[[plugin-authors]]
== Help for plugin authors

The Elasticsearch repository contains examples of:

* a https://github.com/elastic/elasticsearch/tree/master/plugins/site-example[site plugin]
  for serving static HTML, JavaScript, and CSS.
* a https://github.com/elastic/elasticsearch/tree/master/plugins/jvm-example[Java plugin]
  which contains Java code.

These examples provide the bare bones needed to get started.  For more
information about how to write a plugin, we recommend looking at the plugins
listed in this documentation for inspiration.

[NOTE]
.Site plugins
====================================

The example site plugin mentioned above contains all of the scaffolding needed
for integrating with Maven builds.  If you don't plan on using Maven, then all
you really need in your plugin is:

* The `plugin-descriptor.properties` file
* The `_site/` directory
* The `_site/index.html` file

====================================

[float]
=== Plugin descriptor file

All plugins, be they site or Java plugins, must contain a file called
`plugin-descriptor.properties` in the root directory. The format for this file
is described in detail  here:

https://github.com/elastic/elasticsearch/blob/master/dev-tools/src/main/resources/plugin-metadata/plugin-descriptor.properties[`dev-tools/src/main/resources/plugin-metadata/plugin-descriptor.properties`].

Either fill in this template yourself (see
https://github.com/lmenezes/elasticsearch-kopf/blob/master/plugin-descriptor.properties[elasticsearch-kopf]
as an example) or, if you are using Elasticsearch's Maven build system, you
can fill in the necessary values in the `pom.xml` for your plugin. For
instance, see
https://github.com/elastic/elasticsearch/blob/master/plugins/site-example/pom.xml[`plugins/site-example/pom.xml`].

[float]
==== Mandatory elements for all plugins


[cols="<,<,<",options="header",]
|=======================================================================
|Element                    | Type   | Description

|`description`              |String  | simple summary of the plugin

|`version`                  |String  | plugin's version

|`name`                     |String  | the plugin name

|=======================================================================



[float]
==== Mandatory elements for Java plugins


[cols="<,<,<",options="header",]
|=======================================================================
|Element                    | Type   | Description

|`jvm`                      |Boolean | true if the `classname` class should be loaded
from jar files in the root directory of the plugin.
Note that only jar files in the root directory are added to the classpath for the plugin!
If you need other resources, package them into a resources jar.

|`classname`                |String  | the name of the class to load, fully-qualified.

|`java.version`             |String  | version of java the code is built against.
Use the system property `java.specification.version`. Version string must be a sequence
of nonnegative decimal integers separated by "."'s and may have leading zeros.

|`elasticsearch.version`    |String  | version of elasticsearch compiled against.

|=======================================================================

[IMPORTANT]
.Plugin release lifecycle
==============================================

You will have to release a new version of the plugin for each new elasticsearch release.
This version is checked when the plugin is loaded so Elasticsearch will refuse to start
in the presence of plugins with the incorrect `elasticsearch.version`.

==============================================


[float]
==== Mandatory elements for Site plugins


[cols="<,<,<",options="header",]
|=======================================================================
|Element                    | Type   | Description

|`site`                     |Boolean | true to indicate contents of the `_site/`
directory in the root of the plugin should be served.

|=======================================================================


[float]
=== Testing your plugin

When testing a Java plugin, it will only be auto-loaded if it is in the
`plugins/` directory.  Use `bin/plugin install file://path/to/your/plugin`
to install your plugin for testing.

You may also load your plugin within the test framework for integration tests.
Read more in {ref}/integration-tests.html#changing-node-configuration[Changing Node Configuration].


[float]
=== Java Security permissions

Some plugins may need additional security permissions. A plugin can include
the optional `plugin-security.policy` file containing `grant` statements for 
additional permissions. Any additional permissions will be displayed to the user 
with a large warning, and they will have to confirm them when installing the 
plugin interactively. So if possible, it is best to avoid requesting any
spurious permissions!

If you are using the elasticsearch Maven build system, place this file in
`src/main/plugin-metadata` and it will be applied during unit tests as well.

Keep in mind that the Java security model is stack-based, and the additional
permissions will only be granted to the jars in your plugin, so you will have
write proper security code around operations requiring elevated privileges.
It is recommended to add a check to prevent unprivileged code (such as scripts)
from gaining escalated permissions. For example:

[source,java]
--------------------------------------------------
// ES permission you should check before doPrivileged() blocks
import org.elasticsearch.SpecialPermission;

SecurityManager sm = System.getSecurityManager();
if (sm != null) {
  // unprivileged code such as scripts do not have SpecialPermission
  sm.checkPermission(new SpecialPermission());
}
AccessController.doPrivileged(
  // sensitive operation
);
--------------------------------------------------

See http://www.oracle.com/technetwork/java/seccodeguide-139067.html[Secure Coding Guidelines for Java SE]
for more information.