syncthing/vendor/github.com/cznic/lldb/simplefilefiler.go

100 lines
2.6 KiB
Go

// Copyright 2014 The lldb Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// A basic os.File backed Filer.
package lldb
import (
"os"
"github.com/cznic/internal/file"
)
var _ Filer = &SimpleFileFiler{}
// SimpleFileFiler is an os.File backed Filer intended for use where structural
// consistency can be reached by other means (SimpleFileFiler is for example
// wrapped in eg. an RollbackFiler or ACIDFiler0) or where persistence is not
// required (temporary/working data sets).
//
// SimpleFileFiler is the most simple os.File backed Filer implementation as it
// does not really implement BeginUpdate and EndUpdate/Rollback in any way
// which would protect the structural integrity of data. If misused e.g. as a
// real database storage w/o other measures, it can easily cause data loss
// when, for example, a power outage occurs or the updating process terminates
// abruptly.
type SimpleFileFiler struct {
fi file.Interface
name string
nest int
}
// NewSimpleFileFiler returns a new SimpleFileFiler.
func NewSimpleFileFiler(f *os.File) *SimpleFileFiler {
fi, err := file.Open(f)
if err != nil {
return nil
}
sf := &SimpleFileFiler{fi: fi, name: f.Name()}
return sf
}
// BeginUpdate implements Filer.
func (f *SimpleFileFiler) BeginUpdate() error {
f.nest++
return nil
}
// Close implements Filer.
func (f *SimpleFileFiler) Close() (err error) {
if f.nest != 0 {
return &ErrPERM{(f.Name() + ":Close")}
}
return f.fi.Close()
}
// EndUpdate implements Filer.
func (f *SimpleFileFiler) EndUpdate() (err error) {
if f.nest == 0 {
return &ErrPERM{(f.Name() + ":EndUpdate")}
}
f.nest--
return
}
// Name implements Filer.
func (f *SimpleFileFiler) Name() string { return f.name }
// PunchHole implements Filer.
func (f *SimpleFileFiler) PunchHole(off, size int64) (err error) { return nil }
// ReadAt implements Filer.
func (f *SimpleFileFiler) ReadAt(b []byte, off int64) (n int, err error) { return f.fi.ReadAt(b, off) }
// Rollback implements Filer.
func (f *SimpleFileFiler) Rollback() (err error) { return nil }
// Size implements Filer.
func (f *SimpleFileFiler) Size() (int64, error) {
info, err := f.fi.Stat()
if err != nil {
return 0, err
}
return info.Size(), nil
}
// Sync implements Filer.
func (f *SimpleFileFiler) Sync() error { return f.fi.Sync() }
// Truncate implements Filer.
func (f *SimpleFileFiler) Truncate(size int64) (err error) { return f.fi.Truncate(size) }
// WriteAt implements Filer.
func (f *SimpleFileFiler) WriteAt(b []byte, off int64) (n int, err error) { return f.fi.WriteAt(b, off) }