LOG4J-2735 - make PluginCache output reproducible (#321)
Previously, the data written by a PluginCache with identical
categories and entries would vary depending on the order in which
those categories or entries were added to the cache. The ordering of
the elements handled by the annotation processor that populates the
cache is not guaranteed so multiple compilations of identical source
code could result in different output. This prevented projects that
define Log4j2 plugins from having a reproducible build.
This commit updates PluginCache to use TreeMaps to hold categories
and their entries. This ensures that the cache's data is stored and
written in an order determined by sorting their String keys rather
than by when they are added. This makes the cache's output
reproducible, irrespective of the order of the elements handled by
the annotation processor.
diff --git a/log4j-core/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCacheTest.java b/log4j-core/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCacheTest.java
new file mode 100644
index 0000000..c773908
--- /dev/null
+++ b/log4j-core/src/test/java/org/apache/logging/log4j/core/config/plugins/processor/PluginCacheTest.java
@@ -0,0 +1,71 @@
+/*
+ * 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.config.plugins.processor;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class PluginCacheTest {
+
+ @Test
+ public void testOutputIsReproducibleWhenInputOrderingChanges() throws IOException {
+ PluginCache cacheA = new PluginCache();
+ createCategory(cacheA, "one", Arrays.asList("bravo", "alpha", "charlie"));
+ createCategory(cacheA, "two", Arrays.asList("alpha", "charlie", "bravo"));
+ assertEquals(cacheA.getAllCategories().size(), 2);
+ assertEquals(cacheA.getAllCategories().get("one").size(), 3);
+ assertEquals(cacheA.getAllCategories().get("two").size(), 3);
+ PluginCache cacheB = new PluginCache();
+ createCategory(cacheB, "two", Arrays.asList("bravo", "alpha", "charlie"));
+ createCategory(cacheB, "one", Arrays.asList("alpha", "charlie", "bravo"));
+ assertEquals(cacheB.getAllCategories().size(), 2);
+ assertEquals(cacheB.getAllCategories().get("one").size(), 3);
+ assertEquals(cacheB.getAllCategories().get("two").size(), 3);
+ assertArrayEquals(cacheData(cacheA), cacheData(cacheB));
+ }
+
+ private void createCategory(PluginCache cache, String categoryName, List<String> entryNames) {
+ Map<String, PluginEntry> category = cache.getCategory(categoryName);
+ for (String entryName: entryNames) {
+ PluginEntry entry = new PluginEntry();
+ entry.setKey(entryName);
+ entry.setClassName("com.example.Plugin");
+ entry.setName("name");
+ entry.setCategory(categoryName);
+ category.put(entryName, entry);
+ }
+ }
+
+ private byte[] cacheData(PluginCache cache) throws IOException {
+ ByteArrayOutputStream outputB = new ByteArrayOutputStream();
+ cache.writeCache(outputB);
+ return outputB.toByteArray();
+ }
+
+}
diff --git a/log4j-plugins/src/main/java/org/apache/logging/log4j/plugins/processor/PluginCache.java b/log4j-plugins/src/main/java/org/apache/logging/log4j/plugins/processor/PluginCache.java
index 784dece..c731352 100644
--- a/log4j-plugins/src/main/java/org/apache/logging/log4j/plugins/processor/PluginCache.java
+++ b/log4j-plugins/src/main/java/org/apache/logging/log4j/plugins/processor/PluginCache.java
@@ -25,15 +25,15 @@
import java.io.OutputStream;
import java.net.URL;
import java.util.Enumeration;
-import java.util.LinkedHashMap;
import java.util.Map;
+import java.util.TreeMap;
/**
*
*/
public class PluginCache {
private final Map<String, Map<String, PluginEntry>> categories =
- new LinkedHashMap<>();
+ new TreeMap<>();
/**
* Returns all categories of plugins in this cache.
@@ -54,7 +54,7 @@
public Map<String, PluginEntry> getCategory(final String category) {
final String key = category.toLowerCase();
if (!categories.containsKey(key)) {
- categories.put(key, new LinkedHashMap<String, PluginEntry>());
+ categories.put(key, new TreeMap<String, PluginEntry>());
}
return categories.get(key);
}
