Improve validation for StringMatchFilter for null/empty text #3153

log4j-core-test/src/test/java/org/apache/logging/log4j/core/filter/StringMatchFilterTest.java

@@ -0,0 +1,88 @@
+/*
+ * 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.filter;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.apache.logging.log4j.core.Filter;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.test.junit.LoggerContextSource;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit test for {@link StringMatchFilter}.
+ */
+public class StringMatchFilterTest {
+
+    /**
+     * Test that if no match-string is set on the builder, the '{@link StringMatchFilter.Builder#build()}' returns
+     * {@code null}.
+     */
+    @Test
+    public void testFilterBuilderFailsWithNullText() {
+        Assertions.assertNull(StringMatchFilter.newBuilder().build());
+    }
+
+    /**
+     * Test that if a {@code null} string is set as a match-pattern, an {@code IllegalArgumentExeption} is thrown.
+     */
+    @Test
+    void testFilterBuilderFailsWithExceptionOnNullText() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> StringMatchFilter.newBuilder()
+                .setMatchString(null));
+    }
+
+    /**
+     * Test that if an empty ({@code ""}) string is set as a match-pattern, an {@code IllegalArgumentException} is thrown.
+     */
+    @Test
+    void testFilterBuilderFailsWithExceptionOnEmptyText() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> StringMatchFilter.newBuilder()
+                .setMatchString(""));
+    }
+
+    /**
+     * Test that if a {@link StringMatchFilter} is specified with a 'text' attribute it is correctly instantiated.
+     *
+     * @param configuration the configuration
+     */
+    @Test
+    @LoggerContextSource("log4j2-stringmatchfilter-3153-ok.xml")
+    void testConfigurationWithTextPOS(final Configuration configuration) {
+        final Filter filter = configuration.getFilter();
+        assertNotNull(filter, "The filter should not be null.");
+        assertInstanceOf(
+                StringMatchFilter.class, filter, "Expected a StringMatchFilter, but got: " + filter.getClass());
+        assertEquals("FooBar", filter.toString());
+    }
+
+    /**
+     * Test that if a {@link StringMatchFilter} is specified without a 'text' attribute it is not instantiated.
+     *
+     * @param configuration the configuration
+     */
+    @Test
+    @LoggerContextSource("log4j2-stringmatchfilter-3153-nok.xml")
+    void testConfigurationWithTextNEG(final Configuration configuration) {
+        final Filter filter = configuration.getFilter();
+        assertNull(filter, "The filter should be null.");
+    }
+}

log4j-core-test/src/test/resources/log4j2-stringmatchfilter-3153-nok.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ 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.
+  -->
+<Configuration status="warn">
+   <StringMatchFfilter/>
+</Configuration>

log4j-core-test/src/test/resources/log4j2-stringmatchfilter-3153-ok.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ 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.
+  -->
+<Configuration status="warn">
+   <StringMatchFilter text="FooBar"/>
+</Configuration>

log4j-core/src/main/java/org/apache/logging/log4j/core/filter/StringMatchFilter.java

@@ -25,6 +25,8 @@
 import org.apache.logging.log4j.core.config.plugins.Plugin;
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
 import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
+import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;
+import org.apache.logging.log4j.core.util.Assert;
 import org.apache.logging.log4j.message.Message;
 import org.apache.logging.log4j.util.PerformanceSensitive;
 
@@ -41,7 +43,7 @@ public final class StringMatchFilter extends AbstractFilter {
 
     private StringMatchFilter(final String text, final Result onMatch, final Result onMismatch) {
         super(onMatch, onMismatch);
-        this.text = text;
+        this.text = Assert.requireNonEmpty(text, "text");
     }
 
     @Override
@@ -235,21 +237,26 @@ public static StringMatchFilter.Builder newBuilder() {
 
     public static class Builder extends AbstractFilterBuilder<StringMatchFilter.Builder>
             implements org.apache.logging.log4j.core.util.Builder<StringMatchFilter> {
+
         @PluginBuilderAttribute
-        private String text = "";
+        @Required(message = "No text provided for StringMatchFilter")
+        private String text;
 
         /**
          * Sets the text to search in event messages.
          * @param text the text to search in event messages.
          * @return this instance.
          */
         public StringMatchFilter.Builder setMatchString(final String text) {
-            this.text = text;
+            this.text = Assert.requireNonEmpty(text, "The 'text' argument must not be null or empty.");
             return this;
         }
 
         @Override
         public StringMatchFilter build() {
+            if (!isValid()) {
+                return null;
+            }
             return new StringMatchFilter(this.text, this.getOnMatch(), this.getOnMismatch());
         }
     }

src/changelog/.2.x.x/3153_fix_StringMatchFilter_guardNPE.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="changed">
+  <issue id="3153" link="https://github.com/apache/logging-log4j2/issues/3153"/>
+  <description format="asciidoc">Add improved validation to StringMatchFilter for null/empty text. GitHub issue #3153.</description>
+</entry>