【Kafka官方文档翻译】5.5.4. 消息格式

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
        */