MySQL  8.0.15
Source Code Documentation
ERR_Packet

This packet signals that an error occurred.

It contains a SQL state value if CLIENT_PROTOCOL_41 is enabled.

Error texts cannot exceed MYSQL_ERRMSG_SIZE

The Payload of an ERR Packet
TypeNameDescription
int<1> header 0xFF ERR packet header
int<2> error_code error-code
if capabilities & CLIENT_PROTOCOL_41 {
string[1] sql_state_marker # marker of the SQL state
string[5] sql_state SQL state
}
string<EOF> error_message human readable error message

Example:

17 00 00 01 ff 48 04 23 48 59 30 30 30 4e 6f 20
74 61 62 6c 65 73 20 75 73 65 64
.....H.#HY000No
tables used
See also
net_send_error_packet()