tdebase/nsplugins

nsplugins
=========

The 'nsplugins' directory contains various tools used to utilize Netscape(R)
browser plugins in KDE applications.

 - ./       - common headers and utilities

 - viewer/  - provides means to embed a Netscape(R) browser plugin
              into a KDE application.

 - sdk/     - headers from the Netscape(R) browser plugin SDK.

 - control/ - KDE Control Center applet for managing plugins

 - test/    - simple applications to test nsplugin

 - wrapper/ - currently unused.


At the time of writing, nsplugins supports Navigator 4 API plugins
and doesn't support new Mozilla XPCOM components.

Parts
=====

The Netscape(R) browser plugin support consists of 3 parts:
- "PluginPart" KPart which is embedded into KHTML pages
  (alone, it looks no different than a gray rectangle)
- "nspluginviewer", a separate application which is capable of
  actually loading and playing the various Netscape(R) plugins.
- "pluginscan", a small utility to scan predefined directories
  for Netscape(R) browser plugins.

PluginPart's responsibility is to run "nspluginviewer" and instruct
it to display the plugin inside its' rectangle.

* KParts is KDE's standard for embeddable objects, much like
  Microsoft's OLE.

PluginPart / nspluginviewer separation
======================================

Plugins contain 3rd-party code which might crash if badly written
(especially inside our "Netscape emulation" environment).
The PluginPart runs inside the memory space of the embedding application,
making the embedding application susceptible to a crash in the PluginPart.
In our case, the "embedding application" would be the browser, and having
the whole browser shut down just because some plugin crashed is bad.
By loading and talking to the plugin is a separate process
("nspluginviewer"), we prevent such crashes from taking
the browser down with them -- the worst that could happen
is the plugin suddenly disappearing from the page, revealing
PluginPart's gray background.

nspluginviewer to PluginPart communications
===========================================

The communications between the PluginPart and nspluginviewer
are done via DCOP. Messages which nspluginviewer could send
to PluginPart include:
- requestURL(url, target) - make the browser load a URL
- statusMessage(msg)      - change the status bar in the
                            embedding application

(For an updated list of messages, see NSPluginCallbackIface.h)

When received, those messages are mapped to functions in
NSPluginCallback, which in turn calls PluginPart functions.

* DCOP is KDE's standard for RPC, typically used by local
  processes to pass messages.

PluginPart to nspluginviewer communications
===========================================

nspluginviewer's window is, all in all, a simple X11 window,
it can be resized, focused and unfocused with standard X11 functions
as long as we know its' window ID.

PluginPart gets a NSPluginInstance (from NSPluginLoader::newInstance),
which it sees as a regular QWidget. e.g. it can resize the QWidget and
nspluginviewer's window will resize.

This magic happens thanks to KJavaEmbed which NSPluginInstance inherits.
KJavaEmbed inherits QWidget and hooks up to QWidget's events, mapping
those events to the appropriate X11 window operations.
Resizing, focusing in and out is about all PluginPart could ever do
with the nspluginviewer.

How does KJavaEmbed know the window ID of the nspluginviewer window?
NSPluginInstance retrieves it from nspluginviewer with a DCOP call
("int winId()") and gives it to KJavaEmbed.

Main classes
============

- PluginPart class (plugin_part.h, plugin_part.cpp)
  
  A KParts::ReadOnlyPart.
  
- PluginFactory class (plugin_part.h, plugin_part.cpp)

  Creates PluginPart objects.

- NSPluginInstance class (nspluginloader.h, nspluginloader.cpp)

  PluginPart's "looking glass" to "nspluginviewer".

- NSPluginLoader class (nspluginloader.h, nspluginloader.cpp)

  Responsible for starting a new independant process of the
  plugin viewer and initiating DCOP communications with it.
  
- NSPluginCallbackIface (NSPluginCallbackIface.h)

  Defines functions which the nspluginviewer can call in the PluginPart.
  Those function calls would be transfered over DCOP and implemented
  in PluginPart's NSPluginCallback class.


Plugin Scanner
==============

Implemented in: pluginscan.cpp

Utility which scans for Netscape(R) browser plugins in pre-defined
directories (according to KDE's configuration) and writes down
information about the located plugins into the plugin information
cache. To locate all the plugins, it doesn't limit itself to files
with .so extension. A forking mechanism is implemented to prevent
faulty .so's from crashing the scanning process.
	
This utility is usually not invoked standalone, but used by the
KDE Control Center applet which invokes it on:
- explicit request (ie. pressing "Scan for new plugins" button)
- KDE startup (in the applet's initialization code)
- first time the applet is ran

	
Viewer
======

Implemented in: viewer/

The viewer is a KDE component used to embed Netscape(R) plugins
into KDE applications (such as KHTML / Konqueror). To the plugin, it
emulates a Netscape(R) browser, while outside - it offers a standard KParts
object.

NSPluginCallbackIface.h

  Defines functions which the nspluginviewer can call in the PluginPart.
  Those function calls would be transfered over DCOP and implemented
  in PluginPart's NSPluginCallback class.

kxt.h, kxt.cpp

  ...
	
resolve.h

  Some macros to resolve symbols.
	
nsplugin.h, nsplugin.cpp

  The implementation of the interface between KDE and the Netscape(R)
  browser plugin as a KParts object.
	
  Note: This file implements its own NSPluginInstance, which should
  not be confused with PluginPart's NSPluginInstance.

  It implements:
  - The Netscape(R) emulation side:
    g_NPN_* functions, which implement Netscape(R) browser
    plugin API NPN_* C methods accordingly. Our emulation
    of a Netscape(R) browser is as good as those functions are.
    
    By definition, all functions are passed with an NPN ("plugin
    instance") struct, and each NPN has an 'ndata'  pointer member.
    That's good news to us, since we now can use it to point to
    our NSPluginInstance object.
    
    Those functions contain the minimum necessary code to
    call the NSPluginInstance function for the requested operation

  - The KDE side:
    NSPluginInstance implements functions for various g_NPN_*
    operations. Typically those operations will be passed via DCOP
    to the PluginPart -- e.g. a operation which changes the window's
    status bar.
	
viewer.cpp

  A standalone application that executes Netscape plugins.

Control Center applet
=====================

The Control Center applet allows the user to:
- Add additional directories which "pluginscan" would scan for
  Netscape(R) plugins. 
- See which plugins "pluginscan" found (by reading the plugin cache). 
- Force a "pluginscan" rescan.

The KDE Control Center API is well documented in the KDE SDK.

Compatibility notes
===================

Although nsplugins strive for full compatibility with the Netscape(R)
browser plugin execution environment, it still lacks the following features:

- LiveConnect (Netscape Navigator 3.0) Java / JavaScript connectivity

  Support for LiveConnect (for JavaScript support) requires:
  - Reimplementation of Netscape's JRI functions (see sdk/jri.h)
    to communicate back (via DCOP?) with the PluginPart, which'll
    signal them to KHTML's KJS interpretor. KParts::BrowserExtension
    should be extended to support those signals. Of course, only
    JRI calls in the "netscape.javascript" namespace should be handled.
  - Implementation of g_NPN_GetJavaEnv and g_NPN_GetJavaPeer
    (currently they're empty placeholders).
  - Implementing g_NPN_GetValue(NPNVjavascriptEnabledBool, ...)
    (currently always returns "false").
    Should involve adding a slot to KParts::BrowserExtension
    and making KHTML signal it whenever JS gets enabled or disabled.

  LiveConnect will probably never be supported due to JRE ABI issues, and
  the fact that we need to have a JRE with JNI inside the nspluginviewer.
  LiveConnect is almost obsolete as well.  XPConnect will not be integrated
  either.

The current support is enough to run common plugins such as Macromedia(R)
Flash(R) and RealPlayer(R), but some of their functionality might be missing.
For instance, Flash(R) animations cannot call user-defined JavaScript
routines nor can the user control the Flash(R) animation via JavaScript.

Additional documentation
========================

Additional documentation on the Netscape(R) plugin API is available at:

- http://developer.netscape.com/docs/manuals/plugins.html
- http://www.mozilla.org/docs/plugin.html

Author
======

This README was authored Ilya Konstantinov <kde-devel@future.shiny.co.il>.
Thanks go to Matthias Hoelzer-Kluepfel and Stefan Schimanski for writing
the actual code and making it all possible.

Present maintainer of the nsplugin code is George Staikos <staikos@kde.org>