From 7a2364c9571523d094f55d008c8835d49b1c831c Mon Sep 17 00:00:00 2001
From: Ryan Schmitt <rschmitt@apache.org>
Date: Tue, 22 Jul 2025 13:03:53 -0700
Subject: [PATCH] DefaultLayout: Append a newline to the serialized LogEvent

Fixes #3835.
---
 .../core/appender/DefaultLayoutTest.java      | 50 +++++++++++++++++++
 .../log4j/core/config/DefaultLayout.java      | 13 ++---
 src/changelog/.2.x.x/3835-default-layout.xml  | 12 +++++
 3 files changed, 69 insertions(+), 6 deletions(-)
 create mode 100644 log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/DefaultLayoutTest.java
 create mode 100644 src/changelog/.2.x.x/3835-default-layout.xml

diff --git a/log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/DefaultLayoutTest.java b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/DefaultLayoutTest.java
new file mode 100644
index 00000000000..9bfb563f1d2
--- /dev/null
+++ b/log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/DefaultLayoutTest.java
@@ -0,0 +1,50 @@
+/*
+ * 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.logging.log4j.core.appender;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.nio.charset.Charset;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.junit.jupiter.api.Test;
+
+class DefaultLayoutTest {
+    @Test
+    void testDefaultLayout() {
+        PrintStream standardOutput = System.out;
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+        System.setOut(new PrintStream(baos));
+        try {
+            Logger log = LogManager.getLogger(getClass());
+            log.fatal("This is a fatal message");
+            log.error("This is an error message");
+            log.warn("This is a warning message");
+
+            String actualOutput = new String(baos.toByteArray(), Charset.defaultCharset());
+            assertTrue(actualOutput.contains("FATAL This is a fatal message" + System.lineSeparator()));
+            assertTrue(actualOutput.contains("ERROR This is an error message" + System.lineSeparator()));
+            assertFalse(actualOutput.contains("This is a warning message"));
+        } finally {
+            System.setOut(standardOutput);
+        }
+    }
+}
diff --git a/log4j-core/src/main/java/org/apache/logging/log4j/core/config/DefaultLayout.java b/log4j-core/src/main/java/org/apache/logging/log4j/core/config/DefaultLayout.java
index 5aabbec39bb..a425d9ac117 100644
--- a/log4j-core/src/main/java/org/apache/logging/log4j/core/config/DefaultLayout.java
+++ b/log4j-core/src/main/java/org/apache/logging/log4j/core/config/DefaultLayout.java
@@ -42,12 +42,13 @@ private DefaultLayout() {}
     @Override
     public String toSerializable(LogEvent event) {
         return new StatusData(
-                        event.getSource(),
-                        event.getLevel(),
-                        event.getMessage(),
-                        event.getThrown(),
-                        event.getThreadName())
-                .getFormattedStatus();
+                                event.getSource(),
+                                event.getLevel(),
+                                event.getMessage(),
+                                event.getThrown(),
+                                event.getThreadName())
+                        .getFormattedStatus()
+                + System.lineSeparator();
     }
 
     @Override
diff --git a/src/changelog/.2.x.x/3835-default-layout.xml b/src/changelog/.2.x.x/3835-default-layout.xml
new file mode 100644
index 00000000000..877631c9028
--- /dev/null
+++ b/src/changelog/.2.x.x/3835-default-layout.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns="https://logging.apache.org/xml/ns"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:schemaLocation="
+           https://logging.apache.org/xml/ns
+           https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="3835" link="https://github.com/apache/logging-log4j2/issues/3835"/>
+  <description format="asciidoc">
+    Fix missing newlines in default logging configuration for log4j-core.
+  </description>
+</entry>