atomicfile

Overview ¶

Package atomicfile replaces a file whole: a reader opening the path sees the previous content or the new, never a mix, and after a crash the path holds one of the two. It is the one home for that write in this tree; the house lint's ATOMIC-WRITE rule refuses a hand-rolled temporary file renamed into place anywhere else.

The write is github.com/google/renameio/v2 (a uniquely named temporary file, fsync, close, rename) with three choices renameio leaves open made for every caller:

• The mode is exact. renameio.WriteFile keeps the mode of a file already at the path, so a secret once widened to 0644 would stay 0644 however often it is rewritten with 0600; here the mode given is the mode on disk, whatever was there and whatever the umask is.
• The temporary file is created beside the target, never in $TMPDIR, so no write probes another mount and the rename never crosses one.
• The directory is synced after the rename, so the new name, not only the new content, survives a crash.