sql.go

			}
			return rows, nil
		}

		releaseConn(err)
		if err != driver.ErrBadConn {
			return nil, err
		}
	}
	return nil, driver.ErrBadConn
}

// Query executes a prepared query statement with the given arguments
// and returns the query results as a *Rows.
func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
	return s.QueryContext(context.Background(), args...)
}

func rowsiFromStatement(ctx context.Context, ds *driverStmt, args ...interface{}) (driver.Rows, error) {
	var want int
	withLock(ds, func() {
		want = ds.si.NumInput()
	})

	// -1 means the driver doesn't know how to count the number of
	// placeholders, so we won't sanity check input here and instead let the
	// driver deal with errors.
	if want != -1 && len(args) != want {
		return nil, fmt.Errorf("sql: statement expects %d inputs; got %d", want, len(args))
	}

	dargs, err := driverArgs(ds, args)
	if err != nil {
		return nil, err
	}

	ds.Lock()
	defer ds.Unlock()

	rowsi, err := ctxDriverStmtQuery(ctx, ds.si, dargs)
	if err != nil {
		return nil, err
	}
	return rowsi, nil
}

// QueryRowContext executes a prepared query statement with the given arguments.
// If an error occurs during the execution of the statement, that error will
// be returned by a call to Scan on the returned *Row, which is always non-nil.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
//
// Example usage:
//
//  var name string
//  err := nameByUseridStmt.QueryRowContext(ctx, id).Scan(&name)
func (s *Stmt) QueryRowContext(ctx context.Context, args ...interface{}) *Row {
	rows, err := s.QueryContext(ctx, args...)
	if err != nil {
		return &Row{err: err}
	}
	return &Row{rows: rows}
}

// QueryRow executes a prepared query statement with the given arguments.
// If an error occurs during the execution of the statement, that error will
// be returned by a call to Scan on the returned *Row, which is always non-nil.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
//
// Example usage:
//
//  var name string
//  err := nameByUseridStmt.QueryRow(id).Scan(&name)
func (s *Stmt) QueryRow(args ...interface{}) *Row {
	return s.QueryRowContext(context.Background(), args...)
}

// Close closes the statement.
func (s *Stmt) Close() error {
	s.closemu.Lock()
	defer s.closemu.Unlock()

	if s.stickyErr != nil {
		return s.stickyErr
	}
	s.mu.Lock()
	if s.closed {
		s.mu.Unlock()
		return nil
	}
	s.closed = true
	s.mu.Unlock()

	if s.tx == nil {
		return s.db.removeDep(s, s)
	}

	if s.parentStmt != nil {
		// If parentStmt is set, we must not close s.txds since it's stored
		// in the css array of the parentStmt.
		return s.db.removeDep(s.parentStmt, s)
	}
	return s.txds.Close()
}

func (s *Stmt) finalClose() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.css != nil {
		for _, v := range s.css {
			s.db.noteUnusedDriverStatement(v.dc, v.ds)
			v.dc.removeOpenStmt(v.ds)
		}
		s.css = nil
	}
	return nil
}

// Rows is the result of a query. Its cursor starts before the first row
// of the result set. Use Next to advance through the rows:
//
//     rows, err := db.Query("SELECT ...")
//     ...
//     defer rows.Close()
//     for rows.Next() {
//         var id int
//         var name string
//         err = rows.Scan(&id, &name)
//         ...
//     }
//     err = rows.Err() // get any error encountered during iteration
//     ...
type Rows struct {
	dc          *driverConn // owned; must call releaseConn when closed to release
	releaseConn func(error)
	rowsi       driver.Rows
	cancel      func()      // called when Rows is closed, may be nil.
	closeStmt   *driverStmt // if non-nil, statement to Close on close

	// closemu prevents Rows from closing while there
	// is an active streaming result. It is held for read during non-close operations
	// and exclusively during close.
	//
	// closemu guards lasterr and closed.
	closemu sync.RWMutex
	closed  bool
	lasterr error // non-nil only if closed is true

	// lastcols is only used in Scan, Next, and NextResultSet which are expected
	// not to be called concurrently.
	lastcols []driver.Value
}

func (rs *Rows) initContextClose(ctx context.Context) {
	ctx, rs.cancel = context.WithCancel(ctx)
	go rs.awaitDone(ctx)
}

// awaitDone blocks until the rows are closed or the context canceled.
func (rs *Rows) awaitDone(ctx context.Context) {
	<-ctx.Done()
	rs.close(ctx.Err())
}

// Next prepares the next result row for reading with the Scan method. It
// returns true on success, or false if there is no next result row or an error
// happened while preparing it. Err should be consulted to distinguish between
// the two cases.
//
// Every call to Scan, even the first one, must be preceded by a call to Next.
func (rs *Rows) Next() bool {
	var doClose, ok bool
	withLock(rs.closemu.RLocker(), func() {
		doClose, ok = rs.nextLocked()
	})
	if doClose {
		rs.Close()
	}
	return ok
}

func (rs *Rows) nextLocked() (doClose, ok bool) {
	if rs.closed {
		return false, false
	}
	if rs.lastcols == nil {
		rs.lastcols = make([]driver.Value, len(rs.rowsi.Columns()))
	}
	rs.lasterr = rs.rowsi.Next(rs.lastcols)
	if rs.lasterr != nil {
		// Close the connection if there is a driver error.
		if rs.lasterr != io.EOF {
			return true, false
		}
		nextResultSet, ok := rs.rowsi.(driver.RowsNextResultSet)
		if !ok {
			return true, false
		}
		// The driver is at the end of the current result set.
		// Test to see if there is another result set after the current one.
		// Only close Rows if there is no further result sets to read.
		if !nextResultSet.HasNextResultSet() {
			doClose = true
		}
		return doClose, false
	}
	return false, true
}

// NextResultSet prepares the next result set for reading. It returns true if
// there is further result sets, or false if there is no further result set
// or if there is an error advancing to it. The Err method should be consulted
// to distinguish between the two cases.
//
// After calling NextResultSet, the Next method should always be called before
// scanning. If there are further result sets they may not have rows in the result
// set.
func (rs *Rows) NextResultSet() bool {
	var doClose bool
	defer func() {
		if doClose {
			rs.Close()
		}
	}()
	rs.closemu.RLock()
	defer rs.closemu.RUnlock()

	if rs.closed {
		return false
	}

	rs.lastcols = nil
	nextResultSet, ok := rs.rowsi.(driver.RowsNextResultSet)
	if !ok {
		doClose = true
		return false
	}
	rs.lasterr = nextResultSet.NextResultSet()
	if rs.lasterr != nil {
		doClose = true
		return false
	}
	return true
}

// Err returns the error, if any, that was encountered during iteration.
// Err may be called after an explicit or implicit Close.
func (rs *Rows) Err() error {
	rs.closemu.RLock()
	defer rs.closemu.RUnlock()
	if rs.lasterr == io.EOF {
		return nil
	}
	return rs.lasterr
}

// Columns returns the column names.
// Columns returns an error if the rows are closed, or if the rows
// are from QueryRow and there was a deferred error.
func (rs *Rows) Columns() ([]string, error) {
	rs.closemu.RLock()
	defer rs.closemu.RUnlock()
	if rs.closed {
		return nil, errors.New("sql: Rows are closed")
	}
	if rs.rowsi == nil {
		return nil, errors.New("sql: no Rows available")
	}
	return rs.rowsi.Columns(), nil
}

// ColumnTypes returns column information such as column type, length,
// and nullable. Some information may not be available from some drivers.
func (rs *Rows) ColumnTypes() ([]*ColumnType, error) {
	rs.closemu.RLock()
	defer rs.closemu.RUnlock()
	if rs.closed {
		return nil, errors.New("sql: Rows are closed")
	}
	if rs.rowsi == nil {
		return nil, errors.New("sql: no Rows available")
	}
	return rowsColumnInfoSetup(rs.rowsi), nil
}

// ColumnType contains the name and type of a column.
type ColumnType struct {
	name string

	hasNullable       bool
	hasLength         bool
	hasPrecisionScale bool

	nullable     bool
	length       int64
	databaseType string
	precision    int64
	scale        int64
	scanType     reflect.Type
}

// Name returns the name or alias of the column.
func (ci *ColumnType) Name() string {
	return ci.name
}

// Length returns the column type length for variable length column types such
// as text and binary field types. If the type length is unbounded the value will
// be math.MaxInt64 (any database limits will still apply).
// If the column type is not variable length, such as an int, or if not supported
// by the driver ok is false.
func (ci *ColumnType) Length() (length int64, ok bool) {
	return ci.length, ci.hasLength
}

// DecimalSize returns the scale and precision of a decimal type.
// If not applicable or if not supported ok is false.
func (ci *ColumnType) DecimalSize() (precision, scale int64, ok bool) {
	return ci.precision, ci.scale, ci.hasPrecisionScale
}

// ScanType returns a Go type suitable for scanning into using Rows.Scan.
// If a driver does not support this property ScanType will return
// the type of an empty interface.
func (ci *ColumnType) ScanType() reflect.Type {
	return ci.scanType
}

// Nullable returns whether the column may be null.
// If a driver does not support this property ok will be false.
func (ci *ColumnType) Nullable() (nullable, ok bool) {
	return ci.nullable, ci.hasNullable
}

// DatabaseTypeName returns the database system name of the column type. If an empty
// string is returned the driver type name is not supported.
// Consult your driver documentation for a list of driver data types. Length specifiers
// are not included.
// Common type include "VARCHAR", "TEXT", "NVARCHAR", "DECIMAL", "BOOL", "INT", "BIGINT".
func (ci *ColumnType) DatabaseTypeName() string {
	return ci.databaseType
}

func rowsColumnInfoSetup(rowsi driver.Rows) []*ColumnType {
	names := rowsi.Columns()

	list := make([]*ColumnType, len(names))
	for i := range list {
		ci := &ColumnType{
			name: names[i],
		}
		list[i] = ci

		if prop, ok := rowsi.(driver.RowsColumnTypeScanType); ok {
			ci.scanType = prop.ColumnTypeScanType(i)
		} else {
			ci.scanType = reflect.TypeOf(new(interface{})).Elem()
		}
		if prop, ok := rowsi.(driver.RowsColumnTypeDatabaseTypeName); ok {
			ci.databaseType = prop.ColumnTypeDatabaseTypeName(i)
		}
		if prop, ok := rowsi.(driver.RowsColumnTypeLength); ok {
			ci.length, ci.hasLength = prop.ColumnTypeLength(i)
		}
		if prop, ok := rowsi.(driver.RowsColumnTypeNullable); ok {
			ci.nullable, ci.hasNullable = prop.ColumnTypeNullable(i)
		}
		if prop, ok := rowsi.(driver.RowsColumnTypePrecisionScale); ok {
			ci.precision, ci.scale, ci.hasPrecisionScale = prop.ColumnTypePrecisionScale(i)
		}
	}
	return list
}

// Scan copies the columns in the current row into the values pointed
// at by dest. The number of values in dest must be the same as the
// number of columns in Rows.
//
// Scan converts columns read from the database into the following
// common Go types and special types provided by the sql package:
//
//    *string
//    *[]byte
//    *int, *int8, *int16, *int32, *int64
//    *uint, *uint8, *uint16, *uint32, *uint64
//    *bool
//    *float32, *float64
//    *interface{}
//    *RawBytes
//    any type implementing Scanner (see Scanner docs)
//
// In the most simple case, if the type of the value from the source
// column is an integer, bool or string type T and dest is of type *T,
// Scan simply assigns the value through the pointer.
//
// Scan also converts between string and numeric types, as long as no
// information would be lost. While Scan stringifies all numbers
// scanned from numeric database columns into *string, scans into
// numeric types are checked for overflow. For example, a float64 with
// value 300 or a string with value "300" can scan into a uint16, but
// not into a uint8, though float64(255) or "255" can scan into a
// uint8. One exception is that scans of some float64 numbers to
// strings may lose information when stringifying. In general, scan
// floating point columns into *float64.
//
// If a dest argument has type *[]byte, Scan saves in that argument a
// copy of the corresponding data. The copy is owned by the caller and
// can be modified and held indefinitely. The copy can be avoided by
// using an argument of type *RawBytes instead; see the documentation
// for RawBytes for restrictions on its use.
//
// If an argument has type *interface{}, Scan copies the value
// provided by the underlying driver without conversion. When scanning
// from a source value of type []byte to *interface{}, a copy of the
// slice is made and the caller owns the result.
//
// Source values of type time.Time may be scanned into values of type
// *time.Time, *interface{}, *string, or *[]byte. When converting to
// the latter two, time.Format3339Nano is used.
//
// Source values of type bool may be scanned into types *bool,
// *interface{}, *string, *[]byte, or *RawBytes.
//
// For scanning into *bool, the source may be true, false, 1, 0, or
// string inputs parseable by strconv.ParseBool.
func (rs *Rows) Scan(dest ...interface{}) error {
	rs.closemu.RLock()
	if rs.closed {
		rs.closemu.RUnlock()
		return errors.New("sql: Rows are closed")
	}
	rs.closemu.RUnlock()

	if rs.lastcols == nil {
		return errors.New("sql: Scan called without calling Next")
	}
	if len(dest) != len(rs.lastcols) {
		return fmt.Errorf("sql: expected %d destination arguments in Scan, not %d", len(rs.lastcols), len(dest))
	}
	for i, sv := range rs.lastcols {
		err := convertAssign(dest[i], sv)
		if err != nil {
			return fmt.Errorf("sql: Scan error on column index %d: %v", i, err)
		}
	}
	return nil
}

// rowsCloseHook returns a function so tests may install the
// hook through a test only mutex.
var rowsCloseHook = func() func(*Rows, *error) { return nil }

// Close closes the Rows, preventing further enumeration. If Next is called
// and returns false and there are no further result sets,
// the Rows are closed automatically and it will suffice to check the
// result of Err. Close is idempotent and does not affect the result of Err.
func (rs *Rows) Close() error {
	return rs.close(nil)
}

func (rs *Rows) close(err error) error {
	rs.closemu.Lock()
	defer rs.closemu.Unlock()

	if rs.closed {
		return nil
	}
	rs.closed = true

	if rs.lasterr == nil {
		rs.lasterr = err
	}

	err = rs.rowsi.Close()
	if fn := rowsCloseHook(); fn != nil {
		fn(rs, &err)
	}
	if rs.cancel != nil {
		rs.cancel()
	}

	if rs.closeStmt != nil {
		rs.closeStmt.Close()
	}
	rs.releaseConn(err)
	return err
}

// Row is the result of calling QueryRow to select a single row.
type Row struct {
	// One of these two will be non-nil:
	err  error // deferred error for easy chaining
	rows *Rows
}

// Scan copies the columns from the matched row into the values
// pointed at by dest. See the documentation on Rows.Scan for details.
// If more than one row matches the query,
// Scan uses the first row and discards the rest. If no row matches
// the query, Scan returns ErrNoRows.
func (r *Row) Scan(dest ...interface{}) error {
	if r.err != nil {
		return r.err
	}

	// TODO(bradfitz): for now we need to defensively clone all
	// []byte that the driver returned (not permitting
	// *RawBytes in Rows.Scan), since we're about to close
	// the Rows in our defer, when we return from this function.
	// the contract with the driver.Next(...) interface is that it
	// can return slices into read-only temporary memory that's
	// only valid until the next Scan/Close. But the TODO is that
	// for a lot of drivers, this copy will be unnecessary. We
	// should provide an optional interface for drivers to
	// implement to say, "don't worry, the []bytes that I return
	// from Next will not be modified again." (for instance, if
	// they were obtained from the network anyway) But for now we
	// don't care.
	defer r.rows.Close()
	for _, dp := range dest {
		if _, ok := dp.(*RawBytes); ok {
			return errors.New("sql: RawBytes isn't allowed on Row.Scan")
		}
	}

	if !r.rows.Next() {
		if err := r.rows.Err(); err != nil {
			return err
		}
		return ErrNoRows
	}
	err := r.rows.Scan(dest...)
	if err != nil {
		return err
	}
	// Make sure the query can be processed to completion with no errors.
	if err := r.rows.Close(); err != nil {
		return err
	}

	return nil
}

// A Result summarizes an executed SQL command.
type Result interface {
	// LastInsertId returns the integer generated by the database
	// in response to a command. Typically this will be from an
	// "auto increment" column when inserting a new row. Not all
	// databases support this feature, and the syntax of such
	// statements varies.
	LastInsertId() (int64, error)

	// RowsAffected returns the number of rows affected by an
	// update, insert, or delete. Not every database or database
	// driver may support this.
	RowsAffected() (int64, error)
}

type driverResult struct {
	sync.Locker // the *driverConn
	resi        driver.Result
}

func (dr driverResult) LastInsertId() (int64, error) {
	dr.Lock()
	defer dr.Unlock()
	return dr.resi.LastInsertId()
}

func (dr driverResult) RowsAffected() (int64, error) {
	dr.Lock()
	defer dr.Unlock()
	return dr.resi.RowsAffected()
}

func stack() string {
	var buf [2 << 10]byte
	return string(buf[:runtime.Stack(buf[:], false)])
}

// withLock runs while holding lk.
func withLock(lk sync.Locker, fn func()) {
	lk.Lock()
	defer lk.Unlock() // in case fn panics
	fn()
}