fsutil · go-clikit

fsutil writes, locks and checks the files of a program that several users, or several runs, share (decision 37).

It renames the file over the old one, and syncs the directory. A reader sees the old file or the new one, never a part.

Name	What it does
`fsutil.WriteAtomic`	a file replaced whole; a file that exists keeps its mode and group
`fsutil.ExactMode`	gives a file that exists exactly the mode too
`fsutil.Lock`	an exclusive lock in a file beside the shared file
`fsutil.Update`	changes a file under its lock; waits `fsutil.DefaultLockWait`
`fsutil.EnsureDir`	a private directory of the user’s
`fsutil.CheckTrusted`	refuses a file that a user other than this one or root could have written
`fsutil.ErrUntrusted`	what each refusal matches with `errors.Is`

dir, _ := os.MkdirTemp("", "prog-")
defer func() { _ = os.RemoveAll(dir) }()
path := filepath.Join(dir, "inventory")

unlock, err := fsutil.Lock(context.Background(), path, fsutil.DefaultLockWait)
if err != nil {
	fmt.Println(err)
	return
}
defer unlock()

_, err = fsutil.Lock(context.Background(), path, 100*time.Millisecond) // another run
fmt.Println(errors.Is(err, context.DeadlineExceeded))

 true

ExampleLock in fsutil/example_test.go. CI runs it and checks its output.

Fixed interfaces#

The name and the mode of the lock file, and ErrUntrusted. The texts of the errors are not fixed.