content: /*
   * Copyright (C) 2016 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.extractor.ogg;
  
  import static com.google.android.exoplayer2.util.Assertions.checkStateNotNull;
  
  import androidx.annotation.Nullable;
  import com.google.android.exoplayer2.Format;
  import com.google.android.exoplayer2.ParserException;
  import com.google.android.exoplayer2.audio.OpusUtil;
  import com.google.android.exoplayer2.extractor.VorbisUtil;
  import com.google.android.exoplayer2.metadata.Metadata;
  import com.google.android.exoplayer2.util.MimeTypes;
  import com.google.android.exoplayer2.util.ParsableByteArray;
  import com.google.common.collect.ImmutableList;
  import java.util.Arrays;
  import java.util.List;
  import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
  
  /** {@link StreamReader} to extract Opus data out of Ogg byte stream. */
  /* package */ final class OpusReader extends StreamReader {
  
    private static final byte[] OPUS_ID_HEADER_SIGNATURE = {'O', 'p', 'u', 's', 'H', 'e', 'a', 'd'};
    private static final byte[] OPUS_COMMENT_HEADER_SIGNATURE = {
      'O', 'p', 'u', 's', 'T', 'a', 'g', 's'
    };
  
    private boolean firstCommentHeaderSeen;
  
    public static boolean verifyBitstreamType(ParsableByteArray data) {
      return peekPacketStartsWith(data, OPUS_ID_HEADER_SIGNATURE);
    }
  
    @Override
    protected void reset(boolean headerData) {
      super.reset(headerData);
      if (headerData) {
        firstCommentHeaderSeen = false;
      }
    }
  
    @Override
    protected long preparePayload(ParsableByteArray packet) {
      return convertTimeToGranule(OpusUtil.getPacketDurationUs(packet.getData()));
    }
  
    @Override
    @EnsuresNonNullIf(expression = "#3.format", result = false)
    protected boolean readHeaders(ParsableByteArray packet, long position, SetupData setupData)
        throws ParserException {
      if (peekPacketStartsWith(packet, OPUS_ID_HEADER_SIGNATURE)) {
        byte[] headerBytes = Arrays.copyOf(packet.getData(), packet.limit());
        int channelCount = OpusUtil.getChannelCount(headerBytes);
        List<byte[]> initializationData = OpusUtil.buildInitializationData(headerBytes);
  
        if (setupData.format != null) {
          // setupData.format being non-null indicates we've already seen an ID header. Multiple ID
          // headers are not permitted by the Opus spec [1], but have been observed in real files [2],
          // so we just ignore all subsequent ones.
          // [1] https://datatracker.ietf.org/doc/html/rfc7845#section-3 and
          //     https://datatracker.ietf.org/doc/html/rfc7845#section-5
          // [2] https://github.com/google/ExoPlayer/issues/10038
          return true;
        }
        setupData.format =
            new Format.Builder()
                .setSampleMimeType(MimeTypes.AUDIO_OPUS)
                .setChannelCount(channelCount)
                .setSampleRate(OpusUtil.SAMPLE_RATE)
                .setInitializationData(initializationData)
                .build();
        return true;
      } else if (peekPacketStartsWith(packet, OPUS_COMMENT_HEADER_SIGNATURE)) {
        // The comment header must come immediately after the ID header, so the format will already
        // be populated: https://datatracker.ietf.org/doc/html/rfc7845#section-3
        checkStateNotNull(setupData.format);
        if (firstCommentHeaderSeen) {
          // Multiple comment headers are not permitted by the Opus spec [1], but have been observed
          // in real files [2], so we just ignore all subsequent ones.
          // [1] https://datatracker.ietf.org/doc/html/rfc7845#section-3 and
          //     https://datatracker.ietf.org/doc/html/rfc7845#section-5
          // [2] https://github.com/google/ExoPlayer/issues/10038
          return true;
        }
        firstCommentHeaderSeen = true;
        packet.skipBytes(OPUS_COMMENT_HEADER_SIGNATURE.length);
        VorbisUtil.CommentHeader commentHeader =
            VorbisUtil.readVorbisCommentHeader(
                packet, /* hasMetadataHeader= */ false, /* hasFramingBit= */ false);
        @Nullable
        Metadata vorbisMetadata =
            VorbisUtil.parseVorbisComments(ImmutableList.copyOf(commentHeader.comments));
        if (vorbisMetadata == null) {
          return true;
        }
        setupData.format =
            setupData
                .format
                .buildUpon()
                .setMetadata(vorbisMetadata.copyWithAppendedEntriesFrom(setupData.format.metadata))
                .build();
        return true;
      } else {
        // The ID header must come at the start of the file, so the format must already be populated:
        // https://datatracker.ietf.org/doc/html/rfc7845#section-3
        checkStateNotNull(setupData.format);
        return false;
      }
    }
  
    /**
     * Returns true if the given {@link ParsableByteArray} starts with {@code expectedPrefix}. Does
     * not change the {@link ParsableByteArray#getPosition() position} of {@code packet}.
     *
     * @param packet The packet data.
     * @return True if the packet starts with {@code expectedPrefix}, false if not.
     */
    private static boolean peekPacketStartsWith(ParsableByteArray packet, byte[] expectedPrefix) {
      if (packet.bytesLeft() < expectedPrefix.length) {
        return false;
      }
      int startPosition = packet.getPosition();
      byte[] header = new byte[expectedPrefix.length];
      packet.readBytes(header, 0, expectedPrefix.length);
      packet.setPosition(startPosition);
      return Arrays.equals(header, expectedPrefix);
    }
  }
  