[[modules-scripting]]
== Scripting

The scripting module allows to use scripts in order to evaluate custom
expressions. For example, scripts can be used to return "script fields"
as part of a search request, or can be used to evaluate a custom score
for a query and so on.

The scripting module uses by default http://groovy.codehaus.org/[groovy]
as the scripting language with some extensions. Groovy is used since it is extremely
fast and very simple to use.

[WARNING]
.Change in Groovy casting behavour
====================================================

The Groovy upgrade in Elasticsearch 1.6.1 fixed a casting bug, which may
change the behaviour of existing scripts which relied on this bug.  For
instance, before the upgrade, the following script would have returned a
`long` value:

[source,js]
-------------------------
(long) _value / 1000 + 1
-------------------------

After the upgrade, the above script will now return a `float` value.  To
return a `long` value, the script should be rewritten as follows:

[source,js]
-------------------------
(long) (_value / 1000 + 1)
-------------------------

See https://issues.apache.org/jira/browse/GROOVY-4421[GROOVY-4421]
and https://issues.apache.org/jira/browse/GROOVY-5185[GROOVY-5185]
for more information.

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


.Groovy dynamic scripting disabled by default from v1.4.3
[IMPORTANT]
===================================================

Elasticsearch versions 1.3.0-1.3.7 and 1.4.0-1.4.2 have a vulnerability in the
Groovy scripting engine.  The vulnerability allows an attacker to construct
Groovy scripts that escape the sandbox and execute shell commands as the user
running the Elasticsearch Java VM.

If you are running a vulnerable version of Elasticsearch, you should either
upgrade to at least v1.3.8 or v1.4.3, or disable dynamic Groovy scripts by
adding this setting to the `config/elasticsearch.yml` file in all nodes in the
cluster:

[source,yaml]
-----------------------------------
script.groovy.sandbox.enabled: false
-----------------------------------

This will turn off the Groovy sandbox, thus preventing dynamic Groovy scripts
from being accepted as part of a request or retrieved from the special
`.scripts` index. You will still be able to use Groovy scripts stored in files
in the `config/scripts/` directory on every node.

To convert an inline script to a file, take this simple script
as an example:

[source,json]
-----------------------------------
GET /_search
{
    "script_fields": {
        "my_field": {
            "script": "1 + my_var",
            "params": {
              "my_var": 2
            }
        }
    }
}
-----------------------------------

Save the contents of the script as a file called `config/scripts/my_script.groovy`
on every data node in the cluster:

[source,js]
-----------------------------------
1 + my_var
-----------------------------------

Now you can access the script by file name (without the extension):

[source,json]
-----------------------------------
GET /_search
{
    "script_fields": {
        "my_field": {
            "script_file": "my_script",
            "params": {
              "my_var": 2
            }
        }
    }
}
-----------------------------------

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


Additional `lang` plugins are provided to allow to execute scripts in
different languages. All places where a `script` parameter can be used, a `lang` parameter
(on the same level) can be provided to define the language of the
script. The following are the supported scripting languages:

[cols="<,<,<",options="header",]
|=======================================================================
|Language   |Sandboxed |Required plugin
|groovy     |no        |built-in
|expression |yes       |built-in
|mustache   |yes       |built-in
|mvel       |no        |https://github.com/elastic/elasticsearch-lang-mvel[elasticsearch-lang-mvel]
|javascript |no        |https://github.com/elastic/elasticsearch-lang-javascript[elasticsearch-lang-javascript]
|python     |no        |https://github.com/elastic/elasticsearch-lang-python[elasticsearch-lang-python]
|=======================================================================

To increase security, Elasticsearch does not allow you to specify scripts for
non-sandboxed languages with a request. Instead, scripts must be placed in the
`scripts` directory inside the configuration directory (the directory where
elasticsearch.yml is). Scripts placed into this directory will automatically be
picked up and be available to be used. Once a script has been placed in this
directory, it can be referenced by name. For example, a script called
`calculate-score.groovy` can be referenced in a request like this:

[source,sh]
--------------------------------------------------
$ tree config
config
├── elasticsearch.yml
├── logging.yml
└── scripts
    └── calculate-score.groovy
--------------------------------------------------

[source,sh]
--------------------------------------------------
$ cat config/scripts/calculate-score.groovy
log(_score * 2) + my_modifier
--------------------------------------------------

[source,js]
--------------------------------------------------
curl -XPOST localhost:9200/_search -d '{
  "query": {
    "function_score": {
      "query": {
        "match": {
          "body": "foo"
        }
      },
      "functions": [
        {
          "script_score": {
            "lang": "groovy",
            "script_file": "calculate-score",
            "params": {
              "my_modifier": 8
            }
          }
        }
      ]
    }
  }
}'
--------------------------------------------------

The name of the script is derived from the hierarchy of directories it
exists under, and the file name without the lang extension. For example,
a script placed under `config/scripts/group1/group2/test.py` will be
named `group1_group2_test`.

[float]
=== Indexed Scripts
Elasticsearch allows you to store scripts in an internal index known as
`.scripts` and reference them by id. There are REST endpoints to manage
indexed scripts as follows:

Requests to the scripts endpoint look like :
[source,js]
-----------------------------------
/_scripts/{lang}/{id}
-----------------------------------
Where the `lang` part is the language the script is in and the `id` part is the id
of the script. In the `.scripts` index the type of the document will be set to the `lang`.


[source,js]
-----------------------------------
curl -XPOST localhost:9200/_scripts/groovy/indexedCalculateScore -d '{
     "script": "log(_score * 2) + my_modifier"
}'
-----------------------------------

This will create a document with id: `indexedCalculateScore` and type: `groovy` in the
`.scripts` index. The type of the document is the language used by the script.

This script can be accessed at query time by appending `_id` to
the script parameter and passing the script id. So `script` becomes `script_id`.:

[source,js]
--------------------------------------------------
curl -XPOST localhost:9200/_search -d '{
  "query": {
    "function_score": {
      "query": {
        "match": {
          "body": "foo"
        }
      },
      "functions": [
        {
          "script_score": {
            "script_id": "indexedCalculateScore",
            "lang" : "groovy",
            "params": {
              "my_modifier": 8
            }
          }
        }
      ]
    }
  }
}'
--------------------------------------------------

The script can be viewed by:
[source,js]
-----------------------------------
curl -XGET localhost:9200/_scripts/groovy/indexedCalculateScore
-----------------------------------

This is rendered as:

[source,js]
-----------------------------------
'{
     "script": "log(_score * 2) + my_modifier"
}'
-----------------------------------

Indexed scripts can be deleted by:
[source,js]
-----------------------------------
curl -XDELETE localhost:9200/_scripts/groovy/indexedCalculateScore
-----------------------------------

[float]
[[enable-dynamic-scripting]]
=== Enabling dynamic scripting

We recommend running Elasticsearch behind an application or proxy, which
protects Elasticsearch from the outside world. If users are allowed to run
inline scripts (even in a search request) or indexed scripts, then they have
the same access to your box as the user that Elasticsearch is running as. For
this reason dynamic scripting is allowed only for sandboxed languages by default.

First, you should not run Elasticsearch as the `root` user, as this would allow
a script to access or do *anything* on your server, without limitations. Second,
you should not expose Elasticsearch directly to users, but instead have a proxy
application inbetween. If you *do* intend to expose Elasticsearch directly to
your users, then you have to decide whether you trust them enough to run scripts
on your box or not.

deprecated[1.6.0, the `script.disable_dynamic` setting is deprecated in favour of fine-grained settings described as follows]

added[1.6.0, Fine-grained script settings replace the `script.disable_dynamic` setting]

It is possible to enable scripts based on their source, for
every script engine, through the following settings that need to be added to the
`config/elasticsearch.yml` file on every node.

[source,yaml]
-----------------------------------
script.inline: on
script.indexed: on

-----------------------------------

While this still allows execution of named scripts provided in the config, or
_native_ Java scripts registered through plugins, it also allows users to run
arbitrary scripts via the API. Instead of sending the name of the file as the
script, the body of the script can be sent instead or retrieved from the
`.scripts` indexed if previously stored.

There are three possible configuration values for any of the fine-grained
script settings:

[cols="<,<",options="header",]
|=======================================================================
|Value |Description
| `off` |scripting is turned off completely, in the context of the setting being set.
| `on`  |scripting is turned on, in the context of the setting being set.
| `sandbox` |scripts may be executed only for languages that are sandboxed
|=======================================================================

The default values are the following:

[source,yaml]
-----------------------------------
script.inline: sandbox
script.indexed: sandbox
script.file: on

-----------------------------------

NOTE: Global scripting settings affect the `mustache` scripting language.
<<search-template,Search templates>> internally use the `mustache` language,
and will still be enabled by default as the `mustache` engine is sandboxed,
but they will be enabled/disabled according to fine-grained settings
specified in `elasticsearch.yml`. added[1.6.0, `mustache` scripts were previously always on regardless of whether dynamic scripts were enabled or not]

It is also possible to control which operations can execute scripts. The
supported operations are:

[cols="<,<",options="header",]
|=======================================================================
|Value |Description
| `aggs`    |Aggregations (wherever they may be used)
| `mapping` |Mappings (script transform feature)
| `search`  |Search api, Percolator api and Suggester api (e.g filters, script_fields)
| `update`  |Update api
| `plugin`  |Any plugin that makes use of scripts under the generic `plugin` category
|=======================================================================

Plugins can also define custom operations that they use scripts for instead
of using the generic `plugin` category. Those operations can be referred to
in the following form: `${pluginName}_${operation}`.

The following example disables scripting for `update` and `mapping` operations,
regardless of the script source, for any engine. Scripts can still be
executed from sandboxed languages as part of `aggregations`, `search`
and plugins execution though, as the above defaults still get applied.

[source,yaml]
-----------------------------------
script.update: off
script.mapping: off

-----------------------------------

Generic settings get applied in order, operation based ones have precedence
over source based ones. Language specific settings are supported too. They
need to be prefixed with the `script.engine.<engine>` prefix and have
precedence over any other generic settings.

[source,yaml]
-----------------------------------
script.engine.groovy.file.aggs: on
script.engine.groovy.file.mapping: on
script.engine.groovy.file.search: on
script.engine.groovy.file.update: on
script.engine.groovy.file.plugin: on
script.engine.groovy.indexed.aggs: on
script.engine.groovy.indexed.mapping: off
script.engine.groovy.indexed.search: on
script.engine.groovy.indexed.update: off
script.engine.groovy.indexed.plugin: off
script.engine.groovy.inline.aggs: on
script.engine.groovy.inline.mapping: off
script.engine.groovy.inline.search: off
script.engine.groovy.inline.update: off
script.engine.groovy.inline.plugin: off

-----------------------------------

[float]
=== Default Scripting Language

The default scripting language (assuming no `lang` parameter is provided) is
`groovy`. In order to change it, set the `script.default_lang` to the
appropriate language.

[float]
=== Groovy Sandboxing

deprecated[1.6.0,Groovy sandboxing has been disabled by default since 1.4.3 because it has proved to be ineffective. It will be removed completely in 2.0.0"]

Elasticsearch sandboxes Groovy scripts that are compiled and executed in order
to ensure they don't perform unwanted actions. There are a number of options
that can be used for configuring this sandbox:

`script.groovy.sandbox.receiver_whitelist`::

    Comma-separated list of string classes for objects that may have methods
    invoked.

`script.groovy.sandbox.package_whitelist`::

    Comma-separated list of packages under which new objects may be constructed.

`script.groovy.sandbox.class_whitelist`::

    Comma-separated list of classes that are allowed to be constructed.

`script.groovy.sandbox.method_blacklist`::

    Comma-separated list of methods that are never allowed to be invoked,
    regardless of target object.

`script.groovy.sandbox.enabled`::

    Flag to enable the sandbox (defaults to `false` meaning the sandbox is
    disabled).

When specifying whitelist or blacklist settings for the groovy sandbox, all
options replace the current whitelist, they are not additive.

[float]
=== Automatic Script Reloading

The `config/scripts` directory is scanned periodically for changes.
New and changed scripts are reloaded and deleted script are removed
from preloaded scripts cache. The reload frequency can be specified
using `watcher.interval` setting, which defaults to `60s`.
To disable script reloading completely set `script.auto_reload_enabled`
to `false`.

[[native-java-scripts]]
[float]
=== Native (Java) Scripts

Even though `groovy` is pretty fast, this allows to register native Java based
scripts for faster execution.

In order to allow for scripts, the `NativeScriptFactory` needs to be
implemented that constructs the script that will be executed. There are
two main types, one that extends `AbstractExecutableScript` and one that
extends `AbstractSearchScript` (probably the one most users will extend,
with additional helper classes in `AbstractLongSearchScript`,
`AbstractDoubleSearchScript`, and `AbstractFloatSearchScript`).

Registering them can either be done by settings, for example:
`script.native.my.type` set to `sample.MyNativeScriptFactory` will
register a script named `my`. Another option is in a plugin, access
`ScriptModule` and call `registerScript` on it.

Executing the script is done by specifying the `lang` as `native`, and
the name of the script as the `script`.

Note, the scripts need to be in the classpath of elasticsearch. One
simple way to do it is to create a directory under plugins (choose a
descriptive name), and place the jar / classes files there. They will be
automatically loaded.

[float]
=== Lucene Expressions Scripts

[WARNING]
========================
This feature is *experimental* and subject to change in future versions.
========================

Lucene's expressions module provides a mechanism to compile a
`javascript` expression to bytecode.  This allows very fast execution,
as if you had written a `native` script.  Expression scripts can be
used in `script_score`, `script_fields`, sort scripts and numeric aggregation scripts.

See the link:http://lucene.apache.org/core/4_9_0/expressions/index.html?org/apache/lucene/expressions/js/package-summary.html[expressions module documentation]
for details on what operators and functions are available.

Variables in `expression` scripts are available to access:

* Single valued document fields, e.g. `doc['myfield'].value`
* Parameters passed into the script, e.g. `mymodifier`
* The current document's score, `_score` (only available when used in a `script_score`)

There are a few limitations relative to other script languages:

* Only numeric fields may be accessed
* Stored fields are not available
* If a field is sparse (only some documents contain a value), documents missing the field will have a value of `0`

[float]
=== Score

In all scripts that can be used in aggregations, the current
document's score is accessible in `_score`.

[float]
=== Computing scores based on terms in scripts

see <<modules-advanced-scripting, advanced scripting documentation>>

[float]
=== Document Fields

Most scripting revolve around the use of specific document fields data.
The `doc['field_name']` can be used to access specific field data within
a document (the document in question is usually derived by the context
the script is used). Document fields are very fast to access since they
end up being loaded into memory (all the relevant field values/tokens
are loaded to memory). Note, however, that the `doc[...]` notation only
allows for simple valued fields (can’t return a json object from it)
and makes sense only on non-analyzed or single term based fields.

The following data can be extracted from a field:

[cols="<,<",options="header",]
|=======================================================================
|Expression |Description
|`doc['field_name'].value` |The native value of the field. For example,
if its a short type, it will be short.

|`doc['field_name'].values` |The native array values of the field. For
example, if its a short type, it will be short[]. Remember, a field can
have several values within a single doc. Returns an empty array if the
field has no values.

|`doc['field_name'].empty` |A boolean indicating if the field has no
values within the doc.

|`doc['field_name'].multiValued` |A boolean indicating that the field
has several values within the corpus.

|`doc['field_name'].lat` |The latitude of a geo point type.

|`doc['field_name'].lon` |The longitude of a geo point type.

|`doc['field_name'].lats` |The latitudes of a geo point type.

|`doc['field_name'].lons` |The longitudes of a geo point type.

|`doc['field_name'].distance(lat, lon)` |The `plane` distance (in meters)
of this geo point field from the provided lat/lon.

|`doc['field_name'].distanceWithDefault(lat, lon, default)` |The `plane` distance (in meters)
of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].distanceInMiles(lat, lon)` |The `plane` distance (in
miles) of this geo point field from the provided lat/lon.

|`doc['field_name'].distanceInMilesWithDefault(lat, lon, default)` |The `plane` distance (in
miles) of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].distanceInKm(lat, lon)` |The `plane` distance (in
km) of this geo point field from the provided lat/lon.

|`doc['field_name'].distanceInKmWithDefault(lat, lon, default)` |The `plane` distance (in
km) of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].arcDistance(lat, lon)` |The `arc` distance (in
meters) of this geo point field from the provided lat/lon.

|`doc['field_name'].arcDistanceWithDefault(lat, lon, default)` |The `arc` distance (in
meters) of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].arcDistanceInMiles(lat, lon)` |The `arc` distance (in
miles) of this geo point field from the provided lat/lon.

|`doc['field_name'].arcDistanceInMilesWithDefault(lat, lon, default)` |The `arc` distance (in
miles) of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].arcDistanceInKm(lat, lon)` |The `arc` distance (in
km) of this geo point field from the provided lat/lon.

|`doc['field_name'].arcDistanceInKmWithDefault(lat, lon, default)` |The `arc` distance (in
km) of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].factorDistance(lat, lon)` |The distance factor of this geo point field from the provided lat/lon.

|`doc['field_name'].factorDistance(lat, lon, default)` |The distance factor of this geo point field from the provided lat/lon with a default value.

|`doc['field_name'].geohashDistance(geohash)` |The `arc` distance (in meters)
of this geo point field from the provided geohash.

|`doc['field_name'].geohashDistanceInKm(geohash)` |The `arc` distance (in km)
of this geo point field from the provided geohash.

|`doc['field_name'].geohashDistanceInMiles(geohash)` |The `arc` distance (in
miles) of this geo point field from the provided geohash.
|=======================================================================

[float]
=== Stored Fields

Stored fields can also be accessed when executing a script. Note, they
are much slower to access compared with document fields, as they are not
loaded into memory. They can be simply accessed using
`_fields['my_field_name'].value` or `_fields['my_field_name'].values`.

[float]
=== Accessing the score of a document within a script

When using scripting for calculating the score of a document (for instance, with
the `function_score` query), you can access the score using the `_score`
variable inside of a Groovy script.

[float]
=== Source Field

The source field can also be accessed when executing a script. The
source field is loaded per doc, parsed, and then provided to the script
for evaluation. The `_source` forms the context under which the source
field can be accessed, for example `_source.obj2.obj1.field3`.

Accessing `_source` is much slower compared to using `doc`
but the data is not loaded into memory. For a single field access `_fields` may be
faster than using `_source` due to the extra overhead of potentially parsing large documents.
However, `_source` may be faster if you access multiple fields or if the source has already been
loaded for other purposes.


[float]
=== Groovy Built In Functions

There are several built in functions that can be used within scripts.
They include:

[cols="<,<",options="header",]
|=======================================================================
|Function |Description
|`sin(a)` |Returns the trigonometric sine of an angle.

|`cos(a)` |Returns the trigonometric cosine of an angle.

|`tan(a)` |Returns the trigonometric tangent of an angle.

|`asin(a)` |Returns the arc sine of a value.

|`acos(a)` |Returns the arc cosine of a value.

|`atan(a)` |Returns the arc tangent of a value.

|`toRadians(angdeg)` |Converts an angle measured in degrees to an
approximately equivalent angle measured in radians

|`toDegrees(angrad)` |Converts an angle measured in radians to an
approximately equivalent angle measured in degrees.

|`exp(a)` |Returns Euler's number _e_ raised to the power of value.

|`log(a)` |Returns the natural logarithm (base _e_) of a value.

|`log10(a)` |Returns the base 10 logarithm of a value.

|`sqrt(a)` |Returns the correctly rounded positive square root of a
value.

|`cbrt(a)` |Returns the cube root of a double value.

|`IEEEremainder(f1, f2)` |Computes the remainder operation on two
arguments as prescribed by the IEEE 754 standard.

|`ceil(a)` |Returns the smallest (closest to negative infinity) value
that is greater than or equal to the argument and is equal to a
mathematical integer.

|`floor(a)` |Returns the largest (closest to positive infinity) value
that is less than or equal to the argument and is equal to a
mathematical integer.

|`rint(a)` |Returns the value that is closest in value to the argument
and is equal to a mathematical integer.

|`atan2(y, x)` |Returns the angle _theta_ from the conversion of
rectangular coordinates (_x_, _y_) to polar coordinates (r,_theta_).

|`pow(a, b)` |Returns the value of the first argument raised to the
power of the second argument.

|`round(a)` |Returns the closest _int_ to the argument.

|`random()` |Returns a random _double_ value.

|`abs(a)` |Returns the absolute value of a value.

|`max(a, b)` |Returns the greater of two values.

|`min(a, b)` |Returns the smaller of two values.

|`ulp(d)` |Returns the size of an ulp of the argument.

|`signum(d)` |Returns the signum function of the argument.

|`sinh(x)` |Returns the hyperbolic sine of a value.

|`cosh(x)` |Returns the hyperbolic cosine of a value.

|`tanh(x)` |Returns the hyperbolic tangent of a value.

|`hypot(x, y)` |Returns sqrt(_x2_ + _y2_) without intermediate overflow
or underflow.
|=======================================================================

[float]
=== Arithmetic precision in MVEL

When dividing two numbers using MVEL based scripts, the engine tries to
be smart and adheres to the default behaviour of java. This means if you
divide two integers (you might have configured the fields as integer in
the mapping), the result will also be an integer. This means, if a
calculation like `1/num` is happening in your scripts and `num` is an
integer with the value of `8`, the result is `0` even though you were
expecting it to be `0.125`. You may need to enforce precision by
explicitly using a double like `1.0/num` in order to get the expected
result.

