HDFS-16437 ReverseXML processor doesn't accept XML files without the …

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/OfflineImageReconstructor.java

@@ -1761,6 +1761,9 @@ private void processXml() throws Exception {
       XMLEvent ev = expectTag("[section header]", true);
       if (ev.getEventType() == XMLStreamConstants.END_ELEMENT) {
         if (ev.asEndElement().getName().getLocalPart().equals("fsimage")) {
+          if(unprocessedSections.size() == 1 && unprocessedSections.contains(SnapshotDiffSectionProcessor.NAME)){
+            break;
+          }
           throw new IOException("FSImage XML ended prematurely, without " +
               "including section(s) " + StringUtils.join(", ",
               unprocessedSections));

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/TestOfflineImageViewer.java

@@ -1174,6 +1174,42 @@ public void testReverseXmlWrongLayoutVersion() throws Throwable {
     }
   }
 
+  /**
+   * Tests that the ReverseXML processor doesn't accept XML files without the SnapshotDiffSection.
+   */
+  @Test
+  public void testReverseXmlWithoutSnapshotDiffSection() throws Throwable {
+    File imageWSDS = new File(tempDir, "imageWithoutSnapshotDiffSection.xml");
+    PrintWriter writer = new PrintWriter(imageWSDS, "UTF-8");
+    try {
+      writer.println("<?xml version=\"1.0\"?>");
+      writer.println("<fsimage>");
+      writer.println("<version>");
+      writer.println("<layoutVersion>-67</layoutVersion>");
+      writer.println("<onDiskVersion>1</onDiskVersion>");
+      writer.println("<oivRevision>545bbef596c06af1c3c8dca1ce29096a64608478</oivRevision>");
+      writer.println("</version>");
+      writer.println("<FileUnderConstructionSection></FileUnderConstructionSection>");
+      writer.println("<ErasureCodingSection></ErasureCodingSection>");
+      writer.println("<INodeSection><lastInodeId>91488</lastInodeId><numInodes>0</numInodes></INodeSection>");
+      writer.println("<SecretManagerSection><currentId>90</currentId><tokenSequenceNumber>35</tokenSequenceNumber><numDelegationKeys>0</numDelegationKeys><numTokens>0</numTokens></SecretManagerSection>");
+      writer.println("<INodeReferenceSection></INodeReferenceSection>");
+      writer.println("<SnapshotSection><snapshotCounter>0</snapshotCounter><numSnapshots>0</numSnapshots></SnapshotSection>");
+      writer.println("<NameSection><namespaceId>326384987</namespaceId></NameSection>");
+      writer.println("<CacheManagerSection><nextDirectiveId>1</nextDirectiveId><numPools>0</numPools><numDirectives>0</numDirectives></CacheManagerSection>");
+      writer.println("<INodeDirectorySection></INodeDirectorySection>");
+      writer.println("</fsimage>");
+    } finally {
+      writer.close();
+    }
+    try {
+      OfflineImageReconstructor.run(imageWSDS.getAbsolutePath(),
+              imageWSDS.getAbsolutePath() + ".out");
+    } catch (Throwable t) {
+      GenericTestUtils.assertExceptionContains("without SnapshotDiffSection.", t);
+    }
+  }
+
   @Test
   public void testFileDistributionCalculatorForException() throws Exception {
     File fsimageFile = null;