NIFI-1966: Recreated issue that is outlined in JIRA (the reason for re-opening the ticket) that results in 'java.util.NoSuchElementException: No value present' in unit test - Resolved issue where two flows that are both empty but have different fingerprints (due to root group id being different) causes vote election to fail

This closes #995.

Signed-off-by: Bryan Bende <bbende@apache.org>

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-cluster/src/main/java/org/apache/nifi/cluster/coordination/flow/PopularVoteFlowElection.java

@@ -23,10 +23,12 @@ import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.stream.Collectors;
 
 import org.apache.nifi.cluster.protocol.DataFlow;
 import org.apache.nifi.cluster.protocol.NodeIdentifier;
@@ -156,12 +158,24 @@ public class PopularVoteFlowElection implements FlowElection {
             return null;
         }
 
+        final List<FlowCandidate> nonEmptyCandidates = candidateByFingerprint.values().stream()
+            .filter(candidate -> !candidate.isFlowEmpty())
+            .collect(Collectors.toList());
+
+        if (nonEmptyCandidates.isEmpty()) {
+            // All flow candidates are empty flows. Just use one of them.
+            final FlowCandidate electedCandidate = candidateByFingerprint.values().iterator().next();
+            this.electedDataFlow = electedCandidate.getDataFlow();
+            return electedCandidate;
+        }
+
         final FlowCandidate elected;
-        if (candidateByFingerprint.size() == 1) {
-            elected = candidateByFingerprint.values().iterator().next();
+        if (nonEmptyCandidates.size() == 1) {
+            // Only one flow is non-empty. Use that one.
+            elected = nonEmptyCandidates.iterator().next();
         } else {
-            elected = candidateByFingerprint.values().stream()
-                .filter(candidate -> !candidate.isFlowEmpty())  // We have more than 1 fingerprint. Do not consider empty flows.
+            // Choose the non-empty flow that got the most votes.
+            elected = nonEmptyCandidates.stream()
                 .max((candidate1, candidate2) -> Integer.compare(candidate1.getVotes(), candidate2.getVotes()))
                 .get();
         }

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-cluster/src/test/java/org/apache/nifi/cluster/coordination/flow/TestPopularVoteFlowElection.java

@@ -21,6 +21,7 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 import java.io.IOException;
 import java.nio.file.Files;
@@ -34,6 +35,8 @@ import org.apache.nifi.cluster.protocol.StandardDataFlow;
 import org.apache.nifi.fingerprint.FingerprintFactory;
 import org.junit.Test;
 import org.mockito.Mockito;
+import org.mockito.invocation.InvocationOnMock;
+import org.mockito.stubbing.Answer;
 
 public class TestPopularVoteFlowElection {
 
@@ -62,6 +65,43 @@ public class TestPopularVoteFlowElection {
         assertEquals(new String(flow), new String(electedDataFlow.getFlow()));
     }
 
+    @Test
+    public void testDifferentEmptyFlows() throws IOException {
+        final FingerprintFactory fingerprintFactory = Mockito.mock(FingerprintFactory.class);
+        Mockito.when(fingerprintFactory.createFingerprint(Mockito.any(byte[].class))).thenAnswer(new Answer<String>() {
+            @Override
+            public String answer(final InvocationOnMock invocation) throws Throwable {
+                final byte[] flow = invocation.getArgumentAt(0, byte[].class);
+                final String xml = new String(flow);
+
+                // Return the ID of the root group as the fingerprint.
+                final String fingerprint = xml.replaceAll("(?s:(.*<id>)(.*?)(</id>.*))", "$2");
+                return fingerprint;
+            }
+        });
+
+        final PopularVoteFlowElection election = new PopularVoteFlowElection(1, TimeUnit.MINUTES, 3, fingerprintFactory);
+        final byte[] flow1 = Files.readAllBytes(Paths.get("src/test/resources/conf/empty-flow.xml"));
+        final byte[] flow2 = Files.readAllBytes(Paths.get("src/test/resources/conf/different-empty-flow.xml"));
+
+        assertFalse(election.isElectionComplete());
+        assertNull(election.getElectedDataFlow());
+        assertNull(election.castVote(createDataFlow(flow1), createNodeId(1)));
+
+        assertFalse(election.isElectionComplete());
+        assertNull(election.getElectedDataFlow());
+        assertNull(election.castVote(createDataFlow(flow1), createNodeId(2)));
+
+        assertFalse(election.isElectionComplete());
+        assertNull(election.getElectedDataFlow());
+
+        final DataFlow electedDataFlow = election.castVote(createDataFlow(flow2), createNodeId(3));
+        assertNotNull(electedDataFlow);
+
+        final String electedFlowXml = new String(electedDataFlow.getFlow());
+        assertTrue(new String(flow1).equals(electedFlowXml) || new String(flow2).equals(electedFlowXml));
+    }
+
 
     @Test
     public void testEmptyFlowIgnoredIfNonEmptyFlowExists() throws IOException {

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-cluster/src/test/resources/conf/different-empty-flow.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!--
+  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.
+-->
+<flowController encoding-version="1.0">
+  <maxTimerDrivenThreadCount>10</maxTimerDrivenThreadCount>
+  <maxEventDrivenThreadCount>5</maxEventDrivenThreadCount>
+  <rootGroup>
+    <id>11111111-1111-1111-1111-111111111111</id>
+    <name>Empty NiFi Flow</name>
+    <position x="0.0" y="0.0"/>
+    <comment/>
+  </rootGroup>
+  <controllerServices/>
+  <reportingTasks/>
+</flowController>