snapshot.py

# Copyright 2014-2016 OpenMarket Ltd
#
# 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 abc import ABC, abstractmethod
from typing import TYPE_CHECKING, List, Optional, Tuple

import attr
from immutabledict import immutabledict

from synapse.appservice import ApplicationService
from synapse.events import EventBase
from synapse.types import JsonDict, StateMap

if TYPE_CHECKING:
    from synapse.storage.controllers import StorageControllers
    from synapse.storage.databases import StateGroupDataStore
    from synapse.storage.databases.main import DataStore
    from synapse.types.state import StateFilter


class UnpersistedEventContextBase(ABC):
    """
    This is a base class for EventContext and UnpersistedEventContext, objects which
    hold information relevant to storing an associated event. Note that an
    UnpersistedEventContexts must be converted into an EventContext before it is
    suitable to send to the db with its associated event.

    Attributes:
        _storage: storage controllers for interfacing with the database
        app_service: If the associated event is being sent by a (local) application service, that
            app service.
    """

    def __init__(self, storage_controller: "StorageControllers"):
        self._storage: "StorageControllers" = storage_controller
        self.app_service: Optional[ApplicationService] = None

    @abstractmethod
    async def persist(
        self,
        event: EventBase,
    ) -> "EventContext":
        """
        A method to convert an UnpersistedEventContext to an EventContext, suitable for
        sending to the database with the associated event.
        """
        pass

    @abstractmethod
    async def get_prev_state_ids(
        self, state_filter: Optional["StateFilter"] = None
    ) -> StateMap[str]:
        """
        Gets the room state at the event (ie not including the event if the event is a
        state event).

        Args:
            state_filter: specifies the type of state event to fetch from DB, example:
            EventTypes.JoinRules
        """
        pass


@attr.s(slots=True, auto_attribs=True)
class EventContext(UnpersistedEventContextBase):
    """
    Holds information relevant to persisting an event

    Attributes:
        rejected: A rejection reason if the event was rejected, else None

        _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``.

        state_delta_due_to_event: If `state_group` and `state_group_before_event` are not None
            then this is the delta of the state between the two groups.

        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
            ``state_group_before_event``.

            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``.

        partial_state: if True, we may be storing this event with a temporary,
            incomplete state.
    """

    _storage: "StorageControllers"
    rejected: Optional[str] = None
    _state_group: Optional[int] = None
    state_group_before_event: Optional[int] = None
    _state_delta_due_to_event: Optional[StateMap[str]] = None
    prev_group: Optional[int] = None
    delta_ids: Optional[StateMap[str]] = None
    app_service: Optional[ApplicationService] = None

    partial_state: bool = False

    @staticmethod
    def with_state(
        storage: "StorageControllers",
        state_group: Optional[int],
        state_group_before_event: Optional[int],
        state_delta_due_to_event: Optional[StateMap[str]],
        partial_state: bool,
        prev_group: Optional[int] = None,
        delta_ids: Optional[StateMap[str]] = None,
    ) -> "EventContext":
        return EventContext(
            storage=storage,
            state_group=state_group,
            state_group_before_event=state_group_before_event,
            state_delta_due_to_event=state_delta_due_to_event,
            prev_group=prev_group,
            delta_ids=delta_ids,
            partial_state=partial_state,
        )

    @staticmethod
    def for_outlier(
        storage: "StorageControllers",
    ) -> "EventContext":
        """Return an EventContext instance suitable for persisting an outlier event"""
        return EventContext(storage=storage)

    async def persist(self, event: EventBase) -> "EventContext":
        return self

    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.
        """

        return {
            "state_group": self._state_group,
            "state_group_before_event": self.state_group_before_event,
            "rejected": self.rejected,
            "prev_group": self.prev_group,
            "state_delta_due_to_event": _encode_state_dict(
                self._state_delta_due_to_event
            ),
            "delta_ids": _encode_state_dict(self.delta_ids),
            "app_service_id": self.app_service.id if self.app_service else None,
            "partial_state": self.partial_state,
        }

    @staticmethod
    def deserialize(storage: "StorageControllers", 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 = EventContext(
            # 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,
            state_group=input["state_group"],
            state_group_before_event=input["state_group_before_event"],
            prev_group=input["prev_group"],
            state_delta_due_to_event=_decode_state_dict(
                input["state_delta_due_to_event"]
            ),
            delta_ids=_decode_state_dict(input["delta_ids"]),
            rejected=input["rejected"],
            partial_state=input.get("partial_state", False),
        )

        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, state_filter: Optional["StateFilter"] = None
    ) -> 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.

        Arg:
           state_filter: specifies the type of state event to fetch from DB, example: EventTypes.JoinRules

        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.
        """
        if self.rejected:
            raise RuntimeError("Attempt to access state_ids of rejected event")

        assert self._state_delta_due_to_event is not None

        prev_state_ids = await self.get_prev_state_ids(state_filter)

        if self._state_delta_due_to_event:
            prev_state_ids = dict(prev_state_ids)
            prev_state_ids.update(self._state_delta_due_to_event)

        return prev_state_ids

    async def get_prev_state_ids(
        self, state_filter: Optional["StateFilter"] = None
    ) -> 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().

        Args:
            state_filter: specifies the type of state event to fetch from DB, example: EventTypes.JoinRules

        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.
        """

        assert self.state_group_before_event is not None
        return await self._storage.state.get_state_ids_for_group(
            self.state_group_before_event, state_filter
        )


@attr.s(slots=True, auto_attribs=True)
class UnpersistedEventContext(UnpersistedEventContextBase):
    """
    The event context holds information about the state groups for an event. It is important
    to remember that an event technically has two state groups: the state group before the
    event, and the state group after the event. If the event is not a state event, the state
    group will not change (ie the state group before the event will be the same as the state
    group after the event), but if it is a state event the state group before the event
    will differ from the state group after the event.
    This is a version of an EventContext before the new state group (if any) has been
    computed and stored. It contains information about the state before the event (which
    also may be the information after the event, if the event is not a state event). The
    UnpersistedEventContext must be converted into an EventContext by calling the method
    'persist' on it before it is suitable to be sent to the DB for processing.

        state_group_after_event:
             The state group after the event. This will always be None until it is persisted.
             If the event is not a state event, this will be the same as
             state_group_before_event.

        state_group_before_event:
            The ID of the state group representing the state of the room before this event.

        state_delta_due_to_event:
            If the event is a state event, then this is the delta of the state between
             `state_group` and `state_group_before_event`

        prev_group_for_state_group_before_event:
            If it is known, ``state_group_before_event``'s previous state group.

        delta_ids_to_state_group_before_event:
             If ``prev_group_for_state_group_before_event`` is not None, the state delta
             between ``prev_group_for_state_group_before_event`` and ``state_group_before_event``.

        partial_state:
            Whether the event has partial state.

        state_map_before_event:
            A map of the state before the event, i.e. the state at `state_group_before_event`
    """

    _storage: "StorageControllers"
    state_group_before_event: Optional[int]
    state_group_after_event: Optional[int]
    state_delta_due_to_event: Optional[dict]
    prev_group_for_state_group_before_event: Optional[int]
    delta_ids_to_state_group_before_event: Optional[StateMap[str]]
    partial_state: bool
    state_map_before_event: Optional[StateMap[str]] = None

    @classmethod
    async def batch_persist_unpersisted_contexts(
        cls,
        events_and_context: List[Tuple[EventBase, "UnpersistedEventContextBase"]],
        room_id: str,
        last_known_state_group: int,
        datastore: "StateGroupDataStore",
    ) -> List[Tuple[EventBase, EventContext]]:
        """
        Takes a list of events and their associated unpersisted contexts and persists
        the unpersisted contexts, returning a list of events and persisted contexts.
        Note that all the events must be in a linear chain (ie a <- b <- c).

        Args:
            events_and_context: A list of events and their unpersisted contexts
            room_id: the room_id for the events
            last_known_state_group: the last persisted state group
            datastore: a state datastore
        """
        amended_events_and_context = await datastore.store_state_deltas_for_batched(
            events_and_context, room_id, last_known_state_group
        )

        events_and_persisted_context = []
        for event, unpersisted_context in amended_events_and_context:
            if event.is_state():
                context = EventContext(
                    storage=unpersisted_context._storage,
                    state_group=unpersisted_context.state_group_after_event,
                    state_group_before_event=unpersisted_context.state_group_before_event,
                    state_delta_due_to_event=unpersisted_context.state_delta_due_to_event,
                    partial_state=unpersisted_context.partial_state,
                    prev_group=unpersisted_context.state_group_before_event,
                    delta_ids=unpersisted_context.state_delta_due_to_event,
                )
            else:
                context = EventContext(
                    storage=unpersisted_context._storage,
                    state_group=unpersisted_context.state_group_after_event,
                    state_group_before_event=unpersisted_context.state_group_before_event,
                    state_delta_due_to_event=unpersisted_context.state_delta_due_to_event,
                    partial_state=unpersisted_context.partial_state,
                    prev_group=unpersisted_context.prev_group_for_state_group_before_event,
                    delta_ids=unpersisted_context.delta_ids_to_state_group_before_event,
                )
            events_and_persisted_context.append((event, context))
        return events_and_persisted_context

    async def get_prev_state_ids(
        self, state_filter: Optional["StateFilter"] = None
    ) -> StateMap[str]:
        """
        Gets the room state map, excluding this event.

        Args:
            state_filter: specifies the type of state event to fetch from DB

        Returns:
            Maps a (type, state_key) to the event ID of the state event matching
            this tuple.
        """
        if self.state_map_before_event:
            return self.state_map_before_event

        assert self.state_group_before_event is not None
        return await self._storage.state.get_state_ids_for_group(
            self.state_group_before_event, state_filter
        )

    async def persist(self, event: EventBase) -> EventContext:
        """
        Creates a full `EventContext` for the event, persisting any referenced state that
        has not yet been persisted.

        Args:
             event: event that the EventContext is associated with.

        Returns: An EventContext suitable for sending to the database with the event
        for persisting
        """
        assert self.partial_state is not None

        # If we have a full set of state for before the event but don't have a state
        # group for that state, we need to get one
        if self.state_group_before_event is None:
            assert self.state_map_before_event
            state_group_before_event = await self._storage.state.store_state_group(
                event.event_id,
                event.room_id,
                prev_group=self.prev_group_for_state_group_before_event,
                delta_ids=self.delta_ids_to_state_group_before_event,
                current_state_ids=self.state_map_before_event,
            )
            self.state_group_before_event = state_group_before_event

        # if the event isn't a state event the state group doesn't change
        if not self.state_delta_due_to_event:
            state_group_after_event = self.state_group_before_event

        # otherwise if it is a state event we need to get a state group for it
        else:
            state_group_after_event = await self._storage.state.store_state_group(
                event.event_id,
                event.room_id,
                prev_group=self.state_group_before_event,
                delta_ids=self.state_delta_due_to_event,
                current_state_ids=None,
            )

        return EventContext.with_state(
            storage=self._storage,
            state_group=state_group_after_event,
            state_group_before_event=self.state_group_before_event,
            state_delta_due_to_event=self.state_delta_due_to_event,
            partial_state=self.partial_state,
            prev_group=self.state_group_before_event,
            delta_ids=self.state_delta_due_to_event,
        )


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 immutabledict({(etype, state_key): v for etype, state_key, v in input})