Add failure test and changelog entry

Add testNoJarFileLeakOnFailure to verify that a failed JAR configuration
load (missing entry) does not leak file descriptors or hold a lock on
the JAR file.

Add changelog entry for the ConfigurationSource URL leak fix.

Author: SebTardif

log4j-core-test/src/test/java/org/apache/logging/log4j/core/config/ConfigurationSourceTest.java

@@ -104,6 +104,28 @@ void testLoadConfigurationSourceFromJarFile() throws Exception {
         }
     }
 
+    /**
+     * Verifies that a failed JAR configuration load (missing entry) does not leak file descriptors
+     * or hold a lock on the JAR file.
+     */
+    @Test
+    void testNoJarFileLeakOnFailure() throws Exception {
+        final Path jarFile = prepareJarConfigURL(tempDir);
+        // Path inside JAR that does NOT exist
+        final URL brokenJarConfigURL = new URL("jar:" + jarFile.toUri().toURL() + "!/missing/file.xml");
+        final long expectedFdCount = getOpenFileDescriptorCount();
+        final ConfigurationSource configSource = ConfigurationSource.fromUri(brokenJarConfigURL.toURI());
+        assertNull(configSource, "Source should be null for a missing JAR entry");
+        // This can only fail on UNIX
+        assertEquals(expectedFdCount, getOpenFileDescriptorCount(), "File descriptors leaked after failed JAR load");
+        // This can only fail on Windows
+        try {
+            Files.delete(jarFile);
+        } catch (IOException e) {
+            fail("JAR file locked after failed load: " + e.getMessage());
+        }
+    }
+
     private long getOpenFileDescriptorCount() {
         final OperatingSystemMXBean os = ManagementFactory.getOperatingSystemMXBean();
         if (os instanceof UnixOperatingSystemMXBean) {

src/changelog/.2.x.x/fix_configuration_source_url_leak.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="4127" link="https://github.com/apache/logging-log4j2/pull/4127"/>
+  <description format="asciidoc">Fix resource leaks in `ConfigurationSource` when loading configuration via URL fails</description>
+</entry>