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Elasticsearch-Lang-Kotlin

Kotlin scripting language for Elasticsearch. This includes both text scripts and also binary scripts (serialized lambdas sent from the client to execute in the Elasticsearch engine).

A client library is provided that adds extension functions for the Elasticsearch client making it easy to send lambdas as scripts.

see example video: https://vimeo.com/apatrida/es-lang-kotlin (older, but the idea is valid)

BETA release, use at your own risk, for testing purposes only.

Guide

TODO: this is rough guide, but will get you started.

With the plugin enabled, you can run Kotlin scripts in one of two ways:

  • Text based script, which is same as most scripting languages in Elasticsearch.
  • Inline Lambda that is shipped to the server as binary and executed.

In both models, the scripts are validated against the same permission policies as Painless scripting language uses, with some extensions allowing Kotlin stdlib to work. In fact Kotlin stdlib is first validated against the Painless whitelist and anything that passes is allowed to be used.

An example of using a Text based script (works from any language, here the example is in Kotlin but could easily be and development language, or even CURL):

val prep = client.prepareSearch("myIndex")
        .addKotlinScriptField("scriptField1", Script(ScriptType.INLINE, "kotlin", 
          """
            val currentValue = doc.stringVal("badContent") ?: ""
            "^(\\w+)\\s*\\:\\s*(.+)$".toRegex().matchEntire(currentValue)
                    ?.takeIf { it.groups.size > 2 }
                    ?.let {
                        val typeName = it.groups[1]!!.value.toLowerCase()
                        it.groups[2]!!.value.split(',')
                                .map { it.trim().toLowerCase() }
                                .filterNot { it.isBlank() }
                                .map { typeName + ": " + it }
                    } ?: listOf(currentValue)
          """, emptyMap()))
        .setQuery(...)

And a lambda version allows you to use a lambda or function reference as a script (this sample uses the elasticsearch-lang-kotlin-client client library to make this easier and transparent):

val query = client.prepareSearch("myIndex")
            .addKotlinScriptField("scriptField1", emptyMap()) {
                val currentValue = doc["badContent"].asList<String>()
                currentValue.map { value -> badCategoryPattern.toRegex().matchEntire(value)?.takeIf { it.groups.size > 2 } }
                        .filterNotNull()
                        .map {
                            val typeName = it.groups[1]!!.value.toLowerCase()
                            it.groups[2]!!.value.split(',')
                                    .map { it.trim().toLowerCase() }
                                    .filterNot { it.isBlank() }
                                    .map { "$typeName: $it" }
                        }.flatten()
            }.setQuery(...)

or another example of update by query:

val updateQuery = UpdateByQueryAction.INSTANCE.newRequestBuilder(client)
                    .setKotlinScript {
                        val num = _source["number"].asValue(0)
                        if (num >= 4) {
                            ctx["op"] = "delete"
                        } else {
                            _source["number"] = num + 1
                        }
                    }.source("myIndex").filter(...)

To see what helper methods are available to access values from the document, view the base class that your script will inherit: ScriptTemplate.kt

Some tips for accessing common properties:

field syntax notes
ctx._source _source This always checks internally ctx._source then _source so you do not have to special case which one is correct
ctx.value ctx["value"] Reference as a hash lookup
_source _source same, direct reference
doc["field"] doc["field"] Reference as a hash lookup.
doc.field doc["field"] Reference as a hash lookup
_source.field _source["field"] Reference as a hash lookup
params.name param["name"] Reference as a hash lookup
params._agg _agg This actually comes from params["_agg"] internall
_score _score Double value
_value _value Any? value

When using a value you can access it as either single value asValue() or asValue(default) and as a list with asList(). If type cannot be infered, add the type on the call, for example asValue<Int>(). You can also just use the value directly but then you will need to cast it to the correct type. asValue() will do a conversion on basic types if possible.

Both the client library and the script template will surely change, so expect large changes as they are used to build out realistic test cases for every script type in Elasticsearch. Consider these two elements more ALPHA while the rest of the engine is more BETA.

Server Installation:

Plugin Version Client Extension Version Elasticsearch Version Kotlin Version Notes
1.0.0-ES-5.6.7-BETA-06 1.0.0-BETA-06 Elasticsearch 5.6.7 Kotlin 1.2.21
1.0.0-ES-6.2.4-BETA-07 1.0.0-BETA-07 Elasticsearch 6.2.4 Kotlin 1.2.31 current

More information is available under each release.

Install on server using (replace version number with the one you intend to use):

bin/elasticsearch-plugin install https://github.com/kohesive/elasticsearch-lang-kotlin/releases/download/v1.0.0-ES-6.2.4-BETA-07/lang-kotlin-1.0.0-ES-6.2.4-BETA-07.zip

NOTE: You must accept the security permissions, these are only used for the compiler and not scripts which do not run with any extra privileges.

For Elasticsearch versions 5.x, a cluster must enable this setting to use inline Kotlin scripts (and also for Lambdas which appear to be inline scripts to Elasticsearch):

script.engine.kotlin.inline: true

For 6.x this is not required and will result in an error.

(Read script security settings for more information.)

Client Extensions (for Kotlin):

For client library containing extension functions for Kotlin, use the follow artifact from Gradle or Maven:

uy.kohesive.elasticsearch:elasticsearch-lang-kotlin-client:1.0.0-BETA-07

(note that the version number might slightly differ as updates are added to the client that do not require a new server plugin update)

TODO:

  • Smooth out the template class for easier access to everything with less code, still type safe
  • Special case things like Scripted Metric Aggregation to basically hand in the parameters that are needed
  • Special case the template class for different script contexts, AGGS("aggs"), SEARCH("search"), UPDATE("update"), INGEST("ingest");

Development:

NOTE for running tests, you need to run tests with:

 -Djava.security.policy=elasticsearch-lang-kotlin-plugin/src/main/plugin-metadata/plugin-security.policy

Special Thanks

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Elasticsearch plugin for Kotlin Scripting (both text and binary lambda scripting)

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