001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.juneau.rest.server.tracing.otel;
018
019import static org.apache.juneau.commons.utils.StringUtils.*;
020
021import java.util.*;
022
023import org.apache.juneau.rest.server.*;
024
025import io.opentelemetry.context.propagation.*;
026
027/**
028 * {@link TextMapGetter} implementation that reads HTTP request headers from a {@link RestRequest}.
029 *
030 * <p>
031 * Used by {@link OtelTracerHook} to extract W3C {@code traceparent} / {@code tracestate} headers (and
032 * any other propagator-defined headers, e.g. baggage) from incoming requests so the server span can
033 * be created as a child of the caller's trace context.
034 *
035 * <p>
036 * Header lookups are case-insensitive at the underlying {@code RequestHeaderList}, matching the
037 * RFC 9110 contract.
038 *
039 * @since 10.0.0
040 */
041@SuppressWarnings({
042   "java:S6548" // Singleton pattern is intentional; INSTANCE is a stateless, thread-safe TextMapGetter implementation.
043})
044public final class RestRequestTextMapGetter implements TextMapGetter<RestRequest> {
045
046   /** Process-wide singleton instance. */
047   public static final RestRequestTextMapGetter INSTANCE = new RestRequestTextMapGetter();
048
049   private RestRequestTextMapGetter() {}
050
051   @Override /* TextMapGetter */
052   public Iterable<String> keys(RestRequest carrier) {
053      if (carrier == null)
054         return List.of();
055      return carrier.getHeaders().getNames();
056   }
057
058   @Override /* TextMapGetter */
059   public String get(RestRequest carrier, String key) {
060      if (carrier == null || key == null)
061         return null;
062      var header = carrier.getHeaderParam(key);
063      if (! header.isPresent())
064         return null;
065      var value = header.orElse(null);
066      return isEmpty(value) ? null : value;
067   }
068}