Cursor.Prev() out of range issue v1.3.9 #733
Description
Hi, I met an issue during dev. Here's my sample code:
package main
import (
"fmt"
"log"
bolt "go.etcd.io/bbolt"
)
func main() {
aDb, dbErr := bolt.Open("a.db", 0600, nil)
if dbErr != nil {
log.Fatal(dbErr)
}
defer aDb.Close()
aDb.Batch(func(tx *bolt.Tx) error {
// Create data
b, _ := tx.CreateBucketIfNotExists([]byte("test"))
b.Put([]byte("1"), nil)
b.Put([]byte("2"), nil)
b.Put([]byte("3"), nil)
// Next test
fmt.Println("=== Next test ===")
cn := b.Cursor()
cn.Seek([]byte("2")) //2
cn.Next() // 3
cn.Next() // nil (Cursor stops at 3)
kn, _ := cn.Prev() // 2
fmt.Println(string(kn))
// Prev test
fmt.Println("=== Prev test ===")
cp := b.Cursor()
cp.Seek([]byte("2")) //2
cp.Prev() // 1
cp.Prev() // nil (Cursor out of range)
kp, _ := cp.Next() // Should be 2 but nil
fmt.Println(string(kp))
// End
return nil
})
}
The output of the program:
=== Next test ===
2
=== Prev test ===
As you can see I put 3 rows "1", "2" and "3" into the bucket.
Both of "Next test" and "Prev test", I set cursor at "2" initially.
In "Next test", I move cursor to "3", then run Next() again, it returns nil.
Then I run Prev(), the cursor targets to "2".
In "Prev test", I move cursor to "1", then run Prev() again, it returns nil.
Then I run Next(), the cursor targets to nil.
Whatever how many Next() I added in "Prev test", the cursor still targes to nil.
It seems after Cursor.Prev() out of range, it stucks there and can not be use anymore.
I don't know if this is a bug or a correct design, but it's strange.
Do you consider make these 2 situations have similiar behavior?
Thank you very much!
Best