content: /*
   * Copyright The OpenTelemetry Authors
   * SPDX-License-Identifier: Apache-2.0
   */
  
  package com.example.javaagent;
  
  import io.opentelemetry.context.Context;
  import io.opentelemetry.context.ContextKey;
  import io.opentelemetry.context.propagation.TextMapGetter;
  import io.opentelemetry.context.propagation.TextMapPropagator;
  import io.opentelemetry.context.propagation.TextMapSetter;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * See <a
   * href="https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/context/api-propagators.md">
   * OpenTelemetry Specification</a> for more information about Propagators.
   *
   * @see DemoPropagatorProvider
   */
  public class DemoPropagator implements TextMapPropagator {
    private static final String FIELD = "X-demo-field";
    private static final ContextKey<Long> PROPAGATION_START_KEY =
        ContextKey.named("propagation.start");
  
    @Override
    public List<String> fields() {
      return Collections.singletonList(FIELD);
    }
  
    @Override
    public <C> void inject(Context context, C carrier, TextMapSetter<C> setter) {
      Long propagationStart = context.get(PROPAGATION_START_KEY);
      if (propagationStart == null) {
        propagationStart = System.currentTimeMillis();
      }
      setter.set(carrier, FIELD, String.valueOf(propagationStart));
    }
  
    @Override
    public <C> Context extract(Context context, C carrier, TextMapGetter<C> getter) {
      String propagationStart = getter.get(carrier, FIELD);
      if (propagationStart != null) {
        return context.with(PROPAGATION_START_KEY, Long.valueOf(propagationStart));
      } else {
        return context;
      }
    }
  }
  