#BUG: sql.Execute get rows count will panic nil error

[DoMySon]

var result, _ = db.Execute(`insert into (x,y,z) values(1,2,3)`)

var columns = result.Columns()  // there result != nil
var rows  = result.Rows()       // there result == nil (panic)

[dveeden]

Is this with github.com/go-mysql-org/go-mysql/driver or with github.com/go-mysql-org/go-mysql/client?

What version?

Could you give a full example that I can run to reproduce this?

Is there a stack ?

[DoMySon]

it's github.com/go-mysql-org/go-mysql/client, version is v1.10.0
i just execute an insert operation.

[DoMySon]

first result not nil, but next operation always nil then panic

[dveeden]

I can reproduce this with this code:

package main

import (
	"fmt"

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

func main() {
	fd, err := client.Connect("127.0.0.1:3306", "root", "", "test")
	if err != nil {
		panic(err)
	}
	fmt.Printf("fd = %#v\n", fd)

	fd.Execute(`drop table if exists t`)
	fd.Execute(`create table t(x int, y int, z int, primary key (x,y,z))`)

	result, err := fd.Execute(`insert into t(x,y,z) values(1,2,3)`)
	if err != nil {
		panic(err)
	}
	fmt.Printf("result = %#v\n", result)

	rows := result.RowNumber()
	fmt.Printf("rows = %#v\n", rows)

	columns := result.ColumnNumber()
	fmt.Printf("columns = %#v\n", columns)
}

Result:

$ go run main.go 
fd = &client.Conn{Conn:(*packet.Conn)(0xc0000fa980), user:"root", password:"", db:"test", tlsConfig:(*tls.Config)(nil), proto:"tcp", ReadTimeout:0, WriteTimeout:0, BufferSize:65536, serverVersion:"9.1.0", capability:0xdfffffff, ccaps:0x0, attributes:map[string]string{"_client_name":"go-mysql", "_os":"linux", "_platform":"amd64", "_runtime_version":"go1.23.4"}, status:0x2, charset:"utf8", collation:"", salt:[]uint8{0x1d, 0x53, 0x6c, 0xa, 0x6f, 0x3f, 0x7e, 0x1f, 0x31, 0x40, 0x42, 0x23, 0x33, 0x66, 0x60, 0x6d, 0x7f, 0xb, 0x69, 0x3c}, authPluginName:"caching_sha2_password", connectionID:0x15}
result = &mysql.Result{Status:0x2, Warnings:0x0, InsertId:0x0, AffectedRows:0x1, Resultset:(*mysql.Resultset)(nil)}
rows = 0
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x611500]

goroutine 1 [running]:
github.com/go-mysql-org/go-mysql/mysql.(*Resultset).ColumnNumber(0x800620?)
	/home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/mysql/resultset.go:90
main.main()
	/tmp/issue_964/main.go:29 +0x1c5
exit status 2

This is on Linux with MySQL 9.1.0

[dveeden]

The problem here is that ColumnNumber() uses r.Fields while r is nil.

(dlv) s
> github.com/go-mysql-org/go-mysql/mysql.(*Resultset).ColumnNumber() /home/dvaneeden/go/pkg/mod/github.com/go-mysql-org/[email protected]/mysql/resultset.go:89 (PC: 0x786264)
    84:			return 0
    85:		}
    86:		return len(r.Values)
    87:	}
    88:	
=>  89:	func (r *Resultset) ColumnNumber() int {
    90:		return len(r.Fields)
    91:	}
    92:	
    93:	func (r *Resultset) GetValue(row, column int) (interface{}, error) {
    94:		if row >= len(r.Values) || row < 0 {
(dlv) p r
*github.com/go-mysql-org/go-mysql/mysql.Resultset nil

[DoMySon]

Yes, I use a more violent approach here to directly judge

...
if r == nil {
   return 0
}
...

[dveeden]

@DoMySon isn't that the same as what #968 does?

[DoMySon]

@dveeden It's the same

[DoMySon]

However, this situation is not intuitive. In fact, unless it is manually cleared, it will not be empty. There may be a deeper bug.

[lance6716]

@DoMySon Can you provide a full runnable, reproduce code for us? Or answer my questions to explain what's happened in your example?

var result, _ = db.Execute(`insert into (x,y,z) values(1,2,3)`)

var columns = result.Columns()  // there result != nil
var rows  = result.Rows()       // there result == nil (panic)

1. Why didn't you check the error returned from db.Execute? When there's some error, result can be nil.
2. The result in three lines are not related? Why it's not nil and then no modification made but it becomes nil?

[lance6716]

Oh I see your screenshot.

-- update --

The root cause is we always return a not-nil mysql.Result, but it embeds a *Resultset which can be nil. So when calls methods on *Resultset the function receiver is nil, then causes panic.

All exported methods on *Resultset should consider this case because user may call them. I'll keep this issue open and create another PR to fix it.