原文地址：https://kafka.apache.org/0101/documentation.html#messageformat
/**
* 1. 4 byte CRC32 of the message
* 2. 1 byte "magic" identifier to allow format changes, value is 0 or 1
* 3. 1 byte "attributes" identifier to allow annotations on the message independent of the version
* bit 0 ~ 2 : Compression codec.
* 0 : no compression
* 1 : gzip
* 2 : snappy
* 3 : lz4
* bit 3 : Timestamp type
* 0 : create time
* 1 : log append time
* bit 4 ~ 7 : reserved
* 4. (Optional) 8 byte timestamp only if "magic" identifier is greater than 0
* 5. 4 byte key length, containing length K
* 6. K byte key
* 7. 4 byte payload length, containing length V
* 8. V byte payload
*/
