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Adjust _get_rooms_changed comments (#11550)

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C.f. https://github.com/matrix-org/synapse/pull/11494#pullrequestreview-827780886
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David Robertson 2021-12-10 19:19:48 +00:00 committed by GitHub
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changelog.d/11550.misc Normal file
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@ -0,0 +1 @@
Fix an inaccurate and misleading comment in the `/sync` code.

51
synapse/handlers/sync.py
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@ -1662,20 +1662,20 @@ class SyncHandler:
) -> _RoomChanges:
"""Determine the changes in rooms to report to the user.
Ideally, we want to report all events whose stream ordering `s` lies in the
range `since_token < s <= now_token`, where the two tokens are read from the
sync_result_builder.
This function is a first pass at generating the rooms part of the sync response.
It determines which rooms have changed during the sync period, and categorises
them into four buckets: "knock", "invite", "join" and "leave".
If there are too many events in that range to report, things get complicated.
In this situation we return a truncated list of the most recent events, and
indicate in the response that there is a "gap" of omitted events. Additionally:
1. Finds all membership changes for the user in the sync period (from
`since_token` up to `now_token`).
2. Uses those to place the room in one of the four categories above.
3. Builds a `_RoomChanges` struct to record this, and return that struct.
- we include a "state_delta", to describe the changes in state over the gap,
- we include all membership events applying to the user making the request,
even those in the gap.
See the spec for the rationale:
https://spec.matrix.org/v1.1/client-server-api/#syncing
For rooms classified as "knock", "invite" or "leave", we just need to report
a single membership event in the eventual /sync response. For "join" we need
to fetch additional non-membership events, e.g. messages in the room. That is
more complicated, so instead we report an intermediary `RoomSyncResultBuilder`
struct, and leave the additional work to `_generate_room_entry`.
The sync_result_builder is not modified by this function.
"""
@ -1686,16 +1686,6 @@ class SyncHandler:
assert since_token
# The spec
# https://spec.matrix.org/v1.1/client-server-api/#get_matrixclientv3sync
# notes that membership events need special consideration:
#
# > When a sync is limited, the server MUST return membership events for events
# > in the gap (between since and the start of the returned timeline), regardless
# > as to whether or not they are redundant.
#
# We fetch such events here, but we only seem to use them for categorising rooms
# as newly joined, newly left, invited or knocked.
# TODO: we've already called this function and ran this query in
# _have_rooms_changed. We could keep the results in memory to avoid a
# second query, at the cost of more complicated source code.
@ -2009,6 +1999,23 @@ class SyncHandler:
"""Populates the `joined` and `archived` section of `sync_result_builder`
based on the `room_builder`.
Ideally, we want to report all events whose stream ordering `s` lies in the
range `since_token < s <= now_token`, where the two tokens are read from the
sync_result_builder.
If there are too many events in that range to report, things get complicated.
In this situation we return a truncated list of the most recent events, and
indicate in the response that there is a "gap" of omitted events. Lots of this
is handled in `_load_filtered_recents`, but some of is handled in this method.
Additionally:
- we include a "state_delta", to describe the changes in state over the gap,
- we include all membership events applying to the user making the request,
even those in the gap.
See the spec for the rationale:
https://spec.matrix.org/v1.1/client-server-api/#syncing
Args:
sync_result_builder
ignored_users: Set of users ignored by user.