Capstan.Binlog.Event (Capstan v0.1.0)

Binlog event header parse + CRC32 integrity check — the first decode layer.

Every binlog event is a 19-byte header followed by a body:

<<timestamp::32-little, type::8, server_id::32-little, event_size::32-little,
  log_pos::32-little, flags::16-little, body::binary>>

CRC32 posture

The C1 substrate runs with binlog_checksum=CRC32 and the dump negotiates it (SET @master_binlog_checksum), so this module assumes every event carries a trailing 4-byte CRC32 checksum over the whole event minus those 4 bytes. A FORMAT_DESCRIPTION event declares the checksum algorithm on the wire, but C1 does not need to read that byte — the precondition + negotiation already guarantee CRC32.

parse/1 verifies the trailer and, on success, returns the header fields plus the CRC-stripped body. A mismatch fails loudly: {:error, :crc_mismatch}, never a usable event — an integrity failure must never be silently swallowed into something that looks valid. A too-short input returns {:error, :truncated}.

This module does not interpret the body or map type to a name — that is Task 9's decoder, which owns the type-byte → name map and per-type body decode. type here is the raw event-type byte (0..255).

The artificial ROTATE that opens every dump (timestamp=0, log_pos=0) is a normal, CRC-valid event and parses like any other — callers decide what to do with it.

Summary

Types

t()

Binlog event header fields plus the CRC-verified, CRC-stripped body.

Functions

parse(event)

Parses one binlog event: the 19-byte header, splits off the trailing 4-byte CRC32 checksum, and verifies it against the header + body.

Types

t()

@type t() :: %Capstan.Binlog.Event{
  body: binary(),
  event_size: non_neg_integer(),
  flags: non_neg_integer(),
  log_pos: non_neg_integer(),
  server_id: non_neg_integer(),
  timestamp: non_neg_integer(),
  type: 0..255
}

Binlog event header fields plus the CRC-verified, CRC-stripped body.

Functions

parse(event)

@spec parse(binary()) :: {:ok, t()} | {:error, :truncated | :crc_mismatch}

Parses one binlog event: the 19-byte header, splits off the trailing 4-byte CRC32 checksum, and verifies it against the header + body.

Returns {:ok, %Event{}} with the CRC-stripped body on a verified event, {:error, :crc_mismatch} on a checksum mismatch (fail closed), or {:error, :truncated} when event is too short to hold a header and checksum.