Register MediaTypes through SPI (opensearch-project#8938)

* Register MediaTypes through SPI

This commit provides a new SPI interface MediaContentProvider. Modules,
Plugins, Extensions, implement this interface and provide the concrete
MediaType implementations (and MIME aliases) through getMediaTypes and
getAdditionalMediaTypes, respectively. This enables downstream
extensions (e.g., serverless or cloud native implementations) to
register their own custom MediaType and define the serialization format
that is registered when the classloader loads the MediaTypeRegistry
instead of having to register the types explicitly in application code.

Signed-off-by: Nicholas Walter Knize <nknize@apache.org>

* pass the MediaTypeProvider classloader to the SPI ServiceLoader

Signed-off-by: Nicholas Walter Knize <nknize@apache.org>

---------

Signed-off-by: Nicholas Walter Knize <nknize@apache.org>

libs/core/src/main/java/org/opensearch/core/xcontent/MediaTypeRegistry.java

@@ -32,9 +32,16 @@
 
 package org.opensearch.core.xcontent;
 
+import org.opensearch.core.xcontent.spi.MediaTypeProvider;
+
+import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.ServiceLoader;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * Parses supported internet media types
@@ -48,7 +55,25 @@ public final class MediaTypeRegistry {
     // Default mediaType singleton
     private static MediaType DEFAULT_MEDIA_TYPE;
 
-    public static void register(MediaType[] acceptedMediaTypes, Map<String, MediaType> additionalMediaTypes) {
+    // JSON is a core type, so we create a static instance for implementations that require JSON format (e.g., tests)
+    // todo we should explore moving the concrete JSON implementation from the xcontent library to core
+    public static final MediaType JSON;
+
+    static {
+        List<MediaType> mediaTypes = new ArrayList<>();
+        Map<String, MediaType> amt = new HashMap<>();
+        for (MediaTypeProvider provider : ServiceLoader.load(MediaTypeProvider.class, MediaTypeProvider.class.getClassLoader())) {
+            mediaTypes.addAll(provider.getMediaTypes());
+            amt = Stream.of(amt, provider.getAdditionalMediaTypes())
+                .flatMap(map -> map.entrySet().stream())
+                .collect(Collectors.toUnmodifiableMap(Map.Entry::getKey, Map.Entry::getValue));
+        }
+        register(mediaTypes.toArray(new MediaType[0]), amt);
+        JSON = fromMediaType("application/json");
+        setDefaultMediaType(JSON);
+    }
+
+    private static void register(MediaType[] acceptedMediaTypes, Map<String, MediaType> additionalMediaTypes) {
         // ensures the map is not overwritten:
         Map<String, MediaType> typeMap = new HashMap<>(typeWithSubtypeToMediaType);
         Map<String, MediaType> formatMap = new HashMap<>(formatToMediaType);
@@ -150,7 +175,7 @@ public Map<String, String> getParameters() {
         }
     }
 
-    public static void setDefaultMediaType(final MediaType mediaType) {
+    private static void setDefaultMediaType(final MediaType mediaType) {
         if (DEFAULT_MEDIA_TYPE != null) {
             throw new RuntimeException(
                 "unable to reset the default media type from current default [" + DEFAULT_MEDIA_TYPE + "] to [" + mediaType + "]"

libs/core/src/main/java/org/opensearch/core/xcontent/spi/MediaTypeProvider.java

@@ -0,0 +1,29 @@
+/*
+ * 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.core.xcontent.spi;
+
+import org.opensearch.core.xcontent.MediaType;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Service Provider Interface for plugins, modules, extensions providing
+ * their own Media Types
+ *
+ * @opensearch.experimental
+ * @opensearch.api
+ */
+public interface MediaTypeProvider {
+    /** Extensions that implement their own concrete {@link MediaType}s provide them through this interface method */
+    List<MediaType> getMediaTypes();
+
+    /** Extensions that implement additional {@link MediaType} aliases provide them through this interface method */
+    Map<String, MediaType> getAdditionalMediaTypes();
+}

libs/core/src/main/java/org/opensearch/core/xcontent/spi/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.
+ */
+
+/** Service Provider Interface for extensible media types */
+package org.opensearch.core.xcontent.spi;

libs/x-content/src/main/java/org/opensearch/common/xcontent/XContentType.java

@@ -38,11 +38,9 @@
 import org.opensearch.common.xcontent.yaml.YamlXContent;
 import org.opensearch.core.common.io.stream.StreamOutput;
 import org.opensearch.core.xcontent.MediaType;
-import org.opensearch.core.xcontent.MediaTypeRegistry;
 import org.opensearch.core.xcontent.XContent;
 
 import java.io.IOException;
-import java.util.Map;
 
 /**
  * The content type of {@link XContent}.
@@ -131,11 +129,6 @@ public XContent xContent() {
         }
     };
 
-    static {
-        /** a parser of media types */
-        MediaTypeRegistry.register(XContentType.values(), Map.of("application/*", JSON, "application/x-ndjson", JSON));
-    }
-
     private int index;
 
     XContentType(int index) {

libs/x-content/src/main/java/org/opensearch/common/xcontent/spi/XContentProvider.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.common.xcontent.spi;
+
+import org.opensearch.common.xcontent.XContentType;
+import org.opensearch.core.xcontent.MediaType;
+import org.opensearch.core.xcontent.spi.MediaTypeProvider;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Media Type implementations provided by xcontent library
+ *
+ * @opensearch.internal
+ */
+public class XContentProvider implements MediaTypeProvider {
+    /** Returns the concrete {@link MediaType} provided by the xcontent library */
+    @Override
+    public List<MediaType> getMediaTypes() {
+        return List.of(XContentType.values());
+    }
+
+    /** Returns the additional {@link MediaType} aliases provided by the xcontent library */
+    @Override
+    public Map<String, MediaType> getAdditionalMediaTypes() {
+        return Map.of("application/*", XContentType.JSON, "application/x-ndjson", XContentType.JSON);
+    }
+}

libs/x-content/src/main/java/org/opensearch/common/xcontent/spi/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.
+ */
+
+/** SPI implementation for the xcontent library */
+package org.opensearch.common.xcontent.spi;

libs/x-content/src/main/resources/META-INF/services/org.opensearch.core.xcontent.spi.MediaTypeProvider

@@ -0,0 +1,9 @@
+#
+# 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.
+#
+
+org.opensearch.common.xcontent.spi.XContentProvider

server/src/main/java/org/opensearch/transport/TransportService.java

@@ -59,10 +59,8 @@
 import org.opensearch.common.util.concurrent.ThreadContext;
 import org.opensearch.common.util.io.IOUtils;
 import org.opensearch.common.lease.Releasable;
-import org.opensearch.common.xcontent.XContentType;
 import org.opensearch.core.common.Strings;
 import org.opensearch.core.concurrency.OpenSearchRejectedExecutionException;
-import org.opensearch.core.xcontent.MediaTypeRegistry;
 import org.opensearch.node.NodeClosedException;
 import org.opensearch.node.ReportingService;
 import org.opensearch.tasks.Task;
@@ -173,8 +171,6 @@ public void close() {}
         Streamables.registerStreamables();
         /** Registers OpenSearch server specific exceptions (exceptions outside of core library) */
         OpenSearchServerException.registerExceptions();
-        // set the default media type to JSON (fallback if a media type is not specified)
-        MediaTypeRegistry.setDefaultMediaType(XContentType.JSON);
     }
 
     /** does nothing. easy way to ensure class is loaded so the above static block is called to register the streamables */