mirror of
https://github.com/samsonjs/vdirsyncer.git
synced 2026-03-26 09:05:50 +00:00
5a508ae327
* Refactor status management in separate class * Rename to SubStatus, remove unused field * Move item cache out of status * stylefix
559 lines
18 KiB
Python
559 lines
18 KiB
Python
# -*- coding: utf-8 -*-
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'''
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The function in `vdirsyncer.sync` can be called on two instances of `Storage`
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to synchronize them. Due to the abstract API storage classes are implementing,
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the two given instances don't have to be of the same exact type. This allows us
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not only to synchronize a local vdir with a CalDAV server, but also synchronize
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two CalDAV servers or two local vdirs.
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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 . import exceptions
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from .utils import uniq
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sync_logger = logging.getLogger(__name__)
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class SyncError(exceptions.Error):
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'''Errors related to synchronization.'''
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class SyncConflict(SyncError):
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'''
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Two items changed since the last sync, they now have different contents and
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no conflict resolution method was given.
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:param ident: The ident of the item.
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:param href_a: The item's href on side A.
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:param href_b: The item's href on side B.
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'''
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ident = None
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href_a = None
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href_b = None
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class IdentConflict(SyncError):
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'''
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Multiple items on the same storage have the same UID.
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:param storage: The affected storage.
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:param hrefs: List of affected hrefs on `storage`.
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'''
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storage = None
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_hrefs = None
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@property
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def hrefs(self):
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return self._hrefs
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@hrefs.setter
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def hrefs(self, val):
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new_val = set(val)
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assert len(new_val) > 1, val
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self._hrefs = new_val
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class StorageEmpty(SyncError):
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'''
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One storage unexpectedly got completely empty between two synchronizations.
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The first argument is the empty storage.
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:param empty_storage: The empty
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:py:class:`vdirsyncer.storage.base.Storage`.
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'''
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empty_storage = None
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class BothReadOnly(SyncError):
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'''
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Both storages are marked as read-only. Synchronization is therefore not
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possible.
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'''
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class PartialSync(SyncError):
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'''
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Attempted change on read-only storage.
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'''
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storage = None
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class _IdentAlreadyExists(SyncError):
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'''Like IdentConflict, but for internal state. If this bubbles up, we don't
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have a data race, but a bug.'''
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old_href = None
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new_href = None
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def to_ident_conflict(self, storage):
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return IdentConflict(storage=storage,
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hrefs=[self.old_href, self.new_href])
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class _Status(object):
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def __init__(self, ident_to_props):
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self._ident_to_props = ident_to_props
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self._new_ident_to_props = {}
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self._href_to_status_a = dict((meta['href'], (ident, meta))
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for ident, (meta, _)
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in self._ident_to_props.items())
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self._href_to_status_b = dict((meta['href'], (ident, meta))
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for ident, (_, meta)
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in self._ident_to_props.items())
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def insert_ident_a(self, ident, props):
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props_a, props_b = self._new_ident_to_props.get(ident, (None, None))
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if props_a is not None:
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raise _IdentAlreadyExists(old_href=props.href,
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new_href=props_a['href'])
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self._new_ident_to_props[ident] = props.to_status(), props_b
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def insert_ident_b(self, ident, props):
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props_a, props_b = self._new_ident_to_props.get(ident, (None, None))
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if props_b is not None:
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raise _IdentAlreadyExists(old_href=props.href,
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new_href=props_b['href'])
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self._new_ident_to_props[ident] = props_a, props.to_status()
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def update_ident_a(self, ident, props):
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self._new_ident_to_props[ident] = (
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props.to_status(),
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self._new_ident_to_props[ident][1],
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)
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def update_ident_b(self, ident, props):
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self._new_ident_to_props[ident] = (
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self._new_ident_to_props[ident][0],
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props.to_status(),
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)
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def remove_ident(self, ident):
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del self._new_ident_to_props[ident]
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def get_a(self, ident):
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rv = self._ident_to_props[ident][0]
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if rv is None:
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raise KeyError()
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return _ItemMetadata(**rv)
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def get_b(self, ident):
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rv = self._ident_to_props[ident][1]
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if rv is None:
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raise KeyError()
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return _ItemMetadata(**rv)
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def get_new_a(self, ident):
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rv = self._new_ident_to_props[ident][0]
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if rv is None:
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raise KeyError()
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return _ItemMetadata(**rv)
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def get_new_b(self, ident):
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rv = self._new_ident_to_props[ident][1]
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if rv is None:
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raise KeyError()
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return _ItemMetadata(**rv)
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def iter_old(self):
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return iter(self._ident_to_props)
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def iter_new(self):
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return iter(self._new_ident_to_props)
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def rollback(self, ident):
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if ident in self._ident_to_props:
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self._new_ident_to_props[ident] = self._ident_to_props[ident]
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else:
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self._new_ident_to_props.pop(ident, None)
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def get_by_href_a(self, href, default=(None, None)):
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try:
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ident, meta = self._href_to_status_a[href]
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except KeyError:
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return default
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else:
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return ident, _ItemMetadata(**meta)
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def get_by_href_b(self, href, default=(None, None)):
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try:
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ident, meta = self._href_to_status_b[href]
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except KeyError:
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return default
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else:
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return ident, _ItemMetadata(**meta)
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def new_to_old_status(self):
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for meta_a, meta_b in self._new_ident_to_props.values():
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assert meta_a is not None
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assert meta_b is not None
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self._ident_to_props.clear()
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self._ident_to_props.update(self._new_ident_to_props)
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class _SubStatus(object):
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def __init__(self, parent, side):
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self.parent = parent
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assert side in 'ab'
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self.remove_ident = parent.remove_ident
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if side == 'a':
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self.insert_ident = parent.insert_ident_a
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self.update_ident = parent.update_ident_a
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self.get = parent.get_a
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self.get_new = parent.get_new_a
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self.get_by_href = parent.get_by_href_a
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else:
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self.insert_ident = parent.insert_ident_b
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self.update_ident = parent.update_ident_b
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self.get = parent.get_b
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self.get_new = parent.get_new_b
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self.get_by_href = parent.get_by_href_b
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class _ItemMetadata:
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href = None
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hash = None
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etag = None
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def __init__(self, **kwargs):
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for k, v in kwargs.items():
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assert hasattr(self, k)
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setattr(self, k, v)
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def to_status(self):
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return {
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'href': self.href,
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'etag': self.etag,
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'hash': self.hash
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}
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class _StorageInfo(object):
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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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nonlocal storage_nonempty
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storage_nonempty = True
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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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ident, meta = self.status.get_by_href(href)
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if meta is None:
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meta = _ItemMetadata()
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if 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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meta.href = href
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meta.etag = etag
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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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try:
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status = self.status.get(ident)
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except KeyError: # new item
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return True
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meta = self.status.get_new(ident)
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if meta.etag != status.etag: # etag changed
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old_hash = status.hash
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if old_hash is None or meta.hash != old_hash:
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# item actually changed
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return True
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else:
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# only etag changed
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return False
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def set_item_cache(self, ident, item):
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assert self.status.get_new(ident).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 _migrate_status(status):
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for ident in list(status):
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value = status[ident]
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if len(value) == 4:
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href_a, etag_a, href_b, etag_b = value
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status[ident] = ({
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'href': href_a,
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'etag': etag_a,
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}, {
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'href': href_b,
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'etag': etag_b,
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})
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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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_migrate_status(status)
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status_nonempty = bool(status)
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status = _Status(status)
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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(a_info, b_info, conflict_resolution, partial_sync)
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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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status.new_to_old_status()
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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(u'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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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(u'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(u'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(u'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(u'...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 exceptions.UserError(
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'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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try:
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a = a_info.status.get_new(ident)
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except KeyError:
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a = None
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try:
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b = b_info.status.get_new(ident)
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except KeyError:
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b = None
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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:
|
|
# item was modified on both sides
|
|
# OR: missing status
|
|
yield ResolveConflict(ident)
|
|
elif a_changed and not b_changed:
|
|
# item was only modified in a
|
|
yield Update(a_info.get_item_cache(ident), b_info)
|
|
elif not a_changed and b_changed:
|
|
# item was only modified in b
|
|
yield Update(b_info.get_item_cache(ident), a_info)
|
|
elif a and not b:
|
|
if a_info.is_changed(ident):
|
|
# was deleted from b but modified on a
|
|
# OR: new item was created in a
|
|
yield Upload(a_info.get_item_cache(ident), b_info)
|
|
else:
|
|
# was deleted from b and not modified on a
|
|
yield Delete(ident, a_info)
|
|
elif not a and b:
|
|
if b_info.is_changed(ident):
|
|
# was deleted from a but modified on b
|
|
# OR: new item was created in b
|
|
yield Upload(b_info.get_item_cache(ident), a_info)
|
|
else:
|
|
# was deleted from a and not changed on b
|
|
yield Delete(ident, b_info)
|