Fix Neo4jReactiveHealthIndicator NoSuchElementException

Update `Neo4jReactiveHealthIndicator` to ensure that `result.records()`
is called before `result.consume()`. Prior to this commit, the indicator
used `zipWith` to merge records with a summary. This worked with the
previous RxJava based driver, but fails with the Reactor based driver
due to a `NoSuchElementException: Source was empty` error.

Fixes gh-33428

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/neo4j/Neo4jReactiveHealthIndicator.java

@@ -19,9 +19,11 @@
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.neo4j.driver.Driver;
+import org.neo4j.driver.Record;
 import org.neo4j.driver.exceptions.SessionExpiredException;
 import org.neo4j.driver.reactivestreams.ReactiveResult;
 import org.neo4j.driver.reactivestreams.ReactiveSession;
+import org.neo4j.driver.summary.ResultSummary;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.retry.Retry;
@@ -36,6 +38,7 @@
  *
  * @author Michael J. Simons
  * @author Stephane Nicoll
+ * @author Phillip Webb
  * @since 2.4.0
  */
 public final class Neo4jReactiveHealthIndicator extends AbstractReactiveHealthIndicator {
@@ -63,15 +66,40 @@ protected Mono<Health> doHealthCheck(Health.Builder builder) {
 	}
 
 	Mono<Neo4jHealthDetails> runHealthCheckQuery() {
-		// We use WRITE here to make sure UP is returned for a server that supports
-		// all possible workloads
-		return Mono.using(() -> this.driver.session(ReactiveSession.class, Neo4jHealthIndicator.DEFAULT_SESSION_CONFIG),
-				(session) -> {
-					Mono<ReactiveResult> resultMono = Flux.from(session.run(Neo4jHealthIndicator.CYPHER)).single();
-					return resultMono
-							.flatMapMany((result) -> Flux.from(result.records()).zipWith(Flux.from(result.consume())))
-							.map((tuple) -> new Neo4jHealthDetails(tuple.getT1(), tuple.getT2())).single();
-				}, ReactiveSession::close);
+		return Mono.using(this::session, this::healthDetails, ReactiveSession::close);
+	}
+
+	private ReactiveSession session() {
+		return this.driver.session(ReactiveSession.class, Neo4jHealthIndicator.DEFAULT_SESSION_CONFIG);
+	}
+
+	private Mono<Neo4jHealthDetails> healthDetails(ReactiveSession session) {
+		return Mono.from(session.run(Neo4jHealthIndicator.CYPHER)).flatMap(this::healthDetails);
+	}
+
+	private Mono<? extends Neo4jHealthDetails> healthDetails(ReactiveResult result) {
+		Flux<Record> records = Flux.from(result.records());
+		Mono<ResultSummary> summary = Mono.from(result.consume());
+		Neo4jHealthDetailsBuilder builder = new Neo4jHealthDetailsBuilder();
+		return records.single().doOnNext(builder::record).then(summary).map(builder::build);
+	}
+
+	/**
+	 * Builder used to create a {@link Neo4jHealthDetails} from a {@link Record} and a
+	 * {@link ResultSummary}.
+	 */
+	private static class Neo4jHealthDetailsBuilder {
+
+		private Record record;
+
+		void record(Record record) {
+			this.record = record;
+		}
+
+		private Neo4jHealthDetails build(ResultSummary summary) {
+			return new Neo4jHealthDetails(this.record, summary);
+		}
+
 	}
 
 }