Adds example plugin for custom ingest processor (#112282)

* Adds example plugin for custom ingest processor

Adds an example for creating a plugin with a simple custom ingest
processor. The example processor repeats the value of an expected filed
in a document, or ignores it if the expected field does not exist.

Closes #111539

docs/changelog/112282.yaml

@@ -0,0 +1,6 @@
+pr: 112282
+summary: Adds example plugin for custom ingest processor
+area: Ingest Node
+type: enhancement
+issues:
+ - 111539

docs/plugins/development/creating-classic-plugins.asciidoc

@@ -32,12 +32,13 @@ for the plugin. If you need other resources, package them into a resources JAR.
 The {es} repository contains {es-repo}tree/main/plugins/examples[examples of plugins]. Some of these include:
 
 * a plugin with {es-repo}tree/main/plugins/examples/custom-settings[custom settings]
+* a plugin with a {es-repo}tree/main/plugins/examples/custom-processor[custom ingest processor]
 * adding {es-repo}tree/main/plugins/examples/rest-handler[custom rest endpoints]
 * adding a {es-repo}tree/main/plugins/examples/rescore[custom rescorer]
 * a script {es-repo}tree/main/plugins/examples/script-expert-scoring[implemented in Java]
 
 These examples provide the bare bones needed to get started. For more
-information about how to write a plugin, we recommend looking at the 
+information about how to write a plugin, we recommend looking at the
 {es-repo}tree/main/plugins/[source code of existing plugins] for inspiration.
 
 [discrete]
@@ -88,4 +89,4 @@ for more information.
 [[plugin-descriptor-file-classic]]
 ==== The plugin descriptor file for classic plugins
 
-include::plugin-descriptor-file.asciidoc[]
+include::plugin-descriptor-file.asciidoc[]

plugins/examples/custom-processor/build.gradle

@@ -0,0 +1,21 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+apply plugin: 'elasticsearch.esplugin'
+apply plugin: 'elasticsearch.yaml-rest-test'
+
+esplugin {
+  name 'custom-processor'
+  description 'An example plugin showing how to register a custom ingest processor'
+  classname 'org.elasticsearch.example.customprocessor.ExampleProcessorPlugin'
+  licenseFile rootProject.file('SSPL-1.0+ELASTIC-LICENSE-2.0.txt')
+  noticeFile rootProject.file('NOTICE.txt')
+}
+
+dependencies {
+  yamlRestTestRuntimeOnly "org.apache.logging.log4j:log4j-core:${log4jVersion}"
+}

plugins/examples/custom-processor/src/main/java/org/elasticsearch/example/customprocessor/ExampleProcessorPlugin.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.example.customprocessor;
+
+import org.elasticsearch.ingest.Processor;
+import org.elasticsearch.plugins.IngestPlugin;
+import org.elasticsearch.plugins.Plugin;
+
+import java.util.Map;
+
+public class ExampleProcessorPlugin extends Plugin implements IngestPlugin {
+
+    @Override
+    public Map<String, Processor.Factory> getProcessors(Processor.Parameters parameters) {
+        return Map.of(ExampleRepeatProcessor.TYPE, new ExampleRepeatProcessor.Factory());
+    }
+}

plugins/examples/custom-processor/src/main/java/org/elasticsearch/example/customprocessor/ExampleRepeatProcessor.java

@@ -0,0 +1,53 @@
+package org.elasticsearch.example.customprocessor;
+
+import org.elasticsearch.ingest.AbstractProcessor;
+import org.elasticsearch.ingest.ConfigurationUtils;
+import org.elasticsearch.ingest.IngestDocument;
+import org.elasticsearch.ingest.Processor;
+
+import java.util.Map;
+
+/**
+ * Example of adding an ingest processor with a plugin.
+ */
+public class ExampleRepeatProcessor extends AbstractProcessor {
+    public static final String TYPE = "repeat";
+    public static final String FIELD_KEY_NAME = "field";
+
+    private final String field;
+
+    ExampleRepeatProcessor(String tag, String description, String field) {
+        super(tag, description);
+        this.field = field;
+    }
+
+    @Override
+    public IngestDocument execute(IngestDocument document) {
+        Object val = document.getFieldValue(field, Object.class, true);
+
+        if (val instanceof String string) {
+            String repeated = string.concat(string);
+            document.setFieldValue(field, repeated);
+        }
+        return document;
+    }
+
+    @Override
+    public String getType() {
+        return TYPE;
+    }
+
+    public static class Factory implements Processor.Factory {
+
+        @Override
+        public ExampleRepeatProcessor create(
+            Map<String, Processor.Factory> registry,
+            String tag,
+            String description,
+            Map<String, Object> config
+        ) {
+            String field = ConfigurationUtils.readStringProperty(TYPE, tag, config, FIELD_KEY_NAME);
+            return new ExampleRepeatProcessor(tag, description, field);
+        }
+    }
+}

plugins/examples/custom-processor/src/yamlRestTest/java/org/elasticsearch/example/customprocessor/ExampleProcessorClientYamlTestSuiteIT.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+package org.elasticsearch.example.customprocessor;
+
+import com.carrotsearch.randomizedtesting.annotations.Name;
+import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
+import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
+import org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase;
+
+/**
+ * {@link ExampleProcessorClientYamlTestSuiteIT} executes the plugin's REST API integration tests.
+ * <p>
+ * The tests can be executed using the command: ./gradlew :custom-processor:yamlRestTest
+ * <p>
+ * This class extends {@link ESClientYamlSuiteTestCase}, which takes care of parsing the YAML files
+ * located in the src/yamlRestTest/resources/rest-api-spec/test/ directory and validates them against the
+ * custom REST API definition files located in src/yamlRestTest/resources/rest-api-spec/api/.
+ * <p>
+ * Once validated, {@link ESClientYamlSuiteTestCase} executes the REST tests against a single node
+ * integration cluster which has the plugin already installed by the Gradle build script.
+ * </p>
+ */
+public class ExampleProcessorClientYamlTestSuiteIT extends ESClientYamlSuiteTestCase {
+
+    public ExampleProcessorClientYamlTestSuiteIT(@Name("yaml") ClientYamlTestCandidate testCandidate) {
+        super(testCandidate);
+    }
+
+    @ParametersFactory
+    public static Iterable<Object[]> parameters() throws Exception {
+        // The test executes all the test candidates by default
+        // see ESClientYamlSuiteTestCase.REST_TESTS_SUITE
+        return ESClientYamlSuiteTestCase.createParameters();
+    }
+}

plugins/examples/custom-processor/src/yamlRestTest/resources/rest-api-spec/test/customprocessor/10_basic.yml

@@ -0,0 +1,15 @@
+"Custom processor is present":
+  - do:
+      ingest.put_pipeline:
+        id: pipeline1
+        body:  >
+          {
+            "processors": [
+              {
+                "repeat" : {
+                  "field": "test"
+                }
+              }
+            ]
+          }
+  - match: { acknowledged: true }

plugins/examples/custom-processor/src/yamlRestTest/resources/rest-api-spec/test/customprocessor/20_process_document.yml

@@ -0,0 +1,59 @@
+setup:
+  - do:
+      ingest.put_pipeline:
+        id: pipeline1
+        body:  >
+          {
+            "processors": [
+              {
+                "repeat" : {
+                  "field": "to_repeat"
+                }
+              }
+            ]
+          }
+---
+teardown:
+  - do:
+      ingest.delete_pipeline:
+        id: pipeline1
+        ignore: 404
+
+  - do:
+      indices.delete:
+        index: index1
+        ignore: 404
+---
+"Process document":
+  # index a document with field to be processed
+  - do:
+      index:
+        id: doc1
+        index: index1
+        pipeline: pipeline1
+        body: { to_repeat: "foo" }
+  - match: { result: "created" }
+
+  # validate document is processed
+  - do:
+      get:
+        index: index1
+        id: doc1
+  - match: { _source: { to_repeat: "foofoo" } }
+---
+"Does not process document without field":
+  # index a document without field to be processed
+  - do:
+      index:
+        id: doc1
+        index: index1
+        pipeline: pipeline1
+        body: { field1: "foo" }
+  - match: { result: "created" }
+
+  # validate document is not processed
+  - do:
+      get:
+        index: index1
+        id: doc1
+  - match: { _source: { field1: "foo" } }