snegov/cura-te-ipsum
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Code Issues 20 Releases Wiki Activity

Make dry-run genuinely non-mutating (#23)

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* Make dry-run genuinely non-mutating

fs.rsync() now takes a real dry_run code path: every mutating call
(copy, delete, chmod, chown, utime) is skipped, and a missing dst_dir
is never created - the same comparison logic still runs so the yielded
actions match what a real run would do.

backup.initiate_backup() diffs each source directly against the latest
completed snapshot on dry-run, instead of building and discarding a
throwaway staging directory with real hardlinks. cleanup_old_backups()
no longer creates the repo-id file as a side effect of a dry-run.

cli.py skips lock acquisition entirely on dry-run (set_backups_lock()
writes PID/timestamp metadata, itself a mutation) and exposes the
retention policy via --keep-all/--keep-daily/--keep-weekly/
--keep-monthly/--keep-yearly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* Address Copilot review: guard restore lock release, reject negative retention values

- Guard restore --dry-run's finally block the same way backup's is
  guarded, for symmetry (release_backups_lock() was already a safe
  no-op when unheld, but this makes the dry-run contract explicit
  rather than relying on that implementation detail).
- Reject negative --keep-* values via a dedicated argparse type: a
  negative threshold shifts retention comparisons into the future and
  can make cleanup treat every existing backup as deletable.
- Add a restore --dry-run lock-skip regression test, mirroring the
  existing backup one.
- Fix _snapshot_all_stats() in the new dry-run non-mutation test to
  also record the backups_dir root's own stat, not just its children.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

---------

Co-authored-by: Maxim Shulga <maxim.shulga@alludo.com>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
snegovClaude Sonnet 5Maxim Shulga
 authored and GitHub committed 2026-08-09 01:39:53 +00:00
1 parent 699c569cc2
commit 22757ece58
8 files changed
+478 -51
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curateipsum/fs.py
+64 -21
View File
@@ -439,6 +439,18 @@ def update_direntry(src_entry: os.DirEntry,
return copy_direntry(src_entry, dst_entry.path)
def _maybe_update(src_entry: os.DirEntry, dst_entry: os.DirEntry,
dry_run: bool) -> Optional[str]:
"""
update_direntry(), unless dry_run - in which case dst_entry is left
untouched and no digest is available (nothing was actually copied to
hash).
"""
if dry_run:
return None
return update_direntry(src_entry, dst_entry)
def rsync(src_dir,
dst_dir,
dry_run=False) -> Iterable[Tuple[str, Actions, str]]:
@@ -447,6 +459,14 @@ def rsync(src_dir,
Yield (path, action, error message) tuples.
Entries in dst_dir will be removed if not present in src_dir.
Analog of 'rsync --delete -irltpog'.
With dry_run=True, dst_dir is never created, written to, or mutated
in any way (no copy, delete, chmod, chown, or utime call runs) - the
same comparison logic that decides each action still runs, so the
yielded (path, action, message) tuples describe exactly what a real
run would do, but purely by reading src_dir and dst_dir. This lets a
dry run diff straight against the previous, immutable snapshot
instead of a throwaway hardlinked copy.
"""
_lg.debug("Rsync: %s -> %s", src_dir, dst_dir)
@@ -457,13 +477,18 @@ def rsync(src_dir,
raise BackupCreationError(
"Error during reading source directory: %s" % src_root_abs
)
if os.path.exists(dst_root_abs):
if not os.path.isdir(dst_root_abs):
raise BackupCreationError(
"Destination path is not a directory: %s" % dst_root_abs
)
else:
os.mkdir(dst_root_abs)
dst_exists = os.path.exists(dst_root_abs)
if dst_exists and not os.path.isdir(dst_root_abs):
raise BackupCreationError(
"Destination path is not a directory: %s" % dst_root_abs
)
if not dst_exists:
if dry_run:
# Nothing to compare against and nothing to create - every
# source entry below is naturally reported as a CREATE.
dst_root_abs = None
else:
os.mkdir(dst_root_abs)
# Create source map {rel_path: dir_entry}
src_files_map = {
@@ -472,7 +497,8 @@ def rsync(src_dir,
}
# process dst tree
for dst_entry in scantree(dst_root_abs, dir_first=False):
dst_iter = scantree(dst_root_abs, dir_first=False) if dst_root_abs else ()
for dst_entry in dst_iter:
rel_path = dst_entry.path[len(dst_root_abs) + 1:]
src_entry = src_files_map.get(rel_path)
@@ -480,6 +506,9 @@ def rsync(src_dir,
# remove dst entries not existing in source
if src_entry is None:
_lg.debug("Rsync, deleting: %s", rel_path)
if dry_run:
yield rel_path, Actions.DELETE, ""
continue
try:
rm_direntry(dst_entry)
yield rel_path, Actions.DELETE, ""
@@ -513,7 +542,7 @@ def rsync(src_dir,
" (src is a file, dst is not a file): %s",
rel_path)
try:
digest = update_direntry(src_entry, dst_entry)
digest = _maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, digest or ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -525,7 +554,7 @@ def rsync(src_dir,
" (src is a dir, dst is not a dir): %s",
rel_path)
try:
update_direntry(src_entry, dst_entry)
_maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -537,7 +566,7 @@ def rsync(src_dir,
" (src is a symlink, dst is not a symlink): %s",
rel_path)
try:
update_direntry(src_entry, dst_entry)
_maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -547,7 +576,7 @@ def rsync(src_dir,
if src_entry.inode() == dst_entry.inode():
_lg.debug("Rsync, rewriting (shared inode with src): %s", rel_path)
try:
digest = update_direntry(src_entry, dst_entry)
digest = _maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, digest or ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -565,7 +594,7 @@ def rsync(src_dir,
_lg.debug("Rsync, rewriting (different %s): %s",
reason, rel_path)
try:
digest = update_direntry(src_entry, dst_entry)
digest = _maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, digest or ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -577,7 +606,7 @@ def rsync(src_dir,
_lg.debug("Rsync, rewriting (different symlink target): %s",
rel_path)
try:
update_direntry(src_entry, dst_entry)
_maybe_update(src_entry, dst_entry, dry_run)
yield rel_path, Actions.REWRITE, ""
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
@@ -598,25 +627,30 @@ def rsync(src_dir,
# before mutating permissions/ownership in place, or the change
# would silently apply to every older snapshot sharing the inode.
if src_entry.is_file(follow_symlinks=False):
if src_stat.st_mode != dst_stat.st_mode or (
if not dry_run and (src_stat.st_mode != dst_stat.st_mode or (
src_stat.st_uid != dst_stat.st_uid
or src_stat.st_gid != dst_stat.st_gid):
or src_stat.st_gid != dst_stat.st_gid)):
_break_shared_hardlink(dst_entry.path)
# update permissions and ownership
if src_stat.st_mode != dst_stat.st_mode:
_lg.debug("Rsync, updating permissions: %s", rel_path)
os.chmod(dst_entry.path, src_stat.st_mode)
if not dry_run:
os.chmod(dst_entry.path, src_stat.st_mode)
yield rel_path, Actions.UPDATE_PERM, ""
if (src_stat.st_uid != dst_stat.st_uid
or src_stat.st_gid != dst_stat.st_gid):
_lg.debug("Rsync, updating owners: %s", rel_path)
try:
os.chown(dst_entry.path, src_stat.st_uid, src_stat.st_gid)
if dry_run:
yield rel_path, Actions.UPDATE_OWNER, ""
except PermissionError:
_lg.debug("Cannot change ownership (not root): %s", rel_path)
else:
try:
os.chown(dst_entry.path, src_stat.st_uid, src_stat.st_gid)
yield rel_path, Actions.UPDATE_OWNER, ""
except PermissionError:
_lg.debug("Cannot change ownership (not root): %s",
rel_path)
# process remained source entries (new files/dirs/symlinks)
for rel_path, src_entry in src_files_map.items():
@@ -627,6 +661,10 @@ def rsync(src_dir,
yield rel_path, Actions.EXCLUDE, src_kind
continue
if dry_run:
yield rel_path, Actions.CREATE, ""
continue
dst_path = os.path.join(dst_root_abs, rel_path)
_lg.debug("Rsync, creating: %s", rel_path)
try:
@@ -635,6 +673,11 @@ def rsync(src_dir,
except (OSError, BackupCreationError) as exc:
yield rel_path, Actions.ERROR, str(exc)
if dry_run:
# Nothing below this point does anything but restore directory
# mtimes disturbed by the mutations above - none of which ran.
return
# restore dir mtimes in dst, updated by updating files
for src_entry in scantree(src_root_abs, dir_first=True,
one_filesystem=True):