synapse-product/synapse/events/snapshot.py

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# Copyright 2014-2016 OpenMarket Ltd
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#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import TYPE_CHECKING, List, Optional, Tuple, Union
import attr
from frozendict import frozendict
from twisted.internet.defer import Deferred
from synapse.appservice import ApplicationService
from synapse.events import EventBase
from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.types import JsonDict, StateMap
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if TYPE_CHECKING:
from synapse.storage import Storage
from synapse.storage.databases.main import DataStore
@attr.s(slots=True, auto_attribs=True)
class EventContext:
"""
Holds information relevant to persisting an event
Attributes:
rejected: A rejection reason if the event was rejected, else False
_state_group: The ID of the state group for this event. Note that state events
are persisted with a state group which includes the new event, so this is
effectively the state *after* the event in question.
For a *rejected* state event, where the state of the rejected event is
ignored, this state_group should never make it into the
event_to_state_groups table. Indeed, inspecting this value for a rejected
state event is almost certainly incorrect.
For an outlier, where we don't have the state at the event, this will be
None.
Note that this is a private attribute: it should be accessed via
the ``state_group`` property.
state_group_before_event: The ID of the state group representing the state
of the room before this event.
If this is a non-state event, this will be the same as ``state_group``. If
it's a state event, it will be the same as ``prev_group``.
If ``state_group`` is None (ie, the event is an outlier),
``state_group_before_event`` will always also be ``None``.
prev_group: If it is known, ``state_group``'s prev_group. Note that this being
None does not necessarily mean that ``state_group`` does not have
a prev_group!
If the event is a state event, this is normally the same as ``prev_group``.
If ``state_group`` is None (ie, the event is an outlier), ``prev_group``
will always also be ``None``.
Note that this *not* (necessarily) the state group associated with
``_prev_state_ids``.
delta_ids: If ``prev_group`` is not None, the state delta between ``prev_group``
and ``state_group``.
app_service: If this event is being sent by a (local) application service, that
app service.
_current_state_ids: The room state map, including this event - ie, the state
in ``state_group``.
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(type, state_key) -> event_id
For an outlier, this is {}
Note that this is a private attribute: it should be accessed via
``get_current_state_ids``. _AsyncEventContext impl calculates this
on-demand: it will be None until that happens.
_prev_state_ids: The room state map, excluding this event - ie, the state
in ``state_group_before_event``. For a non-state
event, this will be the same as _current_state_events.
Note that it is a completely different thing to prev_group!
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(type, state_key) -> event_id
For an outlier, this is {}
As with _current_state_ids, this is a private attribute. It should be
accessed via get_prev_state_ids.
"""
rejected: Union[bool, str] = False
_state_group: Optional[int] = None
state_group_before_event: Optional[int] = None
prev_group: Optional[int] = None
delta_ids: Optional[StateMap[str]] = None
app_service: Optional[ApplicationService] = None
_current_state_ids: Optional[StateMap[str]] = None
_prev_state_ids: Optional[StateMap[str]] = None
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@staticmethod
def with_state(
state_group: Optional[int],
state_group_before_event: Optional[int],
current_state_ids: Optional[StateMap[str]],
prev_state_ids: Optional[StateMap[str]],
prev_group: Optional[int] = None,
delta_ids: Optional[StateMap[str]] = None,
) -> "EventContext":
return EventContext(
current_state_ids=current_state_ids,
prev_state_ids=prev_state_ids,
state_group=state_group,
state_group_before_event=state_group_before_event,
prev_group=prev_group,
delta_ids=delta_ids,
)
@staticmethod
def for_outlier() -> "EventContext":
"""Return an EventContext instance suitable for persisting an outlier event"""
return EventContext(
current_state_ids={},
prev_state_ids={},
)
async def serialize(self, event: EventBase, store: "DataStore") -> JsonDict:
"""Converts self to a type that can be serialized as JSON, and then
deserialized by `deserialize`
Args:
event: The event that this context relates to
Returns:
The serialized event.
"""
# We don't serialize the full state dicts, instead they get pulled out
# of the DB on the other side. However, the other side can't figure out
# the prev_state_ids, so if we're a state event we include the event
# id that we replaced in the state.
if event.is_state():
prev_state_ids = await self.get_prev_state_ids()
prev_state_id = prev_state_ids.get((event.type, event.state_key))
else:
prev_state_id = None
return {
"prev_state_id": prev_state_id,
"event_type": event.type,
"event_state_key": event.state_key if event.is_state() else None,
"state_group": self._state_group,
"state_group_before_event": self.state_group_before_event,
"rejected": self.rejected,
"prev_group": self.prev_group,
"delta_ids": _encode_state_dict(self.delta_ids),
"app_service_id": self.app_service.id if self.app_service else None,
}
@staticmethod
def deserialize(storage: "Storage", input: JsonDict) -> "EventContext":
"""Converts a dict that was produced by `serialize` back into a
EventContext.
Args:
storage: Used to convert AS ID to AS object and fetch state.
input: A dict produced by `serialize`
Returns:
The event context.
"""
context = _AsyncEventContextImpl(
# We use the state_group and prev_state_id stuff to pull the
# current_state_ids out of the DB and construct prev_state_ids.
storage=storage,
prev_state_id=input["prev_state_id"],
event_type=input["event_type"],
event_state_key=input["event_state_key"],
state_group=input["state_group"],
state_group_before_event=input["state_group_before_event"],
prev_group=input["prev_group"],
delta_ids=_decode_state_dict(input["delta_ids"]),
rejected=input["rejected"],
)
app_service_id = input["app_service_id"]
if app_service_id:
context.app_service = storage.main.get_app_service_by_id(app_service_id)
return context
@property
def state_group(self) -> Optional[int]:
"""The ID of the state group for this event.
Note that state events are persisted with a state group which includes the new
event, so this is effectively the state *after* the event in question.
For an outlier, where we don't have the state at the event, this will be None.
It is an error to access this for a rejected event, since rejected state should
not make it into the room state. Accessing this property will raise an exception
if ``rejected`` is set.
"""
if self.rejected:
raise RuntimeError("Attempt to access state_group of rejected event")
return self._state_group
async def get_current_state_ids(self) -> Optional[StateMap[str]]:
"""
Gets the room state map, including this event - ie, the state in ``state_group``
It is an error to access this for a rejected event, since rejected state should
not make it into the room state. This method will raise an exception if
``rejected`` is set.
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Returns:
Returns None if state_group is None, which happens when the associated
event is an outlier.
Maps a (type, state_key) to the event ID of the state event matching
this tuple.
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"""
if self.rejected:
raise RuntimeError("Attempt to access state_ids of rejected event")
await self._ensure_fetched()
return self._current_state_ids
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async def get_prev_state_ids(self) -> StateMap[str]:
"""
Gets the room state map, excluding this event.
For a non-state event, this will be the same as get_current_state_ids().
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Returns:
Returns {} if state_group is None, which happens when the associated
event is an outlier.
Maps a (type, state_key) to the event ID of the state event matching
this tuple.
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"""
await self._ensure_fetched()
# There *should* be previous state IDs now.
assert self._prev_state_ids is not None
return self._prev_state_ids
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def get_cached_current_state_ids(self) -> Optional[StateMap[str]]:
"""Gets the current state IDs if we have them already cached.
It is an error to access this for a rejected event, since rejected state should
not make it into the room state. This method will raise an exception if
``rejected`` is set.
Returns:
Returns None if we haven't cached the state or if state_group is None
(which happens when the associated event is an outlier).
Otherwise, returns the the current state IDs.
"""
if self.rejected:
raise RuntimeError("Attempt to access state_ids of rejected event")
return self._current_state_ids
async def _ensure_fetched(self) -> None:
return None
@attr.s(slots=True)
class _AsyncEventContextImpl(EventContext):
"""
An implementation of EventContext which fetches _current_state_ids and
_prev_state_ids from the database on demand.
Attributes:
_storage
_fetching_state_deferred: Resolves when *_state_ids have been calculated.
None if we haven't started calculating yet
_event_type: The type of the event the context is associated with.
_event_state_key: The state_key of the event the context is associated with.
_prev_state_id: If the event associated with the context is a state event,
then `_prev_state_id` is the event_id of the state that was replaced.
"""
# This needs to have a default as we're inheriting
_storage: "Storage" = attr.ib(default=None)
_prev_state_id: Optional[str] = attr.ib(default=None)
_event_type: str = attr.ib(default=None)
_event_state_key: Optional[str] = attr.ib(default=None)
_fetching_state_deferred: Optional["Deferred[None]"] = attr.ib(default=None)
async def _ensure_fetched(self) -> None:
if not self._fetching_state_deferred:
self._fetching_state_deferred = run_in_background(self._fill_out_state)
await make_deferred_yieldable(self._fetching_state_deferred)
async def _fill_out_state(self) -> None:
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"""Called to populate the _current_state_ids and _prev_state_ids
attributes by loading from the database.
"""
if self.state_group is None:
# No state group means the event is an outlier. Usually the state_ids dicts are also
# pre-set to empty dicts, but they get reset when the context is serialized, so set
# them to empty dicts again here.
self._current_state_ids = {}
self._prev_state_ids = {}
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return
current_state_ids = await self._storage.state.get_state_ids_for_group(
self.state_group
)
# Set this separately so mypy knows current_state_ids is not None.
self._current_state_ids = current_state_ids
if self._event_state_key is not None:
self._prev_state_ids = dict(current_state_ids)
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key = (self._event_type, self._event_state_key)
if self._prev_state_id:
self._prev_state_ids[key] = self._prev_state_id
else:
self._prev_state_ids.pop(key, None)
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else:
self._prev_state_ids = current_state_ids
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def _encode_state_dict(
state_dict: Optional[StateMap[str]],
) -> Optional[List[Tuple[str, str, str]]]:
"""Since dicts of (type, state_key) -> event_id cannot be serialized in
JSON we need to convert them to a form that can.
"""
if state_dict is None:
return None
return [(etype, state_key, v) for (etype, state_key), v in state_dict.items()]
def _decode_state_dict(
input: Optional[List[Tuple[str, str, str]]]
) -> Optional[StateMap[str]]:
"""Decodes a state dict encoded using `_encode_state_dict` above"""
if input is None:
return None
return frozendict({(etype, state_key): v for etype, state_key, v in input})