source: trunk/icedtea-web/plugin/docs/npplugin_liveconnect_design.html

Last change on this file was 348, checked in by dmik, 13 years ago

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1<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
4 <head>
5 <title>IcedTeaNPPlugin LiveConnect Design</title>
6 </head>
7 <body>
8 <h1>IcedTeaNPPlugin LiveConnect Design</h1>
9 <h2>Plugin Architecture</h2>
10 <ul>
11 <li>Divided into C++ and Java components</li>
12 <li><ul>
13 <li>C++ side talks to the browser</li>
14 <li>Java side talks to the JVM</li>
15 <li>Linked via a FIFO link</li>
16 <li>Common string exchange format (UTF-8)</li>
17 </ul></li>
18 <li>Over 95% of changes in NPPlugin have been on the C++ side</li>
19 <li>Java side has been reused as much as possible to re-use the proven stable code</li>
20 </ul>
21 <h2>C++ Architecture</h2>
22 <ul>
23 <li>Encompassing classes from the LiveConnect engine (which previously resided in Mozilla
24 and was exposed via OJI)</li>
25 <li>Each JavaScript var corresponding to a Java object has a corresponding
26 <code>IcedTeaScriptableJavaObject</code></li>
27 <li>Engine controls the object life and services all requests (get field, set field,
28 invoke method, etc.)</li>
29 </ul>
30 <h2>C++ Architecture (Browser Interface)</h2>
31 <ul>
32 <li>Browser interface consists primarily of <code>IcedTeaScriptableJavaPackageObject</code>,
33 <code>IcedTeaScriptableJavaObject</code> and <code>IcedTeaPluginRequestProcessor</code>.</li>
34 <li>Above classes are unaware of Java interactions and delegate to the Java interfaces
35 for Java interaction.</li>
36 <li>They process all requests coming from the browser and going to the browser (<code>getMember</code>,
37 <code>call</code>, <code>eval</code>, etc.)</li>
38 </ul>
39 <h2>C++ Architecture (Java Interface)</h2>
40 <ul>
41 <li>Java interface consists primarily of <code>IcedTeaJavaRequestProcessor</code>.</li>
42 <li>This class has full knowledge of how the Java side works, and constructs appropriate
43 requests to get all information from Java.</li>
44 <li>The class processes all requests to the JVM.</li>
45 </ul>
46 <h2>Java Architecture</h2>
47 <ul>
48 <li>Java side has two core classes aside from helpers: <code>PluginAppletViewer</code>
49 and <code>PluginAppletSecurityContext</code>.</li>
50 <li><code>PluginAppletViewer</code> is an interface to NetX and processes JS-related
51 requests to and from NetX (the applet).</li>
52 <li><code>PluginAppletSecurityContext</code> is a direct reflection-based interface
53 to the VM. It processes all LiveConnect requests to and from the JVM.</li>
54 <li>Request processing is asynchronous, with scalable generic request processing workers.</li>
55 </ul>
56 <h2>Java Architecture (<code>PluginAppletViewer</code>)</h2>
57 <ul>
58 <li>Control of applet (initialize, resize, destroy, etc.) from browser.</li>
59 <li>Access to JavaScript from the applet (<code>getMember</code>, <code>setMember</code>,
60 <code>call</code>, <code>eval</code>, etc.)</li>
61 </ul>
62 <h2>Java Architecture (<code>PluginAppletSecurityContext</code>)</h2>
63 <ul>
64 <li>Direct access to the JVM from the browser (LiveConnect) via reflection.</li>
65 <li>All reflection is built-in, so C++ side never needs to be aware of the complexities,
66 unlike how OJI was.</li>
67 <li>All VM calls are inside a sandbox, so JavaScript can not do things that the default
68 sandboxed VM can't.</li>
69 </ul>
70 <h2>MessageBus Architecture (C++)</h2>
71 <ul>
72 <li>The link to Java is exposed to the rest of the code via a uniform "MessageBus" interface.</li>
73 <li>Since the code is unaware of the link specifics and has no synchronicity guarantee, the communication
74 medium can be switched relatively easily.</li>
75 <li>Classes interested in the messages implement a <code>BusSubscriber</code> class and subscribe to
76 the bus of interest.</li>
77 <li>When messages come in, the bus notifies all subscribers.</li>
78 </ul>
79 <h2>Example JS->Java Workflow</h2>
80 <ul>
81 <li>Example shows how <code>NPP_HasProperty()</code> works</li>
82 <li>Browser has a link to an <code>IcedTeaScriptableJavaObject</code> representing a Java
83 object instance.</li>
84 <li>It call <code>IcedTeaScriptableJavaObject::HasProperty()</code></li>
85 <li><code>HasProperty()</code> creates an <code>IcedTeaJavaRequestProcessor</code>
86 ("Java processor")</li>
87 <li>The Java processor exposes all necessary APIs to the VM, including <code>hasProperty</code>
88 (called <code>hasField</code> for Java naming consistency).</li>
89 <li>Before making a <code>hasField</code> request, the processor subscribes itself
90 to the "from Java" bus, so that it can read the response.</li>
91 <li>The <code>hasField</code> request is made by the processor and posted to the
92 "to Java" bus.</li>
93 <li>The processor waits for either a response or a timeout.</li>
94 <li>Once a response is received, the processor unsubscribes itself from the
95 "from Java" bus, performs post-processing and returns.</li>
96 <li>The <code>IcedTeaScriptableJavaObject</code> object reads the response and
97 sends it to the browser.</li>
98 </ul>
99 <h2>Example Java->JS Workflow</h2>
100 <ul>
101 <li>All access to JS is via <code>JSObject</code> instances as defined in the
102 LiveConnect specification.</li>
103 <li>If an applet wants to access a member of <code>JSObject</code>, "window"
104 for example, it will call <code>getMember</code> on the window's <code>JSObject</code>.</li>
105 <li><code>getMember</code> calls a similarly named function in
106 <code>PluginAppletViewer</code>.</li>
107 <li><code>PluginAppletViewer</code> constructs a request for the C++ side and
108 posts it on the FIFO link.</li>
109 <li>On the C++ side, <code>IcedTeaPluginRequestProcessor</code> (the plugin
110 processor) is always subscribed to the "from Java" bus.</li>
111 <li>When the <code>getMember</code> request comes through, the plugin processor
112 gets notified.</li>
113 <li>The embedded request</li>
114 </ul>
115 </body>
116</html>
117
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