Added extension Points, initial REST implementation and registering T…

…ransport Actions for extensions (#5518)

* Merge second batch of feature/extensions into main

Signed-off-by: Ryan Bogan <rbogan@amazon.com>

* Update CHANGELOG

Signed-off-by: Ryan Bogan <rbogan@amazon.com>

* Change logger level from info to bug for one call

Signed-off-by: Ryan Bogan <rbogan@amazon.com>

* Removed extension NamedWriteableRegistry implementation and added TODO comments

Signed-off-by: Ryan Bogan <rbogan@amazon.com>

* Rename ExtensionBooleanResponse to AcknowledgedResponse

Signed-off-by: Ryan Bogan <rbogan@amazon.com>

Signed-off-by: Ryan Bogan <rbogan@amazon.com>
Co-authored-by: Daniel (dB.) Doubrovkine <dblock@amazon.com>

CHANGELOG.md

@@ -15,8 +15,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Allow mmap to use new JDK-19 preview APIs in Apache Lucene 9.4+ ([#5151](https://github.com/opensearch-project/OpenSearch/pull/5151))
 - Add feature flag for extensions ([#5211](https://github.com/opensearch-project/OpenSearch/pull/5211))
 - Added jackson dependency to server ([#5366] (https://github.com/opensearch-project/OpenSearch/pull/5366))
-- Added experimental extensions to main ([#5347](https://github.com/opensearch-project/OpenSearch/pull/5347))
 - Adding support to register settings dynamically ([#5495](https://github.com/opensearch-project/OpenSearch/pull/5495))
+- Added experimental support for extensions ([#5347](https://github.com/opensearch-project/OpenSearch/pull/5347)), ([#5518](https://github.com/opensearch-project/OpenSearch/pull/5518))
 - Add CI bundle pattern to distribution download ([#5348](https://github.com/opensearch-project/OpenSearch/pull/5348))
 
 

server/src/main/java/org/opensearch/discovery/PluginRequest.java → server/src/main/java/org/opensearch/discovery/InitializeExtensionRequest.java

@@ -15,62 +15,58 @@
 import org.opensearch.transport.TransportRequest;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Objects;
 
 /**
- * PluginRequest to intialize plugin
+ * InitializeExtensionRequest to intialize plugin
  *
  * @opensearch.internal
  */
-public class PluginRequest extends TransportRequest {
+public class InitializeExtensionRequest extends TransportRequest {
     private final DiscoveryNode sourceNode;
-    /*
-     * TODO change DiscoveryNode to Extension information
-     */
-    private final List<DiscoveryExtensionNode> extensions;
+    private final DiscoveryExtensionNode extension;
 
-    public PluginRequest(DiscoveryNode sourceNode, List<DiscoveryExtensionNode> extensions) {
+    public InitializeExtensionRequest(DiscoveryNode sourceNode, DiscoveryExtensionNode extension) {
         this.sourceNode = sourceNode;
-        this.extensions = extensions;
+        this.extension = extension;
     }
 
-    public PluginRequest(StreamInput in) throws IOException {
+    public InitializeExtensionRequest(StreamInput in) throws IOException {
         super(in);
         sourceNode = new DiscoveryNode(in);
-        extensions = in.readList(DiscoveryExtensionNode::new);
+        extension = new DiscoveryExtensionNode(in);
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         sourceNode.writeTo(out);
-        out.writeList(extensions);
-    }
-
-    public List<DiscoveryExtensionNode> getExtensions() {
-        return extensions;
+        extension.writeTo(out);
     }
 
     public DiscoveryNode getSourceNode() {
         return sourceNode;
     }
 
+    public DiscoveryExtensionNode getExtension() {
+        return extension;
+    }
+
     @Override
     public String toString() {
-        return "PluginRequest{" + "sourceNode=" + sourceNode + ", extensions=" + extensions + '}';
+        return "InitializeExtensionsRequest{" + "sourceNode=" + sourceNode + ", extension=" + extension + '}';
     }
 
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
-        PluginRequest that = (PluginRequest) o;
-        return Objects.equals(sourceNode, that.sourceNode) && Objects.equals(extensions, that.extensions);
+        InitializeExtensionRequest that = (InitializeExtensionRequest) o;
+        return Objects.equals(sourceNode, that.sourceNode) && Objects.equals(extension, that.extension);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(sourceNode, extensions);
+        return Objects.hash(sourceNode, extension);
     }
 }

server/src/main/java/org/opensearch/discovery/PluginResponse.java → server/src/main/java/org/opensearch/discovery/InitializeExtensionResponse.java

@@ -44,14 +44,14 @@
  *
  * @opensearch.internal
  */
-public class PluginResponse extends TransportResponse {
+public class InitializeExtensionResponse extends TransportResponse {
     private String name;
 
-    public PluginResponse(String name) {
+    public InitializeExtensionResponse(String name) {
         this.name = name;
     }
 
-    public PluginResponse(StreamInput in) throws IOException {
+    public InitializeExtensionResponse(StreamInput in) throws IOException {
         name = in.readString();
     }
 
@@ -77,7 +77,7 @@ public String toString() {
     public boolean equals(Object o) {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
-        PluginResponse that = (PluginResponse) o;
+        InitializeExtensionResponse that = (InitializeExtensionResponse) o;
         return Objects.equals(name, that.name);
     }
 

server/src/main/java/org/opensearch/extensions/AcknowledgedResponse.java

@@ -0,0 +1,68 @@
+/*
+ * 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.extensions;
+
+import org.opensearch.common.io.stream.StreamInput;
+import org.opensearch.common.io.stream.StreamOutput;
+import org.opensearch.transport.TransportResponse;
+import java.io.IOException;
+import java.util.Objects;
+
+/**
+ * Generic boolean response indicating the status of some previous request sent to the SDK
+ *
+ * @opensearch.internal
+ */
+public class AcknowledgedResponse extends TransportResponse {
+
+    private final boolean status;
+
+    /**
+     * @param status Boolean indicating the status of the parse request sent to the SDK
+     */
+    public AcknowledgedResponse(boolean status) {
+        this.status = status;
+    }
+
+    public AcknowledgedResponse(StreamInput in) throws IOException {
+        super(in);
+        this.status = in.readBoolean();
+    }
+
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
+        out.writeBoolean(status);
+    }
+
+    @Override
+    public String toString() {
+        return "AcknowledgedResponse{" + "status=" + this.status + "}";
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        AcknowledgedResponse that = (AcknowledgedResponse) o;
+        return Objects.equals(this.status, that.status);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(status);
+    }
+
+    /**
+     * Returns a boolean indicating the success of the request sent to the SDK
+     */
+    public boolean getStatus() {
+        return this.status;
+    }
+
+}

server/src/main/java/org/opensearch/extensions/ExtensionReader.java

@@ -0,0 +1,45 @@
+/*
+ * 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.extensions;
+
+import java.net.UnknownHostException;
+import org.opensearch.cluster.node.DiscoveryNode;
+
+/**
+ * Reference to a method that transports a parse request to an extension. By convention, this method takes
+ * a category class used to identify the reader defined within the JVM that the extension is running on.
+ * Additionally, this method takes in the extension's corresponding DiscoveryNode and a byte array (context) that the
+ * extension's reader will be applied to.
+ *
+ * By convention the extensions' reader is a constructor that takes StreamInput as an argument for most classes and a static method for things like enums.
+ * Classes will implement this via a constructor (or a static method in the case of enumerations), it's something that should
+ * look like:
+ * <pre><code>
+ * public MyClass(final StreamInput in) throws IOException {
+ * *     this.someValue = in.readVInt();
+ *     this.someMap = in.readMapOfLists(StreamInput::readString, StreamInput::readString);
+ * }
+ * </code></pre>
+ *
+ * @opensearch.internal
+ */
+@FunctionalInterface
+public interface ExtensionReader {
+
+    /**
+     * Transports category class, and StreamInput (context), to the extension identified by the Discovery Node
+     *
+     * @param extensionNode Discovery Node identifying the Extension
+     * @param categoryClass Super class that the reader extends
+     * @param context Some context to transport
+     * @throws UnknownHostException if the extension node host IP address could not be determined
+     */
+    void parse(DiscoveryNode extensionNode, Class categoryClass, Object context) throws UnknownHostException;
+
+}