content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * Licensed 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 com.alibaba.nacos.config.server.filter;
  
  import com.alibaba.nacos.common.notify.Event;
  import com.alibaba.nacos.common.notify.NotifyCenter;
  import com.alibaba.nacos.common.notify.listener.SmartSubscriber;
  import com.alibaba.nacos.common.utils.CollectionUtils;
  import com.alibaba.nacos.common.utils.ExceptionUtil;
  import com.alibaba.nacos.persistence.model.event.RaftDbErrorEvent;
  import com.alibaba.nacos.config.server.model.event.RaftDbErrorRecoverEvent;
  import com.alibaba.nacos.consistency.ProtocolMetaData;
  import com.alibaba.nacos.consistency.cp.CPProtocol;
  import com.alibaba.nacos.consistency.cp.MetadataKey;
  import com.alibaba.nacos.core.cluster.Member;
  import com.alibaba.nacos.core.cluster.MemberMetaDataConstants;
  import com.alibaba.nacos.core.cluster.ServerMemberManager;
  import com.alibaba.nacos.persistence.constants.PersistenceConstant;
  import org.springframework.beans.factory.annotation.Autowired;
  
  import javax.annotation.PostConstruct;
  import jakarta.servlet.Filter;
  import jakarta.servlet.FilterChain;
  import jakarta.servlet.ServletException;
  import jakarta.servlet.ServletRequest;
  import jakarta.servlet.ServletResponse;
  import jakarta.servlet.http.HttpServletRequest;
  import jakarta.servlet.http.HttpServletResponse;
  import java.io.IOException;
  import java.security.AccessControlException;
  import java.util.Arrays;
  import java.util.List;
  
  import static com.alibaba.nacos.config.server.utils.LogUtil.DEFAULT_LOG;
  
  /**
   * If the embedded distributed storage is enabled, all requests are routed to the Leader node for processing, and the
   * maximum number of forwards for a single request cannot exceed three.
   *
   * @author <a href="mailto:liaochuntao@live.com">liaochuntao</a>
   */
  public class CircuitFilter implements Filter {
      
      private volatile boolean isDowngrading = false;
      
      private volatile boolean isOpenService = false;
      
      @Autowired
      private ServerMemberManager memberManager;
      
      @Autowired
      private CPProtocol protocol;
      
      @PostConstruct
      protected void init() {
          listenerSelfInCluster();
          registerSubscribe();
      }
      
      @Override
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
              throws IOException, ServletException {
          
          HttpServletRequest req = (HttpServletRequest) request;
          HttpServletResponse resp = (HttpServletResponse) response;
          
          if (!isOpenService) {
              resp.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
                      "In the node initialization, unable to process any requests at this time");
              return;
          }
          
          try {
              // If an unrecoverable exception occurs on this node, the write request operation shall not be processed
              // This is a very important warning message !!!
              if (isDowngrading) {
                  resp.sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE,
                          "Unable to process the request at this time: System triggered degradation");
                  return;
              }
              
              chain.doFilter(req, response);
          } catch (AccessControlException e) {
              resp.sendError(HttpServletResponse.SC_FORBIDDEN, "access denied: " + ExceptionUtil.getAllExceptionMsg(e));
          } catch (Throwable e) {
              DEFAULT_LOG.warn("[CURCUIT-FILTER] Server failed: ", e);
              resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "Server failed, " + e);
          }
      }
      
      @Override
      public void destroy() {
      
      }
      
      private void listenerSelfInCluster() {
          protocol.protocolMetaData().subscribe(PersistenceConstant.CONFIG_MODEL_RAFT_GROUP, MetadataKey.RAFT_GROUP_MEMBER, o -> {
              if (!(o instanceof ProtocolMetaData.ValueItem)) {
                  return;
              }
              final List<String> peers = (List<String>) ((ProtocolMetaData.ValueItem) o).getData();
              if (CollectionUtils.isEmpty(peers)) {
                  isOpenService = false;
                  return;
              }
              final Member self = memberManager.getSelf();
              final String raftAddress = self.getIp() + ":" + self.getExtendVal(MemberMetaDataConstants.RAFT_PORT);
              // Only when you are in the cluster and the current Leader is
              // elected can you provide external services
              isOpenService = peers.contains(raftAddress);
          });
      }
      
      private void registerSubscribe() {
          NotifyCenter.registerSubscriber(new SmartSubscriber() {
              
              @Override
              public void onEvent(Event event) {
                  // @JustForTest
                  // This event only happens in the case of unit tests
                  if (event instanceof RaftDbErrorRecoverEvent) {
                      isDowngrading = false;
                      return;
                  }
                  if (event instanceof RaftDbErrorEvent) {
                      isDowngrading = true;
                  }
              }
              
              @Override
              public List<Class<? extends Event>> subscribeTypes() {
                  return Arrays.asList(RaftDbErrorRecoverEvent.class, RaftDbErrorEvent.class);
              }
          });
      }
      
  }
  