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// +build plan9 windows,!go1.5
// os.Rename on Windows before Go 1.5 and Plan 9 will not overwrite existing
// files, thus we cannot guarantee atomic saving of file by doing rename.
// We will have to do some voodoo to minimize data loss on those systems.
package safefile
import (
"os"
"path/filepath"
)
func rename(oldname, newname string) error {
err := os.Rename(oldname, newname)
if err != nil {
// If newname exists ("original"), we will try renaming it to a
// new temporary name, then renaming oldname to the newname,
// and deleting the renamed original. If system crashes between
// renaming and deleting, the original file will still be available
// under the temporary name, so users can manually recover data.
// (No automatic recovery is possible because after crash the
// temporary name is not known.)
var origtmp string
for {
origtmp, err = makeTempName(newname, filepath.Base(newname))
if err != nil {
return err
}
_, err = os.Stat(origtmp)
if err == nil {
continue // most likely will never happen
}
break
}
err = os.Rename(newname, origtmp)
if err != nil {
return err
}
err = os.Rename(oldname, newname)
if err != nil {
// Rename still fails, try to revert original rename,
// ignoring errors.
os.Rename(origtmp, newname)
return err
}
// Rename succeeded, now delete original file.
os.Remove(origtmp)
}
return nil
}
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