Empty query causes loop

[joriszwart]

By mistake stupid me executed an empty query. This resulted in an (infinite?) loop and hanged my application.

The minimal example below reproduces this. This example uses an in-memory database, but it occurs with a database file as well.

Version: v1.14.7

db, err := sql.Open("sqlite3", ":memory:")
if err != nil {
	panic(err)
}
defer db.Close()

stmt, err := db.Prepare("") // empty query
if err != nil {
	panic(err)
}
defer stmt.Close()

rows, err := stmt.Query()
if err != nil {
	panic(err)
}
defer rows.Close()

count := 0
for rows.Next() {
	var dummy string
	rows.Scan(&dummy) // this can be omitted

	log.Printf("%d: [%+v]\n", count, dummy)
	count++
}

Results in:

0: []
1: []
2: []
3: []
4: []
...

I don't know what the expected behavior should be. Maybe return an error?

[rittneje]

The source of the bug is that sqlite3_prepare_v2 produces a null *sqlite3_stmt with no error when you do this. But this library does not check for that. https://github.com/mattn/go-sqlite3/blob/d33341ff0d20a3b46047dba17ad897b40705c563/sqlite3.go#L1749-L1752

Compounding the issue, each call to sqlite3_step will fail with SQLITE_MISUSE, but it gets dropped because of this: https://github.com/mattn/go-sqlite3/blob/d33341ff0d20a3b46047dba17ad897b40705c563/sqlite3.go#L2105-L2111

Basically, sqlite3_reset always vacuously succeeds when given a null statement, so we end up returning null from each call to Next(). Thus the loop never terminates.

In short, there are two bugs in play:

1. If sqlite3_prepare_v2 yields SQLITE_OK with a null prepared statement it should be treated as an error.
2. If sqlite3_reset yields SQLITE_OK after sqlite3_step fails we should still return an error. (Note: We can't just call lastError() in a situation like this since it might not be set properly. Maybe just convert to an ErrNo?)