content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.journal;
  
  import alluxio.proto.journal.Journal.JournalEntry;
  import alluxio.util.proto.ProtoUtils;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * Class for reading journal entries from an input stream.
   */
  public class JournalEntryStreamReader implements Closeable {
    private static final Logger LOG = LoggerFactory.getLogger(JournalEntryStreamReader.class);
  
    private final InputStream mStream;
    private byte[] mBuffer = new byte[4096];
  
    /**
     * @param stream the stream to read from
     */
    public JournalEntryStreamReader(InputStream stream) {
      mStream = stream;
    }
  
    /**
     * Reads a journal entry from the input stream.
     *
     * @return the journal entry, null if no journal entry is found
     */
    public JournalEntry readEntry() throws IOException {
      int firstByte = mStream.read();
      if (firstByte == -1) {
        return null;
      }
      // All journal entries start with their size in bytes written as a varint.
      int size;
      try {
        size = ProtoUtils.readRawVarint32(firstByte, mStream);
      } catch (IOException e) {
        LOG.warn("Journal entry was truncated in the size portion.");
        throw e;
      }
      if (mBuffer.length < size) {
        mBuffer = new byte[size];
      }
      // Total bytes read so far for journal entry.
      int totalBytesRead = 0;
      while (totalBytesRead < size) {
        // Bytes read in last read request.
        int latestBytesRead = mStream.read(mBuffer, totalBytesRead, size - totalBytesRead);
        if (latestBytesRead < 0) {
          break;
        }
        totalBytesRead += latestBytesRead;
      }
      if (totalBytesRead < size) {
        // This could happen if the master crashed partway through writing the final journal entry. In
        // this case, we can ignore the last entry because it was not acked to the client.
        LOG.warn("Journal entry was truncated. Expected to read {} bytes but only got {}", size,
            totalBytesRead);
        return null;
      }
      return JournalEntry.parser().parseFrom(mBuffer, 0, size);
    }
  
    @Override
    public void close() throws IOException {
      mStream.close();
    }
  }
  