Adds Segment metadata preprocessor hook

pinot-segment-local/src/main/java/org/apache/pinot/segment/local/indexsegment/immutable/ImmutableSegmentLoader.java

@@ -123,6 +123,11 @@ public static ImmutableSegment load(File indexDir, IndexLoadingConfig indexLoadi
     Preconditions.checkArgument(indexDir.isDirectory(), "Index directory: %s does not exist or is not a directory",
         indexDir);
 
+    SegmentMetadataPreProcessor segmentMetadataPreProcessor = SegmentMetadataPreProcessorRegistry.getInstance();
+    if (segmentMetadataPreProcessor != null) {
+      segmentMetadataPreProcessor.process(indexDir, indexLoadingConfig, zkMetadata);
+    }
+
     SegmentMetadataImpl segmentMetadata = new SegmentMetadataImpl(indexDir);
     if (segmentMetadata.getTotalDocs() == 0) {
       return new EmptyIndexSegment(segmentMetadata);

pinot-segment-local/src/main/java/org/apache/pinot/segment/local/indexsegment/immutable/SegmentMetadataPreProcessor.java

@@ -0,0 +1,51 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.segment.local.indexsegment.immutable;
+
+import java.io.File;
+import javax.annotation.Nullable;
+import org.apache.pinot.common.metadata.segment.SegmentZKMetadata;
+import org.apache.pinot.segment.local.segment.index.loader.IndexLoadingConfig;
+
+/**
+ * {@code SegmentMetadataPreProcessor} provides a hook to preprocess a segment's metadata
+ * before the segment is fully loaded by the server.
+ */
+public interface SegmentMetadataPreProcessor {
+  /**
+   * Preprocesses the metadata for a segment located at the given index directory.
+   *
+   * @param indexDir
+   *        The root directory of the segment index containing the segment metadata files.
+   * @param indexLoadingConfig
+   *        The {@link IndexLoadingConfig} used for loading the segment, which may influence
+   *        preprocessing behavior (e.g. table name, segment type, or server-level settings).
+   * @param zkMetadata
+   *        Optional {@link SegmentZKMetadata} associated with the segment, if available.
+   *        This may be {@code null} when the segment is loaded outside of Helix or Zookeeper
+   *        context.
+   *
+   * @throws Exception
+   *         If preprocessing fails and the segment should not be loaded. Throwing an
+   *         exception will abort the segment loading process.
+   */
+  void process(File indexDir, IndexLoadingConfig indexLoadingConfig,
+      @Nullable SegmentZKMetadata zkMetadata)
+      throws Exception;
+}

pinot-segment-local/src/main/java/org/apache/pinot/segment/local/indexsegment/immutable/SegmentMetadataPreProcessorRegistry.java

@@ -0,0 +1,52 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.segment.local.indexsegment.immutable;
+
+import javax.annotation.Nullable;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class SegmentMetadataPreProcessorRegistry {
+  private static final Logger LOGGER = LoggerFactory.getLogger(SegmentMetadataPreProcessorRegistry.class);
+  private static SegmentMetadataPreProcessor _instance = null;
+
+  private SegmentMetadataPreProcessorRegistry() {
+  }
+
+  /**
+   * Get the registered instance of the pre-processor.
+   *
+   * @return The registered instance, or null if none registered
+   */
+  @Nullable
+  public static SegmentMetadataPreProcessor getInstance() {
+    return _instance;
+  }
+
+  /**
+   * Register a pre-processor instance.
+   *
+   * @param instance The pre-processor instance to register
+   */
+  public static void setInstance(SegmentMetadataPreProcessor instance) {
+    _instance = instance;
+    LOGGER.info("Registered SegmentMetadataPreProcessor: {}", instance.getClass().getName());
+  }
+}