fsutil

func CopyFile ¶

func CopyFile(src, dst string) error

CopyFile copies src to dst, creating or truncating dst. It is NOT atomic; wrap it in Publish when a reader may be looking at dst.

func Publish ¶

func Publish(final, seed string, produce func(path string) error) error

Publish produces a file at a private path and moves it to final in one rename, so a reader of final sees the previous file or the finished one — never a truncated, half-written, or missing one.

produce is handed a path that does not exist yet unless seed is set, in which case it starts as a copy of seed (an incremental update copies the current final and edits the copy). It may open, write and close the path however it likes; SQLite writers included.

The work happens in a private directory beside final, for two reasons. A rename is only atomic within one filesystem, and TMPDIR is often another. And a directory of its own makes the publish check structural: when produce returns, that directory must hold exactly the one file. Anything else there — an uncheckpointed `-wal`, a hot `-journal` — is state the file depends on, and renaming the file without it would publish a database missing committed writes. That is refused, not guessed at.

A reader that already has final open keeps reading the file it opened: the rename replaces the name, not the inode. Seeing the new file means reopening.

When final is a symlink, its target is replaced and the link is left alone, as an in-place write through the link would have done.

func WriteFileAtomic ¶

func WriteFileAtomic(path string, data []byte) error

WriteFileAtomic writes data to path through Publish. The file is created 0o600, as the os.CreateTemp-based version this replaced did.