 * Header data for each packet that goes through the read/write pipelines.
 * Includes all of the information about the packet, excluding checksums and
 * actual data.
 *
 * This data includes:
 *  - the offset in bytes into the HDFS block of the data in this packet
 *  - the sequence number of this packet in the pipeline
 *  - whether or not this is the last packet in the pipeline
 *  - the length of the data in this packet
 *  - whether or not this packet should be synced by the DNs.
 * Header data for each packet that goes through the read/write pipelines.
 * Includes all of the information about the packet, excluding checksums and
 * actual data.
 *
 * This data includes:
 *  - the offset in bytes into the HDFS block of the data in this packet
 *  - the sequence number of this packet in the pipeline
 *  - whether or not this is the last packet in the pipeline
 *  - the length of the data in this packet
 *  - whether or not this packet should be synced by the DNs. | PacketHeader.java