Chunk.java

/*
 * 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.chukwa;


import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.chukwa.datacollection.adaptor.*;

/**
 * A chunk is a sequence of bytes at a particular logical offset in a stream,
 * and containing one or more "records". Chunks have various metadata, such as
 * source, format, and pointers to record boundaries within the chunk.
 * 
 */
public interface Chunk {

  // these conceptually are really network addresses
  public String getSource();

  public void setSource(String logSource);

  /**
   * Get the name of the stream that this Chunk is a chunk of
   * 
   * @return the name of this stream; e.g. file name
   */
  public String getStreamName();

  public void setStreamName(String streamName);
  
  // These describe the format of the data buffer
  public String getDataType();

  public void setDataType(String t);

  /**
   * @return the user data in the chunk
   */
  public byte[] getData();

  /**
   * @param logEvent the user data in the chunk
   */
  public void setData(byte[] logEvent);

  /**
   * get/set the <b>end</b> offsets of records in the buffer.
   * 
   * We use end, rather than start offsets, since the first start offset is
   * always 0, but the last end offset specifies how much of the buffer is
   * valid.
   * 
   * More precisely, offsets[i] is the offset in the Chunk of the last byte of
   * record i in this chunk.
   * 
   * @return a list of record end offsets
   */
  public int[] getRecordOffsets();

  public void setRecordOffsets(int[] offsets);

  /**
   * @return the byte offset of the first byte not in this chunk.
   * 
   *         We pick this convention so that subtracting sequence IDs yields
   *         length.
   *         
   *         Furthermore, seqID - length = first byte pos.
   */
  public long getSeqID();

  public void setSeqID(long l);

  /**
   * Retrieve a reference to the adaptor that sent this event. Used by
   * LocalAgent and Connectors to deliver acks to the appropriate place.
   */
  public Adaptor getInitiator();

  /**
   * Estimate the size of this Chunk on the wire, assuming each char of metadata
   * takes two bytes to serialize. This is pessimistic.
   * 
   * @return size in bytes that this Chunk might take once serialized.
   */
  public int getSerializedSizeEstimate();

  /**
   * @return tags.
   * 
   */
  public String getTags();

  /**
   * Add tag.
   * 
   */
  public void addTag(String tag);

  /**
   * Returns the value of a single tag, assuming tags are of the form
   * tagname="val"
   * @param tagName the tag to return
   * @return null if not matched.
   */
  public String getTag(String tagName);
  
  public void write(DataOutput data) throws IOException;
}