[8.7] Avoid NPE in Stateless Get/mGet (#94164)

docs/changelog/94164.yaml

@@ -0,0 +1,5 @@
+pr: 94164
+summary: Avoid NPE in Stateless Get/mGet
+area: CRUD
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/action/get/TransportGetAction.java

@@ -13,7 +13,10 @@
 import org.elasticsearch.action.support.single.shard.TransportSingleShardAction;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.routing.PlainShardIterator;
 import org.elasticsearch.cluster.routing.ShardIterator;
+import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -27,6 +30,7 @@
 import org.elasticsearch.transport.TransportService;
 
 import java.io.IOException;
+import java.util.stream.Collectors;
 
 /**
  * Performs the get operation.
@@ -67,14 +71,27 @@ protected boolean resolveIndex(GetRequest request) {
 
     @Override
     protected ShardIterator shards(ClusterState state, InternalRequest request) {
-        return clusterService.operationRouting()
+        ShardIterator iterator = clusterService.operationRouting()
             .getShards(
                 clusterService.state(),
                 request.concreteIndex(),
                 request.request().id(),
                 request.request().routing(),
                 request.request().preference()
             );
+        if (iterator == null) {
+            return null;
+        }
+        // If it is stateless, only route isPromotableToPrimary shards. This is a temporary workaround until a more cohesive solution can be
+        // implemented for search shards.
+        if (DiscoveryNode.isStateless(clusterService.getSettings())) {
+            return new PlainShardIterator(
+                iterator.shardId(),
+                iterator.getShardRoutings().stream().filter(ShardRouting::isPromotableToPrimary).collect(Collectors.toList())
+            );
+        } else {
+            return iterator;
+        }
     }
 
     @Override

server/src/main/java/org/elasticsearch/action/get/TransportShardMultiGetAction.java

@@ -15,7 +15,10 @@
 import org.elasticsearch.action.support.single.shard.TransportSingleShardAction;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.cluster.routing.PlainShardIterator;
 import org.elasticsearch.cluster.routing.ShardIterator;
+import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -29,6 +32,7 @@
 import org.elasticsearch.transport.TransportService;
 
 import java.io.IOException;
+import java.util.stream.Collectors;
 
 import static org.elasticsearch.core.Strings.format;
 
@@ -81,8 +85,21 @@ protected boolean resolveIndex(MultiGetShardRequest request) {
 
     @Override
     protected ShardIterator shards(ClusterState state, InternalRequest request) {
-        return clusterService.operationRouting()
+        ShardIterator iterator = clusterService.operationRouting()
             .getShards(state, request.request().index(), request.request().shardId(), request.request().preference());
+        if (iterator == null) {
+            return null;
+        }
+        // If it is stateless, only route promotable shards. This is a temporary workaround until a more cohesive solution can be
+        // implemented for search shards.
+        if (DiscoveryNode.isStateless(clusterService.getSettings())) {
+            return new PlainShardIterator(
+                iterator.shardId(),
+                iterator.getShardRoutings().stream().filter(ShardRouting::isPromotableToPrimary).collect(Collectors.toList())
+            );
+        } else {
+            return iterator;
+        }
     }
 
     @Override