content: /*
   * 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.kafka.common.internals;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.security.PrivilegedAction;
  import java.util.Objects;
  import java.util.concurrent.Callable;
  import java.util.concurrent.CompletionException;
  import java.util.concurrent.atomic.AtomicReference;
  import java.util.function.Function;
  
  import javax.security.auth.Subject;
  
  /**
   * This strategy combines the functionality of the {@link LegacyStrategy}, {@link ModernStrategy}, and
   * {@link UnsupportedStrategy} strategies to provide the legacy APIs as long as they are present and not degraded.
   * If the legacy APIs are missing or degraded, this falls back to the modern APIs.
   */
  class CompositeStrategy implements SecurityManagerCompatibility {
  
      private static final Logger log = LoggerFactory.getLogger(CompositeStrategy.class);
      static final CompositeStrategy INSTANCE = new CompositeStrategy(ReflectiveStrategy.Loader.forName());
  
      private final SecurityManagerCompatibility fallbackStrategy;
      private final AtomicReference<SecurityManagerCompatibility> activeStrategy;
  
      // Visible for testing
      CompositeStrategy(ReflectiveStrategy.Loader loader) {
          SecurityManagerCompatibility initial;
          SecurityManagerCompatibility fallback = null;
          try {
              initial = new LegacyStrategy(loader);
              try {
                  fallback = new ModernStrategy(loader);
                  // This is expected for JRE 18+
                  log.debug("Loaded legacy SecurityManager methods, will fall back to modern methods after UnsupportedOperationException");
              } catch (NoSuchMethodException | ClassNotFoundException ex) {
                  // This is expected for JRE <= 17
                  log.debug("Unable to load modern Subject methods, relying only on legacy methods", ex);
              }
          } catch (ClassNotFoundException | NoSuchMethodException e) {
              try {
                  initial = new ModernStrategy(loader);
                  // This is expected for JREs after the removal takes place.
                  log.debug("Unable to load legacy SecurityManager methods, relying only on modern methods", e);
              } catch (NoSuchMethodException | ClassNotFoundException ex) {
                  initial = new UnsupportedStrategy(e, ex);
                  // This is not expected in normal use, only in test environments.
                  log.error("Unable to load legacy SecurityManager methods", e);
                  log.error("Unable to load modern Subject methods", ex);
              }
          }
          Objects.requireNonNull(initial, "initial strategy must be defined");
          activeStrategy = new AtomicReference<>(initial);
          fallbackStrategy = fallback;
      }
  
      private <T> T performAction(Function<SecurityManagerCompatibility, T> action) {
          SecurityManagerCompatibility active = activeStrategy.get();
          try {
              return action.apply(active);
          } catch (UnsupportedOperationException e) {
              // If we chose a fallback strategy during loading, switch to it and retry this operation.
              if (active != fallbackStrategy && fallbackStrategy != null) {
                  if (activeStrategy.compareAndSet(active, fallbackStrategy)) {
                      log.debug("Using fallback strategy after encountering degraded legacy method", e);
                  }
                  return action.apply(fallbackStrategy);
              }
              // If we're already using the fallback strategy, then there's nothing to do to handle these exceptions.
              throw e;
          }
      }
  
      @Override
      public <T> T doPrivileged(PrivilegedAction<T> action) {
          return performAction(compatibility -> compatibility.doPrivileged(action));
      }
  
      @Override
      public Subject current() {
          return performAction(SecurityManagerCompatibility::current);
      }
  
      @Override
      public <T> T callAs(Subject subject, Callable<T> action) throws CompletionException {
          return performAction(compatibility -> compatibility.callAs(subject, action));
      }
  }
  