client,mysql: Add support for Query Attributes

[dveeden]

Just like connection attributes, there are also query attributes in MySQL. These allow one to pass key/value pairs along with queries.

These can be used to add metadata about:

• The page being rendered

• The user for the proxy connection

• A trace ID for debugging

• A shard-id hint

• A follower-read setting

• An application stack listing

• The line of the application code sending the query

• https://dev.mysql.com/doc/refman/8.4/en/query-attributes.html

• https://archive.fosdem.org/2021/schedule/event/mysql_protocl/

In some other languages, etc:

MySQL Client

mysql-9.2.0> query_attributes proxy_user myuser page index.html
mysql-9.2.0> SELECT mysql_query_attribute_string('proxy_user'), mysql_query_attribute_string('page');
+--------------------------------------------+--------------------------------------+
| mysql_query_attribute_string('proxy_user') | mysql_query_attribute_string('page') |
+--------------------------------------------+--------------------------------------+
| myuser                                     | index.html                           |
+--------------------------------------------+--------------------------------------+
1 row in set (0.00 sec)

MySQL Connector/Python

#!/bin/python3
import mysql.connector

c = mysql.connector.connect(host='127.0.0.1',user='root', ssl_disabled=True)

cur = c.cursor(prepared=True)
cur.add_attribute("proxy_user", "myuser")
cur.execute("SELECT ?, mysql_query_attribute_string('proxy_user')", ("hello",))
for row in cur:
    print(row)
cur.close()
c.close()

Output:

('hello', 'myuser')

go-mysql with this PR

package main

import (
	"fmt"

	"github.com/go-mysql-org/go-mysql/client"
	"github.com/go-mysql-org/go-mysql/mysql"
)

func main() {
	conn, err := client.Connect("127.0.0.1:3306", "root", "", "")
	if err != nil {
		panic(err)
	}
	defer conn.Quit()

	proxyAttr := mysql.QueryAttribute{
		Name:  "proxy_user",
		Value: "user1",
	}
	secondAttr := mysql.QueryAttribute{
		Name:  "attr2",
		Value: "value2",
	}
	conn.SetQueryAttributes(proxyAttr, secondAttr)

	fmt.Printf("Sending COM_QUERY \"SELECT mysql_query_attribute_string('proxy_user')\" with attributes: %v, %v\n", proxyAttr, secondAttr)
	r, err := conn.Execute("SELECT mysql_query_attribute_string('proxy_user')")
	if err != nil {
		panic(err)
	}
	defer r.Close()

	for _, row := range r.Values {
		if len(row) != 1 {
			panic("expecting exactly on column")
		}
		fmt.Printf("%s\n", row[0].Value())
	}

	fmt.Printf("Preparing 'SELECT mysql_query_attribute_string(?)' via COM_STMT_PREPARE\n")
	stmt, err := conn.Prepare("SELECT mysql_query_attribute_string(?)")
	if err != nil {
		panic(err)
	}
	defer stmt.Close()

	conn.SetQueryAttributes(proxyAttr)
	fmt.Printf("Sending COM_STMT_EXECUTE with arg: %s, attributes: %v\n", "proxy_user", proxyAttr)
	res, err := stmt.Execute("proxy_user")
	if err != nil {
		panic(err)
	}
	defer res.Close()
	for _, row := range res.Values {
		if len(row) != 1 {
			panic("expecting exactly on column")
		}
		fmt.Printf("%s\n", row[0].Value())
	}
}

Output:

Sending COM_QUERY "SELECT mysql_query_attribute_string('proxy_user')" with attributes: {proxy_user user1}, {attr2 value2}
user1
Preparing 'SELECT mysql_query_attribute_string(?)' via COM_STMT_PREPARE
Sending COM_STMT_EXECUTE with arg: proxy_user, attributes: {proxy_user user1}
user1

[dveeden]

@lance6716 @atercattus this works and is ready for review. However this needs some unit tests etc and more manual testing before it can be merged. Should I add a DNM flag in the title? Add a "hold" flag? Or change the status to draft?

[dveeden]

This is how this looks in Wireshark: