func (f formFile) Open() (io.ReadSeekCloser, error) {
	return f.fh.Open()
}
Open opens the file.
package builtin
import (
	"errors"
	"io"
	"mime"
	"mime/multipart"
	"net/http"
	"net/textproto"
	"net/url"
	"strings"
)
const maxInt = int64(^uint(0) >> 1)
var ErrBadRequest = errors.New("form: bad request")
var ErrRequestEntityTooLarge = errors.New("form: request entity too large")
type File interface {
	Name() string  
	Type() string  
	Size() int     
}
type Opener interface {
	Open() (io.ReadSeekCloser, error)
}
type formFile struct {
	fh *multipart.FileHeader
}
func (f formFile) Name() string {
	return f.fh.Filename
}
func (f formFile) Type() string {
	return f.fh.Header.Get("Content-Type")
}
func (f formFile) Size() int {
	return int(f.fh.Size)
}