Override tracing preferred service name and pin to dynamic config

dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/AgentTestRunner.groovy

@@ -221,6 +221,11 @@ abstract class AgentTestRunner extends DDSpecification implements AgentBuilder.L
       return null
     }
 
+    @Override
+    String getPreferredServiceName() {
+      return null
+    }
+
     @Override
     List<? extends SamplingRule.SpanSamplingRule> getSpanSamplingRules() {
       return null

dd-trace-core/src/main/java/datadog/trace/core/CoreTracer.java

@@ -230,6 +230,11 @@ public AgentHistogram newHistogram(double relativeAccuracy, int maxNumBins) {
     return Histograms.newHistogram(relativeAccuracy, maxNumBins);
   }
 
+  @Override
+  public void updatePreferredServiceName(String serviceName) {
+    dynamicConfig.current().setPreferredServiceName(serviceName).apply();
+  }
+
   PropagationTags.Factory getPropagationTagsFactory() {
     return propagationTagsFactory;
   }
@@ -1533,7 +1538,12 @@ private DDSpanContext buildSpanContext() {
         serviceName = rootSpan != null ? rootSpan.getServiceName() : null;
       }
       if (serviceName == null) {
-        serviceName = CoreTracer.this.serviceName;
+        serviceName = captureTraceConfig().getPreferredServiceName();
+        if (serviceName == null) {
+          // it could be on the initial snapshot but may be overridden to null and service name
+          // cannot be null
+          serviceName = CoreTracer.this.serviceName;
+        }
       }
 
       final CharSequence operationName =

dd-trace-core/src/test/groovy/datadog/trace/core/CoreTracerTest.groovy

@@ -421,6 +421,23 @@ class CoreTracerTest extends DDCoreSpecification {
     cleanup:
     tracer?.close()
   }
+
+  def "test local root service name override"() {
+    setup:
+    def tracer = tracerBuilder().writer(new ListWriter()).serviceName("test").build()
+    tracer.updatePreferredServiceName(preferred)
+    when:
+    def span = tracer.startSpan("", "test")
+    span.finish()
+    then:
+    span.serviceName == expected
+    cleanup:
+    tracer?.close()
+    where:
+    preferred | expected
+    null      | "test"
+    "some"    | "some"
+  }
 }
 
 class ControllableSampler implements Sampler, PrioritySampler {

internal-api/src/main/java/datadog/trace/api/DynamicConfig.java

@@ -107,6 +107,8 @@ public final class Builder {
 
     Double traceSampleRate;
 
+    String preferredServiceName;
+
     Builder() {}
 
     Builder(Snapshot snapshot) {
@@ -121,6 +123,7 @@ public final class Builder {
       this.baggageMapping = snapshot.baggageMapping;
 
       this.traceSampleRate = snapshot.traceSampleRate;
+      this.preferredServiceName = snapshot.preferredServiceName;
     }
 
     public Builder setRuntimeMetricsEnabled(boolean runtimeMetricsEnabled) {
@@ -192,6 +195,11 @@ public Builder setTraceSamplingRules(List<? extends TraceSamplingRule> traceSamp
       return this;
     }
 
+    public Builder setPreferredServiceName(String preferredServiceName) {
+      this.preferredServiceName = preferredServiceName;
+      return this;
+    }
+
     /** Overwrites the current configuration with a new snapshot. */
     public DynamicConfig<S> apply() {
       S oldSnapshot = currentSnapshot;
@@ -289,6 +297,8 @@ public static class Snapshot implements TraceConfig {
 
     final Double traceSampleRate;
 
+    final String preferredServiceName;
+
     protected Snapshot(DynamicConfig<?>.Builder builder, Snapshot oldSnapshot) {
 
       this.runtimeMetricsEnabled = builder.runtimeMetricsEnabled;
@@ -304,6 +314,7 @@ protected Snapshot(DynamicConfig<?>.Builder builder, Snapshot oldSnapshot) {
 
       this.spanSamplingRules = builder.spanSamplingRules;
       this.traceSamplingRules = builder.traceSamplingRules;
+      this.preferredServiceName = builder.preferredServiceName;
     }
 
     private static <K, V> Map<K, V> nullToEmpty(Map<K, V> mapping) {
@@ -350,6 +361,11 @@ public Double getTraceSampleRate() {
       return traceSampleRate;
     }
 
+    @Override
+    public String getPreferredServiceName() {
+      return preferredServiceName;
+    }
+
     @Override
     public List<? extends SpanSamplingRule> getSpanSamplingRules() {
       return spanSamplingRules;
@@ -385,6 +401,8 @@ public String toString() {
           + traceSamplingRules
           + ", traceSampleRate="
           + traceSampleRate
+          + ", preferredServiceName="
+          + preferredServiceName
           + '}';
     }
   }

internal-api/src/main/java/datadog/trace/api/TraceConfig.java

@@ -24,6 +24,13 @@ public interface TraceConfig {
 
   Double getTraceSampleRate();
 
+  /**
+   * The preferred service name to be used for tracing.
+   *
+   * @return null if not set (will use tracing default one)
+   */
+  String getPreferredServiceName();
+
   /**
    * Get the tracer sampler Span Sampling Rules.
    *

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/AgentTracer.java

@@ -296,6 +296,13 @@ default SpanBuilder buildSpan(CharSequence spanName) {
     ProfilingContextIntegration getProfilingContext();
 
     AgentHistogram newHistogram(double relativeAccuracy, int maxNumBins);
+
+    /**
+     * Sets the new service name to be used as a default
+     *
+     * @param serviceName
+     */
+    void updatePreferredServiceName(String serviceName);
   }
 
   public interface SpanBuilder {
@@ -534,6 +541,11 @@ public TraceConfig captureTraceConfig() {
     public AgentHistogram newHistogram(double relativeAccuracy, int maxNumBins) {
       return NoopAgentHistogram.INSTANCE;
     }
+
+    @Override
+    public void updatePreferredServiceName(String serviceName) {
+      // no ops
+    }
   }
 
   public static final class BlackholeAgentSpan extends NoopAgentSpan {
@@ -1260,6 +1272,11 @@ public Double getTraceSampleRate() {
       return null;
     }
 
+    @Override
+    public String getPreferredServiceName() {
+      return null;
+    }
+
     @Override
     public List<? extends SamplingRule.SpanSamplingRule> getSpanSamplingRules() {
       return Collections.emptyList();