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
   *
   *     https://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.avro.ipc;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.nio.ByteBuffer;
  import java.util.List;
  import java.util.concurrent.locks.ReentrantLock;
  
  import org.apache.avro.Protocol;
  
  /** Base transport class used by {@link Requestor}. */
  public abstract class Transceiver implements Closeable {
    private final ReentrantLock channelLock = new ReentrantLock();
  
    public abstract String getRemoteName() throws IOException;
  
    /**
     * Acquires an exclusive lock on the transceiver's channel.
     */
    public void lockChannel() {
      channelLock.lock();
    }
  
    /**
     * Releases the lock on the transceiver's channel if held by the calling thread.
     */
    public void unlockChannel() {
      if (channelLock.isHeldByCurrentThread()) {
        channelLock.unlock();
      }
    }
  
    /**
     * Called by {@link Requestor#request(String,Object)} for two-way messages. By
     * default calls {@link #writeBuffers(List)} followed by {@link #readBuffers()}.
     */
    public List<ByteBuffer> transceive(List<ByteBuffer> request) throws IOException {
      lockChannel();
      try {
        writeBuffers(request);
        return readBuffers();
      } finally {
        unlockChannel();
      }
    }
  
    /**
     * Called by {@link Requestor#request(String,Object,Callback)} for two-way
     * messages using callbacks.
     */
    public void transceive(List<ByteBuffer> request, Callback<List<ByteBuffer>> callback) throws IOException {
      // The default implementation works synchronously
      try {
        List<ByteBuffer> response = transceive(request);
        callback.handleResult(response);
      } catch (IOException e) {
        callback.handleError(e);
      }
    }
  
    /** Called by the default definition of {@link #transceive(List)}. */
    public abstract List<ByteBuffer> readBuffers() throws IOException;
  
    /** Called by {@link Requestor#request(String,Object)} for one-way messages. */
    public abstract void writeBuffers(List<ByteBuffer> buffers) throws IOException;
  
    /**
     * True if a handshake has been completed for this connection. Used to determine
     * whether a handshake need be completed prior to a one-way message. Requests
     * and responses are always prefixed by handshakes, but one-way messages. If the
     * first request sent over a connection is one-way, then a handshake-only
     * response is returned. Subsequent one-way messages over the connection will
     * have no response data sent. Returns false by default.
     */
    public boolean isConnected() {
      return false;
    }
  
    /**
     * Called with the remote protocol when a handshake has been completed. After
     * this has been called and while a connection is maintained,
     * {@link #isConnected()} should return true and #getRemote() should return this
     * protocol. Does nothing by default.
     */
    public void setRemote(Protocol protocol) {
    }
  
    /**
     * Returns the protocol passed to {@link #setRemote(Protocol)}. Throws
     * IllegalStateException by default.
     */
    public Protocol getRemote() {
      throw new IllegalStateException("Not connected.");
    }
  
    @Override
    public void close() throws IOException {
    }
  }
  