Fixed review notes.

Author: AlexeyKuznetsov-DD

dd-trace-api/src/main/java/datadog/trace/api/ConfigDefaults.java

@@ -90,6 +90,8 @@ public final class ConfigDefaults {
 
   // TODO: forced to use 1.0 for testing only, rollback to "0.4" before merging to master;
   static final String DEFAULT_TRACE_AGENT_PROTOCOL_VERSION = ProtocolVersion.V1_0.asConfigValue();
+  // TODO: static final String DEFAULT_TRACE_AGENT_PROTOCOL_VERSION =
+  // ProtocolVersion.V0_4.asConfigValue();
 
   static final boolean DEFAULT_CLIENT_IP_ENABLED = false;
 

dd-trace-api/src/main/java/datadog/trace/api/ProtocolVersion.java

@@ -63,7 +63,7 @@ public static ProtocolVersion fromConfigValue(String value) {
 
   public static ProtocolVersion fromTraceEndpoint(String endpoint) {
     if (endpoint == null) {
-      return null;
+      return V0_4;
     }
 
     String normalized = endpoint.toLowerCase(Locale.ROOT);

dd-trace-core/src/main/java/datadog/trace/common/writer/ddagent/DDAgentMapperDiscovery.java

@@ -47,6 +47,7 @@ public void discover() {
 
       default:
         traceMapper = new TraceMapperV0_4();
+        break;
     }
   }
 

dd-trace-core/src/main/java/datadog/trace/common/writer/ddagent/TraceMapperV1.java

@@ -50,6 +50,7 @@ public final class TraceMapperV1 implements TraceMapper {
   static final int VALUE_TYPE_ARRAY = 6;
 
   // Span kind OTEL values
+  static final int SPAN_KIND_UNSPECIFIED = 0;
   static final int SPAN_KIND_INTERNAL = 1;
   static final int SPAN_KIND_SERVER = 2;
   static final int SPAN_KIND_CLIENT = 3;
@@ -82,6 +83,11 @@ public TraceMapperV1() {
 
   @Override
   public void map(List<? extends CoreSpan<?>> trace, Writable writable) {
+    if (trace.isEmpty()) {
+      // Do nothing if no spans in the trace
+      return;
+    }
+
     CoreSpan<?> firstSpan = trace.get(0);
     firstSpan.processTagsAndBaggage(spanMetadata, false, false);
     Metadata firstSpanMeta = spanMetadata.metadata;
@@ -104,9 +110,6 @@ public void map(List<? extends CoreSpan<?>> trace, Writable writable) {
   }
 
   private Map<String, Object> buildChunkAttributes(List<? extends CoreSpan<?>> trace) {
-    if (trace.isEmpty()) {
-      return emptyMap();
-    }
     CoreSpan<?> localRoot = trace.get(0).getLocalRootSpan();
     CharSequence service = localRoot == null ? null : localRoot.getServiceName();
     if (service == null) {
@@ -238,7 +241,7 @@ private boolean isEncodableSpanEvent(Object event) {
       return false;
     }
     Map<?, ?> eventMap = (Map<?, ?>) event;
-    return asLong(eventMap.get("time_unix_nano")) != null && eventMap.get("name") != null;
+    return eventMap.get("name") != null && asLong(eventMap.get("time_unix_nano")) != null;
   }
 
   private void encodeEventAttributes(Writable writable, int fieldId, Map<?, ?> attrs) {
@@ -545,7 +548,7 @@ private void writeStreamingString(Writable writable, CharSequence value) {
   /** Converts a span kind string to its OTEL uint32 value. */
   static int getSpanKindValue(CharSequence spanKind) {
     if (spanKind == null) {
-      return SPAN_KIND_INTERNAL;
+      return SPAN_KIND_UNSPECIFIED;
     }
 
     switch (spanKind.toString()) {

dd-trace-core/src/test/groovy/datadog/trace/common/writer/ddagent/TraceMapperV1PayloadTest.groovy

@@ -78,7 +78,7 @@ class TraceMapperV1PayloadTest extends DDSpecification {
 
   def "test span kind value conversion"() {
     expect:
-    TraceMapperV1.getSpanKindValue(null) == TraceMapperV1.SPAN_KIND_INTERNAL
+    TraceMapperV1.getSpanKindValue(null) == TraceMapperV1.SPAN_KIND_UNSPECIFIED
     TraceMapperV1.getSpanKindValue(Tags.SPAN_KIND_INTERNAL) == TraceMapperV1.SPAN_KIND_INTERNAL
     TraceMapperV1.getSpanKindValue(Tags.SPAN_KIND_SERVER) == TraceMapperV1.SPAN_KIND_SERVER
     TraceMapperV1.getSpanKindValue(Tags.SPAN_KIND_CLIENT) == TraceMapperV1.SPAN_KIND_CLIENT