Add optional fsync support for fs-write-stream-atomic

feature request

Add optional fsync support to @parcel/fs-write-stream-atomic to improve durability when using atomic writes with streams.

Expected Behavior

When the stream finishes writing the temp file, the library should be able to:

1. fsync the temp file to ensure data is on disk.
2. rename the temp file to the target path.
3. Optionally fsync the parent directory to persist the name/metadata.

This could be opt-in via options, e.g.:

writeStreamAtomic(dest, { fsync: true, fsyncDir: true });

Current Behavior

The library writes to a temp file and then renames it to the target, but does not call fsync on the temp file or the parent directory. After a crash or power loss right after rename, the file contents may not be fully durable.

Possible Solution

• Add options to enable fsync:

  • On stream close: call fdatasync/fsync on the temp file before rename.
  • After rename: attempt to open and fsync the parent directory (best-effort; skip on platforms/filesystems that don’t support it).

• Keep the default behavior unchanged for performance, but allow users to opt in per use case.

Context

We use the package to copy/write large files via streams and need stronger guarantees against data loss on sudden crashes. Atomic rename protects the filename switch, but without fsync we can still end up with a truncated or not-yet-flushed file after a power failure.

Examples

Proposed usage:

import writeStreamAtomic from '@parcel/fs-write-stream-atomic';

const ws = writeStreamAtomic('/path/to/file', { fsync: true, fsyncDir: true });
// pipe(...).on('finish', ...)

Thanks for maintaining this package - it’s very helpful for me. If this proposal makes sense, I’d be happy to open a PR implementing it.