Avoid StringIndexOutOfBoundsException in WebSocketMessageBrokerStats

Prior to this commit, if the TaskExecutor configured in
WebSocketMessageBrokerStats for the inboundChannelExecutor or
outboundChannelExecutor was not a ThreadPoolTaskExecutor, a
StringIndexOutOfBoundsException was thrown when attempting to parse the
results of invoking toString() on the executor.

The reason is that ThreadPoolTaskExecutor delegates to a
ThreadPoolExecutor whose toString() implementation generates text
containing "pool size = ...", and WebSocketMessageBrokerStats'
getExecutorStatsInfo() method relied on the presence of "pool" in the
text returned from toString().

This commit fixes this bug by ensuring that the text returned from
toString() contains "pool" before parsing the text. If "pool" is not
present in the text, getExecutorStatsInfo() now returns "unknown"
instead of throwing a StringIndexOutOfBoundsException.

Closes gh-27209

spring-websocket/src/main/java/org/springframework/web/socket/config/WebSocketMessageBrokerStats.java

 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import java.time.Duration;
 import java.time.Instant;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
 import org.apache.commons.logging.Log;
@@ -49,6 +50,7 @@ import org.springframework.web.socket.messaging.SubProtocolWebSocketHandler;
  * the {@link org.springframework.jmx.export.MBeanExporter MBeanExporter}.
  *
  * @author Rossen Stoyanchev
+ * @author Sam Brannen
  * @since 4.1
  */
 public class WebSocketMessageBrokerStats {
@@ -174,16 +176,14 @@ public class WebSocketMessageBrokerStats {
 	 * Get stats about the executor processing incoming messages from WebSocket clients.
 	 */
 	public String getClientInboundExecutorStatsInfo() {
-		return (this.inboundChannelExecutor != null ?
-				getExecutorStatsInfo(this.inboundChannelExecutor) : "null");
+		return getExecutorStatsInfo(this.inboundChannelExecutor);
 	}
 
 	/**
 	 * Get stats about the executor processing outgoing messages to WebSocket clients.
 	 */
 	public String getClientOutboundExecutorStatsInfo() {
-		return (this.outboundChannelExecutor != null ?
-				getExecutorStatsInfo(this.outboundChannelExecutor) : "null");
+		return getExecutorStatsInfo(this.outboundChannelExecutor);
 	}
 
 	/**
@@ -197,16 +197,31 @@ public class WebSocketMessageBrokerStats {
 			return getExecutorStatsInfo(((ThreadPoolTaskScheduler) this.sockJsTaskScheduler)
 					.getScheduledThreadPoolExecutor());
 		}
-		else {
-			return "unknown";
-		}
+		return "unknown";
 	}
 
-	private String getExecutorStatsInfo(Executor executor) {
-		executor = executor instanceof ThreadPoolTaskExecutor ?
-				((ThreadPoolTaskExecutor) executor).getThreadPoolExecutor() : executor;
-		String str = executor.toString();
-		return str.substring(str.indexOf("pool"), str.length() - 1);
+	private String getExecutorStatsInfo(@Nullable Executor executor) {
+		if (executor == null) {
+			return "null";
+		}
+
+		if (executor instanceof ThreadPoolTaskExecutor) {
+			executor = ((ThreadPoolTaskExecutor) executor).getThreadPoolExecutor();
+		}
+
+		if (executor instanceof ThreadPoolExecutor) {
+			// It is assumed that the implementation of toString() in ThreadPoolExecutor
+			// generates text that ends similar to the following:
+			// pool size = #, active threads = #, queued tasks = #, completed tasks = #]
+			String str = executor.toString();
+			int indexOfPool = str.indexOf("pool");
+			if (indexOfPool != -1) {
+				// (length - 1) omits the trailing "]"
+				return str.substring(indexOfPool, str.length() - 1);
+			}
+		}
+
+		return "unknown";
 	}
 
 	@Override

spring-websocket/src/test/java/org/springframework/web/socket/config/WebSocketMessageBrokerStatsTests.java

+/*
+ * Copyright 2002-2021 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.springframework.web.socket.config;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.task.TaskExecutor;
+import org.springframework.scheduling.TaskScheduler;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Unit tests for {@link WebSocketMessageBrokerStats}.
+ *
+ * @author Sam Brannen
+ * @since 5.3.10
+ * @see org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurationSupportTests
+ */
+class WebSocketMessageBrokerStatsTests {
+
+	private final WebSocketMessageBrokerStats stats = new WebSocketMessageBrokerStats();
+
+	@Test
+	void nullValues() {
+		String expected = "WebSocketSession[null], stompSubProtocol[null], stompBrokerRelay[null], " +
+				"inboundChannel[null], outboundChannel[null], sockJsScheduler[null]";
+		assertThat(stats).hasToString(expected);
+	}
+
+	@Test
+	void inboundAndOutboundChannelsWithThreadPoolTaskExecutor() {
+		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+		executor.afterPropertiesSet();
+
+		stats.setInboundChannelExecutor(executor);
+		stats.setOutboundChannelExecutor(executor);
+
+		assertThat(stats.getClientInboundExecutorStatsInfo()).as("inbound channel stats")
+			.isEqualTo("pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 0");
+		assertThat(stats.getClientOutboundExecutorStatsInfo()).as("outbound channel stats")
+			.isEqualTo("pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 0");
+	}
+
+	@Test
+	void inboundAndOutboundChannelsWithMockedTaskExecutor() {
+		TaskExecutor executor = mock(TaskExecutor.class);
+
+		stats.setInboundChannelExecutor(executor);
+		stats.setOutboundChannelExecutor(executor);
+
+		assertThat(stats.getClientInboundExecutorStatsInfo()).as("inbound channel stats").isEqualTo("unknown");
+		assertThat(stats.getClientOutboundExecutorStatsInfo()).as("outbound channel stats").isEqualTo("unknown");
+	}
+
+	@Test
+	void sockJsTaskSchedulerWithThreadPoolTaskScheduler() {
+		ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
+		scheduler.afterPropertiesSet();
+
+		stats.setSockJsTaskScheduler(scheduler);
+
+		assertThat(stats.getSockJsTaskSchedulerStatsInfo())
+			.isEqualTo("pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 0");
+	}
+
+	@Test
+	void sockJsTaskSchedulerWithMockedTaskScheduler() {
+		TaskScheduler scheduler = mock(TaskScheduler.class);
+
+		stats.setSockJsTaskScheduler(scheduler);
+
+		assertThat(stats.getSockJsTaskSchedulerStatsInfo()).isEqualTo("unknown");
+	}
+
+}