Fix sampling for Azure Functions

agent/agent-bootstrap/src/main/java/com/microsoft/applicationinsights/agent/bootstrap/BytecodeUtil.java

@@ -272,6 +272,10 @@ public static void logErrorOnce(Throwable t) {
     }
   }
 
+  public static boolean shouldSample(String operationId) {
+    return delegate != null && delegate.shouldSample(operationId);
+  }
+
   public static long getTotalMilliseconds(
       long days, int hours, int minutes, int seconds, int milliseconds) {
     return DAYS.toMillis(days)
@@ -435,5 +439,7 @@ void trackAvailability(
     void flush();
 
     void logErrorOnce(Throwable t);
+
+    boolean shouldSample(String shouldSample);
   }
 }

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/classicsdk/BytecodeUtilImpl.java

@@ -441,6 +441,11 @@ public void logErrorOnce(Throwable t) {
     }
   }
 
+  @Override
+  public boolean shouldSample(String operationId) {
+    return sample(operationId, samplingPercentage);
+  }
+
   private static void track(
       AbstractTelemetryBuilder telemetryBuilder, Map<String, String> tags, boolean applySampling) {
 

agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/configuration/Configuration.java

@@ -178,8 +178,6 @@ public static class SamplingPreview {
     // sampled)
     //
     // future goal: make parentBased sampling the default if item count is received via tracestate
-    //
-    // IMPORTANT if changing this default, we need to keep it at least on Azure Functions
     public boolean parentBased;
 
     public List<SamplingOverride> overrides = new ArrayList<>();

agent/instrumentation/azure-functions/src/main/java/io/opentelemetry/javaagent/instrumentation/azurefunctions/InvocationInstrumentation.java

@@ -10,9 +10,11 @@
 
 import com.microsoft.applicationinsights.agent.bootstrap.AzureFunctions;
 import com.microsoft.applicationinsights.agent.bootstrap.AzureFunctionsCustomDimensions;
+import com.microsoft.applicationinsights.agent.bootstrap.BytecodeUtil;
 import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.SpanContext;
+import io.opentelemetry.api.trace.TraceFlags;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.Scope;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
@@ -63,6 +65,19 @@ public static Scope methodEnter(@Advice.Argument(0) Object request)
               .getTextMapPropagator()
               .extract(Context.root(), traceContext, GETTER);
       SpanContext spanContext = Span.fromContext(extractedContext).getSpanContext();
+
+      // recreate SpanContext to override the trace flags since the host currently always sends "00"
+      TraceFlags traceFlags =
+          BytecodeUtil.shouldSample(spanContext.getTraceId())
+              ? TraceFlags.getSampled()
+              : TraceFlags.getDefault();
+      spanContext =
+          SpanContext.createFromRemoteParent(
+              spanContext.getTraceId(),
+              spanContext.getSpanId(),
+              traceFlags,
+              spanContext.getTraceState());
+
       return Context.current()
           .with(Span.wrap(spanContext))
           .with(generateCustomDimensions(request, traceContext))