fix(gcp): map OpenTelemetry trace fields

gcp/logback-logstash-encoder-gcp/src/main/java/no/entur/logging/cloud/gcp/logback/logstash/StackdriverOpenTelemetryTraceMdcJsonProvider.java

@@ -8,27 +8,53 @@
 import java.util.Map;
 
 /**
+ * An MDC provider that maps OpenTelemetry trace fields to the special JSON fields
+ * recognized by Google Cloud Logging.
  *
- * A simple MDC provider. Renames MDC field name traceId to trace.
+ * <p>When the Google Cloud Logging agent ingests structured JSON written to stdout, it promotes
+ * recognized JSON fields into the corresponding {@code LogEntry} fields. In particular:
+ * <ul>
+ *     <li>{@code logging.googleapis.com/trace} becomes {@code LogEntry.trace}</li>
+ *     <li>{@code logging.googleapis.com/spanId} becomes {@code LogEntry.spanId}</li>
+ * </ul>
+ * Unrecognized fields remain in {@code LogEntry.jsonPayload}.
  *
+ * @see <a href="https://docs.cloud.google.com/logging/docs/agent/logging/configuration#special-fields">
+ *     Special fields in structured payloads
+ * </a>
  */
-
 public class StackdriverOpenTelemetryTraceMdcJsonProvider extends AbstractJsonProvider<ILoggingEvent> {
 
+    static final String OPENTELEMETRY_TRACE_ID_KEY = "traceId";
+    static final String OPENTELEMETRY_SPAN_ID_KEY = "spanId";
+    static final String GCP_TRACE_KEY = "logging.googleapis.com/trace";
+    static final String GCP_SPAN_ID_KEY = "logging.googleapis.com/spanId";
+
     @Override
     public void writeTo(JsonGenerator generator, ILoggingEvent event) {
         Map<String, String> mdcProperties = event.getMDCPropertyMap();
         if (mdcProperties != null && !mdcProperties.isEmpty()) {
-            String traceId = mdcProperties.get("traceId");
-            if(traceId != null) {
-                generator.writeStringProperty("trace", traceId);
-            }
+            String traceId = mdcProperties.get(OPENTELEMETRY_TRACE_ID_KEY);
+            String spanId = mdcProperties.get(OPENTELEMETRY_SPAN_ID_KEY);
+
             for (Map.Entry<String, String> entry : mdcProperties.entrySet()) {
                 String key = entry.getKey();
                 String value = entry.getValue();
                 if(key == null || value == null) {
                     continue;
                 }
+
+                if ((GCP_TRACE_KEY.equals(key) && traceId != null)
+                        || (GCP_SPAN_ID_KEY.equals(key) && spanId != null)) {
+                    continue;
+                }
+
+                if (OPENTELEMETRY_TRACE_ID_KEY.equals(key)) {
+                    key = GCP_TRACE_KEY;
+                } else if (OPENTELEMETRY_SPAN_ID_KEY.equals(key)) {
+                    key = GCP_SPAN_ID_KEY;
+                }
+
                 generator.writeStringProperty(key, value);
             }
         }

gcp/logback-logstash-encoder-gcp/src/test/java/no/entur/logging/cloud/gcp/logback/logstash/StackdriverOpenTelemetryTraceMdcJsonProviderTest.java

@@ -0,0 +1,84 @@
+package no.entur.logging.cloud.gcp.logback.logstash;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+import tools.jackson.core.JsonGenerator;
+import tools.jackson.core.json.JsonFactory;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.json.JsonMapper;
+
+import java.io.StringWriter;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import static com.google.common.truth.Truth.assertThat;
+
+public class StackdriverOpenTelemetryTraceMdcJsonProviderTest {
+
+    private static final JsonMapper MAPPER = JsonMapper.builder().build();
+
+    @Test
+    void writeTo_openTelemetryTraceFields_mappedToGcpSpecialFields() throws Exception {
+        Map<String, String> mdc = new LinkedHashMap<>();
+        mdc.put("traceId", "06796866738c859f2f19b7cfb3214824");
+        mdc.put("spanId", "000000000000004a");
+        mdc.put("correlationId", "abc123");
+
+        JsonNode root = write(mdc);
+
+        assertThat(root.get("logging.googleapis.com/trace").asText())
+                .isEqualTo("06796866738c859f2f19b7cfb3214824");
+        assertThat(root.get("logging.googleapis.com/spanId").asText())
+                .isEqualTo("000000000000004a");
+        assertThat(root.get("correlationId").asText()).isEqualTo("abc123");
+        assertThat(root.has("trace")).isFalse();
+        assertThat(root.has("traceId")).isFalse();
+        assertThat(root.has("spanId")).isFalse();
+    }
+
+    @Test
+    void writeTo_existingGcpTraceFields_openTelemetryValuesTakePrecedenceWithoutDuplicates() throws Exception {
+        Map<String, String> mdc = new LinkedHashMap<>();
+        mdc.put("logging.googleapis.com/trace", "legacy-trace");
+        mdc.put("logging.googleapis.com/spanId", "legacy-span");
+        mdc.put("traceId", "06796866738c859f2f19b7cfb3214824");
+        mdc.put("spanId", "000000000000004a");
+
+        JsonNode root = write(mdc);
+
+        assertThat(root.get("logging.googleapis.com/trace").asText())
+                .isEqualTo("06796866738c859f2f19b7cfb3214824");
+        assertThat(root.get("logging.googleapis.com/spanId").asText())
+                .isEqualTo("000000000000004a");
+        assertThat(root.size()).isEqualTo(2);
+    }
+
+    @Test
+    void writeTo_existingGcpTraceFields_preservedWithoutOpenTelemetryValues() throws Exception {
+        Map<String, String> mdc = new LinkedHashMap<>();
+        mdc.put("logging.googleapis.com/trace", "existing-trace");
+        mdc.put("logging.googleapis.com/spanId", "existing-span");
+
+        JsonNode root = write(mdc);
+
+        assertThat(root.get("logging.googleapis.com/trace").asText()).isEqualTo("existing-trace");
+        assertThat(root.get("logging.googleapis.com/spanId").asText()).isEqualTo("existing-span");
+    }
+
+    private static JsonNode write(Map<String, String> mdcMap) throws Exception {
+        StackdriverOpenTelemetryTraceMdcJsonProvider provider =
+                new StackdriverOpenTelemetryTraceMdcJsonProvider();
+        ILoggingEvent event = Mockito.mock(ILoggingEvent.class);
+        Mockito.when(event.getMDCPropertyMap()).thenReturn(mdcMap);
+
+        StringWriter stringWriter = new StringWriter();
+        JsonFactory factory = new JsonFactory();
+        try (JsonGenerator generator = factory.createGenerator(stringWriter)) {
+            generator.writeStartObject();
+            provider.writeTo(generator, event);
+            generator.writeEndObject();
+        }
+        return MAPPER.readTree(stringWriter.toString());
+    }
+}