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.grid.web;
  
  import static java.net.HttpURLConnection.HTTP_MOVED_TEMP;
  import static org.openqa.selenium.remote.http.Route.get;
  
  import java.net.URL;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  import java.util.function.Function;
  import java.util.function.Supplier;
  import java.util.logging.Logger;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.json.Json;
  import org.openqa.selenium.remote.http.HttpHandler;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  import org.openqa.selenium.remote.http.Routable;
  import org.openqa.selenium.remote.http.Route;
  
  public class GridUiRoute implements Routable {
  
    private static final Logger LOG = Logger.getLogger("selenium");
  
    private static final String GRID_RESOURCE = "javascript/grid-ui/build";
    private static final String GRID_RESOURCE_WITH_PREFIX = String.format("/%s", GRID_RESOURCE);
  
    private final Route routes;
  
    public GridUiRoute(String prefix) {
      Require.nonNull(prefix, "Prefix cannot be null");
      URL uiRoot = GridUiRoute.class.getResource(GRID_RESOURCE_WITH_PREFIX);
      if (uiRoot != null) {
        ResourceHandler uiHandler = new ResourceHandler(new ClassPathResource(uiRoot, GRID_RESOURCE));
        HttpResponse uiRedirect =
            new HttpResponse().setStatus(HTTP_MOVED_TEMP).addHeader("Location", prefix.concat("/ui"));
  
        Supplier<HttpHandler> redirectHandler = () -> req -> uiRedirect;
  
        Routable appendRoute =
            Route.combine(consoleRoute(prefix, redirectHandler), uiRoute(prefix, () -> uiHandler));
        if (!prefix.isEmpty()) {
          appendRoute = Route.combine(appendRoute, redirectRoute(prefix, redirectHandler));
        }
  
        routes = Route.combine(get("/").to(redirectHandler), appendRoute);
      } else {
        LOG.warning("It was not possible to load the Grid UI.");
        Json json = new Json();
        routes = Route.matching(req -> false).to(() -> new NoHandler(json));
      }
    }
  
    @Override
    public boolean matches(HttpRequest req) {
      return routes.matches(req);
    }
  
    @Override
    public HttpResponse execute(HttpRequest req) {
      return routes.execute(req);
    }
  
    private static Routable uiRoute(String prefix, Supplier<HttpHandler> handler) {
      return buildRoute(
          "/ui", prefix, path -> Route.prefix(path).to(Route.matching(req -> true).to(handler)));
    }
  
    private static Routable consoleRoute(String prefix, Supplier<HttpHandler> handler) {
      return buildRoute("/grid/console", prefix, path -> get(path).to(handler));
    }
  
    private static Routable buildRoute(String url, String prefix, Function<String, Route> mapper) {
      List<String> subPaths =
          prefix.isEmpty() ? Collections.singletonList(url) : Arrays.asList(prefix + url, url);
      return subPaths.stream().map(mapper).reduce(Route::combine).get();
    }
  
    private static Routable redirectRoute(String prefix, Supplier<HttpHandler> handler) {
      prefix = prefix.endsWith("/") ? prefix.substring(0, prefix.length() - 1) : prefix;
      return get(prefix).to(handler);
    }
  }
  