CASSANDRA-21097: parseGossipInfo improper assumption might fail to parse gossip output after a node restart

test/distributed/org/apache/cassandra/distributed/shared/ClusterUtils.java

@@ -122,6 +122,20 @@
 public class ClusterUtils
 {
     private static final Logger logger = LoggerFactory.getLogger(ClusterUtils.class);
+
+    /**
+     * Pattern to match gossip endpoint addresses in both formats:
+     * - "/127.0.0.1" (hostname not resolved)
+     * - "localhost/127.0.0.1" (hostname cached after getHostName() call)
+     * - "localhost/127.0.0.1:7000" (with port)
+     *
+     * Java's InetAddress caches hostname at the object level. Once any code path calls
+     * getHostName() on gossip endpoint InetAddress objects, subsequent toString() calls
+     * return "hostname/IP" instead of "/IP".
+     *
+     * @see <a href="https://issues.apache.org/jira/browse/CASSANDRA-21097">CASSANDRA-21097</a>
+     */
+    private static final Pattern GOSSIP_ENDPOINT_PATTERN = Pattern.compile("^[^\\s/]*/(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})(:\\d+)?$");
     /**
      * Start the instance with the given System Properties, after the instance has started, the properties will be cleared.
      */
@@ -1270,14 +1284,15 @@ public static void assertGossipInfo(IInstance instance,
         Assert.assertEquals(Long.toString(expectedHeartbeat), gossipState.get("heartbeat")); //TODO do we really mix these two?
     }
 
-    private static Map<String, Map<String, String>> parseGossipInfo(String str)
+    @VisibleForTesting
+    static Map<String, Map<String, String>> parseGossipInfo(String str)
     {
         Map<String, Map<String, String>> map = new HashMap<>();
         String[] lines = str.split("\n");
         String currentInstance = null;
         for (String line : lines)
         {
-            if (line.startsWith("/"))
+            if (GOSSIP_ENDPOINT_PATTERN.matcher(line).matches())
             {
                 // start of new instance
                 currentInstance = line;

test/distributed/org/apache/cassandra/distributed/shared/ClusterUtilsParseGossipInfoTest.java

@@ -0,0 +1,137 @@
+/*
+ * 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.cassandra.distributed.shared;
+
+import java.util.Map;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Tests for ClusterUtils.parseGossipInfo method.
+ *
+ * CASSANDRA-21097: Tests that parseGossipInfo handles both endpoint address formats:
+ * - "/127.0.0.1" (hostname not resolved)
+ * - "localhost/127.0.0.1" (hostname cached after getHostName() call)
+ */
+public class ClusterUtilsParseGossipInfoTest
+{
+    /**
+     * Tests parsing gossip info with standard format where endpoint starts with "/".
+     * This is the format when InetAddress hostname has NOT been resolved.
+     */
+    @Test
+    public void testParseGossipInfoWithSlashPrefix()
+    {
+        String gossipInfo = "/127.0.0.1:7012\n" +
+                            "  generation:1234567890\n" +
+                            "  heartbeat:100\n" +
+                            "/127.0.0.2:7012\n" +
+                            "  generation:1234567891\n" +
+                            "  heartbeat:101\n";
+
+        Map<String, Map<String, String>> result = ClusterUtils.parseGossipInfo(gossipInfo);
+
+        assertNotNull(result);
+        assertEquals(2, result.size());
+        assertTrue(result.containsKey("/127.0.0.1:7012"));
+        assertTrue(result.containsKey("/127.0.0.2:7012"));
+        assertEquals("1234567890", result.get("/127.0.0.1:7012").get("generation"));
+        assertEquals("100", result.get("/127.0.0.1:7012").get("heartbeat"));
+        assertEquals("1234567891", result.get("/127.0.0.2:7012").get("generation"));
+        assertEquals("101", result.get("/127.0.0.2:7012").get("heartbeat"));
+    }
+
+    /**
+     * Tests parsing gossip info with hostname prefix format.
+     * This is the format when InetAddress.getHostName() has been called,
+     * causing the hostname to be cached in the InetAddress object.
+     *
+     * CASSANDRA-21097: This test would fail before the fix because the parser
+     * only checked for lines starting with "/" and would throw NPE when
+     * encountering "localhost/127.0.0.1" format.
+     */
+    @Test
+    public void testParseGossipInfoWithHostnamePrefix()
+    {
+        String gossipInfo = "localhost/127.0.0.1:7012\n" +
+                            "  generation:1234567890\n" +
+                            "  heartbeat:100\n" +
+                            "localhost/127.0.0.2:7012\n" +
+                            "  generation:1234567891\n" +
+                            "  heartbeat:101\n";
+
+        Map<String, Map<String, String>> result = ClusterUtils.parseGossipInfo(gossipInfo);
+
+        assertNotNull(result);
+        assertEquals(2, result.size());
+        assertTrue(result.containsKey("localhost/127.0.0.1:7012"));
+        assertTrue(result.containsKey("localhost/127.0.0.2:7012"));
+        assertEquals("1234567890", result.get("localhost/127.0.0.1:7012").get("generation"));
+        assertEquals("100", result.get("localhost/127.0.0.1:7012").get("heartbeat"));
+        assertEquals("1234567891", result.get("localhost/127.0.0.2:7012").get("generation"));
+        assertEquals("101", result.get("localhost/127.0.0.2:7012").get("heartbeat"));
+    }
+
+    /**
+     * Tests parsing gossip info with mixed formats (both with and without hostname).
+     */
+    @Test
+    public void testParseGossipInfoWithMixedFormats()
+    {
+        String gossipInfo = "/127.0.0.1:7012\n" +
+                            "  generation:1234567890\n" +
+                            "  heartbeat:100\n" +
+                            "localhost/127.0.0.2:7012\n" +
+                            "  generation:1234567891\n" +
+                            "  heartbeat:101\n";
+
+        Map<String, Map<String, String>> result = ClusterUtils.parseGossipInfo(gossipInfo);
+
+        assertNotNull(result);
+        assertEquals(2, result.size());
+        assertTrue(result.containsKey("/127.0.0.1:7012"));
+        assertTrue(result.containsKey("localhost/127.0.0.2:7012"));
+    }
+
+    /**
+     * Tests parsing gossip info without port numbers.
+     */
+    @Test
+    public void testParseGossipInfoWithoutPort()
+    {
+        String gossipInfo = "/127.0.0.1\n" +
+                            "  generation:1234567890\n" +
+                            "  heartbeat:100\n" +
+                            "localhost/127.0.0.2\n" +
+                            "  generation:1234567891\n" +
+                            "  heartbeat:101\n";
+
+        Map<String, Map<String, String>> result = ClusterUtils.parseGossipInfo(gossipInfo);
+
+        assertNotNull(result);
+        assertEquals(2, result.size());
+        assertTrue(result.containsKey("/127.0.0.1"));
+        assertTrue(result.containsKey("localhost/127.0.0.2"));
+    }
+
+}