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:

[lance6716]

@dveeden seems CI is broken. It may be a good sign to modify the failing cases to cover the new code.

[dveeden]

Example

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", "", "",
                func(c *client.Conn) error {
                        c.IncludeLine(2)
                        return nil
                },
        )
        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 one 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())
        }
}

This lets users:

• Set query attributes for regular queries and prepared statements
• Use IncludeLine to send the file+line to the server as query attribute

[lance6716]

will check protocol code soon

[lance6716]

5 / 6 files viewed

[lance6716]

Seems we only support golang string and uint64 as the type of Value. Please add this usage in comments.

BTW I haven't clearly understood what types are supported in MySQL query attributes. I have found the function mysql_query_attribute_string, so MySQL only supports string type?

[dveeden]

The mysql_query_attribute_string() function returns the value of the query attribute as string. But a client may use other types to actually send data.

https://dev.mysql.com/doc/refman/9.1/en/query-attributes.html#query-attribute-functions

Here is an example which uses an int/MYSQL_TYPE_LONG and a string.

#include <stdio.h>
#include <string.h>
#include <mysql.h>

MYSQL mysql;

int main() {
  MYSQL_BIND bind[2];
  char *mystr = "test test";
  const char *name[2] = {"foo", "bar"};
  unsigned int ssl_mode = SSL_MODE_DISABLED;
  int intparam = 1;

  mysql_init(&mysql);

  mysql_options(&mysql,MYSQL_OPT_SSL_MODE, &ssl_mode);
  if (!mysql_real_connect(&mysql, "127.0.0.1", "root", "", "test", 0, NULL, 0)) {
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
            mysql_error(&mysql));
  }

  unsigned long mystrlen = strlen(mystr);
  bind[0].buffer_type = MYSQL_TYPE_STRING;
  bind[0].buffer = mystr;
  bind[0].length = &mystrlen;
  bind[0].is_null = 0;

  unsigned long intparamlen = sizeof(int);
  bind[1].buffer_type = MYSQL_TYPE_LONG;
  bind[1].buffer = (char *) &intparam;
  bind[1].length = &intparamlen;
  bind[1].is_null = 0;
  mysql_bind_param(&mysql, 2, bind, name);

  const char *query = "SELECT mysql_query_attribute_string('foo'), mysql_query_attribute_string('bar')";
  mysql_real_query(&mysql, query, strlen(query));
  MYSQL_RES *result = mysql_store_result(&mysql);
  MYSQL_ROW row = mysql_fetch_row(result);
  unsigned long *lengths = mysql_fetch_lengths(result);
  for(int i = 0; i < 2; i++)
  {
      printf("attribute %d: [%.*s]\n", i+1, (int) lengths[i], row[i] ? row[i] : "NULL");
  }
  mysql_free_result(result);

  mysql_close(&mysql);
}

dvaneeden@dve-carbon:~/dev/mysql-qattr$ gcc -Wall -Wextra $(mysql_config --cflags --libs) -o qattr qattr.c 
dvaneeden@dve-carbon:~/dev/mysql-qattr$ ./qattr 
attribute 1: [test test]
attribute 2: [1]

[lance6716]

this part is a bit complicated, I'll review later 😂

[dveeden]

mysql/mysql-server#595 / http://bugs.mysql.com/bug.php?id=117391 might help while reviewing this.

[lance6716]

LGTM. I can help to add test in next PR.

[lance6716]

Should we allow NULL query attributes so the bitmap will have 1? 🤔 we can add it in next PR.

[lance6716]

Suggested change

	if (s.conn.capability&CLIENT_QUERY_ATTRIBUTES > 0) && (s.conn.includeLine >= 0) {
	if s.conn.capability&CLIENT_QUERY_ATTRIBUTES > 0 && s.conn.includeLine >= 0 {

the old code has clear priority. It's OK to keep it.

[lance6716]

linter error

  client/conn_test.go:203:24: Error return value of `s.c.SetQueryAttributes` is not checked (errcheck)
  	s.c.SetQueryAttributes(qa)
  	                      ^
  client/conn_test.go:204:36: unnecessary conversion (unconvert)
  	expected := []mysql.QueryAttribute([]mysql.QueryAttribute{mysql.QueryAttribute{Name: "qattr1", Value: "qattr1val"}})