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sqlite: implement driver.SessionResetter and driver.Validator #72

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sqlite: implement driver.SessionResetter and driver.Validator #72

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26 changes: 26 additions & 0 deletions sqlite.go
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Original file line number Diff line number Diff line change
Expand Up @@ -275,6 +275,32 @@ func (c *conn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, e
// Raw is so ConnInitFunc can cast to SQLConn.
func (c *conn) Raw(fn func(any) error) error { return fn(c) }

// ResetSession is called prior to executing a query on the connection
// if the connection has been used before. If the driver returns ErrBadConn
// the connection is discarded.
func (c *conn) ResetSession(ctx context.Context) error {
if c.txState != txStateNone {
return errors.New("cannot ResetSession on a connection with an active transaction")
}

// ensure that all prepared statements are reset and unbound
if c.stmts != nil {
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nil check is redundant because a range over a nil map does nothing

for _, s := range c.stmts {
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this is almost right. in practice it would basically work. but the problem are statements created with persist=false, which don't get put into c.stmts.

if err := s.resetAndClear(); err != nil {
return err
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Should this return ErrBadConn?

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In the above case we could and probably should. In this particular case, that's unclear because:

ErrBadConn should be returned by a driver to signal to the sql package that a driver.Conn is in a bad state (such as the server having earlier closed the connection) and the sql package should retry on a new connection.

To prevent duplicate operations, ErrBadConn should NOT be returned if there's a possibility that the database server might have performed the operation. Even if the server sends back an error, you shouldn't return ErrBadConn.

Errors will be checked using errors.Is. An error may wrap ErrBadConn or implement the Is(error) bool method.

If we have potentially completed a tx we can not disambiguate between these conditions so we should not match BadConn.

}
}
}

return nil
}

// IsValid is called prior to placing the connection into the
// connection pool. The connection will be discarded if false is returned.
func (c *conn) IsValid() bool {
return true
}

type readOnlyKey struct{}

// ReadOnly applies the query_only pragma to the connection.
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7 changes: 7 additions & 0 deletions sqlite_test.go
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Expand Up @@ -20,6 +20,13 @@ import (
"github.com/tailscale/sqlite/sqliteh"
)

// SessionResetter and Validator are required in order for conns to be returned
// to database/sql connection pools.
var (
_ driver.SessionResetter = (*conn)(nil)
_ driver.Validator = (*conn)(nil)
)

func TestOpenDB(t *testing.T) {
db := openTestDB(t)
var journalMode string
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