i2p.www/www.i2p2/pages/plugin_spec.html

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<h2>
Specification Version 0.16
2010-07-26
</h2>
<p> 
Page last updated July 2010, current as of router version 0.8.
<h3>Overview</h3>
<p> 
This document specifies
a .xpi2p file format (like the Firefox .xpi), but with a simple
plugin.config description file instead of an XML install.rdf file.
This file format is used for both initial plugin installs and plugin updates.
<p>
In addition, this document provides a brief overview of how the router installs plugins,
and policies and guidelines for plugin developers.
<p>
The basic .xpi2p file format is the same as a i2pupdate.sud file
(the format used for router updates),
but the installer will let the user install the
addon even if it doesn't know the signer's key yet.

<p>
The standard directory structure will let users install the following types of addons:
<ul>
<li>
	 console webapps
<li>
	 new eepsite with cgi-bin, webapps
<li>
	 console themes
<li>
	 console translations
<li>
	 Java programs
<li>
	 Java programs in a separate JVM
<li>
	 Any shell script or program
</ul>

<p>
A plugin installs all its files in ~/.i2p/plugins/name/ (%APPDIR%\I2P\plugins\name\ on Windows). The installer will prevent
installation anywhere else, although the plugin can access libraries elsewhere when running.

<p>
This should be viewed only as a way to make installation, uninstallation, and upgrading easier,
and to lessen basic inter-plugin conflicts.

<p>
There is essentially no security model once the plugin is running, however. The plugin runs
in the same JVM and with the same permissions as the router, and has full access to the file
system, the router, executing external programs, etc.

<h3>Details</h3>
<p>
foo.xpi2p is a sud file containing the following:
<pre>
	Standard .sud header prepended to the zip file, containing the following:
	        40-byte <a href="how_cryptography.html#DSA">DSA signature</a>
		16-byte plugin version in UTF-8, padded with trailing zeroes if necessary

	Zip file containing the following:

		(REQUIRED) plugin.config file:
		(standard I2P config file, UTF-8 containing key=value lines, comments start with #)
		Containing the following properties:

		(* = required)
			The first three must be identical to those in the installed plugin for an update plugin.

			*name (will be installed in this directory name)
				For native plugins, you may want separate names in different packages -
				foo-windows and foo-linux, for example
			*key (<a href="how_cryptography.html#DSA">DSA public key</a> as 172 B64 chars ending with '=')
			*signer (yourname@mail.i2p recommended)

			*version (must be in a format VersionComparator can parse, e.g. 1.2.3-4)
				16 bytes max (must match sud version)
				Valid number separators are '.', '-', and '_'
				This must be greater than the one in the installed plugin for an update plugin.


			The following items are displayed on configclients.jsp if present:

			date (Java time - long int)
			author (yourname@mail.i2p recommended)
			websiteURL (http://foo.i2p/)
			updateURL (http://foo.i2p/foo.xpi2p)
				The update checker will check bytes 41-56 at this URL
				to determine whether a newer version is available
				( Should the checker fetch with ?currentVersion=1.2.3?...
				  No. If the dev wants to have the URL contain the current version, just
				  set it in the config file, and remember to change it every release)
			description
			description_xx (for language xx)
			license
			disableStop=true
				Default false.
				If true, the stop button will not be shown. Use this if there are no
				webapps and no clients with stopargs.

			The following items are used to add a link on the console summary bar:

			consoleLinkName (will be added to summary bar)
			consoleLinkName_xx (for language xx)
			consoleLinkURL (/appname/index.jsp)
			consoleLinkTooltip (supported as of 0.7.12-6)
			consoleLinkTooltip_xx (lang xx as of 0.7.12-6)
			

			The following items are used by the plugin installer:

			type (app/theme/locale/webapp/...) (unimplemented, probably not necessary)
			min-i2p-version
			max-i2p-version
			min-java-version
			min-jetty-version
			max-jetty-version
			required-platform-OS (unimplemented - perhaps will be displayed only, not verified)
			other-requirements (unimplemented e.g. python x.y - not verified by the installer, just displayed to the user)
			dont-start-at-install=true
				Default false.
			router-restart-required=true
				Default false.
				dont-start-at-install must be true for this to take effect.
				This does not restart the router, it just informs the user that a restart is required.
			update-only=true
				Default false.
				If true, will fail if an installation does not exist.
			install-only=true
				Default false.
				If true, will fail if an installation exists.
			min-installed-version (to update over, if an installation exists)
			max-installed-version (to update over, if an installation exists)
			depends=plugin1,plugin2,plugin3 (unimplemented - is this too hard? proposed by sponge)
			depends-version=0.3.4,,5.6.7 (unimplemented)

			The following item is used for translation plugins:
			langs=xx,yy,Klingon,... (unimplemented) (yy is the country flag)

		Each of the following directories or files is optional, but something must be there or it won't do anything:
			
		console/
			locale/
				Only jars containing new resource bundles (translations) for apps in the base I2P installation.
				Bundles for this plugin should go inside console/webapp/foo.war or lib/foo.jar

			themes/
				New themes for the router console
				Place each theme in a subdirectory.

			webapps/
				(See important notes below about webapps)
				.wars
				These will be run at install time unless disabled in webapps.config
				The war name does not have to be the same as the plugin name.
				Do not duplicate war names in the base I2P installation.

			webapps.config 
				Same format as router's webapps.config
				Also used to specify additional jars in $PLUGIN/lib/ or $I2P/lib for the webapp classpath,
				with webapps.warname.classpath=$PLUGIN/lib/foo.jar,$I2P/lib/bar.jar
				NOTE: Currently, the classpath line is only loaded if the warname is
				the same as the plugin name.
				NOTE: Prior to router version 0.7.12-9, the router looked for plugin.warname.startOnLoad instead
				of webapps.warname.startOnLoad. For compatibility with older router versions, a plugin
				wishing to disable a war should include both lines.

		eepsite/
			(See important notes below about eepsites)
			cgi-bin/
			docroot/
			logs/
			webapps/
			jetty.xml
				The installer will have to do variable substitution in here to set the path
				The location and name of this file doesn't really matter, as long as it is set in
				clients.config - it may be more convenient to be up one level from here
				(that's what the zzzot plugin does)

		lib/
			Put any jars here, and specify them in a classpath line in console/webapps.config and/or clients.config

		clients.config (same format as router's clients.config)
			These will be run when a plugin is started
			Start at client #0, number consecutively
			New property clientApp.0.stopargs=foo bar stop baz
				If present, the class will be called with these args to stop the client
				All stop tasks are called with zero delay
				Note: The router can't tell if your clients are running or not.
                                Each should handle stopping an app that isn't running without complaint.
				That probably goes for starting a client that is already started too.
			New property clientApp.0.uninstallargs=foo bar uninstall baz
				If present, the class will be called with these args just before deleting $PLUGIN
				All stop tasks are called with zero delay
			New property clientApp.0.classpath=$I2P/lib/foo.bar,$PLUGIN/lib/bar.jar
			The plugin runner will do variable substitution in the args and stopargs lines as follows:
				$I2P => i2p base installation dir;
				$CONFIG => i2p config dir (typically ~/.i2p)
				$PLUGIN => this plugin's installation dir (typically ~/.i2p/plugins/appname)
			(See important notes below about running shell scripts or external programs)
</pre>


<h3>Plugin installer tasks</h3>
This lists what happens when a plugin is installed by I2P.
<ul>

    <li>The .xpi2p file is downloaded.</li>
    <li>The .sud signature is verified against stored keys.
        If there is no matching key, the .sud is extracted, the key is loaded from the properties, then verified and stored.</li>
    <li>Verify the integrity of the zip file.</li>
    <li>Extract the plugin.config file.</li>
    <li>Verify the I2P version, to make sure the plugin will work.</li>
    <li>Check that webapps don't duplicate the existing $I2P applications.</li>
    <li>Stop the existing plugin (if present).</li>
    <li>Verify that the install directory does not exist yet if update=false, or ask to overwrite.</li>
    <li>Verify that the install directory does exist if update=false, or ask to create.</li>
    <li>Unzip the plugin in to appDir/plugins/name/</li>
    <li>Add the plugin to plugins.config</li>
</ul>

<h3>
Plugin starter tasks
</h3>
This lists what happens when plugins are started.
First, plugins.config is checked to see which plugins need to be started.
For each plugin:
<ul>
    <li>Check clients.config, and load and start each item (add the configured jars to the classpath).</li>
    <li>Check console/webapp and console/webapp.config. Load and start required items (add the configured jars to the classpath).</li>
    <li>Add console/locale/foo.jar to the translation classpath if present.</li>
    <li>Add console/theme to the theme search path if present.</li>
    <li>Add the summary bar link.</li>
</ul>

<h3>
Console webapp notes
</h3>
<p>
Console webapps with background tasks should implement a ServletContextListener
(see seedless or i2pbote for examples), or override destroy() in the servlet,
so that they can be stopped.
As of router version 0.7.12-3, console webapps will always be stopped before they
are restarted, so you do not need to worry about multiple instances,
as long as you do this.
Also as of router version 0.7.12-3, console webapps will be stopped at router shutdown.
<p>
Don't bundle library jars in the webapp; put them in lib/ and put a classpath in webapps.config.
Then you can make separate install and update plugins, where the update plugin does not
contain the library jars.
<p>
Don't include .java or .jsp files; otherwise jetty will recompile them at installation.
<p>
For now, a webapp needing to add classpath files in $PLUGIN must be the same name as the plugin.
For example, a webapp in plugin foo must be named foo.war.


<h3>
Eepsite notes
</h3>
<p>
It isn't clear how to have a plugin install to an existing eepsite.
The router has no hook to the eepsite, and it may or may not be running,
and there may be more than one.
Better is to start your own Jetty instance and I2PTunnel instance,
for a brand new eepsite.
<p>
 It can instantiate a new I2PTunnel (kinda like the i2ptunnel CLI does),
  but it won't appear in the i2ptunnel gui of course, that's a different instance.
But that's ok. Then you can start and stop i2ptunnel and jetty together.
<p>
So don't count on the router to automatically merge this with some existing eepsite. It probably won't happen.
Start a new I2PTunnel and Jetty from clients.config.
The best examples of this are the zzzot and pebble plugins,
available at <a href="http://stats.i2p/i2p/plugins/">zzz's plugins page</a>.
<p>
How to get path substitution into jetty.xml?
See zzzot and pebble plugins for examples.


<h3>
Client start/stop notes
</h3>
<p>
The router has no way to monitor the state of clients started via clients.config.
The plugin author should handle multiple start or stop calls gracefully, if at all possible,
by keeping a static state table, or using PID files, etc.
Avoid logging or exceptions on multiple starts or stops.
This also goes for a stop call without a previous start.
As of router version 0.7.12-3, plugins will be stopped at router shutdown,
which means that all clients with stopargs in clients.config will be called,
whether or not they were previously started.


<h3>
Shell script and external program notes
</h3>
<p>
To run shell scripts or other external programs, see <a href="http://zzz.i2p/topics/141">zzz.i2p</a>
<p>
To work on both Windows and Linux, write a small Java class that checks the OS type, then
runs ShellCommand on either the .bat or a .sh file you provide.
<p>
External programs won't be stopped when the router stops, and a second copy will
fire up when the router starts. To work around this, you could
write a wrapper class or shell script that does the usual storage of the PID
in a PID file, and check for it on start.




<h3>
Other plugin guidelines
</h3>
<ul>
<li>
See i2p.scripts branch or any of the sample plugins on zzz's page for a xpi2p file generator to make it easy.
<li>
Pack200 of jars and wars is strongly recommended for plugins, it generally shrinks plugins by 60-65%.
See any of the sample plugins on zzz's page for an example.
Pack200 unpacking is supported on routers 0.7.11-5 or higher, which is essentially all routers that
support plugins at all.

<li>
 Plugins should not attempt to write anywhere in $I2P as it may be readonly, and that isn't good policy anyway.
<li>
 Plugins may write to $CONFIG but keeping files in $PLUGIN only is recommended.
All files in $PLUGIN will be deleted at uninstall.
Files elsewhere will not be deleted at uninstall unless the plugin does it explicitly
with a client in clients.config run with uninstallargs.
If the user may want to save data after uninstallation, the uninstallargs hook
could ask.

<li>
 $CWD may be anywhere; do not assume it is in a particular place, do not attempt to read or write files relative to $CWD.
<li>
 Java programs should find out where they are with the directory getters in I2PAppContext.
<li>
 Plugin directory is I2PAppContext.getGlobalContext().getAppDir().getAbsolutePath() + "/plugins/" + appname,
  or put a $PLUGIN argument in the args line in clients.config.
There is no reliable way to find the i2p install or config or plugin directory without using the
context API in i2p.jar.
<li>
 See <a href="http://zzz.i2p/topics/16">Howto</a> for info on generating signing keys and generating/verifying keys and sud files
<li>
 All config files must be UTF-8.
<li>
 To run in a separate JVM, use ShellCommand with java -cp foo:bar:baz my.main.class arg1 arg2 arg3.
Of course, it will be a lot harder to stop the plugin then...
But with some trickery with PID files it should be possible.
<li>
 As an alternative to stopargs in clients.config,
 a Java client may register a shutdown hook with I2PAppContext.addShutdownTask().
 But this wouldn't shut down a plugin when upgrading, so stopargs is recommended.
  Also, set all created threads to daemon mode.
<li>
 Do not include classes duplicating those in the standard installation. Extend the classes if necessary.
<li>
 Beware of the different classpath definitions in wrapper.config between old and new installations -
 see classpath section below.
<li>
 Clients will reject duplicate keys with different keynames, and duplicate keynames with different keys,
  and different keys or keynames in upgrade packages. Safeguard your keys. Only generate them once.
<li>
 Do not modify the plugin.config file at runtime as it will be overwritten on upgrade.
  Use a different config file in the directory for storing runtime configuration.
<li>
 In general, plugins should not require access to $I2P/lib/router.jar. Do not access router classes,
unless you are doing something special.
The router may in the future implement a restricted classpath for plugins that prevents
access to router classes.
<li>
Since each version must be higher than the one before, you could enhance your build
script to add a build number to the end of the version.
This helps for testing. Most of zzz's plugins have that feature, check build.xml for an example.
<li>
Plugins must never call System.exit().
<li>
Please respect licenses by meeting license requirements for any software you bundle.

</ul>

<h3>
Classpaths
</h3>

The following jars in $I2P/lib can be assumed to be in the standard classpath for all I2P installations,
no matter how old or how new the original installation:
<p>
 i2p.jar, router.jar, jbigi.jar, sam.jar, mstreaming.jar, streaming.jar, i2ptunnel.jar,
 org.mortbay.jetty.jar, javax.servlet.jar, jasper-compiler.jar, jasper-runtime.jar,
 commons-logging.jar, commons-el.jar, wrapper.jar, systray.jar, systray4j.jar
<p>

 Anything not listed above may not be present in everybody's classpath, even if you
 have it in the classpath in YOUR version of i2p.
 If you need any jar not listed above, add $I2P/lib/foo.jar to the classpath specified
 in clients.config or webapps.config in your plugin.
<p>
Previously, a classpath entry specified in clients.config was added to the classpath for
the entire JVM.
However, as of 0.7.13-3, this was fixed using class loaders, and now, as originally intended,
the specified classpath in clients.config is only for the particular thread.
See the section on JVM crashes below, and
<a href="http://zzz.i2p/topics/633">this thread on zzz.i2p</a> for background.
Therefore, specify the full required classpath for each client.


<h3>
Java Version Notes
</h3>
While most I2P users are running a 1.6 (6.0) JVM, we support 1.5 (5.0) and higher JVMs.
Unless you require 1.6 features, you should create your plugin so it works on 1.5.
<p>
If your plugin <b>does not require 1.6</b>:
<ul>
<li>
Ensure that all java and jsp files are compiled with source="1.5" target="1.5".
<li>
Ensure that all bundled library jars are also for 1.5 or lower.
<li>
If you are using pack200, any 1.6 classes in a jar will
cause pack200 to create a 1.6 pack format, and
plugin installation will fail on a 1.5 system
with the misleading message "plugin is corrupt".
</ul>

<p>
If your plugin <b>requires 1.6</b>:
<ul>
<li>
Note that on your download page.
<li>
Add min-java-version=1.6 to your plugin.config
<li>
If you are using pack200, plugin installation will fail on a 1.5 system
with the misleading message "plugin is corrupt".
</ul>


<h3>
JVM Crashes When Updating
</h3>
Note - this should all be fixed now.
<p>
The JVM has a tendency to crash when updating jars in a plugin if that plugin was running
since i2p was started (even if the plugin was later stopped).
This may have been fixed with the class loader implementation in 0.7.13-3, but it may not.
For further testing.
<p>
The safest is to design your plugin with the jar inside the war (for a webapp), or to require a restart
after update, or don't update the jars in your plugin.
<p>
Due to the way class loaders work inside a webapp, it _may_ be safe to have external jars if
you specify the classpath in webapps.config.
More testing is required to verify this.
Don't specify the classpath with a 'fake' client in clients.config if it's only
needed for a webapp - use webapps.config instead.
<p>
The least safe, and apparently the source of most crashes, is clients with plugin jars specified
in the classpath in clients.config.

<p>
None of this should be a problem on initial install - you should not ever have to require a restart
for an initial install of a plugin.

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