[GitHub] [ozone] elek commented on a change in pull request #2360: HDDS-5188. Replace GRPC based closed-container replication with Netty based streaming

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elek commented on a change in pull request #2360:
URL: https://github.com/apache/ozone/pull/2360#discussion_r673760896



##########
File path: hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/ContainerStreamingSource.java
##########
@@ -0,0 +1,101 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.ozone.container.replication;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.apache.hadoop.hdds.protocol.datanode.proto.ContainerProtos.ContainerDataProto.State;
+import org.apache.hadoop.hdds.scm.container.common.helpers.StorageContainerException;
+import org.apache.hadoop.ozone.container.common.impl.ContainerSet;
+import org.apache.hadoop.ozone.container.keyvalue.KeyValueContainer;
+import org.apache.hadoop.ozone.container.stream.StreamingSource;
+
+/**
+ * Streaming source for closed-container replication.
+ */
+public class ContainerStreamingSource implements StreamingSource {
+
+  private ContainerSet containerSet;
+
+  public ContainerStreamingSource(ContainerSet containerSet) {
+    this.containerSet = containerSet;
+  }
+
+  @Override
+  public Map<String, Path> getFilesToStream(String id) {
+
+    Map<String, Path> filesToStream = new HashMap<>();
+
+    final long containerId = Long.parseLong(id);
+    final KeyValueContainer container =
+        (KeyValueContainer) containerSet.getContainer(containerId);
+
+    try {
+      container.release();
+    } catch (StorageContainerException e) {
+      throw new RuntimeException("Container couldn't be released: " + id, e);
+    }
+
+    if (container.getContainerState() != State.CLOSED
+        && container.getContainerState() != State.QUASI_CLOSED) {
+      throw new RuntimeException(
+          "Only (quasi)closed containers can be exported, but ContainerId=: "
+              + id + " is in state " + container.getContainerState());
+    }
+
+    try {
+
+      final File dbPath =
+          container.getContainerData().getContainerDBFile();
+
+      final List<Path> dbFiles =
+          Files.list(dbPath.toPath()).collect(Collectors.toList());

Review comment:
       That's an interesting question, I never realized that streams are `AutoClosable`. Tried to find out more information and found this one: 
   
   https://www.baeldung.com/java-stream-close
   
   > When dealing with these sorts of streams, we shouldn't close them explicitly.
   
   I tried to check the implementation of `Files.list`/`Files.walk` and based on my understanding we don't need to close them as there are no open resources (I think `AbstractPipeline.close() is called in both cases). 
   
   But please let me know if I am wrong.




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