/**
    * 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.hadoop.hbase.client;
  
  import java.io.IOException;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.CoprocessorEnvironment;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.client.ConnectionManager.HConnectionImplementation;
  import org.apache.hadoop.hbase.coprocessor.RegionCoprocessorEnvironment;
  import org.apache.hadoop.hbase.regionserver.HRegionServer;
  import org.apache.hadoop.hbase.regionserver.RegionServerServices;
  import org.apache.hadoop.hbase.security.UserProvider;
  
  /**
   * Connection to an HTable from within a Coprocessor. We can do some nice tricks since we know we
   * are on a regionserver, for instance skipping the full serialization/deserialization of objects
   * when talking to the server.
   * <p>
   * You should not use this class from any client - its an internal class meant for use by the
   * coprocessor framework.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public class CoprocessorHConnection extends HConnectionImplementation {
    private static final NonceGenerator NO_NONCE_GEN = new ConnectionManager.NoNonceGenerator();
  
    /**
     * Create an unmanaged {@link HConnection} based on the environment in which we are running the
     * coprocessor. The {@link HConnection} must be externally cleaned up (we bypass the usual HTable
     * cleanup mechanisms since we own everything).
     * @param env environment hosting the {@link HConnection}
     * @return an unmanaged {@link HConnection}.
     * @throws IOException if we cannot create the connection
     */
    public static ClusterConnection getConnectionForEnvironment(CoprocessorEnvironment env)
        throws IOException {
      // this bit is a little hacky - just trying to get it going for the moment
      if (env instanceof RegionCoprocessorEnvironment) {
        RegionCoprocessorEnvironment e = (RegionCoprocessorEnvironment) env;
        RegionServerServices services = e.getRegionServerServices();
        if (services instanceof HRegionServer) {
          return new CoprocessorHConnection((HRegionServer) services);
        }
      }
      return ConnectionManager.createConnectionInternal(env.getConfiguration());
    }
  
    private final ServerName serverName;
    private final HRegionServer server;
  
    /**
     * Legacy constructor
     * @param delegate
     * @param server
     * @throws IOException if we cannot create the connection
     * @deprecated delegate is not used
     */
    @Deprecated
    public CoprocessorHConnection(ClusterConnection delegate, HRegionServer server)
        throws IOException {
      this(server);
    }
  
    /**
     * Constructor that uses server configuration
     * @param server
     * @throws IOException if we cannot create the connection
     */
    public CoprocessorHConnection(HRegionServer server) throws IOException {
      this(server.getConfiguration(), server);
    }
  
    /**
     * Constructor that accepts custom configuration
     * @param conf
     * @param server
     * @throws IOException if we cannot create the connection
     */
    public CoprocessorHConnection(Configuration conf, HRegionServer server) throws IOException {
      super(conf, false, null, UserProvider.instantiate(conf).getCurrent(), server.getClusterId());
     this.server = server;
     this.serverName = server.getServerName();
   }
 
   @Override
   public org.apache.hadoop.hbase.protobuf.generated.ClientProtos.ClientService.BlockingInterface
       getClient(ServerName serverName) throws IOException {
     // client is trying to reach off-server, so we can't do anything special
     if (!this.serverName.equals(serverName)) {
       return super.getClient(serverName);
     }
     // the client is attempting to write to the same regionserver, we can short-circuit to our
     // local regionserver
     return server.getRSRpcServices();
   }
 
   @Override
   public NonceGenerator getNonceGenerator() {
     return NO_NONCE_GEN; // don't use nonces for coprocessor connection
   }
 }