Migrate KNNEngine interfaces

server/src/main/java/org/opensearch/index/knn/engine/BaseSpaceType.java

@@ -0,0 +1,62 @@
+/*
+ * 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.knn.engine;
+
+/**
+ * Interface contains spaces supported for approximate nearest neighbor search in the k-NN plugin. Each engine's methods are
+ * expected to support a subset of these spaces. Validation should be done in the jni layer and an exception should be
+ * propagated up to the Java layer. Additionally, naming translations should be done in jni layer as well. For example,
+ * nmslib calls the inner_product space "negdotprod". This translation should take place in the nmslib's jni layer.
+ */
+public interface BaseSpaceType {
+    public abstract float scoreTranslation(float rawScore);
+
+    /**
+     * Get KNNVectorSimilarityFunction that maps to this SpaceType
+     *
+     * @return KNNVectorSimilarityFunction
+     */
+    public BaseVectorSimilarityFunction getKnnVectorSimilarityFunction();
+
+    /**
+     * Validate if the given byte vector is supported by this space type
+     *
+     * @param vector     the given vector
+     */
+    public void validateVector(byte[] vector);
+
+    /**
+     * Validate if the given float vector is supported by this space type
+     *
+     * @param vector     the given vector
+     */
+    public void validateVector(float[] vector);
+
+    /**
+     * Validate if given vector data type is supported by this space type
+     *
+     * @param vectorDataType the given vector data type
+     */
+    public void validateVectorDataType(BaseVectorDataType vectorDataType);
+
+    /**
+     * Get space type name in engine
+     *
+     * @return name
+     */
+    public String getValue();
+
+    /**
+     * Translate a score to a distance for this space type
+     *
+     * @param score score to translate
+     * @return translated distance
+     */
+    public float scoreToDistanceTranslation(float score);
+}

server/src/main/java/org/opensearch/index/knn/engine/BaseVectorDataType.java

@@ -0,0 +1,35 @@
+/*
+ * 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.knn.engine;
+
+import org.apache.lucene.document.FieldType;
+import org.apache.lucene.util.BytesRef;
+
+/**
+ * General interface for vector data types
+ */
+public interface BaseVectorDataType {
+    /**
+     * Creates a KnnVectorFieldType based on the VectorDataType using the provided dimension and
+     * VectorSimilarityFunction.
+     *
+     * @param dimension                   Dimension of the vector
+     * @param knnVectorSimilarityFunction KNNVectorSimilarityFunction for a given spaceType
+     * @return FieldType
+     */
+    public FieldType createKnnVectorFieldType(int dimension, BaseVectorSimilarityFunction knnVectorSimilarityFunction);
+
+    /**
+     * Deserializes float vector from BytesRef.
+     *
+     * @param binaryValue Binary Value
+     * @return float vector deserialized from binary value
+     */
+    public float[] getVectorFromBytesRef(BytesRef binaryValue);
+}

server/src/main/java/org/opensearch/index/knn/engine/BaseVectorSimilarityFunction.java

@@ -0,0 +1,23 @@
+/*
+ * 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.knn.engine;
+
+import org.apache.lucene.index.VectorSimilarityFunction;
+
+/**
+ * Wrapper interface of VectorSimilarityFunction to support more function than what Lucene provides
+ */
+public interface BaseVectorSimilarityFunction {
+    public VectorSimilarityFunction getVectorSimilarityFunction();
+
+    public float compare(float[] var1, float[] var2);
+
+    public float compare(byte[] var1, byte[] var2);
+
+}

server/src/main/java/org/opensearch/index/knn/engine/VectorEngine.java

@@ -0,0 +1,38 @@
+/*
+ * 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.knn.engine;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.apache.lucene.util.Version;
+
+/**
+ * VectorEngine is an interface that vector search engines in plugins must implement. It contains methods 
+ * for getting the name and configurations of the engine
+ */
+public interface VectorEngine {
+    /**
+     * Gets the name of the KNNEngine.
+     *
+     * @return the name of the KNNEngine
+     */
+    String getName();
+
+    /**
+     * Gets the version of the library that is being used. In general, this can be used for ensuring compatibility of
+     * serialized artifacts. For instance, this can be used to check if a given file that was created on a different
+     * cluster is compatible with this instance of the library.
+     *
+     * @return the string representing the library's version
+     */
+    default String getVersion() {
+        return Version.LATEST.toString();
+    }
+}

server/src/main/java/org/opensearch/index/knn/engine/package-info.java

@@ -0,0 +1,10 @@
+/*
+ * 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.
+ */
+
+/** Common interfaces for knn plugins to extend. */
+package org.opensearch.index.knn.engine;

server/src/main/java/org/opensearch/plugins/VectorSearchPlugin.java

@@ -0,0 +1,25 @@
+/*
+ * 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.plugins;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.opensearch.index.knn.engine.VectorEngine;
+
+/**
+ * An extension point for {@link Plugin} implementations to add custom knn engine implementations
+ *
+ * @opensearch.api
+ */
+public interface VectorSearchPlugin {
+    default Map<String, VectorEngine> getKnnEngines() {
+        return Collections.emptyMap();
+    }
+}