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// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
package utils
import (
"errors"
"fmt"
"io"
"io/fs"
"os"
"path/filepath"
)
var _ = fmt.Print
func AtomicCreateSymlink(oldname, newname string) (err error) {
err = os.Symlink(oldname, newname)
if err == nil {
return nil
}
if !errors.Is(err, fs.ErrExist) {
return err
}
if et, err := os.Readlink(newname); err == nil && et == oldname {
return nil
}
for {
tempname := newname + RandomFilename()
err = os.Symlink(oldname, tempname)
if err == nil {
err = os.Rename(tempname, newname)
if err != nil {
os.Remove(tempname)
}
return err
}
if !errors.Is(err, fs.ErrExist) {
return err
}
}
}
func AtomicWriteFile(path string, data io.Reader, perm os.FileMode) (err error) {
npath, err := filepath.EvalSymlinks(path)
if errors.Is(err, fs.ErrNotExist) {
err = nil
npath = path
}
if err == nil {
path = npath
path, err = filepath.Abs(path)
if err == nil {
var f *os.File
f, err = os.CreateTemp(filepath.Dir(path), filepath.Base(path)+".atomic-write-")
if err == nil {
removed := false
defer func() {
if err == nil {
err = f.Close()
} else {
f.Close()
}
if !removed {
os.Remove(f.Name())
removed = true
}
}()
if _, err = io.Copy(f, data); err == nil {
if err = f.Chmod(perm); err == nil {
if err = f.Sync(); err == nil { // Sync before rename to ensure we dont end up with a zero sized file
if err = os.Rename(f.Name(), path); err == nil {
removed = true
}
}
}
}
}
}
}
return
}
func AtomicUpdateFile(path string, data io.Reader, perms ...fs.FileMode) (err error) {
perm := fs.FileMode(0o644)
if len(perms) > 0 {
perm = perms[0]
}
s, err := os.Stat(path)
if err == nil {
perm = s.Mode().Perm()
}
return AtomicWriteFile(path, data, perm)
}
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