@Override
  public O serve(ServiceRequestContext ctx, I req) throws Exception {
    final TraceData traceData = getTraceData(ctx, req);
    final String method = req instanceof RpcRequest ? ((RpcRequest) req).method() : ctx.method();
    final ServerRequestAdapter requestAdapter = new InternalServerRequestAdapter(method, traceData);

    final ServerSpan serverSpan = serverInterceptor.openSpan(requestAdapter);
    final boolean sampled;
    if (serverSpan != null) {
      ctx.onEnter(() -> serverInterceptor.setSpan(serverSpan));
      ctx.onExit(serverInterceptor::clearSpan);
      sampled = serverSpan.getSample();
    } else {
      sampled = false;
    }

    try {
      final O res = delegate().serve(ctx, req);
      if (sampled) {
        ctx.requestLogFuture()
            .thenAcceptBoth(
                res.closeFuture(), (log, unused) -> closeSpan(ctx, serverSpan, log, res))
            .exceptionally(CompletionActions::log);
      }
      return res;
    } finally {
      serverInterceptor.clearSpan();
    }
  }
  private static SpanCollectingReporter testServiceInvocation(boolean sampled) throws Exception {
    SpanCollectingReporter reporter = new SpanCollectingReporter();

    Brave brave =
        new Brave.Builder(TEST_SERVICE)
            .reporter(reporter)
            .traceSampler(Sampler.create(1.0f))
            .build();

    @SuppressWarnings("unchecked")
    Service<ThriftCall, ThriftReply> delegate = mock(Service.class);

    TraceData traceData =
        TraceData.builder()
            .sample(sampled)
            .spanId(SpanId.builder().traceId(1).spanId(2).parentId(3L).build())
            .build();

    TracingServiceImpl stub = new TracingServiceImpl(delegate, brave, traceData);

    ThriftCall req = new ThriftCall(0, HelloService.Iface.class, "hello", "trustin");
    DefaultRequestLog reqLog = new DefaultRequestLog();
    reqLog.start(mock(Channel.class), SessionProtocol.H2C, "localhost", TEST_METHOD, "/");
    reqLog.end();

    ServiceRequestContext ctx = mock(ServiceRequestContext.class);
    // AbstractTracingService prefers RpcRequest.method() to ctx.method(), so "POST" should be
    // ignored.
    when(ctx.method()).thenReturn("POST");
    when(ctx.requestLogFuture()).thenReturn(reqLog);
    ctx.onEnter(ArgumentMatchers.isA(Runnable.class));
    ctx.onExit(ArgumentMatchers.isA(Runnable.class));

    ThriftReply res = new ThriftReply(0, "Hello, trustin!");
    when(delegate.serve(ctx, req)).thenReturn(res);

    // do invoke
    stub.serve(ctx, req);

    verify(delegate, times(1)).serve(eq(ctx), eq(req));
    return reporter;
  }