code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC 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.openqa.selenium.environment.webserver;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME;
  
  import java.io.UncheckedIOException;
  import java.time.Instant;
  import java.time.ZoneId;
  import java.time.ZonedDateTime;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  import org.openqa.selenium.remote.http.Contents;
  import org.openqa.selenium.remote.http.HttpHandler;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  
  class EchoHandler implements HttpHandler {
  
    private static final String EPOCH_START =
        RFC_1123_DATE_TIME.format(ZonedDateTime.ofInstant(Instant.ofEpochMilli(0), ZoneId.of("UTC")));
    private static final String RESPONSE_STRING =
        "<html><head><title>Done</title></head><body>"
            + "<h1>Method: <span id='method'>%s</span></h1>"
            + "<h1>Headers</h1><table id='headers'><tbody>%s</tbody></table>"
            + "<h1>Body:</h1><pre>%s</pre>"
            + "</body></html>";
  
    @Override
    public HttpResponse execute(HttpRequest request) throws UncheckedIOException {
      HttpResponse response = new HttpResponse();
      response.setHeader("Content-Type", "text/html");
      // Don't Cache Anything  at the browser
      response.setHeader("Cache-Control", "no-cache");
      response.setHeader("Pragma", "no-cache");
      response.setHeader("Expires", EPOCH_START);
  
      String method = request.getMethod().toString();
      String headers =
          StreamSupport.stream(request.getHeaderNames().spliterator(), false)
              .flatMap(
                  name ->
                      StreamSupport.stream(request.getHeaders(name).spliterator(), false)
                          .map(
                              value -> String.format("<tr><td>%s</td><td>%s</td></tr>", name, value)))
              .collect(Collectors.joining(""));
      String body = Contents.utf8String(request.getContent());
  
      response.setContent(
          Contents.string(String.format(RESPONSE_STRING, method, headers, body), UTF_8));
  
      return response;
    }
  }
  