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//
// Copyright (c) SAS Institute Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Implement atomic write-rename file pattern. Instead of opening the named
// file it creates a temporary file next to it, then on Commit() renames it. If
// the file is Close()d before Commit() then it is unlinked instead.
package atomicfile
import (
"errors"
"io"
"io/ioutil"
"os"
"path/filepath"
"runtime"
)
// File-like interface used by several functions in this package. Some of them
// may open a file or stdio directly without atomic semantics, in which case
// Commit() is an alias for Close()
type AtomicFile interface {
io.Reader
io.ReaderAt
io.Writer
io.WriterAt
io.Seeker
Truncate(size int64) error
// Close and unlink the underlying file object, discarding the contents.
// No-op if Close() or Commit() was already called.
io.Closer
// Get the underlying *File object
GetFile() *os.File
// Complete the write-rename pattern and close the file
Commit() error
}
type atomicFile struct {
*os.File
name string
}
// Open a temporary file for reading and writing which will ultimately be
// renamed to the given name when Commit() is called.
func New(name string) (AtomicFile, error) {
tempfile, err := ioutil.TempFile(filepath.Dir(name), filepath.Base(name)+".tmp")
if err != nil {
return nil, err
}
f := &atomicFile{tempfile, name}
runtime.SetFinalizer(f, (*atomicFile).Close)
return f, nil
}
func (f *atomicFile) GetFile() *os.File {
return f.File
}
func (f *atomicFile) Close() error {
if f.File == nil {
return nil
}
f.File.Close()
os.Remove(f.File.Name())
f.File = nil
runtime.SetFinalizer(f, nil)
return nil
}
func (f *atomicFile) Commit() error {
if f.File == nil {
return errors.New("file is closed")
}
_ = f.File.Chmod(0644)
if err := f.File.Close(); err != nil {
return err
}
// rename can't overwrite on windows
if err := os.Remove(f.name); err != nil && !os.IsNotExist(err) {
return err
}
if err := os.Rename(f.File.Name(), f.name); err != nil {
return err
}
f.File = nil
runtime.SetFinalizer(f, nil)
return nil
}
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