Fix NPE in RollingFileManger

This PR fixes a `NullPointerException` in
`RollingFileManager#createParentDir`.

Closes #1645

Author: ppkarwasz

log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/RollingFileManagerTest.java

@@ -16,7 +16,17 @@
  */
 package org.apache.logging.log4j.core.appender.rolling;
 
-import java.io.*;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.Reader;
 import java.nio.charset.StandardCharsets;
 import org.apache.logging.log4j.core.LoggerContext;
 import org.apache.logging.log4j.core.appender.RollingFileAppender;
@@ -26,8 +36,8 @@
 import org.apache.logging.log4j.core.layout.PatternLayout;
 import org.apache.logging.log4j.core.lookup.StrSubstitutor;
 import org.apache.logging.log4j.core.util.IOUtils;
-import org.junit.Assert;
 import org.junit.Test;
+import org.junitpioneer.jupiter.Issue;
 
 public class RollingFileManagerTest {
 
@@ -75,14 +85,14 @@ public RolloverDescription rollover(final RollingFileManager manager) throws Sec
                     .withPolicy(new SizeBasedTriggeringPolicy(100))
                     .build();
 
-            Assert.assertNotNull(appender);
+            assertNotNull(appender);
             final String testContent = "Test";
             try (final RollingFileManager manager = appender.getManager()) {
-                Assert.assertEquals(file.getAbsolutePath(), manager.getFileName());
+                assertEquals(file.getAbsolutePath(), manager.getFileName());
                 manager.writeToDestination(testContent.getBytes(StandardCharsets.US_ASCII), 0, testContent.length());
             }
             try (final Reader reader = new InputStreamReader(new FileInputStream(file), StandardCharsets.US_ASCII)) {
-                Assert.assertEquals(testContent, IOUtils.toString(reader));
+                assertEquals(testContent, IOUtils.toString(reader));
             }
         }
     }
@@ -125,7 +135,7 @@ public RolloverDescription rollover(final RollingFileManager manager) throws Sec
                 null,
                 null,
                 configuration);
-        Assert.assertNotNull(manager);
+        assertNotNull(manager);
         manager.initialize();
 
         // Get the initialTime of this original log file
@@ -139,9 +149,43 @@ public RolloverDescription rollover(final RollingFileManager manager) throws Sec
         manager.rollover();
 
         // If the rollover fails, then the size should not be reset
-        Assert.assertNotEquals(0, manager.getFileSize());
+        assertNotEquals(0, manager.getFileSize());
 
         // The initialTime should not have changed
-        Assert.assertEquals(initialTime, manager.getFileTime());
+        assertEquals(initialTime, manager.getFileTime());
+    }
+
+    @Test
+    @Issue("https://github.com/apache/logging-log4j2/issues/1645")
+    public void testCreateParentDir() {
+        final Configuration configuration = new NullConfiguration();
+        final RollingFileManager manager = RollingFileManager.getFileManager(
+                null,
+                "testCreateParentDir.log.%d{yyyy-MM-dd}",
+                true,
+                false,
+                NoOpTriggeringPolicy.INSTANCE,
+                DirectWriteRolloverStrategy.newBuilder()
+                        .withConfig(configuration)
+                        .build(),
+                null,
+                PatternLayout.createDefaultLayout(configuration),
+                0,
+                true,
+                true,
+                null,
+                null,
+                null,
+                configuration);
+        assertNotNull(manager);
+        try {
+            final File file = new File("file_in_current_dir.log");
+            assertNull(file.getParentFile());
+            manager.createParentDir(file);
+        } catch (final Throwable t) {
+            fail("createParentDir failed: " + t.getMessage());
+        } finally {
+            manager.close();
+        }
     }
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/appender/rolling/RollingFileManager.java

@@ -356,7 +356,11 @@ public String getFileName() {
     @Override
     protected void createParentDir(File file) {
         if (directWrite) {
-            file.getParentFile().mkdirs();
+            final File parent = file.getParentFile();
+            // If the parent is null the file is in the current working directory.
+            if (parent != null) {
+                parent.mkdirs();
+            }
         }
     }
 

src/changelog/.2.x.x/fix_create_parent_dir.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="http://logging.apache.org/log4j/changelog"
+       xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.2.xsd"
+       type="fixed">
+  <issue id="1645" link="https://github.com/apache/logging-log4j2/pull/1645"/>
+  <description format="asciidoc">
+    Fix NPE in `RollingFileManager`.
+  </description>
+</entry>