org.apache.solr.util.tracing.HttpServletCarrier Maven / Gradle / Ivy

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Apache Solr (module: core)
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.solr.util.tracing;

import io.opentracing.propagation.TextMap;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import javax.servlet.http.HttpServletRequest;

/** A Carrier for extract Span context out of request headers */
public class HttpServletCarrier implements TextMap {
  private Iterator> it;

  public HttpServletCarrier(HttpServletRequest request) {
    this.it =
        new Iterator<>() {

          Enumeration headerNameIt = request.getHeaderNames();
          String headerName = null;
          Enumeration headerValue = null;

          @Override
          public boolean hasNext() {
            if (headerValue != null && headerValue.hasMoreElements()) {
              return true;
            }

            return headerNameIt.hasMoreElements();
          }

          @Override
          public Map.Entry next() {
            if (!hasNext()) {
              throw new NoSuchElementException();
            }

            if (headerValue == null || !headerValue.hasMoreElements()) {
              headerName = headerNameIt.nextElement();
              headerValue = request.getHeaders(headerName);
            }

            String key = headerName;
            String val = headerValue.nextElement();

            return new Map.Entry<>() {
              @Override
              public String getKey() {
                return key;
              }

              @Override
              public String getValue() {
                return val;
              }

              @Override
              public String setValue(String value) {
                throw new UnsupportedOperationException();
              }
            };
          }
        };
  }

  @Override
  public Iterator> iterator() {
    return it;
  }

  @Override
  public void put(String key, String value) {
    throw new UnsupportedOperationException(
        "HttpServletCarrier should only be used with Tracer.extract()");
  }
}