SOLR-16339: refine "no servers hosting shard" wording (apache#968)

solr/CHANGES.txt

@@ -154,6 +154,8 @@ Other Changes
 
 * SOLR-16332: Upgrade Jetty to 9.4.48.v20220622 (Chris Sabelstrom, janhoy)
 
+* SOLR-16339: Refined "no servers hosting shard" SolrException wording. (Christine Poerschke)
+
 Build
 ---------------------
 * SOLR-16204: Change Lucene dependency to Lucene 9.1.0 (Elia Porciani via Alessandro Benedetti)

solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java

@@ -31,6 +31,7 @@
 import org.apache.solr.client.solrj.impl.LBHttp2SolrClient;
 import org.apache.solr.client.solrj.impl.LBSolrClient;
 import org.apache.solr.client.solrj.request.QueryRequest;
+import org.apache.solr.client.solrj.routing.NoOpReplicaListTransformer;
 import org.apache.solr.client.solrj.routing.ReplicaListTransformer;
 import org.apache.solr.client.solrj.util.AsyncListener;
 import org.apache.solr.client.solrj.util.Cancellable;
@@ -148,7 +149,7 @@ public void submit(
 
     pending.incrementAndGet();
     // if there are no shards available for a slice, urls.size()==0
-    if (urls.size() == 0) {
+    if (urls.isEmpty()) {
       // TODO: what's the right error code here? We should use the same thing when
       // all of the servers for a shard are down.
       SolrException exception =
@@ -318,14 +319,26 @@ public void prepDistributed(ResponseBuilder rb) {
         // be an optimization?
       }
 
-      for (int i = 0; i < rb.slices.length; i++) {
-        if (!ShardParams.getShardsTolerantAsBool(params)
-            && replicaSource.getReplicasBySlice(i).isEmpty()) {
-          // stop the check when there are no replicas available for a shard
-          // todo fix use of slices[i] which can be null if user specified urls in shards param
-          throw new SolrException(
-              SolrException.ErrorCode.SERVICE_UNAVAILABLE,
-              "no servers hosting shard: " + rb.slices[i]);
+      if (!ShardParams.getShardsTolerantAsBool(params)) {
+        for (int i = 0; i < rb.slices.length; i++) {
+          if (replicaSource.getReplicasBySlice(i).isEmpty()) {
+            final ReplicaSource allActiveReplicaSource =
+                new CloudReplicaSource.Builder()
+                    .params(params)
+                    .zkStateReader(zkController.getZkStateReader())
+                    .allowListUrlChecker(AllowListUrlChecker.ALLOW_ALL)
+                    .replicaListTransformer(NoOpReplicaListTransformer.INSTANCE)
+                    .collection(cloudDescriptor.getCollectionName())
+                    .onlyNrt(false)
+                    .build();
+            final String adjective =
+                (allActiveReplicaSource.getReplicasBySlice(i).isEmpty() ? "active" : "eligible");
+            // stop the check when there are no replicas available for a shard
+            // todo fix use of slices[i] which can be null if user specified urls in shards param
+            throw new SolrException(
+                SolrException.ErrorCode.SERVICE_UNAVAILABLE,
+                "no " + adjective + " servers hosting shard: " + rb.slices[i]);
+          }
         }
       }
     } else {

solr/core/src/test/org/apache/solr/handler/component/SearchHandlerTest.java

@@ -263,7 +263,7 @@ public void testRequireZkConnectedDistrib() throws Exception {
       try (HttpSolrClient httpSolrClient =
           new HttpSolrClient.Builder(connectedReplica.getCoreUrl()).build()) {
         ignoreException("ZooKeeper is not connected");
-        ignoreException("no servers hosting shard:");
+        ignoreException("no active servers hosting shard:");
         JettySolrRunner disconnectedJetty = miniCluster.getReplicaJetty(disconnectedReplica);
         disconnectedJetty.getCoreContainer().getZkController().getZkClient().close();
         req.process(httpSolrClient);
@@ -272,12 +272,12 @@ public void testRequireZkConnectedDistrib() throws Exception {
       } catch (Exception e) {
         assertTrue(
             "Unrecognized exception message: " + e,
-            e.getMessage().contains("no servers hosting shard:")
+            e.getMessage().contains("no active servers hosting shard:")
                 || e.getMessage().contains("ZooKeeper is not connected"));
       }
     } finally {
       miniCluster.shutdown();
-      unIgnoreException("no servers hosting shard:");
+      unIgnoreException("no active servers hosting shard:");
       unIgnoreException("ZooKeeper is not connected");
     }
   }

solr/solrj/src/java/org/apache/solr/client/solrj/routing/NoOpReplicaListTransformer.java

@@ -0,0 +1,28 @@
+/*
+ * 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.solr.client.solrj.routing;
+
+import java.util.List;
+
+public final class NoOpReplicaListTransformer implements ReplicaListTransformer {
+
+  public static final ReplicaListTransformer INSTANCE = new NoOpReplicaListTransformer();
+
+  private NoOpReplicaListTransformer() {}
+
+  public <T> void transform(List<T> choices) {}
+}

solr/solrj/src/java/org/apache/solr/client/solrj/routing/NodePreferenceRulesComparator.java

@@ -100,13 +100,7 @@ public NodePreferenceRulesComparator(
     }
   }
 
-  private static final ReplicaListTransformer NOOP_RLT =
-      new ReplicaListTransformer() {
-        @Override
-        public <T> void transform(List<T> choices) {
-          // Cannot use a method reference because of generic types!
-        }
-      };
+  private static final ReplicaListTransformer NOOP_RLT = NoOpReplicaListTransformer.INSTANCE;
   private static final ReplicaListTransformerFactory NOOP_RLTF =
       (String configSpec, SolrParams requestParams, ReplicaListTransformerFactory fallback) ->
           NOOP_RLT;

solr/solrj/src/test/org/apache/solr/client/solrj/routing/ReplicaListTransformerTest.java

@@ -68,17 +68,6 @@ public <T> void transform(List<T> choices) {
     }
   }
 
-  // A transformer that makes no transformation
-  private static class ToyNoOpReplicaListTransformer implements ReplicaListTransformer {
-
-    public ToyNoOpReplicaListTransformer() {}
-
-    public <T> void transform(List<T> choices) {
-      // no-op
-      log.info("No-Op transform ignoring input: {}", choices);
-    }
-  }
-
   @Test
   public void testTransform() throws Exception {
 
@@ -99,7 +88,7 @@ protected ReplicaListTransformer getReplicaListTransformer(final SolrQueryReques
               final SolrParams params = req.getParams();
 
               if (params.getBool("toyNoTransform", false)) {
-                return new ToyNoOpReplicaListTransformer();
+                return NoOpReplicaListTransformer.INSTANCE;
               }
 
               final String regex = params.get("toyRegEx");