From 039e9bf837963115d11c7107040e7e3c542b24b6 Mon Sep 17 00:00:00 2001
From: Aswin Shakil Balasubramanian <aswin.shakil47@gmail.com>
Date: Wed, 21 Feb 2024 14:10:43 -0800
Subject: [PATCH] HDDS-10408. NPE causes OM crash in Snapshot Purge request

---
 .../om/request/snapshot/OMSnapshotPurgeRequest.java   | 11 +++++++++++
 .../hadoop/ozone/om/snapshot/SnapshotUtils.java       |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/snapshot/OMSnapshotPurgeRequest.java b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/snapshot/OMSnapshotPurgeRequest.java
index 0fa9087e25e7..3f4d746adb54 100644
--- a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/snapshot/OMSnapshotPurgeRequest.java
+++ b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/request/snapshot/OMSnapshotPurgeRequest.java
@@ -35,6 +35,8 @@
 import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos;
 import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.OMRequest;
 import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.SnapshotPurgeRequest;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.util.HashMap;
@@ -49,6 +51,8 @@
  */
 public class OMSnapshotPurgeRequest extends OMClientRequest {
 
+  private static final Logger LOG = LoggerFactory.getLogger(OMSnapshotPurgeRequest.class);
+
   public OMSnapshotPurgeRequest(OMRequest omRequest) {
     super(omRequest);
   }
@@ -83,6 +87,13 @@ public OMClientResponse validateAndUpdateCache(OzoneManager ozoneManager, TermIn
         SnapshotInfo fromSnapshot = omMetadataManager.getSnapshotInfoTable()
             .get(snapTableKey);
 
+        if (fromSnapshot == null) {
+          // Snapshot may have been purged in the previous iteration of SnapshotDeletingService.
+          LOG.warn("The snapshot {} is not longer in snapshot table, It maybe removed in the previous " +
+                  "Snapshot purge request.", snapTableKey);
+          continue;
+        }
+
         SnapshotInfo nextSnapshot = SnapshotUtils
             .getNextActiveSnapshot(fromSnapshot,
                 snapshotChainManager, omSnapshotManager);
diff --git a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotUtils.java b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotUtils.java
index 89823995d0cd..2041fa791a76 100644
--- a/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotUtils.java
+++ b/hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotUtils.java
@@ -40,6 +40,7 @@
 import java.util.UUID;
 
 import static org.apache.hadoop.ozone.OzoneConsts.OM_KEY_PREFIX;
+import static org.apache.hadoop.ozone.om.exceptions.OMException.ResultCodes.INVALID_SNAPSHOT_ERROR;
 import static org.apache.hadoop.ozone.om.OmMetadataManagerImpl.DIRECTORY_TABLE;
 import static org.apache.hadoop.ozone.om.OmMetadataManagerImpl.FILE_TABLE;
 import static org.apache.hadoop.ozone.om.OmMetadataManagerImpl.KEY_TABLE;
@@ -148,6 +149,10 @@ public static SnapshotInfo getNextActiveSnapshot(SnapshotInfo snapInfo,
     // If the snapshot is deleted in the previous run, then the in-memory
     // SnapshotChainManager might throw NoSuchElementException as the snapshot
     // is removed in-memory but OMDoubleBuffer has not flushed yet.
+    if (snapInfo == null) {
+      throw new OMException("Snapshot Info is null. Cannot get the next snapshot", INVALID_SNAPSHOT_ERROR);
+    }
+
     try {
       while (chainManager.hasNextPathSnapshot(snapInfo.getSnapshotPath(),
           snapInfo.getSnapshotId())) {