content: /*
   * Copyright 2021 The Android Open Source Project
   *
   * 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.google.android.exoplayer2.source.rtsp;
  
  import com.google.android.exoplayer2.upstream.DataSourceUtil;
  import java.io.IOException;
  
  /** Factory for {@link UdpDataSourceRtpDataChannel}. */
  /* package */ final class UdpDataSourceRtpDataChannelFactory implements RtpDataChannel.Factory {
  
    private final long socketTimeoutMs;
  
    /**
     * Creates a new instance.
     *
     * @param socketTimeoutMs A positive number of milliseconds to wait before lack of received RTP
     *     packets is treated as the end of input.
     */
    public UdpDataSourceRtpDataChannelFactory(long socketTimeoutMs) {
      this.socketTimeoutMs = socketTimeoutMs;
    }
  
    @Override
    public RtpDataChannel createAndOpenDataChannel(int trackId) throws IOException {
      UdpDataSourceRtpDataChannel firstChannel = new UdpDataSourceRtpDataChannel(socketTimeoutMs);
      UdpDataSourceRtpDataChannel secondChannel = new UdpDataSourceRtpDataChannel(socketTimeoutMs);
  
      try {
        // From RFC3550 Section 11: "For UDP and similar protocols, RTP SHOULD use an even destination
        // port number and the corresponding RTCP stream SHOULD use the next higher (odd) destination
        // port number". Some RTSP servers are strict about this rule. We open a data channel first,
        // and depending its port number, open the next data channel with a port number that is either
        // the higher or the lower.
  
        // Using port zero will cause the system to generate a port.
        firstChannel.open(RtpUtils.getIncomingRtpDataSpec(/* portNumber= */ 0));
        int firstPort = firstChannel.getLocalPort();
        boolean isFirstPortEven = firstPort % 2 == 0;
        int portToOpen = isFirstPortEven ? firstPort + 1 : firstPort - 1;
        secondChannel.open(RtpUtils.getIncomingRtpDataSpec(/* portNumber= */ portToOpen));
  
        if (isFirstPortEven) {
          firstChannel.setRtcpChannel(secondChannel);
          return firstChannel;
        } else {
          secondChannel.setRtcpChannel(firstChannel);
          return secondChannel;
        }
      } catch (IOException e) {
        DataSourceUtil.closeQuietly(firstChannel);
        DataSourceUtil.closeQuietly(secondChannel);
        throw e;
      }
    }
  
    @Override
    public RtpDataChannel.Factory createFallbackDataChannelFactory() {
      return new TransferRtpDataChannelFactory(/* timeoutMs= */ socketTimeoutMs);
    }
  }
  