Kafka Fetch API的协议规格和Wireshark抓包的对比

在Kafka中，Fetch API是用于从Broker获取消息的手段。

下面对Kafka Fetch API的协议规格（版本0）和Wireshark的抓包进行了对比分析。

参考：kafka.apache.org/protocol.ht…

Request

Fetch Request (Version: 0) => replica_id max_wait_ms min_bytes [topics] 
  replica_id => INT32
  max_wait_ms => INT32
  min_bytes => INT32
  topics => topic [partitions] 
    topic => STRING
    partitions => partition fetch_offset partition_max_bytes 
      partition => INT32
      fetch_offset => INT64
      partition_max_bytes => INT32

FIELD	DESCRIPTION
replica_id	The broker ID of the follower, of -1 if this request is from a consumer.
max_wait_ms	The maximum time in milliseconds to wait for the response.
min_bytes	The minimum bytes to accumulate in the response.
topics	The topics to fetch.
topic	The name of the topic to fetch.
partitions	The partitions to fetch.
partition	The partition index.
fetch_offset	The message offset.
partition_max_bytes	The maximum bytes to fetch from this partition. See KIP-74 for cases where this limit may not be honored.

• Replica ID: -1：正如表格中的描述，“-1 if this request is from a consumer”
• Max Bytes: 32768：对应配置项fetch.message.max.bytes（默认值 32768）

// Fetch is the namespace for controlling how many bytes are retrieved by any
// given request.
Fetch struct {
...
    // The default number of message bytes to fetch from the broker in each
    // request (default 32768). This should be larger than the majority of
    // your messages, or else the consumer will spend a lot of time
    // negotiating sizes and not actually consuming. Similar to the JVM's
    // `fetch.message.max.bytes`.
    Default int32

Response

Fetch Response (Version: 0) => [responses] 
  responses => topic [partitions] 
    topic => STRING
    partitions => partition_index error_code high_watermark records 
      partition_index => INT32
      error_code => INT16
      high_watermark => INT64
      records => RECORDS

FIELD	DESCRIPTION
responses	The response topics.
topic	The topic name.
partitions	The topic partitions.
partition_index	The partition index.
error_code	The error code, or 0 if there was no fetch error.
high_watermark	The current high water mark.
records	The record data.

• high_watermark似乎不在Response中