MYSQLND_MAX_ALLOWED_USER_LEN  481 ext/mysqlnd/mysqlnd_wireprotocol.c #define AUTH_WRITE_BUFFER_LEN (MYSQLND_HEADER_SIZE + MYSQLND_MAX_ALLOWED_USER_LEN + SCRAMBLE_LENGTH + MYSQLND_MAX_ALLOWED_DB_LEN + 1 + 4096)
MYSQLND_MAX_ALLOWED_USER_LEN  509 ext/mysqlnd/mysqlnd_wireprotocol.c 		len = MIN(strlen(packet->user), MYSQLND_MAX_ALLOWED_USER_LEN);