Disallow duplicate keys in JTL templates

Author: vy

log4j-layout-template-json-test/src/test/java/org/apache/logging/log4j/layout/template/json/util/JsonReaderTest.java

@@ -24,6 +24,8 @@
 import org.apache.logging.log4j.core.util.Integers;
 import org.assertj.core.api.Assertions;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class JsonReaderTest {
 
@@ -234,6 +236,7 @@ void test_invalid_array_end_3() {
     void test_valid_objects() {
         test("{}", Collections.emptyMap());
         test("{\"foo\":\"bar\"}", Collections.singletonMap("foo", "bar"));
+        test("{\"x\":{\"x\": \"x\"}}", Collections.singletonMap("x", Collections.singletonMap("x", "x")));
     }
 
     @Test
@@ -299,6 +302,21 @@ void test_invalid_object_key() {
                 .hasMessage("was expecting an object key at index 13: ARRAY_END");
     }
 
+    @ParameterizedTest
+    @CsvSource(
+            value = {
+                "a|7|{\"a\":1,\"a\":2}",
+                "a|13|{\"a\":1,\"b\":2,\"a\":3}",
+                "c|24|{\"a\":1,\"b\":{\"c\":2,\"d\":3,\"c\":4}}"
+            },
+            delimiter = '|')
+    void test_conflicting_object_key_1(final String key, final int index, final String json) {
+        Assertions.assertThatThrownBy(() -> JsonReader.read(json))
+                .as("key=`%s`, index=%d, json=`%s`", key, index, json)
+                .isInstanceOf(IllegalArgumentException.class)
+                .hasMessage("found duplicate object key at index %d: %s", index, key);
+    }
+
     @Test
     @SuppressWarnings("DoubleBraceInitialization")
     public void test_nesting() {

log4j-layout-template-json/src/main/java/org/apache/logging/log4j/layout/template/json/util/JsonReader.java

@@ -282,6 +282,10 @@ private Map<String, Object> readObject() {
                         final String message = String.format(
                                 "was expecting an object key at index %d: %s", readTokenStartIndex, readToken);
                         throw new IllegalArgumentException(message);
+                    } else if (object.containsKey(key)) {
+                        final String message =
+                                String.format("found duplicate object key at index %d: %s", readTokenStartIndex, key);
+                        throw new IllegalArgumentException(message);
                     }
                 } else {
                     expectDelimiter(Delimiter.OBJECT_END, readToken);

src/changelog/.2.x.x/change_JsonReader_dup_key.xml

@@ -0,0 +1,7 @@
+<?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">
+  <description format="asciidoc">Disallow duplicate keys in JSON Template Layout templates</description>
+</entry>