ContextUtils.java

/*
 * Copyright 2017, OpenCensus Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.opencensus.trace.unsafe;

import io.grpc.Context;
import io.opencensus.internal.Utils;
import io.opencensus.trace.BlankSpan;
import io.opencensus.trace.Span;

/*>>>
import org.checkerframework.checker.nullness.qual.Nullable;
*/

/**
 * Util methods/functionality to interact with the {@link io.grpc.Context}.
 *
 * <p>Users must interact with the current Context via the public APIs in {@link
 * io.opencensus.trace.Tracer} and avoid usages of the {@link #CONTEXT_SPAN_KEY} directly.
 *
 * @since 0.5
 */
final class ContextUtils {
  // No instance of this class.
  private ContextUtils() {}

  /** The {@link io.grpc.Context.Key} used to interact with {@link io.grpc.Context}. */
  private static final Context.Key</*@Nullable*/ Span> CONTEXT_SPAN_KEY =
      Context.<Span>key("opencensus-trace-span-key");

  /**
   * Creates a new {@code Context} with the given value set.
   *
   * @param context the parent {@code Context}.
   * @param span the value to be set.
   * @return a new context with the given value set.
   * @since 0.21
   */
  public static Context withValue(Context context, @javax.annotation.Nullable Span span) {
    return Utils.checkNotNull(context, "context").withValue(CONTEXT_SPAN_KEY, span);
  }

  /**
   * Returns the value from the specified {@code Context}.
   *
   * @param context the specified {@code Context}.
   * @return the value from the specified {@code Context}.
   * @since 0.21
   */
  public static Span getValue(Context context) {
    @javax.annotation.Nullable
    Span span = CONTEXT_SPAN_KEY.get(Utils.checkNotNull(context, "context"));
    return span == null ? BlankSpan.INSTANCE : span;
  }
}