Fix #42

tests/test_sync.py

@@ -91,6 +91,7 @@ def test_deletion():
 
     item = Item(u'UID:1')
     a.upload(item)
+    a.upload(Item(u'UID:2'))
     sync(a, b, status)
     b.delete('1.txt', b.get('1.txt')[1])
     sync(a, b, status)
@@ -192,3 +193,17 @@ def test_uses_get_multi(monkeypatch):
 
     sync(a, b, {})
     assert get_multi_calls == [[expected_href]]
+
+
+def test_empty_storage_dataloss():
+    a = MemoryStorage()
+    b = MemoryStorage()
+    a.upload(Item(u'UID:1'))
+    a.upload(Item(u'UID:2'))
+    status = {}
+    sync(a, b, status)
+    with pytest.raises(exceptions.StorageEmpty):
+        sync(MemoryStorage(), b, status)
+
+    with pytest.raises(exceptions.StorageEmpty):
+        sync(a, MemoryStorage(), status)

vdirsyncer/cli.py

@@ -14,6 +14,7 @@ from vdirsyncer.sync import sync
 from vdirsyncer.utils import expand_path, split_dict, parse_options
 from vdirsyncer.storage import storage_names
 import vdirsyncer.log as log
+import vdirsyncer.exceptions as exceptions
 import argvard
 
 
@@ -196,6 +197,11 @@ def _main(env, file_cfg):
 
     sync_command = argvard.Command()
 
+    @sync_command.option('--force-delete status_name')
+    def force_delete(context, status_name):
+        '''Pretty please delete all my data.'''
+        context.setdefault('force_delete', set()).add(status_name)
+
     @sync_command.main('[pairs...]')
     def sync_main(context, pairs=None):
         '''
@@ -209,6 +215,7 @@ def _main(env, file_cfg):
         from the pair "bob".
         '''
         actions = []
+        force_delete = context.get('force_delete', set())
         for pair_name, collection in parse_pairs_args(pairs, all_pairs):
             a_name, b_name, pair_options, storage_defaults = \
                 all_pairs[pair_name]
@@ -225,7 +232,8 @@ def _main(env, file_cfg):
                 'pair_name': pair_name,
                 'collection': collection,
                 'pair_options': pair_options,
-                'general': general
+                'general': general,
+                'force_delete': force_delete
             })
 
         processes = general.get('processes', 0) or len(actions)
@@ -249,7 +257,7 @@ def _sync_collection(x):
 
 
 def sync_collection(config_a, config_b, pair_name, collection, pair_options,
-                    general):
+                    general, force_delete):
     status_name = '_'.join(filter(bool, (pair_name, collection)))
     pair_description = ' from '.join(filter(bool, (collection, pair_name)))
 
@@ -258,6 +266,20 @@ def sync_collection(config_a, config_b, pair_name, collection, pair_options,
 
     cli_logger.info('Syncing {}'.format(pair_description))
     status = load_status(general['status_path'], status_name)
-    sync(a, b, status,
-         pair_options.get('conflict_resolution', None))
+    try:
+        sync(
+            a, b, status,
+            conflict_resolution=pair_options.get('conflict_resolution', None),
+            force_delete=status_name in force_delete
+        )
+    except exceptions.StorageEmpty as e:
+        side = 'a' if e.empty_storage is a else 'b'
+        storage = e.empty_storage
+        cli_logger.error('{pair_description}: Storage "{side}" ({storage}) '
+                         'was completely emptied. Use "--force-delete '
+                         '{status_name}" to synchronize that emptyness to '
+                         'the other side, or delete the status by yourself to '
+                         'restore the empty side from the other one.'
+                         .format(**locals()))
+        sys.exit(1)
     save_status(general['status_path'], status_name, status)

vdirsyncer/exceptions.py

@@ -51,3 +51,12 @@ class SyncError(Error):
 
 class SyncConflict(SyncError):
     pass
+
+
+class StorageEmpty(SyncError):
+    '''One storage unexpectedly got completely empty between two
+    synchronizations. The first argument is the empty storage.'''
+
+    @property
+    def empty_storage(self):
+        return self.args[0]

vdirsyncer/sync.py

@@ -42,7 +42,8 @@ def prepare_list(storage, href_to_status):
             yield href, props
 
 
-def sync(storage_a, storage_b, status, conflict_resolution=None):
+def sync(storage_a, storage_b, status, conflict_resolution=None,
+         force_delete=False):
     '''Syncronizes two storages.
 
     :param storage_a: The first storage
@@ -56,6 +57,10 @@ def sync(storage_a, storage_b, status, conflict_resolution=None):
     :param conflict_resolution: Either 'a wins' or 'b wins'. If none is
         provided, the sync function will raise
         :py:exc:`vdirsyncer.exceptions.SyncConflict`.
+    :param force_delete: When one storage got completely emptied between two
+        syncs, :py:exc:`vdirsyncer.exceptions.StorageEmpty` is raised for
+        safety. Setting this parameter to ``True`` disables this safety
+        measure.
     '''
     a_href_to_status = dict(
         (href_a, (uid, etag_a))
@@ -69,6 +74,9 @@ def sync(storage_a, storage_b, status, conflict_resolution=None):
     list_a = dict(prepare_list(storage_a, a_href_to_status))
     list_b = dict(prepare_list(storage_b, b_href_to_status))
 
+    if bool(list_a) != bool(list_b) and status and not force_delete:
+        raise exceptions.StorageEmpty(storage_b if list_a else storage_a)
+
     a_uid_to_href = dict((x['uid'], href) for href, x in iteritems(list_a))
     b_uid_to_href = dict((x['uid'], href) for href, x in iteritems(list_b))
     del a_href_to_status, b_href_to_status