[Backport 2.x] Register MediaTypes through SPI

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

@@ -61,10 +61,8 @@
 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;
@@ -176,8 +174,6 @@ 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 */