From 092f8caf7af19506ed6488a1f3aa4fd087d3fb91 Mon Sep 17 00:00:00 2001
From: Ray Mattingly <rmattingly@apache.org>
Date: Mon, 17 Mar 2025 13:11:56 -0400
Subject: [PATCH] HBASE-29186 RegionPlanConditionals can produce a null pointer
 (#6796)

Co-authored-by: Ray Mattingly <rmattingly@hubspot.com>
Signed-off-by: Nick Dimiduk <ndimiduk@apache.org>
---
 .../balancer/RegionPlanConditional.java       | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionPlanConditional.java b/hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionPlanConditional.java
index 8de371d341cd..063f3ba5f726 100644
--- a/hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionPlanConditional.java
+++ b/hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionPlanConditional.java
@@ -18,6 +18,7 @@
 package org.apache.hadoop.hbase.master.balancer;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -85,8 +86,8 @@ boolean isViolating(RegionPlan regionPlan) {
 
     // Check Server
     int[] destinationRegionIndices = cluster.regionsPerServer[destinationServerIdx];
-    Set<RegionInfo> serverRegions = Arrays.stream(cluster.regionsPerServer[destinationServerIdx])
-      .mapToObj(idx -> cluster.regions[idx]).collect(Collectors.toSet());
+    Set<RegionInfo> serverRegions =
+      getRegionsFromIndex(destinationServerIdx, cluster.regionsPerServer);
     for (int regionIdx : destinationRegionIndices) {
       serverRegions.add(cluster.regions[regionIdx]);
     }
@@ -100,8 +101,7 @@ boolean isViolating(RegionPlan regionPlan) {
 
     // Check Host
     int hostIdx = cluster.serverIndexToHostIndex[destinationServerIdx];
-    Set<RegionInfo> hostRegions = Arrays.stream(cluster.regionsPerHost[hostIdx])
-      .mapToObj(idx -> cluster.regions[idx]).collect(Collectors.toSet());
+    Set<RegionInfo> hostRegions = getRegionsFromIndex(hostIdx, cluster.regionsPerHost);
     if (isViolatingHost(regionPlan, hostRegions)) {
       return true;
     }
@@ -112,8 +112,7 @@ boolean isViolating(RegionPlan regionPlan) {
 
     // Check Rack
     int rackIdx = cluster.serverIndexToRackIndex[destinationServerIdx];
-    Set<RegionInfo> rackRegions = Arrays.stream(cluster.regionsPerRack[rackIdx])
-      .mapToObj(idx -> cluster.regions[idx]).collect(Collectors.toSet());
+    Set<RegionInfo> rackRegions = getRegionsFromIndex(rackIdx, cluster.regionsPerRack);
     if (isViolatingRack(regionPlan, rackRegions)) {
       return true;
     }
@@ -130,4 +129,13 @@ boolean isViolatingHost(RegionPlan regionPlan, Set<RegionInfo> destinationRegion
   boolean isViolatingRack(RegionPlan regionPlan, Set<RegionInfo> destinationRegions) {
     return false;
   }
+
+  private Set<RegionInfo> getRegionsFromIndex(int index, int[][] regionsPerIndex) {
+    int[] regionIndices = regionsPerIndex[index];
+    if (regionIndices == null) {
+      return Collections.emptySet();
+    }
+    return Arrays.stream(regionIndices).mapToObj(idx -> cluster.regions[idx])
+      .collect(Collectors.toSet());
+  }
 }