mirror of
https://github.com/samsonjs/vdirsyncer.git
synced 2026-03-27 09:15:50 +00:00
313 lines
11 KiB
Python
313 lines
11 KiB
Python
'''
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The `sync` function in `vdirsyncer.sync` can be called on two instances of
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`Storage` to synchronize them. Apart from the defined errors, this is the only
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public API of this module.
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The algorithm is based on the blogpost "How OfflineIMAP works" by Edward Z.
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Yang: http://blog.ezyang.com/2012/08/how-offlineimap-works/
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Some modifications to it are explained in
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https://unterwaditzer.net/2016/sync-algorithm.html
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'''
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import contextlib
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import itertools
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import logging
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from ..exceptions import UserError
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from ..utils import uniq
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from .status import SubStatus, ItemMetadata
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from .exceptions import BothReadOnly, IdentAlreadyExists, PartialSync, \
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StorageEmpty, SyncConflict
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sync_logger = logging.getLogger(__name__)
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class _StorageInfo:
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'''A wrapper class that holds prefetched items, the status and other
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things.'''
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def __init__(self, storage, status):
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self.storage = storage
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self.status = status
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self._item_cache = {}
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def prepare_new_status(self):
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storage_nonempty = False
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prefetch = []
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def _store_props(ident, props):
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try:
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self.status.insert_ident(ident, props)
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except IdentAlreadyExists as e:
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raise e.to_ident_conflict(self.storage)
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for href, etag in self.storage.list():
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storage_nonempty = True
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ident, meta = self.status.get_by_href(href)
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if meta is None or meta.href != href or meta.etag != etag:
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# Either the item is completely new, or updated
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# In both cases we should prefetch
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prefetch.append(href)
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else:
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# Metadata is completely identical
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_store_props(ident, meta)
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# Prefetch items
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for href, item, etag in (self.storage.get_multi(prefetch)
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if prefetch else ()):
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_store_props(item.ident, ItemMetadata(
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href=href,
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hash=item.hash,
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etag=etag
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))
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self.set_item_cache(item.ident, item)
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return storage_nonempty
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def is_changed(self, ident):
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old_meta = self.status.get(ident)
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if old_meta is None: # new item
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return True
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new_meta = self.status.get_new(ident)
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return (
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new_meta.etag != old_meta.etag # etag changed
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# item actually changed
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and (old_meta.hash is None or new_meta.hash != old_meta.hash)
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)
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def set_item_cache(self, ident, item):
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actual_hash = self.status.get_new(ident).hash
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assert actual_hash == item.hash
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self._item_cache[ident] = item
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def get_item_cache(self, ident):
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return self._item_cache[ident]
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def sync(storage_a, storage_b, status, conflict_resolution=None,
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force_delete=False, error_callback=None, partial_sync='revert'):
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'''Synchronizes two storages.
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:param storage_a: The first storage
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:type storage_a: :class:`vdirsyncer.storage.base.Storage`
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:param storage_b: The second storage
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:type storage_b: :class:`vdirsyncer.storage.base.Storage`
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:param status: {ident: (href_a, etag_a, href_b, etag_b)}
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metadata about the two storages for detection of changes. Will be
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modified by the function and should be passed to it at the next sync.
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If this is the first sync, an empty dictionary should be provided.
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:param conflict_resolution: A function that, given two conflicting item
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versions A and B, returns a new item with conflicts resolved. The UID
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must be the same. The strings `"a wins"` and `"b wins"` are also
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accepted to mean that side's version will always be taken. If none
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is provided, the sync function will raise :py:exc:`SyncConflict`.
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:param force_delete: When one storage got completely emptied between two
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syncs, :py:exc:`StorageEmpty` is raised for
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safety. Setting this parameter to ``True`` disables this safety
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measure.
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:param error_callback: Instead of raising errors when executing actions,
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call the given function with an `Exception` as the only argument.
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:param partial_sync: What to do when doing sync actions on read-only
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storages.
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- ``error``: Raise an error.
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- ``ignore``: Those actions are simply skipped.
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- ``revert`` (default): Revert changes on other side.
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'''
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if storage_a.read_only and storage_b.read_only:
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raise BothReadOnly()
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if conflict_resolution == 'a wins':
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conflict_resolution = lambda a, b: a
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elif conflict_resolution == 'b wins':
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conflict_resolution = lambda a, b: b
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status_nonempty = bool(next(status.iter_old(), None))
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with status.transaction():
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a_info = _StorageInfo(storage_a, SubStatus(status, 'a'))
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b_info = _StorageInfo(storage_b, SubStatus(status, 'b'))
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a_nonempty = a_info.prepare_new_status()
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b_nonempty = b_info.prepare_new_status()
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if status_nonempty and not force_delete:
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if a_nonempty and not b_nonempty:
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raise StorageEmpty(empty_storage=storage_b)
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elif not a_nonempty and b_nonempty:
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raise StorageEmpty(empty_storage=storage_a)
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actions = list(_get_actions(a_info, b_info))
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with storage_a.at_once(), storage_b.at_once():
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for action in actions:
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try:
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action.run(
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a_info,
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b_info,
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conflict_resolution,
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partial_sync
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)
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except Exception as e:
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if error_callback:
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error_callback(e)
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else:
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raise
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class Action:
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def _run_impl(self, a, b): # pragma: no cover
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raise NotImplementedError()
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def run(self, a, b, conflict_resolution, partial_sync):
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with self.auto_rollback(a, b):
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if self.dest.storage.read_only:
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if partial_sync == 'error':
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raise PartialSync(self.dest.storage)
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elif partial_sync == 'ignore':
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self.rollback(a, b)
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return
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else:
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assert partial_sync == 'revert'
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self._run_impl(a, b)
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@contextlib.contextmanager
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def auto_rollback(self, a, b):
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try:
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yield
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except BaseException as e:
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self.rollback(a, b)
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raise e
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def rollback(self, a, b):
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a.status.parent.rollback(self.ident)
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class Upload(Action):
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def __init__(self, item, dest):
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self.item = item
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self.ident = item.ident
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self.dest = dest
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def _run_impl(self, a, b):
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if self.dest.storage.read_only:
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href = etag = None
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else:
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sync_logger.info('Copying (uploading) item {} to {}'
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.format(self.ident, self.dest.storage))
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href, etag = self.dest.storage.upload(self.item)
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assert href is not None
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self.dest.status.insert_ident(self.ident, ItemMetadata(
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href=href,
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hash=self.item.hash,
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etag=etag
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))
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class Update(Action):
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def __init__(self, item, dest):
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self.item = item
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self.ident = item.ident
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self.dest = dest
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def _run_impl(self, a, b):
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if self.dest.storage.read_only:
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meta = ItemMetadata(hash=self.item.hash)
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else:
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sync_logger.info('Copying (updating) item {} to {}'
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.format(self.ident, self.dest.storage))
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meta = self.dest.status.get_new(self.ident)
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meta.etag = \
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self.dest.storage.update(meta.href, self.item, meta.etag)
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self.dest.status.update_ident(self.ident, meta)
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class Delete(Action):
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def __init__(self, ident, dest):
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self.ident = ident
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self.dest = dest
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def _run_impl(self, a, b):
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meta = self.dest.status.get_new(self.ident)
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if not self.dest.storage.read_only:
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sync_logger.info('Deleting item {} from {}'
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.format(self.ident, self.dest.storage))
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self.dest.storage.delete(meta.href, meta.etag)
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self.dest.status.remove_ident(self.ident)
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class ResolveConflict(Action):
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def __init__(self, ident):
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self.ident = ident
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def run(self, a, b, conflict_resolution, partial_sync):
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with self.auto_rollback(a, b):
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sync_logger.info('Doing conflict resolution for item {}...'
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.format(self.ident))
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meta_a = a.status.get_new(self.ident)
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meta_b = b.status.get_new(self.ident)
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if meta_a.hash == meta_b.hash:
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sync_logger.info('...same content on both sides.')
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elif conflict_resolution is None:
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raise SyncConflict(ident=self.ident, href_a=meta_a.href,
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href_b=meta_b.href)
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elif callable(conflict_resolution):
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item_a = a.get_item_cache(self.ident)
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item_b = b.get_item_cache(self.ident)
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new_item = conflict_resolution(item_a, item_b)
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if new_item.hash != meta_a.hash:
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Update(new_item, a).run(a, b, conflict_resolution,
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partial_sync)
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if new_item.hash != meta_b.hash:
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Update(new_item, b).run(a, b, conflict_resolution,
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partial_sync)
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else:
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raise UserError('Invalid conflict resolution mode: {!r}'
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.format(conflict_resolution))
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def _get_actions(a_info, b_info):
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for ident in uniq(itertools.chain(a_info.status.parent.iter_new(),
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a_info.status.parent.iter_old())):
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a = a_info.status.get_new(ident)
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b = b_info.status.get_new(ident)
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if a and b:
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a_changed = a_info.is_changed(ident)
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b_changed = b_info.is_changed(ident)
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if a_changed and b_changed:
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# item was modified on both sides
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# OR: missing status
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yield ResolveConflict(ident)
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elif a_changed and not b_changed:
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# item was only modified in a
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yield Update(a_info.get_item_cache(ident), b_info)
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elif not a_changed and b_changed:
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# item was only modified in b
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yield Update(b_info.get_item_cache(ident), a_info)
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elif a and not b:
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if a_info.is_changed(ident):
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# was deleted from b but modified on a
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# OR: new item was created in a
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yield Upload(a_info.get_item_cache(ident), b_info)
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else:
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# was deleted from b and not modified on a
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yield Delete(ident, a_info)
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elif not a and b:
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if b_info.is_changed(ident):
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# was deleted from a but modified on b
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# OR: new item was created in b
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yield Upload(b_info.get_item_cache(ident), a_info)
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else:
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# was deleted from a and not changed on b
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yield Delete(ident, b_info)
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