Kafka
Binary Layout
| Field | Internal Name | Description | Type / Format | Example / Values |
|---|---|---|---|---|
| Size | length | Total size of the request (excluding this field) | int32 | e.g. 0x0000012C |
| API Key | api_key | Identifies the type of request | int16 | 0 = Produce, 1 = Fetch, etc. |
| API Version | api_version | Version of the API being used | int16 | e.g. 7 |
| Correlation ID | correlation_id | Used to match requests to responses | int32 | e.g. 12345 |
| Client ID | client_id | Optional identifier of the client | string (nullable) | e.g. "my-client" |
| Request Body | (varies by API) | The actual request payload | Structured binary | Depends on api_key and api_version |
Common API Keys
| API Key | Name | Purpose |
|---|---|---|
0 | Produce | Send messages to a topic |
1 | Fetch | Retrieve messages from a topic |
3 | Metadata | Get topic/partition info |
8 | Offset | Get earliest/latest offsets |
18 | ApiVersions | Discover supported API versions |
21 | SaslHandshake | SASL authentication handshake |
22 | SaslAuthenticate | SASL authentication |
42 | DescribeCluster | Get cluster metadata |
Primitive Types Used
| Type | Description |
|---|---|
int8/16/32/64 | Signed integers (big-endian) |
string | Length-prefixed UTF-8 string |
array<T> | Length-prefixed array of type T |
bytes | Length-prefixed byte array |
varint | Variable-length integer (zigzag encoding) |
Response Structure
| Field | Description |
|---|---|
correlation_id | Matches the request |
response_body | Depends on the request type |