Support additional fields in logback encoder (#59)

Author: felixbarny

logback-ecs-encoder/README.md

@@ -64,3 +64,16 @@ All you have to do is to use the `co.elastic.logging.logback.EcsEncoder` instead
 |includeMarkers   |boolean|`false`|Log [Markers](https://logging.apache.org/log4j/2.0/manual/markers.html) as [`tags`](https://www.elastic.co/guide/en/ecs/current/ecs-base.html) |
 |stackTraceAsArray|boolean|`false`|Serializes the [`error.stack_trace`](https://www.elastic.co/guide/en/ecs/current/ecs-error.html) as a JSON array where each element is in a new line to improve readability. Note that this requires a slightly more complex [Filebeat configuration](../README.md#when-stacktraceasarray-is-enabled).|
 |includeOrigin    |boolean|`false`|If `true`, adds the [`log.origin.file.name`](https://www.elastic.co/guide/en/ecs/current/ecs-log.html), [`log.origin.file.line`](https://www.elastic.co/guide/en/ecs/current/ecs-log.html) and [`log.origin.function`](https://www.elastic.co/guide/en/ecs/current/ecs-log.html) fields. Note that you also have to set `includeLocation="true"` on your loggers and appenders if you are using the async ones. |
+
+To include any custom field in the output, use following syntax:
+
+```xml
+<additionalField>
+    <key>foo</key>
+    <value>bar</value>
+</additionalField>
+<additionalField>
+    <key>baz</key>
+    <value>qux</value>
+</additionalField>
+```

logback-ecs-encoder/src/main/java/co/elastic/logging/logback/EcsEncoder.java

@@ -30,11 +30,14 @@
 import ch.qos.logback.classic.spi.ThrowableProxy;
 import ch.qos.logback.core.encoder.EncoderBase;
 import co.elastic.logging.EcsJsonSerializer;
+import co.elastic.logging.JsonUtils;
 import org.slf4j.Marker;
 
 import java.nio.charset.Charset;
+import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.Iterator;
+import java.util.List;
 import java.util.Set;
 
 public class EcsEncoder extends EncoderBase<ILoggingEvent> {
@@ -46,6 +49,7 @@ public class EcsEncoder extends EncoderBase<ILoggingEvent> {
     private ThrowableProxyConverter throwableProxyConverter;
     private Set<String> topLevelLabels = new HashSet<String>(EcsJsonSerializer.DEFAULT_TOP_LEVEL_LABELS);
     private boolean includeOrigin;
+    private List<Pair> additionalFields = new ArrayList<Pair>();
 
     @Override
     public byte[] headerBytes() {
@@ -69,6 +73,7 @@ public byte[] encode(ILoggingEvent event) {
         EcsJsonSerializer.serializeServiceName(builder, serviceName);
         EcsJsonSerializer.serializeThreadName(builder, event.getThreadName());
         EcsJsonSerializer.serializeLoggerName(builder, event.getLoggerName());
+        serializeAdditionalFields(builder);
         EcsJsonSerializer.serializeLabels(builder, event.getMDCPropertyMap(), topLevelLabels);
         if (includeOrigin) {
             StackTraceElement[] callerData = event.getCallerData();
@@ -86,7 +91,22 @@ public byte[] encode(ILoggingEvent event) {
         // all these allocations kinda hurt
         return builder.toString().getBytes(UTF_8);
     }
-    
+
+    private void serializeAdditionalFields(StringBuilder builder) {
+        if (!additionalFields.isEmpty()) {
+            for (int i = 0, size = additionalFields.size(); i < size; i++) {
+                Pair additionalField = additionalFields.get(i);
+                if (additionalField.getKey() != null) {
+                    builder.append('\"');
+                    JsonUtils.quoteAsString(additionalField.getKey(), builder);
+                    builder.append("\":\"");
+                    JsonUtils.quoteAsString(additionalField.getValue(), builder);
+                    builder.append("\",");
+                }
+            }
+        }
+    }
+
     public void addTopLevelLabel(String topLevelLabel) {
         this.topLevelLabels.add(topLevelLabel);
     }
@@ -130,4 +150,37 @@ public void setStackTraceAsArray(boolean stackTraceAsArray) {
     public void setIncludeOrigin(boolean includeOrigin) {
         this.includeOrigin = includeOrigin;
     }
+
+    public void addAdditionalField(Pair pair) {
+        this.additionalFields.add(pair);
+    }
+
+    public static class Pair {
+        private String key;
+        private String value = "";
+
+        public Pair() {
+        }
+
+        public Pair(String key, String value) {
+            this.key = key;
+            this.value = value;
+        }
+
+        public String getKey() {
+            return key;
+        }
+
+        public void setKey(String key) {
+            this.key = key;
+        }
+
+        public String getValue() {
+            return value;
+        }
+
+        public void setValue(String value) {
+            this.value = value;
+        }
+    }
 }

logback-ecs-encoder/src/test/java/co/elastic/logging/logback/AbstractEcsEncoderTest.java

@@ -47,6 +47,13 @@ public void debug(String message) {
         logger.debug(message);
     }
 
+    @Test
+    void testAdditionalFields() throws Exception {
+        debug("test");
+        assertThat(getLastLogLine().get("foo").textValue()).isEqualTo("bar");
+        assertThat(getLastLogLine().get("baz").textValue()).isEqualTo("qux");
+    }
+
     @Test
     void testMarker() throws Exception {
         Marker parent = MarkerFactory.getMarker("parent");

logback-ecs-encoder/src/test/java/co/elastic/logging/logback/EcsEncoderTest.java

@@ -47,6 +47,8 @@ void setUp() {
         ecsEncoder.setStackTraceAsArray(true);
         ecsEncoder.setIncludeOrigin(true);
         ecsEncoder.addTopLevelLabel("top_level");
+        ecsEncoder.addAdditionalField(new EcsEncoder.Pair("foo", "bar"));
+        ecsEncoder.addAdditionalField(new EcsEncoder.Pair("baz", "qux"));
         ecsEncoder.start();
         appender.setEncoder(ecsEncoder);
         appender.start();

logback-ecs-encoder/src/test/resources/logback-config.xml

@@ -7,6 +7,14 @@
             <includeOrigin>true</includeOrigin>
             <stackTraceAsArray>true</stackTraceAsArray>
             <topLevelLabel>top_level</topLevelLabel>
+            <additionalField>
+                <key>foo</key>
+                <value>bar</value>
+            </additionalField>
+            <additionalField>
+                <key>baz</key>
+                <value>qux</value>
+            </additionalField>
         </encoder>
     </appender>
     <root level="DEBUG">