[Backport 2.x] feat: constant keyword field

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ## [Unreleased 2.x]
 ### Added
 - Add explicit dependency to validatePom and generatePom tasks ([#12909](https://github.com/opensearch-project/OpenSearch/pull/12909))
+- Constant Keyword Field ([#12285](https://github.com/opensearch-project/OpenSearch/pull/12285))
 - [Concurrent Segment Search] Perform buildAggregation concurrently and support Composite Aggregations ([#12697](https://github.com/opensearch-project/OpenSearch/pull/12697))
 - Convert ingest processor supports ip type ([#12818](https://github.com/opensearch-project/OpenSearch/pull/12818))
 - Allow setting KEYSTORE_PASSWORD through env variable ([#12865](https://github.com/opensearch-project/OpenSearch/pull/12865))

server/src/main/java/org/opensearch/index/mapper/ConstantKeywordFieldMapper.java

@@ -0,0 +1,191 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.mapper;
+
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.Query;
+import org.opensearch.OpenSearchParseException;
+import org.opensearch.common.annotation.PublicApi;
+import org.opensearch.common.regex.Regex;
+import org.opensearch.index.fielddata.IndexFieldData;
+import org.opensearch.index.fielddata.plain.ConstantIndexFieldData;
+import org.opensearch.index.query.QueryShardContext;
+import org.opensearch.search.aggregations.support.CoreValuesSourceType;
+import org.opensearch.search.lookup.SearchLookup;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Supplier;
+
+/**
+ * Index specific field mapper
+ *
+ * @opensearch.api
+ */
+@PublicApi(since = "2.14.0")
+public class ConstantKeywordFieldMapper extends ParametrizedFieldMapper {
+
+    public static final String CONTENT_TYPE = "constant_keyword";
+
+    private static final String valuePropertyName = "value";
+
+    /**
+     * A {@link Mapper.TypeParser} for the constant keyword field.
+     *
+     * @opensearch.internal
+     */
+    public static class TypeParser implements Mapper.TypeParser {
+        @Override
+        public Mapper.Builder parse(String name, Map<String, Object> node, ParserContext parserContext) throws MapperParsingException {
+            if (!node.containsKey(valuePropertyName)) {
+                throw new OpenSearchParseException("Field [" + name + "] is missing required parameter [value]");
+            }
+            Object value = node.remove(valuePropertyName);
+            if (!(value instanceof String)) {
+                throw new OpenSearchParseException("Field [" + name + "] is expected to be a string value");
+            }
+            return new Builder(name, (String) value);
+        }
+    }
+
+    private static ConstantKeywordFieldMapper toType(FieldMapper in) {
+        return (ConstantKeywordFieldMapper) in;
+    }
+
+    /**
+     * Builder for the binary field mapper
+     *
+     * @opensearch.internal
+     */
+    public static class Builder extends ParametrizedFieldMapper.Builder {
+
+        private final Parameter<String> value;
+
+        public Builder(String name, String value) {
+            super(name);
+            this.value = Parameter.stringParam(valuePropertyName, false, m -> toType(m).value, value);
+        }
+
+        @Override
+        public List<Parameter<?>> getParameters() {
+            return Arrays.asList(value);
+        }
+
+        @Override
+        public ConstantKeywordFieldMapper build(BuilderContext context) {
+            return new ConstantKeywordFieldMapper(
+                name,
+                new ConstantKeywordFieldMapper.ConstantKeywordFieldType(buildFullName(context), value.getValue()),
+                multiFieldsBuilder.build(this, context),
+                copyTo.build(),
+                this
+            );
+        }
+    }
+
+    /**
+     * Field type for Index field mapper
+     *
+     * @opensearch.internal
+     */
+    @PublicApi(since = "2.14.0")
+    protected static final class ConstantKeywordFieldType extends ConstantFieldType {
+
+        protected final String value;
+
+        public ConstantKeywordFieldType(String name, String value) {
+            super(name, Collections.emptyMap());
+            this.value = value;
+        }
+
+        @Override
+        public String typeName() {
+            return CONTENT_TYPE;
+        }
+
+        @Override
+        protected boolean matches(String pattern, boolean caseInsensitive, QueryShardContext context) {
+            return Regex.simpleMatch(pattern, value, caseInsensitive);
+        }
+
+        @Override
+        public Query existsQuery(QueryShardContext context) {
+            return new MatchAllDocsQuery();
+        }
+
+        @Override
+        public IndexFieldData.Builder fielddataBuilder(String fullyQualifiedIndexName, Supplier<SearchLookup> searchLookup) {
+            return new ConstantIndexFieldData.Builder(fullyQualifiedIndexName, name(), CoreValuesSourceType.BYTES);
+        }
+
+        @Override
+        public ValueFetcher valueFetcher(QueryShardContext context, SearchLookup searchLookup, String format) {
+            if (format != null) {
+                throw new IllegalArgumentException("Field [" + name() + "] of type [" + typeName() + "] doesn't " + "support formats.");
+            }
+
+            return new SourceValueFetcher(name(), context) {
+                @Override
+                protected Object parseSourceValue(Object value) {
+                    String keywordValue = value.toString();
+                    return Collections.singletonList(keywordValue);
+                }
+            };
+        }
+    }
+
+    private final String value;
+
+    protected ConstantKeywordFieldMapper(
+        String simpleName,
+        MappedFieldType mappedFieldType,
+        MultiFields multiFields,
+        CopyTo copyTo,
+        ConstantKeywordFieldMapper.Builder builder
+    ) {
+        super(simpleName, mappedFieldType, multiFields, copyTo);
+        this.value = builder.value.getValue();
+    }
+
+    public ParametrizedFieldMapper.Builder getMergeBuilder() {
+        return new ConstantKeywordFieldMapper.Builder(simpleName(), this.value).init(this);
+    }
+
+    @Override
+    protected void parseCreateField(ParseContext context) throws IOException {
+
+        final String value;
+        if (context.externalValueSet()) {
+            value = context.externalValue().toString();
+        } else {
+            value = context.parser().textOrNull();
+        }
+        if (value == null) {
+            throw new IllegalArgumentException("constant keyword field [" + name() + "] must have a value");
+        }
+
+        if (!value.equals(fieldType().value)) {
+            throw new IllegalArgumentException("constant keyword field [" + name() + "] must have a value of [" + this.value + "]");
+        }
+
+    }
+
+    @Override
+    public ConstantKeywordFieldMapper.ConstantKeywordFieldType fieldType() {
+        return (ConstantKeywordFieldMapper.ConstantKeywordFieldType) super.fieldType();
+    }
+
+    @Override
+    protected String contentType() {
+        return CONTENT_TYPE;
+    }
+}

server/src/main/java/org/opensearch/indices/IndicesModule.java

@@ -46,6 +46,7 @@
 import org.opensearch.index.mapper.BinaryFieldMapper;
 import org.opensearch.index.mapper.BooleanFieldMapper;
 import org.opensearch.index.mapper.CompletionFieldMapper;
+import org.opensearch.index.mapper.ConstantKeywordFieldMapper;
 import org.opensearch.index.mapper.DataStreamFieldMapper;
 import org.opensearch.index.mapper.DateFieldMapper;
 import org.opensearch.index.mapper.DocCountFieldMapper;
@@ -168,6 +169,7 @@ public static Map<String, Mapper.TypeParser> getMappers(List<MapperPlugin> mappe
         mappers.put(FieldAliasMapper.CONTENT_TYPE, new FieldAliasMapper.TypeParser());
         mappers.put(GeoPointFieldMapper.CONTENT_TYPE, new GeoPointFieldMapper.TypeParser());
         mappers.put(FlatObjectFieldMapper.CONTENT_TYPE, FlatObjectFieldMapper.PARSER);
+        mappers.put(ConstantKeywordFieldMapper.CONTENT_TYPE, new ConstantKeywordFieldMapper.TypeParser());
 
         for (MapperPlugin mapperPlugin : mapperPlugins) {
             for (Map.Entry<String, Mapper.TypeParser> entry : mapperPlugin.getMappers().entrySet()) {

server/src/test/java/org/opensearch/index/mapper/ConstantKeywordFieldMapperTests.java

@@ -0,0 +1,114 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.index.mapper;
+
+import org.apache.lucene.index.IndexableField;
+import org.opensearch.OpenSearchParseException;
+import org.opensearch.common.CheckedConsumer;
+import org.opensearch.common.compress.CompressedXContent;
+import org.opensearch.common.xcontent.XContentFactory;
+import org.opensearch.common.xcontent.json.JsonXContent;
+import org.opensearch.core.common.bytes.BytesReference;
+import org.opensearch.core.xcontent.MediaTypeRegistry;
+import org.opensearch.core.xcontent.XContentBuilder;
+import org.opensearch.index.IndexService;
+import org.opensearch.plugins.Plugin;
+import org.opensearch.test.InternalSettingsPlugin;
+import org.opensearch.test.OpenSearchSingleNodeTestCase;
+import org.junit.Before;
+
+import java.io.IOException;
+import java.util.Collection;
+
+import static org.hamcrest.Matchers.containsString;
+
+public class ConstantKeywordFieldMapperTests extends OpenSearchSingleNodeTestCase {
+
+    private IndexService indexService;
+    private DocumentMapperParser parser;
+
+    @Override
+    protected Collection<Class<? extends Plugin>> getPlugins() {
+        return pluginList(InternalSettingsPlugin.class);
+    }
+
+    @Before
+    public void setup() {
+        indexService = createIndex("test");
+        parser = indexService.mapperService().documentMapperParser();
+    }
+
+    public void testDefaultDisabledIndexMapper() throws Exception {
+
+        XContentBuilder mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("type")
+            .startObject("properties")
+            .startObject("field")
+            .field("type", "constant_keyword")
+            .field("value", "default_value")
+            .endObject()
+            .startObject("field2")
+            .field("type", "keyword")
+            .endObject();
+        mapping = mapping.endObject().endObject().endObject();
+        DocumentMapper mapper = parser.parse("type", new CompressedXContent(mapping.toString()));
+
+        MapperParsingException e = expectThrows(MapperParsingException.class, () -> mapper.parse(source(b -> {
+            b.field("field", "sdf");
+            b.field("field2", "szdfvsddf");
+        })));
+        assertThat(
+            e.getMessage(),
+            containsString(
+                "failed to parse field [field] of type [constant_keyword] in document with id '1'. Preview of field's value: 'sdf'"
+            )
+        );
+
+        final ParsedDocument doc = mapper.parse(source(b -> {
+            b.field("field", "default_value");
+            b.field("field2", "field_2_value");
+        }));
+
+        final IndexableField field = doc.rootDoc().getField("field");
+
+        // constantKeywordField should not be stored
+        assertNull(field);
+    }
+
+    public void testMissingDefaultIndexMapper() throws Exception {
+
+        final XContentBuilder mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("type")
+            .startObject("properties")
+            .startObject("field")
+            .field("type", "constant_keyword")
+            .endObject()
+            .startObject("field2")
+            .field("type", "keyword")
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject();
+
+        OpenSearchParseException e = expectThrows(
+            OpenSearchParseException.class,
+            () -> parser.parse("type", new CompressedXContent(mapping.toString()))
+        );
+        assertThat(e.getMessage(), containsString("Field [field] is missing required parameter [value]"));
+    }
+
+    private final SourceToParse source(CheckedConsumer<XContentBuilder, IOException> build) throws IOException {
+        XContentBuilder builder = JsonXContent.contentBuilder().startObject();
+        build.accept(builder);
+        builder.endObject();
+        return new SourceToParse("test", "1", BytesReference.bytes(builder), MediaTypeRegistry.JSON);
+    }
+}