mysql::binlog::event::Log_event_footer Class Reference

The footer, in the current version of the MySQL server, only contains the checksum algorithm descriptor. More...

#include <binlog_event.h>

Public Member Functions
	Log_event_footer ()
	Log_event_footer (Event_reader &reader, Log_event_type event_type, const Format_description_event *fde)
	This ctor will create a new object of Log_event_footer, and will adjust the event reader buffer size with respect to CRC usage. More...
	Log_event_footer (enum_binlog_checksum_alg checksum_alg_arg)

Static Public Member Functions
static enum_binlog_checksum_alg	get_checksum_alg (Event_reader &reader)
	Wrapper to call get_checksum_alg(const char *, ulong) function based on the event reader object (which knows both buffer and buffer length). More...
static enum_binlog_checksum_alg	get_checksum_alg (const char *buf, unsigned long len)
	The method returns the checksum algorithm used to checksum the binary log from a Format Description Event serialized buffer. More...
static bool	event_checksum_test (unsigned char *buf, unsigned long event_len, enum_binlog_checksum_alg alg)
	Tests the checksum algorithm used for the binary log, and asserts in case if the checksum algorithm is invalid. More...

Public Attributes
enum_binlog_checksum_alg	checksum_alg

Detailed Description

The footer, in the current version of the MySQL server, only contains the checksum algorithm descriptor.

The descriptor is contained in the FDE of the binary log. This is common for all the events contained in that binary log, and defines the algorithm used to checksum the events contained in the binary log.

The footer contains the following:

Common-Footer

Name	Format	Description
checkusm_alg	enum_checksum_alg	Algorithm used to checksum the events contained in the binary log

Note

checksum value is not generated with the event. On master's side, it is calculated right before writing the event into the binary log. The data_written field of the event is adjusted (+BINLOG_CHECKSUM_LEN) to consider the checksum value as part of the event. On reading the event, if the Format Description Event (FDE) used when serializing the event tells that the events have checksum information, the checksum value can be retrieved from a particular offset of the serialized event buffer (event length - BINLOG_CHECKSUM_LEN) and checked for corruption by computing a new value over the event buffer. It is not required after that. Therefore, the checksum value is not required to be stored in the instance as a class member.

Constructor & Destructor Documentation

Log_event_footer() [1/3]

mysql::binlog::event::Log_event_footer::Log_event_footer ( )

inline

Log_event_footer() [2/3]

mysql::binlog::event::Log_event_footer::Log_event_footer	(	Event_reader &	reader,
		Log_event_type	event_type,
		const Format_description_event *	fde
	)

This ctor will create a new object of Log_event_footer, and will adjust the event reader buffer size with respect to CRC usage.

Parameters

reader	the Event_reader containing the serialized event (including header, event data and optional checksum information).
event_type	the type of the event the footer belongs to.
fde	An FDE event, used to get information about CRC.

Log_event_footer() [3/3]

mysql::binlog::event::Log_event_footer::Log_event_footer ( enum_binlog_checksum_alg  checksum_alg_arg )

inlineexplicit

Member Function Documentation

event_checksum_test()

bool mysql::binlog::event::Log_event_footer::event_checksum_test ( unsigned char *  event_buf, unsigned long  event_len, enum_binlog_checksum_alg  alg  )

static

Tests the checksum algorithm used for the binary log, and asserts in case if the checksum algorithm is invalid.

Parameters

event_buf	point to the buffer containing serialized event
event_len	length of the event accounting possible checksum alg
alg	checksum algorithm used for the binary log

Return values

true	if test fails
false	as success

get_checksum_alg() [1/2]

enum_binlog_checksum_alg mysql::binlog::event::Log_event_footer::get_checksum_alg ( const char *  buf, unsigned long  len  )

static

The method returns the checksum algorithm used to checksum the binary log from a Format Description Event serialized buffer.

The method returns the checksum algorithm used to checksum the binary log.

For MySQL server versions < 5.6, the algorithm is undefined.

Parameters

buf	buffer holding serialized FD event.
len	length of the event buffer.

Return values

BINLOG_CHECKSUM_ALG_UNDEF	originator is checksum-unaware (effectively no checksum).
BINLOG_CHECKSUM_ALG_OFF	no checksum.
other	the actual checksum algorithm descriptor.

For MySQL server versions < 5.6, the algorithm is undefined. For the higher versions, the type is decoded from the FORMAT_DESCRIPTION_EVENT.

Parameters

buf	buffer holding serialized FD event
len	netto (possible checksum is stripped off) length of the event buf

Returns

the version-safe checksum alg descriptor where zero designates no checksum, 255 - the orginator is checksum-unaware (effectively no checksum) and the actual [1-254] range alg descriptor.

get_checksum_alg() [2/2]

enum_binlog_checksum_alg mysql::binlog::event::Log_event_footer::get_checksum_alg ( Event_reader &  reader )

static

Wrapper to call get_checksum_alg(const char *, ulong) function based on the event reader object (which knows both buffer and buffer length).

Parameters

[in]

reader

The Event_reader object associated to the event buffer of the FD event.

Return values

BINLOG_CHECKSUM_ALG_UNDEF	originator is checksum-unaware (effectively no checksum).
BINLOG_CHECKSUM_ALG_OFF	no checksum.
other	the actual checksum algorithm descriptor.

Member Data Documentation

checksum_alg

enum_binlog_checksum_alg mysql::binlog::event::Log_event_footer::checksum_alg

Master side:
The value is set by caller of FD(Format Description) constructor
In the FD case it's propagated into the last byte
of post_header_len[].
Slave side:
On the slave side the value is assigned from post_header_len[last]
of the last seen FD event.

TODO(WL#7546): Revisit this comment when encoder is moved in libbinlogevent

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The documentation for this class was generated from the following files:

• libs/mysql/binlog/event/binlog_event.h
• libs/mysql/binlog/event/binlog_event.cpp