#55 Work around for TokenFilter-vs-Delegate ordering bug.

Author: vy

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Fix NPE in `StringTruncatingGeneratorDelegate`. (#53)
 
+- Implement work around for FasterXML/jackson-core#609 triggered when
+  `maxStringLength` is used in combination with
+  `emptyPropertyExclusionEnabled=true`. (#55)
+
 ### (2019-10-15) v0.21
 
 - Add feature comparison matrix.

layout/src/main/java/com/vlkan/log4j2/logstash/layout/LogstashLayoutSerializationContexts.java

@@ -91,12 +91,13 @@ private static JsonGenerator createJsonGenerator(
             if (prettyPrintEnabled) {
                 jsonGenerator.setPrettyPrinter(PRETTY_PRINTER);
             }
-            if (emptyPropertyExclusionEnabled) {
-                jsonGenerator = new FilteringGeneratorDelegate(jsonGenerator, NullExcludingTokenFilter.INSTANCE, true, true);
-            }
             if (maxStringLength > 0) {
                 jsonGenerator = new StringTruncatingGeneratorDelegate(jsonGenerator, maxStringLength);
             }
+            // TokenFilter has to come last due to FasterXML/jackson-core#609.
+            if (emptyPropertyExclusionEnabled) {
+                jsonGenerator = new FilteringGeneratorDelegate(jsonGenerator, NullExcludingTokenFilter.INSTANCE, true, true);
+            }
             return jsonGenerator;
         } catch (IOException error) {
             throw new RuntimeException("failed creating JsonGenerator", error);

layout/src/test/java/com/vlkan/log4j2/logstash/layout/LogstashLayoutTest.java

@@ -1420,4 +1420,39 @@ public void test_StackTraceObjectResolver_against_getStackTrace_failures() throw
 
     }
 
+    @Test
+    public void test_maxStringLength_with_emptyPropertyExclusionEnabled() throws Exception {
+
+        // Create the event template.
+        ObjectNode eventTemplateRootNode = JSON_NODE_FACTORY.objectNode();
+        eventTemplateRootNode.put("message", "${json:message}");
+        String eventTemplate = eventTemplateRootNode.toString();
+
+        // Create the layout.
+        int maxStringLength = eventTemplate.length();
+        Configuration configuration = ConfigurationBuilderFactory.newConfigurationBuilder().build();
+        LogstashLayout layout = LogstashLayout
+                .newBuilder()
+                .setConfiguration(configuration)
+                .setEventTemplate(eventTemplate)
+                .setMaxStringLength(maxStringLength)
+                .setEmptyPropertyExclusionEnabled(true)
+                .build();
+
+        // Create the log event.
+        SimpleMessage message = new SimpleMessage(StringUtils.repeat('m', maxStringLength) + 'x');
+        LogEvent logEvent = Log4jLogEvent
+                .newBuilder()
+                .setLoggerName(LogstashLayoutTest.class.getSimpleName())
+                .setMessage(message)
+                .build();
+
+        // Check the serialized event.
+        String serializedLogEvent = layout.toSerializable(logEvent);
+        JsonNode rootNode = OBJECT_MAPPER.readTree(serializedLogEvent);
+        String expectedMessage = message.getFormattedMessage().substring(0, maxStringLength);
+        assertThat(point(rootNode, "message").asText()).isEqualTo(expectedMessage);
+
+    }
+
 }