server: DBeaver hangs on SELECT DATABASE() response

[dveeden]

@rfyim Did you ever get this to work?

I happen to be doing the same thing as you, the same way. Mine is hanging on select database() though sent from dbeaver.

func (h ProxyRequestHandler) HandleQuery(query string) (*mysql.Result, error) {
	log.Println("In HandleQuery")
	log.Println(query)
	r, err := h.remoteDb.Execute(query)
	if err != nil {
		return nil, err
	}
	log.Printf("Executed query: %d", r.AffectedRows)
	return r, nil
}

Originally posted by @matttm in #915

[dveeden]

Tested with DBeaver CE 24.3.4.202502021521 and MySQL Connector/J 8.2.0

[dveeden]

So this isn't a bug.

The example is only setup to handle a single connection and DBeaver uses multiple.

It works with this code:

package main

import (
	"fmt"
	"net"
	"strings"

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

type ServerHandler struct {
	Conn *client.Conn
}

type Config struct {
	Host     string
	Port     int
	User     string
	Password string
}

func NewServerHandler(cfg Config) (*ServerHandler, error) {
	conn, err := client.Connect(fmt.Sprintf("%s:%d", cfg.Host, cfg.Port), cfg.User, cfg.Password, "")
	if err != nil {
		return nil, err
	}
	if err = conn.Ping(); err != nil {
		return nil, err
	}
	return &ServerHandler{
		Conn: conn,
	}, nil
}

func (h ServerHandler) UseDB(dbName string) error {
	return h.Conn.UseDB(dbName)
}

func (h ServerHandler) HandleQuery(query string) (*mysql.Result, error) {
	res, err := h.Conn.Execute(query)

	// SET doesn't seem to work due to EOF/OK differences
	if strings.Contains(query, `SET NAMES`) {
		return nil, nil
	}
	if strings.Contains(query, `set autocommit=0`) {
		return nil, nil
	}
	return res, err
}

func (h ServerHandler) HandleFieldList(table string, fieldWildcard string) ([]*mysql.Field, error) {
	return h.Conn.FieldList(table, fieldWildcard)
}
func (h ServerHandler) HandleStmtPrepare(query string) (int, int, interface{}, error) {
	stmt, err := h.Conn.Prepare(query)
	if err != nil {
		return 0, 0, nil, err
	}
	return stmt.ParamNum(), stmt.ColumnNum(), stmt, nil
}
func (h ServerHandler) HandleStmtExecute(context interface{}, query string, args []interface{}) (*mysql.Result, error) {
	return context.(*client.Stmt).Execute(args...)
}

func (h ServerHandler) HandleStmtClose(context interface{}) error {
	return context.(*client.Stmt).Close()
}

func (h ServerHandler) HandleOtherCommand(cmd byte, data []byte) error {
	return mysql.NewError(
		mysql.ER_UNKNOWN_ERROR,
		fmt.Sprintf("command %d is not supported now", cmd),
	)
}

func handleCon(c net.Conn) {
	cfg := Config{
		Host: "127.0.0.1",
		Port: 3306,
		User: "root",
	}
	sh, err := NewServerHandler(cfg)
	if err != nil {
		panic(err)
	}
	conn, err := server.NewConn(c, "root", "", sh)
	if err != nil {
		panic(err)
	}
	for {
		if err := conn.HandleCommand(); err != nil {
			if strings.Contains(err.Error(), "connection closed") {
				continue
			}
			panic(err)
		}
	}
}

func main() {
	l, err := net.Listen("tcp", "127.0.0.1:4000")
	if err != nil {
		panic(err)
	}
	for {
		c, err := l.Accept()
		if err != nil {
			panic(err)
		}
		go handleCon(c)
	}
}

Things that we might consider to change:

1. Change the example to handle multiple connections.
2. Add a note about handling multiple connections
3. Expose the error for connection closed to make it easier to check. Or use an existing error like io.EOF if that makes sense.

[dveeden]

With this I was also able to run sysbench --mysql-host=127.0.0.1 --mysql-port=4000 --mysql-user=root --mysql-db=test oltp_read_only run --max-time=30 --threads=10

[matttm]

Though I'm new to the underlying processes of mysql. i'm happy to try implementing one of these ways forward.

I assume with approach one, the work should be done in the server package?

[dveeden]

The example I posted in here works. The example in the readme doesn't as that only handles a single connection

[matttm]

Hey @dveeden, hope you're doing good. I have been able to create my proxy, with help from the above.
https://github.com/matttm/imposter-db/blob/554c4959e0e2684b89bc315ba99aec9ce0bc3872/remote-handler.go#L30

Can you ellaborate more on the comment in your above code, in HandleQuery:

	// SET doesn't seem to work due to EOF/OK differences

I am encountering an error like this from other commands, besides set, like an update command:

panic: io.ReadFull(header) failed. err EOF: connection was bad

What is very weird is that, I can execute the same command in different environments and get different results. Like I can execute this update command through DBeaver successfully, but if I use another go program that uses go-sql-driver, I will get this error..

Looking at this in wireshark shows a response package to be malformed, but. I haven't spent enough time there to figure out what's going on exactly. I do Think this might be related to this comment though.