HDFS-16537.Fix oev decode xml error

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLogOp.java

@@ -2864,6 +2864,7 @@ void resetSubFields() {
       clientMachine = null;
       newLength = 0L;
       timestamp = 0L;
+      truncateBlock = null;
     }
 
     TruncateOp setPath(String src) {
@@ -2934,8 +2935,9 @@ protected void toXml(ContentHandler contentHandler) throws SAXException {
           Long.toString(newLength));
       XMLUtils.addSaxString(contentHandler, "TIMESTAMP",
           Long.toString(timestamp));
-      if(truncateBlock != null)
+      if (truncateBlock != null) {
         FSEditLogOp.blockToXml(contentHandler, truncateBlock);
+      }
     }
 
     @Override
@@ -2945,8 +2947,12 @@ void fromXml(Stanza st) throws InvalidXmlException {
       this.clientMachine = st.getValue("CLIENTMACHINE");
       this.newLength = Long.parseLong(st.getValue("NEWLENGTH"));
       this.timestamp = Long.parseLong(st.getValue("TIMESTAMP"));
-      if (st.hasChildren("BLOCK"))
-        this.truncateBlock = FSEditLogOp.blockFromXml(st);
+      if (st.hasChildren("BLOCK")) {
+        this.truncateBlock =
+            FSEditLogOp.blockFromXml(st.getChildren("BLOCK").get(0));
+      } else {
+        this.truncateBlock = null;
+      }
     }
 
     @Override

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestFSEditLogOp.java

@@ -0,0 +1,125 @@
+/**
+ * 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.hadoop.hdfs.server.namenode;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.apache.hadoop.hdfs.protocol.Block;
+import org.apache.hadoop.hdfs.util.XMLUtils.InvalidXmlException;
+import org.apache.hadoop.hdfs.util.XMLUtils.Stanza;
+import org.junit.jupiter.api.Test;
+
+public class TestFSEditLogOp {
+
+  @Test
+  public void testFromXmlWithoutBlockResetsTruncateBlock()
+      throws InvalidXmlException {
+    FSEditLogOp.TruncateOp op = new FSEditLogOp.TruncateOp();
+    op.setPath("/src")
+        .setClientName("client")
+        .setClientMachine("machine")
+        .setNewLength(123L)
+        .setTimestamp(10L)
+        .setTruncateBlock(new Block(1L, 2L, 3L));
+
+    Stanza root = new Stanza();
+    root.addChild("SRC", stanzaValue("/src"));
+    root.addChild("CLIENTNAME", stanzaValue("client"));
+    root.addChild("CLIENTMACHINE", stanzaValue("machine"));
+    root.addChild("NEWLENGTH", stanzaValue("123"));
+    root.addChild("TIMESTAMP", stanzaValue("10"));
+
+    op.fromXml(root);
+
+    assertEquals("/src", op.src);
+    assertEquals("client", op.clientName);
+    assertEquals("machine", op.clientMachine);
+    assertEquals(123L, op.newLength);
+    assertEquals(10L, op.timestamp);
+    assertNull(op.truncateBlock);
+  }
+
+  @Test
+  public void testFromXmlWithBlockSetsTruncateBlock()
+      throws InvalidXmlException {
+    FSEditLogOp.TruncateOp op = new FSEditLogOp.TruncateOp();
+
+    Stanza root = new Stanza();
+    root.addChild("SRC", stanzaValue("/src2"));
+    root.addChild("CLIENTNAME", stanzaValue("client2"));
+    root.addChild("CLIENTMACHINE", stanzaValue("machine2"));
+    root.addChild("NEWLENGTH", stanzaValue("200"));
+    root.addChild("TIMESTAMP", stanzaValue("20"));
+    root.addChild("BLOCK", blockStanza(7L, 100L, 9L));
+
+    op.fromXml(root);
+
+    assertEquals("/src2", op.src);
+    assertEquals("client2", op.clientName);
+    assertEquals("machine2", op.clientMachine);
+    assertEquals(200L, op.newLength);
+    assertEquals(20L, op.timestamp);
+    assertNotNull(op.truncateBlock);
+    assertEquals(7L, op.truncateBlock.getBlockId());
+    assertEquals(100L, op.truncateBlock.getNumBytes());
+    assertEquals(9L, op.truncateBlock.getGenerationStamp());
+  }
+
+  /**
+   * When stanza has multiple BLOCK children, fromXml uses the first one
+   * (st.getChildren("BLOCK").get(0)).
+   */
+  @Test
+  public void testFromXmlWithMultipleBlocksUsesFirst()
+      throws InvalidXmlException {
+    FSEditLogOp.TruncateOp op = new FSEditLogOp.TruncateOp();
+
+    Stanza root = new Stanza();
+    root.addChild("SRC", stanzaValue("/path"));
+    root.addChild("CLIENTNAME", stanzaValue("c"));
+    root.addChild("CLIENTMACHINE", stanzaValue("m"));
+    root.addChild("NEWLENGTH", stanzaValue("0"));
+    root.addChild("TIMESTAMP", stanzaValue("0"));
+    root.addChild("BLOCK", blockStanza(1L, 10L, 100L));
+    root.addChild("BLOCK", blockStanza(2L, 20L, 200L));
+
+    op.fromXml(root);
+
+    assertNotNull(op.truncateBlock);
+    assertEquals(1L, op.truncateBlock.getBlockId());
+    assertEquals(10L, op.truncateBlock.getNumBytes());
+    assertEquals(100L, op.truncateBlock.getGenerationStamp());
+  }
+
+  private static Stanza stanzaValue(String value) {
+    Stanza s = new Stanza();
+    s.setValue(value);
+    return s;
+  }
+
+  private static Stanza blockStanza(long blockId, long numBytes,
+      long genstamp) {
+    Stanza block = new Stanza();
+    block.addChild("BLOCK_ID", stanzaValue(Long.toString(blockId)));
+    block.addChild("NUM_BYTES", stanzaValue(Long.toString(numBytes)));
+    block.addChild("GENSTAMP", stanzaValue(Long.toString(genstamp)));
+    return block;
+  }
+}