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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
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<title>IcedTeaNPPlugin LiveConnect Design</title>
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<h1>IcedTeaNPPlugin LiveConnect Design</h1>
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<h2>Plugin Architecture</h2>
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<li>Divided into C++ and Java components</li>
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<li>C++ side talks to the browser</li>
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<li>Java side talks to the JVM</li>
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<li>Linked via a FIFO link</li>
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<li>Common string exchange format (UTF-8)</li>
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<li>Over 95% of changes in NPPlugin have been on the C++ side</li>
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<li>Java side has been reused as much as possible to re-use the proven stable code</li>
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<h2>C++ Architecture</h2>
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<li>Encompassing classes from the LiveConnect engine (which previously resided in Mozilla
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and was exposed via OJI)</li>
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<li>Each JavaScript var corresponding to a Java object has a corresponding
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<code>IcedTeaScriptableJavaObject</code></li>
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<li>Engine controls the object life and services all requests (get field, set field,
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invoke method, etc.)</li>
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<h2>C++ Architecture (Browser Interface)</h2>
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<li>Browser interface consists primarily of <code>IcedTeaScriptableJavaPackageObject</code>,
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<code>IcedTeaScriptableJavaObject</code> and <code>IcedTeaPluginRequestProcessor</code>.</li>
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<li>Above classes are unaware of Java interactions and delegate to the Java interfaces
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for Java interaction.</li>
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<li>They process all requests coming from the browser and going to the browser (<code>getMember</code>,
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<code>call</code>, <code>eval</code>, etc.)</li>
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<h2>C++ Architecture (Java Interface)</h2>
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<li>Java interface consists primarily of <code>IcedTeaJavaRequestProcessor</code>.</li>
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<li>This class has full knowledge of how the Java side works, and constructs appropriate
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requests to get all information from Java.</li>
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<li>The class processes all requests to the JVM.</li>
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<h2>Java Architecture</h2>
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<li>Java side has two core classes aside from helpers: <code>PluginAppletViewer</code>
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and <code>PluginAppletSecurityContext</code>.</li>
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<li><code>PluginAppletViewer</code> is an interface to NetX and processes JS-related
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requests to and from NetX (the applet).</li>
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<li><code>PluginAppletSecurityContext</code> is a direct reflection-based interface
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to the VM. It processes all LiveConnect requests to and from the JVM.</li>
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<li>Request processing is asynchronous, with scalable generic request processing workers.</li>
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<h2>Java Architecture (<code>PluginAppletViewer</code>)</h2>
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<li>Control of applet (initialize, resize, destroy, etc.) from browser.</li>
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<li>Access to JavaScript from the applet (<code>getMember</code>, <code>setMember</code>,
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<code>call</code>, <code>eval</code>, etc.)</li>
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<h2>Java Architecture (<code>PluginAppletSecurityContext</code>)</h2>
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<li>Direct access to the JVM from the browser (LiveConnect) via reflection.</li>
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<li>All reflection is built-in, so C++ side never needs to be aware of the complexities,
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unlike how OJI was.</li>
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<li>All VM calls are inside a sandbox, so JavaScript can not do things that the default
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sandboxed VM can't.</li>
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<h2>MessageBus Architecture (C++)</h2>
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<li>The link to Java is exposed to the rest of the code via a uniform "MessageBus" interface.</li>
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<li>Since the code is unaware of the link specifics and has no synchronicity guarantee, the communication
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medium can be switched relatively easily.</li>
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<li>Classes interested in the messages implement a <code>BusSubscriber</code> class and subscribe to
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the bus of interest.</li>
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<li>When messages come in, the bus notifies all subscribers.</li>
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<h2>Example JS->Java Workflow</h2>
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<li>Example shows how <code>NPP_HasProperty()</code> works</li>
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<li>Browser has a link to an <code>IcedTeaScriptableJavaObject</code> representing a Java
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<li>It call <code>IcedTeaScriptableJavaObject::HasProperty()</code></li>
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<li><code>HasProperty()</code> creates an <code>IcedTeaJavaRequestProcessor</code>
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("Java processor")</li>
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<li>The Java processor exposes all necessary APIs to the VM, including <code>hasProperty</code>
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(called <code>hasField</code> for Java naming consistency).</li>
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<li>Before making a <code>hasField</code> request, the processor subscribes itself
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to the "from Java" bus, so that it can read the response.</li>
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<li>The <code>hasField</code> request is made by the processor and posted to the
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<li>The processor waits for either a response or a timeout.</li>
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<li>Once a response is received, the processor unsubscribes itself from the
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"from Java" bus, performs post-processing and returns.</li>
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<li>The <code>IcedTeaScriptableJavaObject</code> object reads the response and
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sends it to the browser.</li>
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<h2>Example Java->JS Workflow</h2>
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<li>All access to JS is via <code>JSObject</code> instances as defined in the
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LiveConnect specification.</li>
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<li>If an applet wants to access a member of <code>JSObject</code>, "window"
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for example, it will call <code>getMember</code> on the window's <code>JSObject</code>.</li>
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<li><code>getMember</code> calls a similarly named function in
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<code>PluginAppletViewer</code>.</li>
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<li><code>PluginAppletViewer</code> constructs a request for the C++ side and
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posts it on the FIFO link.</li>
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<li>On the C++ side, <code>IcedTeaPluginRequestProcessor</code> (the plugin
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processor) is always subscribed to the "from Java" bus.</li>
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<li>When the <code>getMember</code> request comes through, the plugin processor
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<li>The embedded request</li>
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plugin/docs/npplugin_liveconnect_design.html
