contextがキャンセルされたときに*sql.Connが無効になるかの検証

log.txt

% go version
go version go1.23.0 darwin/arm64
% grep mysql go.mod
	github.com/go-sql-driver/mysql v1.8.1 // indirect
% go run main.go
n1: 0
n1: 0
[mysql] 2024/10/05 11:02:35 connection.go:49: invalid connection
2024/10/05 11:02:35 QueryRowContext failed (n2): driver: bad connection
exit status 1

main.go

package main

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"log"
	"time"

	_ "github.com/go-sql-driver/mysql"
)

func run(ctx context.Context, db *sql.DB) error {
	db.PingContext(ctx)
	conn, err := db.Conn(context.TODO()) // *sql.Connの生成時にはcontextを渡さない

	if err != nil {
		return err
	}

	defer conn.Close()

	for range 10 {
		var n1 int
		err = conn.QueryRowContext(ctx, "select sleep(1)").Scan(&n1)

		if err != nil {
			if errors.Is(err, context.DeadlineExceeded) || errors.Is(err, context.Canceled) {
				break
			} else {
				return fmt.Errorf("QueryRowContext failed (n1): %w", err)
			}
		}

		fmt.Println("n1:", n1)
	}

	var n2 int
	err = conn.QueryRowContext(ctx, "select 2").Scan(&n2)

	if err != nil {
		return fmt.Errorf("QueryRowContext failed (n2): %w", err)
	}

	fmt.Println("n2:", n2)
	return nil
}

func main() {
	db, err := sql.Open("mysql", "root@tcp(localhost:13306)/mysql")

	if err != nil {
		log.Fatal(err)
	}

	defer db.Close()
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	err = run(ctx, db)

	if err != nil {
		log.Fatal(err)
	}
}