Restore exception phrase in DisconnectedClientHelper

Effectively revert 203fa7, and add implementation comment and tests.

See gh-34264

Author: rstoyanchev

Diff for: spring-web/src/main/java/org/springframework/web/util/DisconnectedClientHelper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -36,8 +36,11 @@
  */
 public class DisconnectedClientHelper {
 
+	// Look for server response connection issues (aborted), not onward connections
+	// to other servers (500 errors).
+
 	private static final Set<String> EXCEPTION_PHRASES =
-			Set.of("broken pipe", "connection reset");
+			Set.of("broken pipe", "connection reset by peer");
 
 	private static final Set<String> EXCEPTION_TYPE_NAMES =
 			Set.of("AbortedException", "ClientAbortException",
@@ -79,7 +82,6 @@ else if (logger.isDebugEnabled()) {
 	 * <li>ClientAbortException or EOFException for Tomcat
 	 * <li>EofException for Jetty
 	 * <li>IOException "Broken pipe" or "connection reset by peer"
-	 * <li>SocketException "Connection reset"
 	 * </ul>
 	 */
 	public static boolean isClientDisconnectedException(Throwable ex) {

Diff for: spring-web/src/test/java/org/springframework/web/util/DisconnectedClientHelperTests.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2002-2025 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.util;
+
+import java.io.EOFException;
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.catalina.connector.ClientAbortException;
+import org.eclipse.jetty.io.EofException;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
+import reactor.netty.channel.AbortedException;
+
+import org.springframework.web.context.request.async.AsyncRequestNotUsableException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link DisconnectedClientHelper}.
+ * @author Rossen Stoyanchev
+ */
+public class DisconnectedClientHelperTests {
+
+	@ParameterizedTest
+	@ValueSource(strings = {"broKen pipe", "connection reset By peer"})
+	void exceptionPhrases(String phrase) {
+		Exception ex = new IOException(phrase);
+		assertThat(DisconnectedClientHelper.isClientDisconnectedException(ex)).isTrue();
+
+		ex = new IOException(ex);
+		assertThat(DisconnectedClientHelper.isClientDisconnectedException(ex)).isTrue();
+	}
+
+	@Test
+	void connectionResetExcluded() {
+		Exception ex = new IOException("connection reset");
+		assertThat(DisconnectedClientHelper.isClientDisconnectedException(ex)).isFalse();
+	}
+
+	@ParameterizedTest
+	@MethodSource("disconnectedExceptions")
+	void name(Exception ex) {
+		assertThat(DisconnectedClientHelper.isClientDisconnectedException(ex)).isTrue();
+	}
+
+	static List<Exception> disconnectedExceptions() {
+		return List.of(
+				new AbortedException(""), new ClientAbortException(""),
+				new EOFException(), new EofException(), new AsyncRequestNotUsableException(""));
+	}
+
+}