge mode and quite a few hacks to leverage a local WebSocket server for communication between the WebView and native code. It's slow, unreliable and insecure, unfortunately.
2. Servo does not have something similar to WebViewAssetLoader to "host" local files for the WebView therefore this plugin has a local web server to host the assets from the www directory.

Updating the Servo version

If you want to update the Servo version yourself check out the README in /libs directory where and how to get the latest build of Servo.

Funding

This project is funded through NGI Mobifree Fund, a fund established by NLnet with financial support from the European Commission's Next Generation Internet program. Learn more at the NLnet project page.