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All Kafka APIs

Heartbeat

This page encodes the smallest legal instance of the request and the response: numeric fields are zero, strings and byte arrays are empty, every array carries exactly one sample element, and any records field holds one empty 61-byte RecordBatch v2. Version 4 is a flexible version, so every struct is terminated by a uvarint tagged-field count and strings and arrays carry compact length-plus-one prefixes. Sizes below include the leading int32 size prefix.

API key
12
Encoded at
v4
Flexible versions
4+
Headers
req v2, resp v1
Request versions
0-4
Response versions
0-4
Request size
23 bytes
Response size
16 bytes
framerpc headerrequest bodyRecordBatchRecordresponse bodytagged_fields

Request

HeartbeatRequest v4, request header v2, 23 bytes on the wire

byte layout (23 bytes, 16 bytes per row)

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object tree

HeartbeatRequest             message v4                                [0x0000, 23B]
+-- Frame                                                              [0x0000, 4B]   length-delimited framing
|   +-- size                 int32            = 19                     [0x0000, 4B]   number of bytes that follow, patched after encoding
+-- RequestHeader            v2                                        [0x0004, 11B]  common request header
|   +-- request_api_key      int16            = 12 (Heartbeat)         [0x0004, 2B]   numeric id of the API being invoked
|   +-- request_api_version  int16            = 4                      [0x0006, 2B]   version of the API being invoked
|   +-- correlation_id       int32            = 0                      [0x0008, 4B]   echoed back by the broker in the response
|   +-- client_id            nullable_string  = "" (int16 len=0)       [0x000c, 2B]   always a non-flexible int16-prefixed string
|   +-- tagged_fields        uvarint          = 0                      [0x000e, 1B]   number of tagged fields in the header
+-- HeartbeatRequest         struct                                    [0x000f, 8B]   message body, version 4
    +-- GroupId              string           = "" (compact, len+1=1)  [0x000f, 1B]   The group id.
    +-- GenerationId         int32            = 0                      [0x0010, 4B]   The generation of the group.
    +-- MemberId             string           = "" (compact, len+1=1)  [0x0014, 1B]   The member ID.
    +-- GroupInstanceId      string           = "" (compact, len+1=1)  [0x0015, 1B]   The unique identifier of the consumer instance provided by end user.
    +-- tagged_fields        uvarint          = 0                      [0x0016, 1B]   number of tagged fields in this struct

kafka message schema (.json)

{
  "apiKey": 12,
  "type": "request",
  "listeners": ["broker"],
  "name": "HeartbeatRequest",
  // Version 1 and version 2 are the same as version 0.
  //
  // Starting from version 3, we add a new field called groupInstanceId to indicate member identity across restarts.
  //
  // Version 4 is the first flexible version.
  "validVersions": "0-4",
  "flexibleVersions": "4+",
  "fields": [
    { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
      "about": "The group id." },
    { "name": "GenerationId", "type": "int32", "versions": "0+",
      "about": "The generation of the group." },
    { "name": "MemberId", "type": "string", "versions": "0+",
      "about": "The member ID." },
    { "name": "GroupInstanceId", "type": "string", "versions": "3+",
      "nullableVersions": "3+", "default": "null",
      "about": "The unique identifier of the consumer instance provided by end user." }
  ]
}

Response

HeartbeatResponse v4, response header v1, 16 bytes on the wire

byte layout (16 bytes, 16 bytes per row)

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object tree

HeartbeatResponse       message v4        [0x0000, 16B]
+-- Frame                                 [0x0000, 4B]   length-delimited framing
|   +-- size            int32       = 12  [0x0000, 4B]   number of bytes that follow, patched after encoding
+-- ResponseHeader      v1                [0x0004, 5B]   common response header
|   +-- correlation_id  int32       = 0   [0x0004, 4B]   matches the correlation_id of the request
|   +-- tagged_fields   uvarint     = 0   [0x0008, 1B]   number of tagged fields in the header
+-- HeartbeatResponse   struct            [0x0009, 7B]   message body, version 4
    +-- ThrottleTimeMs  int32       = 0   [0x0009, 4B]   The duration in milliseconds for which the request was throttled due to a q...
    +-- ErrorCode       int16       = 0   [0x000d, 2B]   The error code, or 0 if there was no error.
    +-- tagged_fields   uvarint     = 0   [0x000f, 1B]   number of tagged fields in this struct

kafka message schema (.json)

{
  "apiKey": 12,
  "type": "response",
  "name": "HeartbeatResponse",
  // Version 1 adds throttle time.
  //
  // Starting in version 2, on quota violation, brokers send out responses before throttling.
  //
  // Starting from version 3, heartbeatRequest supports a new field called groupInstanceId to indicate member identity across restarts.
  //
  // Version 4 is the first flexible version.
  "validVersions": "0-4",
  "flexibleVersions": "4+",
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "1+", "ignorable": true,
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "ErrorCode", "type": "int16", "versions": "0+",
      "about": "The error code, or 0 if there was no error." }
  ]
}