Add error_callback to sync()

tests/test_sync.py

@@ -419,6 +419,10 @@ class ActionIntentionallyFailed(Exception):
     pass
 
 
+def action_failure(*a, **kw):
+    raise ActionIntentionallyFailed()
+
+
 class SyncMachine(RuleBasedStateMachine):
     Status = Bundle('status')
     Storage = Bundle('storage')
@@ -452,12 +456,9 @@ class SyncMachine(RuleBasedStateMachine):
 
     @rule(s=Storage)
     def actions_fail(self, s):
-        def blowup(*a, **kw):
-            raise ActionIntentionallyFailed()
-
-        s.upload = blowup
-        s.update = blowup
-        s.delete = blowup
+        s.upload = action_failure
+        s.update = action_failure
+        s.delete = action_failure
 
     @rule(target=Status)
     def newstatus(self):
@@ -478,17 +479,25 @@ class SyncMachine(RuleBasedStateMachine):
         status=Status,
         a=Storage, b=Storage,
         force_delete=st.booleans(),
-        conflict_resolution=st.one_of((st.just('a wins'), st.just('b wins')))
+        conflict_resolution=st.one_of((st.just('a wins'), st.just('b wins'))),
+        with_error_callback=st.booleans()
     )
-    def sync(self, status, a, b, force_delete, conflict_resolution):
+    def sync(self, status, a, b, force_delete, conflict_resolution,
+             with_error_callback):
         assume(a is not b)
         old_items_a = self._get_items(a)
         old_items_b = self._get_items(b)
-        failed_sync = False
 
         a.instance_name = 'a'
         b.instance_name = 'b'
 
+        errors = []
+
+        if with_error_callback:
+            error_callback = errors.append
+        else:
+            error_callback = None
+
         try:
             # If one storage is read-only, double-sync because changes don't
             # get reverted immediately.
@@ -496,10 +505,13 @@ class SyncMachine(RuleBasedStateMachine):
                 old_status = deepcopy(status)
                 sync(a, b, status,
                      force_delete=force_delete,
-                     conflict_resolution=conflict_resolution)
+                     conflict_resolution=conflict_resolution,
+                     error_callback=error_callback)
+
+            for e in errors:
+                raise e
         except ActionIntentionallyFailed:
-            assert status == old_status
-            failed_sync = True
+            pass
         except BothReadOnly:
             assert a.read_only and b.read_only
             assume(False)
@@ -508,16 +520,42 @@ class SyncMachine(RuleBasedStateMachine):
                 raise
             else:
                 assert not list(a.list()) or not list(b.list())
-                return status
+        else:
+            items_a = self._get_items(a)
+            items_b = self._get_items(b)
 
-        items_a = self._get_items(a)
-        items_b = self._get_items(b)
+            assert items_a == items_b
+            assert items_a == old_items_a or not a.read_only
+            assert items_b == old_items_b or not b.read_only
 
-        assert items_a == items_b or failed_sync
-        assert items_a == old_items_a or not a.read_only
-        assert items_b == old_items_b or not b.read_only
-
-        assert set(a.items) | set(b.items) == set(status) or failed_sync
+            assert set(a.items) | set(b.items) == set(status)
 
 
 TestSyncMachine = SyncMachine.TestCase
+
+
+@pytest.mark.parametrize('error_callback', [True, False])
+def test_rollback(error_callback):
+    a = MemoryStorage()
+    b = MemoryStorage()
+    status = {}
+
+    a.items['0'] = ('', Item('UID:0'))
+    b.items['1'] = ('', Item('UID:1'))
+
+    b.upload = b.update = b.delete = action_failure
+
+    if error_callback:
+        errors = []
+
+        sync(a, b, status=status, conflict_resolution='a wins',
+             error_callback=errors.append)
+
+        assert len(errors) == 1
+        assert isinstance(errors[0], ActionIntentionallyFailed)
+
+        assert len(status) == 1
+        assert status['1']
+    else:
+        with pytest.raises(ActionIntentionallyFailed):
+            sync(a, b, status=status, conflict_resolution='a wins')

vdirsyncer/sync.py

@@ -11,6 +11,7 @@ Yang. http://blog.ezyang.com/2012/08/how-offlineimap-works/
 '''
 import itertools
 import logging
+import sys
 
 from . import exceptions
 from .utils import uniq
@@ -226,7 +227,7 @@ def _compress_meta(meta):
 
 
 def sync(storage_a, storage_b, status, conflict_resolution=None,
-         force_delete=False):
+         force_delete=False, error_callback=None):
     '''Synchronizes two storages.
 
     :param storage_a: The first storage
@@ -246,6 +247,8 @@ def sync(storage_a, storage_b, status, conflict_resolution=None,
         syncs, :py:exc:`StorageEmpty` is raised for
         safety. Setting this parameter to ``True`` disables this safety
         measure.
+    :param error_callback: Instead of raising errors when executing actions,
+        call the given function with an `Exception` as the only argument.
     '''
     if storage_a.read_only and storage_b.read_only:
         raise BothReadOnly()
@@ -277,13 +280,19 @@ def sync(storage_a, storage_b, status, conflict_resolution=None,
 
     actions = list(_get_actions(a_info, b_info))
 
-    with storage_a.at_once():
-        with storage_b.at_once():
-            for action in actions:
+    with storage_a.at_once(), storage_b.at_once():
+        for action in actions:
+            try:
                 action.run(a_info, b_info, conflict_resolution)
+            except Exception as e:
+                if error_callback:
+                    error_callback(e)
+                else:
+                    raise
 
     status.clear()
-    for ident in uniq(itertools.chain(a_info.new_status, b_info.new_status)):
+    for ident in uniq(itertools.chain(a_info.new_status,
+                                      b_info.new_status)):
         status[ident] = (
             _compress_meta(a_info.new_status[ident]),
             _compress_meta(b_info.new_status[ident])