replication: Handle empty previous gtid

[dveeden]

From mysqlbinlog --read-from-remote-server --hexdump ...:

# at 127
#241120 10:36:02 server id 1  end_log_pos 158 CRC32 0xa7f45443
# Position  Timestamp   Type   Source ID        Size      Source Pos    Flags
# 0000007f 82 ad 3d 67   23   01 00 00 00   1f 00 00 00   9e 00 00 00   80 00
# 00000092 01 00 00 00 00 00 00 01  43 54 f4 a7             |........CT..|
# 	Previous-GTIDs
# [empty]

This event is from MySQL 9.1.0

mysql-9.1.0> show binlog events from 127 limit 1;
+---------------+-----+----------------+-----------+-------------+------+
| Log_name      | Pos | Event_type     | Server_id | End_log_pos | Info |
+---------------+-----+----------------+-----------+-------------+------+
| binlog.000001 | 127 | Previous_gtids |         1 |         158 |      |
+---------------+-----+----------------+-----------+-------------+------+
1 row in set (0.00 sec)

So the uuidCount is 1 (from 01 00 00 00 00 00 00 01)

Note that 43 54 f4 a7 is the CRC32 0xa7f45443 checksum.

Without this, this happens:

[2024/11/20 10:37:40] [error] binlogstreamer.go:78 close sync with err: Err: runtime error: slice bounds out of range [:24] with capacity 12
 Stack: goroutine 8 [running]:
github.com/go-mysql-org/go-mysql/mysql.Pstack(...)
	/home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/mysql/util.go:25
github.com/go-mysql-org/go-mysql/replication.(*BinlogSyncer).onStream.func1()
	/home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/replication/binlogsyncer.go:730 +0x7e
panic({0x834dc0?, 0xc0000285e8?})
	/usr/lib/golang/src/runtime/panic.go:785 +0x132
github.com/go-mysql-org/go-mysql/replication.(*PreviousGTIDsEvent).Decode(0xc0000228a0, {0xc00002e8f4, 0x0?, 0xc})
	/home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/replication/event.go:239 +0x4ea
github.com/go-mysql-org/go-mysql/replication.(*BinlogParser).parseEvent(0xc0000d2190, 0xc0000285d0, {0xc00002e8f4, 0xc, 0xc}, {0xc00002e8e1?, 0xc00008de58?, 0x407f47?})
	/home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/replication/parser.go:328 +0x59f
github.com/go-mysql-org/go-mysql/replication.(*BinlogParser).Parse(0xc0000d2190, {0xc00002e8e1, 0x1f, 0x1f})

This is because it expects 8 bytes for the uuidCount an 16 bytes for the UUID, making 24 in total. But there is only 8 for the uuidCount and 4 for the checksum, resulting in a capacity of 12.

[dveeden]

This is with syncer.StartSyncGTID() and the gtidSet set to the last GTID processed by the MySQL server.