Override tracing preferred service name and pin to dynamic config

Author: amarziali

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

@@ -1533,7 +1533,7 @@ private DDSpanContext buildSpanContext() {
         serviceName = rootSpan != null ? rootSpan.getServiceName() : null;
       }
       if (serviceName == null) {
-        serviceName = CoreTracer.this.serviceName;
+        serviceName = captureTraceConfig().defaultServiceName;
       }
 
       final CharSequence operationName =
@@ -1611,6 +1611,7 @@ public void run() {
 
   protected class ConfigSnapshot extends DynamicConfig.Snapshot {
     final Sampler sampler;
+    final String defaultServiceName;
 
     protected ConfigSnapshot(
         DynamicConfig<ConfigSnapshot>.Builder builder, ConfigSnapshot oldSnapshot) {
@@ -1623,6 +1624,12 @@ protected ConfigSnapshot(
       } else {
         sampler = Sampler.Builder.forConfig(CoreTracer.this.initialConfig, this);
       }
+      final String preferredName = SpanNaming.instance().localRoot().getPreferredServiceName();
+      if (preferredName != null) {
+        this.defaultServiceName = preferredName;
+      } else {
+        this.defaultServiceName = CoreTracer.this.serviceName;
+      }
     }
   }
 }

internal-api/src/main/java/datadog/trace/api/naming/SpanNaming.java

@@ -4,6 +4,7 @@
 import datadog.trace.api.naming.v0.NamingSchemaV0;
 import datadog.trace.api.naming.v1.NamingSchemaV1;
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 /** This is the main entry point to drive span naming decisions. */
 public class SpanNaming {
@@ -14,21 +15,38 @@ private static class Singleton {
     private static SpanNaming INSTANCE = new SpanNaming();
   }
 
+  public static class ForLocalRoot {
+    private final boolean mutable;
+    private volatile String preferredServiceName;
+
+    public ForLocalRoot(final Config config) {
+      this.mutable = !config.isServiceNameSetByUser();
+    }
+
+    @Nullable
+    public String getPreferredServiceName() {
+      return preferredServiceName;
+    }
+
+    public boolean maybeOverrideServiceName(final String serviceName) {
+      if (mutable) {
+        preferredServiceName = serviceName;
+      }
+      return mutable;
+    }
+  }
+
   public static SpanNaming instance() {
     return Singleton.INSTANCE;
   }
 
   private final NamingSchema namingSchema;
   private final int version;
 
-  // Choice of version will be driven by a configuration parameter when all the instrumentations'
-  // naming will be addressed
-  private SpanNaming() {
-    this(Config.get().getSpanAttributeSchemaVersion());
-  }
+  private final ForLocalRoot localRootNaming;
 
-  private SpanNaming(final int version) {
-    this.version = version;
+  private SpanNaming() {
+    this.version = Config.get().getSpanAttributeSchemaVersion();
     switch (version) {
       case 1:
         namingSchema = new NamingSchemaV1();
@@ -37,13 +55,19 @@ private SpanNaming(final int version) {
         namingSchema = new NamingSchemaV0();
         break;
     }
+    this.localRootNaming = new ForLocalRoot(Config.get());
   }
 
   @Nonnull
   public NamingSchema namingSchema() {
     return namingSchema;
   }
 
+  @Nonnull
+  public ForLocalRoot localRoot() {
+    return localRootNaming;
+  }
+
   public int version() {
     return version;
   }

internal-api/src/test/groovy/datadog/trace/api/naming/NamingV0ForkedTest.groovy

@@ -1,5 +1,6 @@
 package datadog.trace.api.naming
 
+import datadog.trace.api.Config
 import datadog.trace.api.config.GeneralConfig
 import datadog.trace.api.config.TracerConfig
 import datadog.trace.test.util.DDSpecification
@@ -23,4 +24,21 @@ class NamingV0ForkedTest extends DDSpecification {
     assert schema.cache().service("anything") == null
     assert schema.cloud().serviceForRequest("any", "anything") == null
   }
+
+  def "test local root service name override"() {
+    setup:
+    if (ddService != null) {
+      injectSysConfig("dd.service", ddService)
+    }
+    def instance = new SpanNaming.ForLocalRoot(Config.get())
+    when:
+    def overridden = instance.maybeOverrideServiceName("some")
+    then:
+    overridden == bool
+    instance.getPreferredServiceName() == expected
+    where:
+    ddService | expected | bool
+    null      | "some"   | true
+    "thing"   | null     | false
+  }
 }